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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Shouldn't be so suprised. It peaks at 5,800 in a LT4 with manifolds. Not to mention my L31 intake was ported and had a 78mm bored throttle body.
We put a 92-95 "W" cam in my brothers 97 S10, ported the lower intake, put shorties on it and it makes peak power at 5,500.
When the time comes,the undertaker oughta love you cuz after he gives you an enema,he'll be able to bury you in matchbox !!! That's funny rite there.IDC who ya are !!!
Shouldn't be so suprised. It peaks at 5,800+ in a LT4 with manifolds. Not to mention my L31 intake was ported and had a 78mm bored throttle body.
We put a 92-95 "W" cam in my brothers 97 S10, ported the lower intake, put shorties on it and it makes peak power at 5,500.
You see, that's why nobody believes you; you bend the truth too much. We've now gone from "Stock L31 put down 198 RWHP, with bolt-ons and tune put down 240 RWHP through stock manifolds. LT4 cam + LT1 manifolds made 280 RWHP " and "this is my production LT4 cammed bolt-on L31" to a ........... ported manifold. Seems your definition of "bolt-on" may be a bit different from the norm Fess up, what other tricks did you use?
Forget that irrelevant comment about the peak rpm in an LT4. You know as well as I do that you can put the same cam with an L31 vs an LT4 intake manifold and see anywhere from a 600 to 1000+ rpm peak difference. You'd be the only man on the planet to make that up by porting that peanut port L31 intake! You're a magician, man
You see, that's why nobody believes you; you bend the truth too much. We've now gone from "Stock L31 put down 198 RWHP, with bolt-ons and tune put down 240 RWHP through stock manifolds. LT4 cam LT1 manifolds made 280 RWHP " and "this is my production LT4 cammed bolt-on L31" to a ........... ported manifold. Seems your definition of "bolt-on" may be a bit different from the norm Fess up, what other tricks did you use?
Forget that irrelevant comment about the peak rpm in an LT4. You know as well as I do that you can put the same cam with an L31 vs an LT4 intake manifold and see anywhere from a 600 to 1000 rpm peak difference. You'd be the only man on the planet to make that up by porting that peanut port L31 intake! You're a magician, man
Assuming a 20% loss,the tune & bolt ons woulda gained 52 HP.IDK what other bolt ons could do that,since by your own admission,headers weren't included.What other bolt ons are we talking about.TB spacer,CAI,underdrive pulleys???All of those may give a 10 to 15 HP gain,if that.
If anyone else wishes to contribute I'm looking for the following information:
Engine type and size with bore/stroke.
Connecting rod length.
Cylinder head material.
Calculated compression ratio.
Camshaft specs w/ adv duration, LSA and ICL.
Compression test results (warm or cold).
Test elevation and temperature.[/QUOTE]
Well I'm off work this coming Monday and I really want to do a comp test .. I just got the engine built and it has around 850 miles on the build .. so Monday I will come back and "edit" this post with the results bit I'll go ahead and give the engine specs now..
305sbc .030 over , speed pro hyper flattops 5cc reliefs, Molly rings .021 top gap .018 second gap , .0015 skirt clearance , trick flow 175cc heads, 56cc chamber, stock bottom end balanced 5.7 rod, calculated CR 10.5-10.7 , summit dual plane mid rise intake , Howards HR cam 214/218@.050 .488/.495 lift + 1.6 RR comes out at .520/.528 lift on 114 LSA & 110CL adv. Dur 264/270 I think ... so how exactly do u do a CR test screw it in unplug the coil ? And turn it over a few times ?
91' firebird .. 305 TBI .030 over , balanced bottom end , speed pro hyper flattops , 10.6:1 CR , all ARP rod bolts and main studs , melling HV oil pump , trick flow super 23 175cc heads, Howards HR 214/218@.050 .488/.495 lift on 114 LSA , full roller 1.6 RR = .520/.528 lift , summit dual plane intake port matched , shorty headers into 2.5" Y w full 3" flow master system and 3" cutout in front of axle , msd billet dizzy, 620cfm TBI , custom CAI , tubular adjustabke LCA pan hard , umi torque arm wonder bar , BMR trans cross member , COMP engineering SFC's, disc rear w 4.10's, drilled an slotted rotors, EBL flash , VRFPR, WBO2,
If anyone else wishes to contribute I'm looking for the following information:
Engine type and size with bore/stroke.
Connecting rod length.
Cylinder head material.
Calculated compression ratio.
Camshaft specs w/ adv duration, LSA and ICL.
Compression test results (warm or cold).
Test elevation and temperature.
Well I'm off work this coming Monday and I really want to do a comp test .. I just got the engine built and it has around 850 miles on the build .. so Monday I will come back and "edit" this post with the results bit I'll go ahead and give the engine specs now..
305sbc .030 over , speed pro hyper flattops 5cc reliefs, Molly rings .021 top gap .018 second gap , .0015 skirt clearance , trick flow 175cc heads, 56cc chamber, stock bottom end balanced 5.7 rod, calculated CR 10.5-10.7 , summit dual plane mid rise intake , Howards HR cam 214/218@.050 .488/.495 lift 1.6 RR comes out at .520/.528 lift on 114 LSA & 110CL adv. Dur 264/270 I think ... so how exactly do u do a CR test screw it in unplug the coil ? And turn it over a few times ?
91' firebird .. 305 TBI .030 over , balanced bottom end , speed pro hyper flattops , 10.6:1 CR , all ARP rod bolts and main studs , melling HV oil pump , trick flow super 23 175cc heads, Howards HR 214/218@.050 .488/.495 lift on 114 LSA , full roller 1.6 RR = .520/.528 lift , summit dual plane intake port matched , shorty headers into 2.5" Y w full 3" flow master system and 3" cutout in front of axle , msd billet dizzy, 620cfm TBI , custom CAI , tubular adjustabke LCA pan hard , umi torque arm wonder bar , BMR trans cross member , COMP engineering SFC's, disc rear w 4.10's, drilled an slotted rotors, EBL flash , VRFPR, WBO2,[/QUOTE]
You'll get more accurate results on a warm engine.Be sure the battery is fully charged so you can maintain cranking rpm on ea cylinder,preferably approx 150 rpm.Take your highest reading on 7 to 10 needle pulses.Just my opinion,but,I woulda opened those top ring gaps up a lil more for that kinda CR.
Assuming a 20% loss,the tune & bolt ons woulda gained 52 HP.IDK what other bolt ons could do that,since by your own admission,headers weren't included.What other bolt ons are we talking about.TB spacer,CAI,underdrive pulleys???All of those may give a 10 to 15 HP gain,if that.
E-fans, Underdrive Pulley, 78MM throttle body, 1.6:1 rockers, stock LT1 manifolds and removed the cats.
... so how exactly do u do a CR test screw it in unplug the coil ? And turn it over a few times ?
Up to temperature is best to start.
Remove all of the plugs.
Open the throttle blades (and choke if so equipped) and keep them held open for the duration of the test.
Disable the ignition. Pull and ground the coil wire or pull the fuse on the igniton box (if so equipped).
Crank the engine half a dozen revolutions or so. Personally I like to crank while watching the gauge and stop once there's no longer any advancement in the readings. A remote starter really helps if it's a one man deal.
Hey skinny,
Better late than never, huh!
Finally got my hands on my daughter's car (in sig) and put a compression tester to it. Checked 5 cylinders and they varied from 185 to 191 psi. I'm about 600' elevation. Engine cold.
Vortec iron heads. Re-assembled Vortec shortblock. ZZ3 cam. 9.6 SCR. 8.1 DCR. .038-.040" quench clearance. Runs great on 87 octane.
Back from the dead for sure.
I'll get back to my notes and start a follow-up to this old thread. I have new data of my own to add too.
May take a few days as I'm away at work (fly-in job) but I did bring my older laptop with me that has my programs and such in it. This might prove interesting. Yours was one of the engines I wanted to analyse (87 octane).
Specs on that cam? Or I'll look it up. Adv duration, LSA, ICL.
Thanks.
Wow! I just reread this thread. I didn't realise how passionate people are about their builds and the results.
Well, as I stated earlier, my intention isn't to start any sort of confrontation. I'm just looking for for some numbers and assembling (or hoping to assemble) a little data base. Plus, looking for those who may have done what I wasn't able to.
More to come (I hope).
The more information the better.
Engine type with bore/stroke.
Connecting rod length.
Cylinder head material.
Calculated compression ratio. Camshaft specs w/ adv duration, LSA and ICL. (Please)
Compression test results (warm or cold).
I've gone through my records and pulled up a few Vortec and Vortec based builds.
I have compression tests for all of them.
Engine 2004
350: 4.00” x 3.48"
5 cc piston
.030” deck (undecked block with numbers ranging from .026" to .034".)
Vortec heads (assumed 64 cc)
Comp 268H flat tappet w/ 1.5 rockers. 268 adv, 218 @ 050”, 60 ABDC IVC.
Corteco 55063 head gasket .028” x 4.130”
9.8 SCR / 8.12 DCR
Cranking pressure 200-205
Engine 2007
353: 4.020” x 3.48”
5 cc piston
.030" deck (same short as above)”
Vortec heads. Decked .006”. 63 cc (?)
Comp XR276HR. 276/282, 224/230, 110 LSA, 106 ICL, 64 ABDC IVC
Victor Reinz 5746 head gasket .026” x 4.120”
10.05 SCR / 8.08 DCR
Cranking pressure 185-190
Engine 2014
355: 4.030” x 3.48”
5 cc piston
.014” deck (measured all 8)
RHS Pro Torker Vortec heads. 64 cc
Custom cam. 274/282, 224/230, .574”/ .569”, 63 ABDC IVC
Victor Reinz 5746 head gasket .026” x 4.120”
10.37 SCR / 8.4 DCR
Cranking pressure 200+
The first two iterations always got premium fuel. I may have run a few tanks of mid grade now and then. I'm certain neither liked regular fuel.
The 2014 lump was the problem child. The resulting DCR was higher than I would have liked but it was the result of swapping short blocks after a failure with the previous original. The reduced deck pushed the values up. This is the one I had several posts ( and arguments) about but in the end, I had to acquiesce to the demons of detonation. I pulled the heads, worked the chambers to add a couple of cc's and fattened up the head gasket. I never did get around to a proper timing curve. Thing is, the cranking pressures weren't off the charts when compared to previous successful builds. I may have some skewed results there. Temps and atmospheric pressure of the test day may have had an impact. I don't know.
That said, it still pushed my nearly 3700 lb Camaro to a corrected 12.48 @ 109 mph. The best paper time slip was 12.6 @ 107 with a 1300' DA. I'm sure it would have been low 12's had I tuned it. Timing was very lazy and the AFRs were dead lean at the top due to a fuelling issue.
So, the point of this is collect some info and see what others have done.
Your engine 86LG is not dissimilar to either one of my first two in the SCR/DCR. I quite possibly could have run on lower grade fuel but my timing curves were very aggressive. Little cams and little heads meant that power production would be low. The timing curve had to be right on. I'd like to know the curve of your chip.
At some point I'll work out the theoretical compression ratios of these examples. I have more than a few tech papers on the subject and what one can expect from a given DCR and fuel octane requirements. It'll be interesting to compare theory to reality.
For what's it's worth the theoretical cranking pressure for the three combinations I've listed are:
Engine 2004: 196 psi (actual 200-205)
Engine 2007: 195 psi (actual 185-190)
Engine 2014: 206 psi (actual 200+) Based on this cranking pressure, if that had been aluminium headed instead of iron, I think that engine would have been excellent. Probably everything I had planned on with high compression and a short cam torque producer. Too bad. It cost a lot money for that failure.
So my results and the compression pressure calculator are pretty much in sync. The 04 engine is a bit of an anomaly in that I'n not entirely certain of the cam specs. It was a
Clevite single pattern cam and I don't trust the cam card. It said 288 adv and 218 @ .050". Talk about lazy. The compression test numbers don't support that in the least.
Somewhere I have the 2014 values when I took it apart for heads and cam. They were quite a bit lower that what it tested at when it was fresher. The valves guides and intake valve stems were smoked.
As for the Firebird engine, theoretical cranking pressure should be around 195. That's using the IC event values given. The calculator adds 210 degrees to that number and bases the results on that.
I know I’m resurrecting an old thread here but I was very excited to find it here on TGO through a google search.
I myself have a gm L31R crate engine bone stock unopened with a gmpp 14097396 camshaft (supposedly) I bought it off Facebook
DESCRIPTION
This hydraulic roller design is used on the 383 truck and Ramjet 350.
The duration at lash point in degrees (intake/exhaust) is 288/308; duration at .050" tappet lift (intake/exhaust) is 196/206 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 431/451. Valve lash is zero/zero and lobe centerline is 109 degrees.
My compression numbers were all 208-230psi warm at 200’ above sea level pulling one plug at a time until they were all out. I had the choke warmed up and the quadrajet wide open 70 hours on the build.
I am also plagued by detonation/preignition. One major difference though, this engine lives in my boat. It’s set up with a marine intake, pertronix flamethrower 3 dizy and I’ve tried both ACDelco plugs and Denso plugs gapped to .040 I’ll have to check back on the plug specs.
Is this cranking pressure unreasonably high? I do trust the gauge even though it’s an actron from autozone.
I find those cam specs to be somewhat unusual. The advertised duration of 288 and the .050" value of 196 don't seem reasonable. Even the old and ancient Clevite flat tappet I first ran was 288/218.
Could be though that GMPP likes them that way. I couldn't find an online presence for the PN posted but my surfing ability is a little limited with this phone.
Now if the advertised numbers are exaggerated then the very high cranking compression could be explained.
What I don't know offhand (phone again) is the static compression ratio of the L31. Is it 9:1? 9.5?
Once I get a few more details I can crunch some numbers .
I find those cam specs to be somewhat unusual. The advertised duration of 288 and the .050" value of 196 don't seem reasonable. Even the old and ancient Clevite flat tappet I first ran was 288/218.
Could be though that GMPP likes them that way. I couldn't find an online presence for the PN posted but my surfing ability is a little limited with this phone.
Now if the advertised numbers are exaggerated then the very high cranking compression could be explained.
What I don't know offhand (phone again) is the static compression ratio of the L31. Is it 9:1? 9.5?
Once I get a few more details I can crunch some numbers .
GM "lash point" duration numbers are screwy and meaningless IMO (very difficult to measure!). That "195" cam has somewhere around 250 deg intake duration at .006" tappet lift (typically referred to as advertised duration). Yes, listed stock L31 Vortec SCR is 9.4:1.
mxcrazed, Are you getting detonation running 92/93 octane fuel with lake/sea water running through the engine? Even with the constant loading in marine use, I would have thought your cranking pressure would still be ok.
I have the factory (PleasureCraft Marine) powerplant in a ski/wakeboard boat, and is exactly as you describe yours (Vortec / "395" cam). If the dash temp gauge is correct, it runs about 160 degF and I have no detonation issues running 87 octane E10 (regular pump fuel).
GM "lash point" duration numbers are screwy and meaningless IMO (very difficult to measure!). That "195" cam has somewhere around 250 deg intake duration at .006" tappet lift (typically referred to as advertised duration). Yes, listed stock L31 Vortec SCR is 9.4:1.
I though I might hear from you.
Thanks for the info.
Originally Posted by mxcrazed
My compression numbers were all 208-230psi warm at 200’ above sea level
I am also plagued by detonation/preignition.
Is this cranking pressure unreasonably high?
Using an advertised duration of 250 (as suggested above), my compression calculator indicates a theoretical cranking compression of 219 PSI.
Seems to jive with your findings.
For a street engine, I would say you're past the edge of what can and can't be used. For a boat, with continuous operation at peak torque (which is where combustion pressures are highest) I can't say.
Keep in mind that detonation and pre-ignition are two different things.
But I'm guessing you have engine rattling under load. My first thought is timing. That would contribute to a detonation issue.
If the engine build is a poor one, where attention wasn't given to the assembly, there could be hot spots in the combustion chamber which result from sharp edges and the like which get hot enough to ignite the fuel/air mixture before the spark.
There may be other contributing factors but these are the basic points to investigate.
Personally, if 86LG4Bird has the same engine spec and no issues, I'd follow his lead on this one.
Check that timing though.
Another thought is the fuel trim. Any notion what the air/fuel ratio might be?
I am running closed cooling using a heat exchanger the thermostat housing reads 165°. The tank has only had 93 in it for quite some time so it should be a true 93 octane. 8° base timing 10° in by 1500rpm and another 10° in by 3000rpm for a total of 28°
Im starting to believe that I have a plug wire leaking somewhere, I hear an irregular/random occasional tick/click in the engine compartment but I wasn’t sure if it was noise from the outdrive. I did get zapped by the coil wire when I put my hand on it but I changed it and the issue persists. I have changed the plugs and added dielectric grease, still hear the tick. I have grabbed and manipulated all of the boots no more zaps. Wires have only 75 hours or so on them (Sierra Marine hi perf suppression type)
I am definitely getting worse performance than last season before it was only detonating at WOT after 20-30 seconds maybe more. I believed that I was emptying the fuel bowls so I did some investigating and found air in the fuel supply which I traced to a defective fuel pick up. I also increased the seat in the carb from .130” to .135” so I figure fuel delivery is good.
Now it’s breaking up while planing off if I get into the throttle too quickly. I have also changed to my least aggressive propeller which isn’t producing any more WOT rpm than the old one (4000 ish) before the engine falls apart.
Plugs look rich more than anything else. That would help suppress spark knock.
Does the engine consume oil? With 70 hours, I would hope not.
Simple experimentation would be to pull out some of the timing. Even to the point where it runs like crap. Admittedly, 28° at 4000 isn't a whole helluva lot. But if the symptoms go away with reduced timing...
One indicator is that the problem is getting worse. Has something let go? Or letting go? Now that said, with something like a distributor or timing chain, approaching failure tends to reduce compression pressure as the timing backs off or the cam retards.
Now one thing that comes to mind is the fuel. How fresh is the gas?
Another is the phrase "breaking up" as opposed to detonation. Such is the limitation of text as opposed to being there.
I'm working through a misfire presently and am having a difficult time discerning between what is a misfire and what might be detonation. I'm suspicious of my ignition and have a wholesale change in the works to eliminate the variables.
... before it was only detonating at WOT after 20-30 seconds maybe more.
I would not run that type of plug (iridium maybe?) under any high load duty. After a short time under load, that thin center electrode cannot transfer the heat adequately and can light up like a glow plug. You should be running a simple copper plug like an NGK TR55, TR6, or Autolite 104.
Engine type and size with bore/stroke. SBC 334, 3.766 x 3.75
Connecting rod length. 5.7
Cylinder head material. IRON World Products 305 Torquer 58cc, ported, 2.02/1.6
Calculated compression ratio. 9.87:1
Camshaft specs w/ adv duration, LSA and ICL. 264, 108, 108
Compression test results (warm or cold). COLD
Test elevation and temperature. 177 ft, 50º F
ISKY 264-MEGA HYDRAULIC FT
Application: Tremendous torque & good mid-range power.
9-10.5:1 compr., good idle, stock converter.
3.23-3.70 axle ratio. Up to 625 CFM Carb.
RPM-Range: 2000-5800
Valve Lift Int/Ext: .450/.450 (1.5), .480/.480 (1.6)
Valve Lash Hot Int/Ext: .000/.000
ADV Duration Int/Ext: 264/264
.050 Duration Int/Ext: 214/214
Lobe Center: 108 108° LSA /108° ICL = straight up
Seat-to-seat timing (Wallace) (IN .007", EX .010") ISKY IVO is 24.0° BTDC (- indicates ATDC) IVC is 60.0° ABDC
EVO is 60.0° BBDC
EVC is 24.0° ATDC (- indicates BTDC)
Overlap is 48°
.050" Valve Events
IN Opens 1 ATDC IN Closes 35 ABDC
EX Opens 35 BBDC EX Closes 1 BTDC
Wallace Dynamic Compression Ratio Calculator (Use seat to seat specs for Intake spec for best results) Number of Cylinders : 8 Bore in Inches : 3.766 Stroke in Inches : 3.75 Rod Length in Inches : 5.7 Static Compression Ratio : 9.87 (:1) Inlet Valve Closes ABDC : 60º (.007") Boost Pressure in PSI : 0 Target Altitude : 177 (Feet) Static compression ratio of 9.87:1. Effective stroke is 3.05 inches.
Your dynamic compression ratio is 8.18:1. Your dynamic cranking pressure is 163.62 PSI. V/P (Volume to Pressure Index) is 133
Cranking Compression Test PEAK/1st crank, Peak took about 7 cranks 2) 165/114# 4) 160/113# 6) 165/115# 8) 174/116# 1) 162/110# 3) 168/112# 5) 162/112# 7) 167/112#
Anything else you want to know skinny z?
Last edited by NoEmissions84TA; 07-20-2018 at 06:52 PM.
@skinnyz
I agree that the mixture looks rich as well, even so I have installed 10% richer primary jets and raised the secondary metering rods .05 to thwart det even further since removing those plugs which had about 60 hours on them in case the rich condition was simply at idle. (Likely sacrificing power)
Like you suggested I will have to try to pull even more timing to see if the symptoms improve. How much would you recommend I pull?
As for the timing set and distributor they are all brand new as well and the timing is much more consistent at every rpm than with the 1,200 hour 305. I could see the slop in the timing chain on the old setup as the timing fluctuated +/- 1-2° this set is rich steady. I have also painstakingly confirmed tdc on several occasions ensuring that I wasn’t stopping the piston btdc with the finder. I also have a nice clear moroso pointer and tape on the balancer to eliminate confusion.
The fuel should be a good true 93 octane as I have put about 100 gallons through the 45 gallon tank 10-20 gallons at a time while using star-tron fuel conditioner.
@lg4bird
I personally wouldn’t use Autolite plugs in anything but my string trimmer. Which nkg’s are cooler the tr6’s? These plugs are iridium and they were specified by mercruiser for this application, that being said I wanted to go with copper when I changed to the Denso Iridium Power but couldn’t cross over to any that were available at the time. The AC Delco heat range is apparently proprietary information, lame
I know I’m resurrecting an old thread here but I was very excited to find it here on TGO through a google search.
I myself have a gm L31R crate engine bone stock unopened with a gmpp 14097396 camshaft (supposedly) I bought it off Facebook
DESCRIPTION
This hydraulic roller design is used on the 383 truck and Ramjet 350.
The duration at lash point in degrees (intake/exhaust) is 288/308; duration at .050" tappet lift (intake/exhaust) is 196/206 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 431/451. Valve lash is zero/zero and lobe centerline is 109 degrees.
My compression numbers were all 208-230psi warm at 200’ above sea level pulling one plug at a time until they were all out. I had the choke warmed up and the quadrajet wide open 70 hours on the build.
I am also plagued by detonation/preignition. One major difference though, this engine lives in my boat. It’s set up with a marine intake, pertronix flamethrower 3 dizy and I’ve tried both ACDelco plugs and Denso plugs gapped to .040 I’ll have to check back on the plug specs.
Is this cranking pressure unreasonably high? I do trust the gauge even though it’s an actron from autozone.
The 395' cam is 256/264 @ .006, 196/206 @ .050 when I degreed it. Mine was right at 109* LSA and dropped in on a 107* ICL with the 40K mile GM single roller chain.
With a set of 906 heads milled .020", .016" steel shim head gaskets and that cam with 1.7 rockers I was getting about 210 psi in every cylinder at 600 ft elevation.
I also had massive spark knock at heavy load at anything over about 26-28* of timing. It was so bad that I added a flex fuel sensor and swapped my Express over to run on E85. I gained a considerable amount of both HP and TQ running 104 octane E85 over 93 octane pump gas.
TR55's are stock heat range for the L31 engine.
TR6's are one step colder.
The GM Marine engines and GMPP crate engines specify a 42 heat range. 2 ranges cooler than a Vortec truck. I always ran Delco copper MR42LTS plugs.
Also running that rich, I would suspect a decent amount of carbon buildup which will increase cylinder pressure and could cause detonation. I have used B12 with a homade system to pull it into the intake to clean out the carbon. Two 1/4" vacuum hose t's and some vacuum hose. Tee one of the emds of the first T into the PCV fitting. Then T the side of one T into the center of that T. Then hook a final hose to the center of the 2nd T. You just made an atomizer with two seperate atomizers. Warm up the engine to operating temp. Hook up the contraption. Put the hose off the 2nd T into the can. Start the engine and run it at about 1,000 rpm until the can Is practically 2/3s empty. Idle the engine and block off both extra air ports and let the engine stall. Let it sit for about 1 hour. Fire it up and then run the absolute hell out of it. It will smoke like a freight train at first but it will clean alot of carbon out of it.
Thanks for the reply fast355 I was hoping you would chime in since you had wrote about marine engines In earlier posts. This build should be a legitimate copy of the marine engines everyone sells Volvo penta , mercruiser, indmar with the exception maybe of the head gaskets but they all come out to 9.4:1 scr. The long block is a brand new L31R gmpp crate engine with the cam swap. Your build should have a couple points higher scr and longer duration at .050 so I would hope my build would be more knock resistant but you’ll have a .024 quench with the shim gasket and stock deck height so it might be a toss up.
The plugs I had in there initially were AC Delco 41-993, now I have a set of Denso IT16’s in there. I ordered a set of tr55’s yesterday but I won’t run them now knowing what you told me.
I also have an Accel ignition coil installed which might heat things up even further. I wanted to use a .32 ohm pertronix coil but it draws too much current for the wiring so I switched to the Accel. Should I run cooler plug than the 42, swap a stock coil in, open up the gap maybe?
It may also be that I am over propped the old engine design was 4K-4,400rpm wot the vortec marine engines are 5k-5,200rpm
As of now my plan is to try a smaller prop, colder plugs and new plug wires.
All above 210 psi cold test at 12K miles with the 275DEH, 10.3:1, high tension rings, I didn't tested yet with the XE284H
The theoretical cranking compression with your current specs shows 204 PSI.
If that's reasonably close then the 284 should yield somewhere around 184 PSI.
To get back to the 200+ cranking pressure, the static compression ratio needs to be at least 11:1.
Best results come from knowing the actual intake valve closing point.
Cranking Compression Test PEAK/1st crank, Peak took about 7 cranks 2) 165/114# 4) 160/113# 6) 165/115# 8) 174/116# 1) 162/110# 3) 168/112# 5) 162/112# 7) 167/112#
Anything else you want to know skinny z?
Perhaps this is where the calculator has it's failing. That stroked 334 with that cam (IVC at 60°) has a theoretical cranking compression of 203 PSI. And that would fall in line with the your DCR of 8.1:1.
Both calculators (your Wallace and my on-line version) are showing the same DCR.
Makes me wonder where things aren't lining up.
FWIW - 1986 LB9. 100% stock. 160k. 190-195 psi across the board.
GD
Any cam specs? The internet doesn't say much other than 179° intake duration but that must be at .050" rather than seat to seat.
I did find that they were a 9.5:1 engine.
FWIW - 1986 LB9. 100% stock. 160k. 190-195 psi across the board.
GD
That engine should have flat top pistons and the peanut grind but the flat tappet version. Mellings CS-23. Pulling that cam up on Mellings cam spec PDF.
The peanut roller cam CS-39 shows to be
252/260 @ .006
179/194 @ .050
.351/.385 lift
109 LSA
106 ICL.
My old stock 1983 G20 Van showed about the same cranking PSI but it had a little more cam (274 350 grind) and flat top pistons with 53cc chambers. I calculated it a little over 10:1. I could not run more than 26° of timing on 87 with it. 6° BTDC is all it would take timing wise before it started knocking at WOT. Running 93 octane I was able to run 10° in the hotter months and 14° in cooler months. All timing quoted with a good cooling system and 160°F thermostat.
I was 195 psi in all 8 cylinders at 180K miles.
This was as it came from GM in 1983 to my knowledge. It came from GM with an HEI that had both mechanical and vacuum advance as well as a facty ESC system that used a knock sensor and a tip-in vacuum switch that retarded the timing briefly about 10° on vacuum dropping from initial heavy throttle opening.
Stock 305 3.736" bore
Flat top with 6cc of eyebrow reliefs
Factory 3.8x0.020" steel shim head gasket
14022601 heads that cc'd at 53cc
CS-2 equivalent cam
260/271 @ .006
193/204 @ 0.050
.390/.410 lift
112 LSA
108 ICL
That engine should have flat top pistons and the peanut grind but the flat tappet version. Mellings CS-23. Pulling that cam up on Mellings cam spec PDF.
With that duration value and at 9.5:1, cranking pressure (theoretically) would be around 228 PSI.
So much for the real vs theoretical. But maybe the mileage and altitude (or more specifically the DA of the test day) could account for the results.
Using 252 intake duration gets 219 PSI.
Any idea what the IVC point is?
It came from GM with an HEI that had both mechanical and vacuum advance as well as a factory ESC system that used a knock sensor and a tip-in vacuum switch that retarded the timing briefly about 10° on vacuum dropping from initial heavy throttle opening.
Now that is an interesting feature.
I rely on my vacuum advance doing that job but in all reality, unless I really get into it, manifold vacuum is still high enough to give me over-advance issues.
20 initial, 14 mechanical (all in by 3500 and deliberately lazy) and 16 vacuum (all in @ 10").
At cruise, I can be as much as 50 and light to moderate acceleration induces some spark knock. That's with a 10.2:1 iron headed SCR (8.1:1 DCR) and 180 engine temps. (I really should go back to the 160 stat).
Sadly, this shortblock is getting pretty old and my compression test results no longer reflect what they should be. Leakdown testing showed some serious issues. The heads are fresh so it's the cylinder bores (and possibly broken rings and ring lands) that are the problem.
Well I have occasion to do a lot of compression tests (on stock engines with stock cams), and on 9.5-9.7 engines.. they are always (brand new, broken in, etc) 195 psi. And I'm very close to sea level. Between 150 and 200 ft at my house and about the same at my shop. The turbocharged engines running 8.2 to 8.5 comp. typically come back around 155 to 165 psi. The 8.9 engines are usually about 180. In my hundreds of tests over the last decade it's always been that way. I currently use a Snap-On comp tester that's about two years old,but have probably owned half a dozen in the last 10 years and they all agree.
I think there's something wrong with the theory. It's not matching with reality at least in my experience.
Well I have occasion to do a lot of compression tests (on stock engines with stock cams), and on 9.5-9.7 engines.. they are always (brand new, broken in, etc) 195 psi.
The qualifier there is stock engines with stock cams.
I'm sure you would agree that all 9.5:1 will not exhibit the same compression test results as that it's IVC related as much as anything.
Originally Posted by GeneralDisorder
I think there's something wrong with the theory. It's not matching with reality at least in my experience. GD
It's interesting to note that for the most part (as indicated by some of the posts in this thread) theory does match real world results, however I'm not maintaining that it's always the case. Theories are just that.
Yeah I have no idea what the IVC is. I know it's not a high performance cam. LoL. But the engines I normally work on are, comparatively speaking, pretty high performance even in stock form. 4 cylinder, 2.5 liter, making 170 HP at 5500 or so. That's the equivalent of a 5.0 making 340 HP. They are more modern and have 4 valves per cylinder. No fancy valve timing or anything though, and they are flat tappet. Still 195 psi cranking pressure. A static compression test seems to have a lot more to do with the static compression ratio than the cam profile. I'm sure it affects it, but I'm not convinced. I feel like the cam profile would affect how many revolutions it takes to get there, but the ultimate pressure is going to be more or less the same. The engine is still an air pump and the efficiency at a given rpm is affected by the valve timing, but the ultimate pressure it can achieve given a long enough pumping time should stay pretty consistent.
Perhaps this is where the calculator has it's failing. That stroked 334 with that cam (IVC at 60°) has a theoretical cranking compression of 203 PSI. And that would fall in line with the your DCR of 8.1:1.
Both calculators (your Wallace and my on-line version) are showing the same DCR.
Makes me wonder where things aren't lining up.
Using a Wallace Racing calculator. I used 29.75 for Barometer - close as I could estimate for 177 ft.
02-22-2014, 08:28 AM
Fess up, what other tricks did you use?
