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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!
I've been searching for quite some time on potential builds for my 1984 Z28. One interesting one that kept popping up over and over is a Vortec and Hotcam combo. It seemed to offer good power for the street (I haven't been to a track in YEARS) but still have some good manners in terms of idle and vacuum. For background I want something that is fun to drive, runs easily on pump gas, and has few headaches. I already have a 2500 RPM torque converter and 3.73 gears. Up top will be a Holly 650 DP and Performer RPM and exhaust will be handled buy 1 3/4" SLP shorties fed to a 3" Hooker cat back.
I want to keep it budget friendly as I don't drive it as much as I'd like so the L31 Seems like a good start. I'll get the heads checked, cleaned up with new seals, and reworked to handle the extra lift (LS6 or Alex parts springs). Back to the original point of the post though, the Hotcam looks like a good match but given its an older design, would something else work better? I found 2 other possibilities, one from Comp and the other from Lunati. The ones I'm looking at are below:
Of the 3 I like the Lunati best. Much faster ramps than the Hotcam and more lift. Compared to the comp the duration is a bit shorter which might help the lower end and the it has more of a split profile which should help the Vortec's relatively poor exhaust port. At least those are my thoughts, what does anyone else think? Am I splitting hairs here? Is there another option that might work better?
Also last thing, would using a thinner head gasket to bump the compression help out with these cams or would it not matter?
I’d give the edge to the comp 224/230. Very good street cam with decent sound as well with the 110 lsa.
hotcam is very fun too tho. I’ve tuned/used them. They idle stock just about, very smooth and drivable but the lazier lobe does bleed off some lower end power the faster lobes tend to gain under the curve.
same with the Lunati. It will be very close to the comp cam in performance.
cant go wrong with either of them but the hotcam can often be found used for 100-150$ lol so its cheaper if you can get it. Also the comp 224/230 can be found on the lt1 based forums used from time to time in the 112 lsa version.
the hotcam will run with less spring pressure. The others i would do a better double spring like the alexs parts kit.
The GM (Crane) cam was designed as a very low-effort upgrade that taxed the supporting parts very little. It was quite popular with Vortecs when they first came out and did work well for the most part. Not "the best", but certainly, "good enough" for lots of folks.
The Comp and Voodoo are MUCH more aggressive; have more of what some people know as "major intensity", i.e. ramp rate. The Voodoo series in particular needs all the spring you can possible give it because of that.
Really high lift doesn't do much good with Vortecs. Their advantage is their high low-lift flow #s; their disadvantage is that the intake flow quits increasing at much past .450" or so. Of course the exhaust side is the same as any other GM head, so the valve ceases to be The Bottleneck at relatively low lift there too. Duration is more of a help with Vortec exhaust than lift.
None of them will work in a stock L31 without some sort of head work. Either beehive springs, cutting the spring pockets & guides, or SOMETHING. My preference would be LS springs; although probably not the stock LS6 ones for either the Comp or the Voodoo. I'd go with PAC 1218 for those. The reason for that is, it's too easy to hit water when enlarging the spring pockets in those heads; there's a "hump" in the top surface that you have to cut into sideways, and the "corner" of the pocket tends to hit water. 1.45" springs (Comp 986 for example) have been used but I think some people have hit water trying to do that. Not sure if they were trying to increase installed height (lower the pocket) too, that would certainly make it worse. Sticking with stock diameter, and leaving the spring pocket alone, seems safest to me, which the PAC 1218 fits with.
I'm not a fan of Alex's stuff. While some people seem to get good results, others don't, and I'm always a bit leery of anything that sounds too good to be true. I would not go that route myself. There's too many other options that don't cost that much more and don't have the shady kind of character to them.
I’d give the edge to the comp 224/230. Very good street cam with decent sound as well with the 110 lsa.
hotcam is very fun too tho. I’ve tuned/used them. They idle stock just about, very smooth and drivable but the lazier lobe does bleed off some lower end power the faster lobes tend to gain under the curve.
same with the Lunati. It will be very close to the comp cam in performance.
cant go wrong with either of them but the hotcam can often be found used for 100-150$ lol so its cheaper if you can get it. Also the comp 224/230 can be found on the lt1 based forums used from time to time in the 112 lsa version.
the hotcam will run with less spring pressure. The others i would do a better double spring like the alexs parts kit.
Thanks for the advice, it kind of falls in line with my thoughts that the Comp and Lunati would be close in performance and a step up from the Hotcam. The only reason I initially thought Lunati was for the bit shorter duration might give me a touch more low end, but with the 2500 TC and 3.73s on street tires will it really matter... Also, what are your thoughts on the stock 9.4 CR with these cams? Is it sufficient or should I try to bump it up with the thinner head gasket? Thanks!!
The GM (Crane) cam was designed as a very low-effort upgrade that taxed the supporting parts very little. It was quite popular with Vortecs when they first came out and did work well for the most part. Not "the best", but certainly, "good enough" for lots of folks.
The Comp and Voodoo are MUCH more aggressive; have more of what some people know as "major intensity", i.e. ramp rate. The Voodoo series in particular needs all the spring you can possible give it because of that.
Really high lift doesn't do much good with Vortecs. Their advantage is their high low-lift flow #s; their disadvantage is that the intake flow quits increasing at much past .450" or so. Of course the exhaust side is the same as any other GM head, so the valve ceases to be The Bottleneck at relatively low lift there too. Duration is more of a help with Vortec exhaust than lift.
None of them will work in a stock L31 without some sort of head work. Either beehive springs, cutting the spring pockets & guides, or SOMETHING. My preference would be LS springs; although probably not the stock LS6 ones for either the Comp or the Voodoo. I'd go with PAC 1218 for those. The reason for that is, it's too easy to hit water when enlarging the spring pockets in those heads; there's a "hump" in the top surface that you have to cut into sideways, and the "corner" of the pocket tends to hit water. 1.45" springs (Comp 986 for example) have been used but I think some people have hit water trying to do that. Not sure if they were trying to increase installed height (lower the pocket) too, that would certainly make it worse. Sticking with stock diameter, and leaving the spring pocket alone, seems safest to me, which the PAC 1218 fits with.
I'm not a fan of Alex's stuff. While some people seem to get good results, others don't, and I'm always a bit leery of anything that sounds too good to be true. I would not go that route myself. There's too many other options that don't cost that much more and don't have the shady kind of character to them.
Wow, thanks for the info on the spring pockets, I didn't know it was so close to the surface. I'll stick with the safest options, no reason to risk it when there are other ways of working it.
As for the cams, what would be your preference based on the rest of the car and my goals? Any other suggestions? Also is the 9.4 CR OK or do I need to try and get it bumped up? Thanks!!
You’d probably want screw in studs installed and the seal bosses cut down to gain lift clearance. There are plenty of 1.25-1.29” diam springs that will work with hyd rollers so no need to worry about cutting out pockets wider imo
should beable to get the lift clearance fairly easily with proper seals and retainers, possible .050” offset locks to raise assembly up.
i like more comp if you can find it. But depends on how deep the pistons are in the hole. If a non decked block they could be .025 in. That would leave .015-.025 as optimal gasket thickness for the typical .040” quench height. GM and i think MR gasket sold a .028” composite gasket that worked well for me. SOme guys use the .015 shim style gaskets, i believe thats what oem L98’s had. They Can work. Resurface the heads for smoothness and maybe try that copper spray to help sealing, thats as good as you will get for compression. It wont be much of a change though, so don’t sacrifice sealing for those few tenths.
Thanks again Orr for the help, if it will only bump it up a couple tenths it won't change much and probably not worth messing with for a strictly street car. Anything you would change with the head, cam, TC, gear ratio combo given what I am looking to get out of it?
I've gone down the Vortec/XR276HR route. It took my 3700 lb Camaro into the 12's with a few supporting parts. For the record: My thoughts are that the Hot Cam is dated and it has a 112 LSA, the VooDoo has a 112 LSA as well. The 276, while not perfect, is a better fit IMO. There are other choices but that's a whole other ball game.
The short list I think has been covered.
Springs: I used Comps 26918 with no machine work needed although I did cut the guides for a Viton seal. The PAC springs mentioned are a less expensive alternative from what I understand. Offset keepers will likely be needed to get the proper installed height. I used an .050" taller keeper from Crane. Can't say I care for Alex's stuff either. No reason other than the word "ghetto" which tends to follow the brand around.
Screw in studs: I originally ran the heads out of the box with a flat tappet 218@.050" w/.454" lift cam. It was great until I missed a shift a bent a couple of valves. The next step was the full monty with springs, screw-in studs, guide plates, 1.6 ratio rockers and pushrod holes clearanced. If I were to do it again with that level of performance, I'd skip the guide plates and use the self guided rockers. It skips a machining step and takes some work out of the valve train setup. A simple screw in stud with no spot facing of the stud boss can make it a DIY project.
Compression ratio: While it's not the be all and end all at this level, getting to 10:1 with the 276 pays off. 9.4:1 is a little weak. With the heads off, you can access the measurements needed, I.E. piston below deck, piston dish/valve relief volume. With that you can see what head gasket or head milling will get you. If the heads are used then you'll probably have to mill them to get them flat. Do the math and rather than .003-.006" for flatness, go a little more. I've the info somewhere that dictates how many thou equals how many cc in chamber volume. Compression is not only a HP output tool but it also helps with the fuel economy. Some folks don't care. I do.
As for the rest, I'd skip the double pumper for a vacuum secondary carb and absolutely look at getting a stall converter.
And slicks. Because you'll need them.
Problem is, .001"s is thickness; and you hafta know how many sq .001"s the chamber is, so you can multiply em together and come up with a volume. And EVERY head casting is a bit different, and EVERY individual head, even every individual CHAMBER, is slightly different shape.
Best you can can do is, a "rule of thumb". Which is somewhat specific to a particular head casting #.
Best anybody usually comes up with is, approx 1cc per .020" or so for SBC heads. Could be anywhere from 1cc per .030" for the old closed-chamber small-footprint "bathtub" heads, up to maybe 1cc per .016" for the real open-chamber 70s smogger crap. And worse yet, as you take off more deck and the chamber shrinks, so also the volume you reduce grows. Ye lays yer money down and ye takes yer chances. But if you think THAT's tough, try big block heads sometime, which vary over almost a 2:1 chamber footprint area.
Use your burette and whatever else as you go. Measure, measure, cut; measure, measure, cut; and so on. "Measure twice, cut once".
Last edited by sofakingdom; 08-05-2020 at 09:56 PM.
My people tell me .006" per cc for flat milling.
.0075" per cc for angle milling.
But as usual, as Kingdom says, each head is unique.
The above tends to be a guideline for Vortec and similar Vortec copies.
I went .026" to get from 68cc (as measured) to a target 64cc. The chamber measured ended up at 65.4cc. These chambers were not standard though.
Intake Valve Lift with Factory Rocker Arm Ratio:0.495 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.502 in.
Valve Lift with Factory Rocker Arm Ratio:0.495 int./0.502 exh.
Lobe Separation (degrees):110
Computer-Controlled Compatible:No
Valve Springs Required:No
Quantity:Sold individually.
In-Store Pickup:Choose In-store pick-up (OH, NV, GA, TX) on our web site.
Melling M-Select Class 2 camshafts are perfect for any ride. They have good idle quality, low-rpm torque, and mid-range performance. These cams will work with stock or slightly modified engines with manual or automatic transmissions. Order the model designed for fitment on your vehicle.
Its so hard to compare cams that have equal .50" lift and LSAs, as it comes down to the lobe profiles. Part of me wants to think the cheaper cams are just knock-offs of the brand name cams.
That said, with the way Modern lobe design is I'd just spend the extra on a current profile. Its not that much extra, and its an internal part that is not all that fun to change.
...with the way modern lobe design is I'd just spend the extra on a current profile. Its not that much extra, and its an internal part that is not all that fun to change.
Exactly.
Looking at the Melling's .050" vs it's adv. duration, that's 224 to 283. Compare that to the previously mentioned XR267HR with the same 224@.050", advertised is less at 276.
There's a real benefit to the faster profile.
Exactly.
Looking at the Melling's .050" vs it's adv. duration, that's 224 to 283. Compare that to the previously mentioned XR267HR with the same 224@.050", advertised is less at 276.
There's a real benefit to the faster profile.
Having run aggressive lobes and mild lobes, there is a slight power gain to be found with an aggressive lobe, however in a street engine that needs 100K mile durability or more I have found the valvetrain life to be extended considerably with a milder grind like a magnum lobe. The cam in my current 383 is ground on magnum lobes and makes plenty of power. Better to get your power through headflow and supporting components than through a very aggressive cam lobe. Just my $0.02. I have run a XFI cam in a couple of different engines. SBC and Modern Hemi. Both had a crazy amount of valvetrain noise. Noisier in fact than my Magnum lobe/Rhoads V-Max lifter. The XFI lobes smack the valves on the seat on closing and will drive a knock sensor crazy without desensitizing it.
I guess it depends what intake it will be run under, but even with the common 4 deg advance, those hot cam spec cams all seem to make really good torque everywhere. Even on the lt1’s. Tpi is a brutal torque machine
Exactly.
Looking at the Melling's .050" vs it's adv. duration, that's 224 to 283. Compare that to the previously mentioned XR267HR with the same 224@.050", advertised is less at 276.
There's a real benefit to the faster profile.
Be careful saying that bro, lots of times they offer the @ 50 specs with stock 1.5 ratios, and then the next cam is rated @ 50 with 1.6 ratios. Especially with the gen1 sbc stuff. I know it's only a couple degrees of duration, but make sure you are comparing apples to apples.
Be careful saying that bro, lots of times they offer the @ 50 specs with stock 1.5 ratios, and then the next cam is rated @ 50 with 1.6 ratios. Especially with the gen1 sbc stuff. I know it's only a couple degrees of duration, but make sure you are comparing apples to apples.
Originally Posted by F-BIRD'88
The duration of the Melling cam is likely @.004" VS .006"..
Originally Posted by T.L.
Yeah, you can't compare advertised duration between different cam manufacturers unless they took their measurements at the same lift. That's why .050 is used as the industry standard. Comp Cams measures their adv duration @ .006 . Other MFGs use .004, or .010.
I'm not here to stir up ****. Or to argue. But .002" in the difference? And on the slowest part of the ramp? I'll take that for what it is and that's a reasonable observation but with the considerable differences between the two cams, it doesn't amount to much. But I get it.
Still, the Melling is a slow outdated cam period. Reminds me of the "Clevite" flat hydraulic I ran way back when. 218@.050 with 284 advertised! I don't care where it was measured from. It was pretty lazy by today's (and yesterday's) offerings.
Doesn't comp often use o.oo2 as their seat open/close vs the 0.006 that is more common?
And even if they all use 0.006, is that figured at the lifter,? or at the valve?
Their "creative advertising" makes it very difficult to make an apples to apples comparison. Is all I was saying Skinnyz
I remember a discussion at speedtalk, more than one actually where Mike was asked to help compare 3 cams, and it ended with him determining they were all basically identical. I wish I could find it. And they all had listed specs that on paper were vastly different.
I remember a discussion at speedtalk, more than one actually where Mike was asked to help compare 3 cams, and it ended with him determining they were all basically identical. I wish I could find it. And they all had listed specs that on paper were vastly different.
Valve lash difference.. and check height difference
Comp is .006" @lifter.. Crane is .004" or .0045" @lifter.
The SAE spec is .006" + lash (solids) @valve.
Not all cams are listed using SAE spec.
Their "creative advertising" makes it very difficult to make an apples to apples comparison. Is all I was saying Skinnyz
Understood. That's why an informed consumer is the best consumer. I haven't come across that Speed Talk thread but I'll dig for it. Sounds interesting. Not so much the solid vs lifter profiles but the measuring points and the impact they have on advertised duration. I.e. .002" as opposed to.006".
A good start would be all the cam companies listing the .020", .050", and .200" durations above the lash ramp. If the lash ramp is .010", the durations would be measured at .030", .060", and .210" If the lash ramp is .015", the durations would be measured at .035", .065", and .215" This would at least give you an apples to apples comparison
so you can see lash ramps being different can really change the measurements
but for hyd rollers i believe Mike said most have a .004-.006 lash ramp and thus are closer in comparison, but i think some lobes may not have any lash ramp. Thats why not all hyd rollers can be run with solid lifters
You need to look at how the differences effect how the engine runs by what is going on at the valve where it matters vs paper comparidions..
..050" duratons specs do not change .200" durations do not change .020" durations do not change because these are all measured at the lifter..
the cam does not change.. Its the changes that are at the valve that matters as to how the running engine runs and performs.
Fair enough F-Bird. But we have to start somewhere.
Then we can get into how something as seemingly simple as setting the lash on a hydraulic lifter can have different effects if done with different specifications such as bottoming out a hydraulic rather than 1/2 turn down. Changes quite a bit.
This just in. I fired off an email to Milling regarding how they measure.
Message Hello
I'm interested in your 22280 camshaft.
Can you tell me at what lift the advertised duration is measured at? I mostly work with a .006" lift for those numbers however some specs are measured at .004". Other I've found to be .010".
Thanks in advance.
Kevin
Hi Kevin, here is the spec sheet I have listing this camshaft. It says SAE specs which should be @ .006” but I know what you mean. That is why it is most common to use the @ .050” duration numbers for consistency.
You need to look at how the differences effect how the engine runs by what is going on at the valve where it matters vs paper comparidions..
..050" duratons specs do not change .200" durations do not change .020" durations do not change because these are all measured at the lifter..
the cam does not change.. Its the changes that are at the valve that matters as to how the running engine runs and performs.
right but thats much harder to do. Theres deflection in the system that could vary depending on the components used, and how the deflection changes with different rates of acceleration from different lobes in an actual running engine at rpm, temperature growth effects...tough to compare. Paper specs extrapolated to the valve thru rocker ratio and geometry can suffice for now.
This just in. I fired off an email to Milling regarding how they measure.
Message Hello
I'm interested in your 22280 camshaft.
Can you tell me at what lift the advertised duration is measured at? I mostly work with a .006" lift for those numbers however some specs are measured at .004". Other I've found to be .010".
Thanks in advance.
Kevin
Hi Kevin, here is the spec sheet I have listing this camshaft. It says SAE specs which should be @ .006” but I know what you mean. That is why it is most common to use the @ .050” duration numbers for consistency.
He is refering to .006" @the valve (SAE spec) which is .004" at the cam. These are not lazy hyd ramps. But likely will run quiet assuming the lifters are working right. 110LSA 107/113... Move it to 104/116.
It will GLH.. 1.6 in rockers may help a bit.
Understood. That's why an informed consumer is the best consumer.
in the case of cams, I figure guys like Mike Jones have literally invested their lives into camshaft design and development. And I say what I want out of the engine/combo... And trust him to deliver.. but that's not the case with crane, comp, and erson etc.. call the same company twice in the same day and give the exact same info to them and you'll get a different recommendation. I guess there is more than one way to skin a cat, but for me. I have kind of silently read and followed along with stuff Guys like Speier, jones, Uratchko, Cris straub, Carl Hinkson of cnc blocks, Mark Oneil of probe, sheldon barr's of lgm.. and others of their caliber. and when and if I needed something that is in their area of expertise.. I'll trust them, blindly and lay my money down. Because of their reputations for delivering results. But, I'm just a street car guy, not a racer. Your mileage may vary.
But now that I think about it... Isn't that being a wise, and semi informed consumer?
Yeah, I probably spent six months reading posts here from guys like Orr, 1989transamgta, and others before I spent a dime on the vettes 385 build. Hard to argue real world results from guys that have been there and done that
Who's got the money to be buying and testing cam after cam for a street car? For a max effort track car sure. I think the key is knowing who is full of ****, and who is actually making power. Then build comparably
Yeah. Not many people out there test cams. For cookie cutter combos like your typical oem Ls builds some shops have done cam tests to tweak designs and then sell them as their shelf grind for that particular combo. Or some guys cut so many cams for customers for that combo and received feedback from dynos or track results to know exactly what to expect.
but not everyone runs the same identical combo of parts, especially sbc guys with different heads intakes headers exhaust systems transmissions etc
broad brush: typical 350-383 cubes, 10-11:1 comp, intake supporting say 6000 rpm peak, typical decent longtubes, half decent Flowing exhaust, yada yada, sure you can get a dozen cams from dozen different but competent cam guys and end up plus or minus 5-6 deg duration difference and possibly 5-15 hp difference, if that. Its always good to go with a guy who has built or can show you examples of similar parts lists doing what you want to do, and their cam will repeat results in that ball park. Guys who might not have done exactly what you have done but understand airflow and engines may get you pretty close with room to gain more with testing. They may be off 10-20 hp from another guy who is experienced with that combo. They may not be down any power.
cam guys have their math, programs, and some experience to draw from to get the closest first pass cam suggestion. After that, dyno testing track testing different valve events to get what you want is the best thing you can do to get the perfect cam. But realistically thats not gonna happen for 99% of enthusiasts
Translation: You pick cams based on opinion and how that makes you feel VS testing.
This is untrue.
I select cams based on EXPERT opinion. I also, in the absence of a real dyno, stand on the shoulders of those giants that DO.
I science it out as much as is practically possible. Understanding the theory and what a given engine needs (the given in this case is a Gen 1 SBC) helps me make an informed decision.
I also run computer simulations. However I find that they often don't correlate to what those previously mentioned giants have found in the real world (and my computer software is a little dated).
I also have conversations much like this one. I've read your posts many times and often find there's some pearl of wisdom I can take away from it. Like many others here.
Lastly, I examine what has worked for me in the past, how it performed, what it's failings were and vow not to repeat if there's a change that's relevant.
08-03-2020, 10:31 AM
But if you think THAT's tough, try big block heads sometime, which vary over almost a 2:1 chamber footprint area.
