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Last Christmas I purchased a nice 1987 IROC with the L98 with 27k miles from a private collector who stored the car indoors. The paint and interior are pretty much perfect and it shows well and looks amazing! Despite the condition of the car, it has a few small leaks from age going on at the rear main seal, oil pan and valve covers not to mention the classic plume of smoke at start up from leaky valve stem seals. There is also an occasional oil burning smell at stop lights. This does not show well and a car this nice deserves better and since the engine has to come out anyway, I figured why not add some power in the process. Initially I thought about just porting the factory components and there was a thread where someone did exactly that on Speed-Talk found here https://www.speed-talk.com/forum/viewtopic.php?t=55886
The guy who ported those components went from a total cfm airflow from throttle body to head of a 185cfm stock to a fully ported 219cfm total @.500". Thats enough for 350hp but I knew aftermarket factory appearing components are the way to go. The caveat is it has to drive nice and look completely stock, BUT PERFORM. I am wanting 350-400hp with possible room to grow. Meaning the parts can be used on a 383 in case there is a problem with this engine at a later date. Im sorry but I have to edit it at this point and say this is NOT another "more RPM" build and this car will NOT end up as an ongoing science project. I understand the limitations of the intake, computer and driveline these cars have and I am not interested in using a nice IROC just to prove a point. This is aimed for those guys who want better performance from their cars while not dealing with constant headaches.
Moving on... This is a nice good weather cruiser/show car that could use a little more power just to be able to stay ahead of the modern (insert FWD 300hp V6) traffic. After watching numerous attempts at trying to get more RPM from the TPI intake, I have often wondered what kind of average power can be attained just by maximizing the TPI system in the RPM it was made to perform in while paying attention to port size, airspeed and port shape.
The car at the local Car/Airplane show this past Feb.
When it comes to maximizing the power the TPI system puts out, I am pretty much restricted by the tube runner sizes at the plenum. The biggest runners available are Arizona Speed and Marine 1.75" OD runner. 1.75" OD with the .060" wall thickness calculates to a 1.63" ID giving it a cross sectional area of 2.08". This means that 2.08" will have to be the average CSA for the port and this is actually fine for a 350 with an RPM of 6000rpm. If you use a port bigger at the base, the runners will still limit the HP being made as they will be the choke point of the system and possibly cause HP loss as the localized velocities in the runners are higher than in the base. The aim is to get the port as even and steady as possible while maintaining or tapering as it flows into the cylinder head. The runners will flow 260cfm @ 300fps. But by increasing the airspeed through the intake, you can make a smaller port flow more air. There are limits to what your airspeeds can be. Too fast and it'll reach sonic choke and the port will no longer flow and make power.
Here is the best description on flow written by Larry Meaux, the creator of PipeMax.
the "Best Fit" to Taylor's data regarding Induction System temperature
was approx. = 105.5 degrees F = approx. Speed of Sound= 1165 feet per sec
Taylor recommended Inlet Mach numbers from .40 to .60 Mach
from his data with various Engine types, it was discovered that
an Inlet Mach Index of .50 to .60 was "Controlling" ,
or in other words, was the RPM-HP limiting factor .
the Z-Factor Inlet Mach Index, works better with 2,3,4,5 valve Heads
with relatively low lift cams or low L/D Ratios
.60 Z-Factor times 1165 fps Speed of Sound at 105.5 F = 699 fps
DeskTop Dyno 's Book also state a limiting FPS speed of 700 fps..which is
very close to 699 fps, probably just rounded-off to 700 fps.
700 fps = 111.81 Inches of Water Flow Test Pressure
also 700 fps = 4.038 psi pressure differential = 127.5 % PerCent Potential Volumetric Efficiency
There is a tremendous amount of Research SAE Data by individual groups and Companies like GM and especially Honda SAE research papers,
and also in Books like Philip H Smiths and Taylor, all "correlating"
to the fact that .50 to .60 Mach is the "Controlling" or RPM-Power limiting
speed . (.55 Mach is average)
.50 Mach = 582.5 fps @ 105.5F = 77.4 Inches of Water
.60 Mach = 699.0 fps = 111.5 Inches of Water
700 Fps times .5 = 350 FPS , and 350 FPS = approx. 28" Inches of Water
Flow Testing at 28 Inches of Water is roughly "half" the Air Speed Velocity
in Live Engine conditions.
77.4 + 111.5 Inches = 94.5 Inches of Water average depression at Z-Index
to get a more realistic picture of Engine CFM demand thru an Intake Port or Induction System it would be better to simulate or Flow Test Cyl Heads
somewhere between atleast 60 Inches to as much as 120 Inches
it would seem the "Ultimate FlowBench" would be one that was capable
of "Wet Flow" testing at 120" Inches of Water Test Pressure
Flow Testing at only 28" Inches simulates an Engine fairly closely,
but 28" also is similiar to 238.8 mph
and a "Live Engine" at .55 Mach Choke = 436.9 mph
sure you'll discover/learn some things at 238.8 MPH
but there's more to be discovered at 436.9 MPH
sort of like a NASCAR , if you did all your Testing at 100 MPH,
the Car would look great going around Curves at 100 MPH,
but do the same Curve tests at 200+ MPH, and now you can see the Driver fighting to keep the Car turning those same Curves without spinning out
(= Flow Separation in Live Engine).
Looking at all my Flow Test data thru all the years of Flow Testing many different Brands/Styles of Cylinder Heads, to get a decent idea or correlation to a Live Engine, you need a bare minimum of 25" Test Pressure on a Steady-State Flow device like a FlowBench.
i've noticed in some Cyl Heads over the years that Flow CFM can change dramatically above 28" ....that is some Cyl Heads take a dive in Flow CFM above 28" inches. usually as you go from 28" to approx 34 inches.
So far all my data, it looks like we really need to be Flow Testing Heads
above 34" to make sure its not taking a dive....any Head that has had a Flow separation problem has shown up by 34" Inches, whereas at 28" has sometimes hidden the flow separation problem because 28" is on the verge of too slow velocity in some Cyl Head port shapes.
i mostly Flow test at 36" and spot check at 48" and use Software to convert back to 28".
Darin Morgan previously mentioned in another Post, that IRL Cylinder Head developement was being conducted at well over 100" Inches of Water Flow Test pressure.The differential we are concerned about though is between cylinder and the intake runner...not the runner to atmosphere.yes its the combination of the "Flow Lag-Time" and "pressure differential" between the Cylinder -vs- the Intake Bowl/Runner ..that setsup the Mach limiting velocity relative to temperature gradient in the Induction System.
So there you have it.
Many people who do TPI intake modifications only port match the entrance and the exits. This leaves a pinch point in the center of the intake where the first bend is after the runner flange. It also makes the airspeeds speed up, slow down and speed up again which takes the average airspeeds and lessens them among possibly creating a localized velocity in the port that can hit sonic choke or worse, end up being the actual pinch point of the intake runner track. It is good porting practice to take pitot tube readings when you are porting something and to also try and get the port areas localized velocities to flow as close as possible to each other as too high a localized velocity can create an airspeed under higher depression that will shut off flow.
So now that we know all this and now we know that simply bolting an AFR head to a port matched intake is not the best route for making the most HP, having a custom ported cylinder head and intake is the best way to go. For this I called Charles Servedio whom has worked with David Vizard to help me get the project done. We spoke on several occasions (still do and I probably annoy him with questions) and decided ultimately the Dart SS 165cc head is the perfect head for my project. The modern chamber will allow a better burn rate with less timing, help stave off detonation and can be ported to the users liking. These heads are often used in circle track rule class racing and have been used on 383's making WELL over 500hp ported. PN# 10024365
As you can see, these are high quality gray iron which will flex and return to original shape instead of cracking. These also are using the correct 87-95 intake bolt pattern and they are drilled for the correct centerbolt valve covers.
Camshaft wise is to be determined and is something I would like to talk about. There is a lot of cam theory going around and that covers a lot of information. I can tell you that the idea behind this is squeeze as much VE as possible which means as the piston rounds BDC and the intake valve is closing, I need to have a later IVC even with low lift flow to inertia ram the intake charge into the cylinder. The downside of inertia ramming can be reversion at lower RPM. So Im not really sure what to do here. I have thought about having Charlie cut 50* seats to help prevent reversion and couple that with a later IVC and we are looking at that.
Using Vizards cam calculator, a 350 would want a 108 LSA and I think I could run one that tight if I kept the duration down. As a matter of fact, GM sells a 215/223 .473/.473 108 cam in its SP357 crate engine with iron Vortec heads and it actually has LESS overlap than a Lingenfelter 219 does. Just goes to show you, not all tight LSA cams have major overlap. All that being said, I want the car to have a noticeable idle but nothing choppy. I need the car to idle with AC, drive very well and still pull to 6000.
I will probably have Mike Jones cut a custom cam for this so I am leaving as little on table as possible. As David Vizard says, a custom cam and a shelf cam cost difference is negligent, so why not pick the right cam? That being said, I have a very nice brand new Lingenfelter 219 already which is a proven TPI cam thatll drive nice, but Ive never seen a 219 pull to 6000rpm. What I am most impressed by lately is Jim Halls 355 which pulled clean to 5900 at 396hp with long runners using a TPIS Lil Chubs 220/224 .500/.500 110 LSA. Thats an amazing TPI engine and he should be very proud. What do you guys think would work best?
For reference, a ported stock intake can flow right around 245-260cfm depending on the bench and whos porting it. This may be enough to match the ASM runners for cfm, but just because you can get 260cfm out of once piece, and you get 260cfm out of the next doesnt mean youll end up with 260cfm total flow. Intake components all have a resistance to flow and that resistance is like series resistors in an electrical schematic. You may get 260 cfm out of the runners and base but bolted together you are looking more like 235cfm. Initially I was going to do this job with a SDPC vortec base, but parts availability and the discovery of total flow ported made me cancel that idea and grab a better base. This actually worked out fine because the head I ended up needing is better for the job anyway thanks to the port sizes.
Subscribed! Thanks for posting. I have similar goals for my 91 formula 350. What cam are you planning on running, and do you plan to do anything with the transmission and rear end?
Here is another video of the ported stock base on speedtalk. Basically what Charlie is doing here is checking over his previous work and looking at cfm and port shape to see if there can be any improvements made. He is also starting to look at some airspeeds in the intake to see where it can be helped.
Back on the bench with more porting trying to get an average of airspeeds inside the base of the TPI system using the ported Dart heads. More porting as an experiment to gain some insight for when the TPIS piece arrives.
Camshaft wise is to be determined and is something I would like to talk about. There is a lot of cam theory going around and that covers a lot of information. I can tell you that the idea behind this is squeeze as much VE as possible which means as the piston rounds BDC and the intake valve is closing, I need to have a later IVC even with low lift flow to inertia ram the intake charge into the cylinder. The downside of inertia ramming can be reversion at lower RPM. So Im not really sure what to do here. I have thought about having Charlie cut 50* seats to help prevent reversion and couple that with a later IVC and we are looking at that.
Using Vizards cam calculator, a 350 would want a 108 LSA and I think I could run one that tight if I kept the duration down. As a matter of fact, GM sells a 215/223 .473/.473 108 cam in its SP357 crate engine with iron Vortec heads and it actually has LESS overlap than a Lingenfelter 219 does. Just goes to show you, not all tight LSA cams have major overlap. All that being said, I want the car to have a noticeable idle but nothing choppy. I need the car to idle with AC, drive very well and still pull to 6000.
I will probably have Mike Jones cut a custom cam for this so I am leaving as little on table as possible. As David Vizard says, a custom cam and a shelf cam cost difference is negligent, so why not pick the right cam? That being said, I have a very nice brand new Lingenfelter 219 already which is a proven TPI cam thatll drive nice, but Ive never seen a 219 pull to 6000rpm. What I am most impressed by lately is Jim Halls 355 which pulled clean to 5900 at 396hp with long runners using a TPIS Lil Chubs 220/224 .500/.500 110 LSA. Thats an amazing TPI engine and he should be very proud. What do you guys think would work best?
Lloyd Elliot and I collaberated to fix the Comp Cams mess in my 383 I built that Lloyd ported the heads on. The cam going into it is basically an Erson clone of the LPE219. 265/269 @ 0.006, 217/218 @ 0.050, 0.544 lift with a 1.6 rocker, 112 LSA and 112 ICL that will be advanced to a 108 ICL. I did not realize how similar they were until after the fact. Not a LTR TPI, but I absolutely expect that cam to carry power to 6K in the 383 using an Indmar marine manifold with a 92mm 4 bolt LS throttle body. The Indmar manifold has about 6" long runners and a big, tall open plenum. Street & Performance's old SBC "TPI" intake was a chromed version with a dual 58mm throttle body.
The cam coming out is 271/284 @ 0.006, 218/228 @ 0.050, 108 LSA, 106 ICL and I had already dropped it from 1.7 rockers to a 1.6/1.5 split. With 61.5* overlap @ 0.006 and 7* overlap at 0.050" with the somewhat early IVC, it was not happy moving around 7,000 lbs at lower rpm. At 750 rpm the overlap is very noticeable even in an 11:1 383. It played havoc with the P59s misfire detection so much I eventually just disabled it so it would stop unlocking the torque converter under 65 mph. At 55-65 the overlap induced misfiring was so prevelant at light throttle cruising that the PCM would unlock the converter. Rolling along 75-80 it would eventually smooth out enough at ~3K it would eventually lock again and hold lockup at 2,500.
That TPIS Lil Chub sounds very similar in specs to a Melling 22280. That is not a radical cam in a 350, but a very noticeable one in terms of idle and low speed drivability. It has some chop and it will eat some fuel at lower rpm from the overlap.
Early IVC trying to build cylinder pressure I presume? I would honestly think less compression and a 112 would be the hot ticket for a van like that. Back during Hurricane Harvey, Texas lost all fuel and 87 was the only thing around if you could find it. The general public sucked all the 87 dry in 2 days, then went for the mid grade and supreme too. Within 3 days we were dry. Flooding everywhere, couldnt get gas to move and I actually went and bailed people out all along the Texas coast. When I got back, there were still problems going and getting fuel was one of them. My point is, for a driver that actually gets driven a lot, I wouldnt set anything up NOT to run on 87. Im sure you could on that rig but it definitely wanted more ocatane. Let me know how you like the new cam.
Early IVC trying to build cylinder pressure I presume? I would honestly think less compression and a 112 would be the hot ticket for a van like that. Back during Hurricane Harvey, Texas lost all fuel and 87 was the only thing around if you could find it. The general public sucked all the 87 dry in 2 days, then went for the mid grade and supreme too. Within 3 days we were dry. Flooding everywhere, couldnt get gas to move and I actually went and bailed people out all along the Texas coast. When I got back, there were still problems going and getting fuel was one of them. My point is, for a driver that actually gets driven a lot, I wouldnt set anything up NOT to run on 87. Im sure you could on that rig but it definitely wanted more ocatane. Let me know how you like the new cam.
We had the same issue here in DFW. I was putting 100 miles a day on my Infiniti M56S. People that did not even need or use a tank of fuel a month rushed out and filled their tank. The M56S is like 12.5:1 static from the factory, it actually ran on 87 in normal driving just fine although the fuel mileage tanked because of the knock control logic. Nissan uses the knock sensors as a closed loop timing control system that tries to advance the timing as much as possible. You can cut the timing table 10* on those and the ECU will add the timing right back.
I run E85 about 99.5% of the time, hence the higher compression. I will not setup anything for 87 myself. Setting it up for 91 octane at a minimum more makes up for the price difference in better fuel mileage. That 383 will run on 87 though with the timing retarded a bit if push came to shove.
I'll be following this with interest. Maybe even have something of value to contribute.
I was going to ask in another thread where that Speier chart came from. What software is it?
So nobody has done anything like this here? Nobody has custom ported anything and taken measurements to see what the airspeeds were or what size port they ended up with?
About the only person here at thirdgen that would have the tools for that kind of job would be Chad. I might be wrong but in all of my years here, I can't think of someone that has first hand knowledge for generating the information you're looking for..
Plenty though have done lots of testing in other ways.
I'll ask a question somewhat outside of the envelope you're working in. Regarding a stock GM TPI intake tract, what are your thoughts on how it would stack up with a DZ architecture 302 CID? A 4" x 3" bore and stroke deal. There's a fellow here at thirdgen that is contemplating just that.
I will probably have Mike Jones cut a custom cam for this so I am leaving as little on table as possible. As David Vizard says, a custom cam and a shelf cam cost difference is negligent, so why not pick the right cam? That being said, I have a very nice brand new Lingenfelter 219 already which is a proven TPI cam thatll drive nice, but Ive never seen a 219 pull to 6000rpm.
Isn't the Lingenfelter cam an outdated lobe profile? Long on the seat, short at .050"? Seems to me, IIRC, the advertised duration numbers were difficult to come by.
As for Vizard...I've followed him for years. Straight talker. But at SpeedTalk he gets slammed regularly. Not even sure what to make of it.
Jones seems to be the go to guy.
For Skinny Z since he said the Lingenfelter cam card was hard to find. 270/270 @ 0.006.
I did not realize the Erson I had custom ground through Lloyd Elliot was the same for all practical purposes until later. Slightly less lift, I might still run a 1.7 rocker on the intake.
I can see how the short cam timing would boost the slower engine speed torque.
Here's an overlay of the LPE219 and my Jones spec'd cam on a 10.2:1 357 and small heads.
Plenty more torque below peak. Keep in mind that my cam was spec'd twice. One for street/strip, another for drag racing. This is the drag race spec.
Where do you suppose the peak TQ and HP RPMs will tune to with the TPI?
I've used Vizard's Torque Master to experiment with cam selection. One of the features is induction length and where to expect those peaks.
As an example, a short cammed 383 that makes peak HP at 5400 RPM (small heads again) with an induction length of 11.5" (valve to intake runner entry in the single plane plenum) will have tuned values of 6400 HP and 5000 TQ. Add an inch and a half to that length, for 13" total, and the RPM peaks shift to 5700 HP and 4400 TQ.
You can see the benefit of the longer induction being better aligned with the cam duration.
How long is the TPI induction altogether? I'd think 13" and counting? (Taking into account that an SBC port is about 5.25")
I can see how the short cam timing would boost the slower engine speed torque.
Here's an overlay of the LPE219 and my Jones spec'd cam on a 10.2:1 357 and small heads.
Plenty more torque below peak. Keep in mind that my cam was spec'd twice. One for street/strip, another for drag racing. This is the drag race spec.
Where do you suppose the peak TQ and HP RPMs will tune to with the TPI?
I've used Vizard's Torque Master to experiment with cam selection. One of the features is induction length and where to expect those peaks.
As an example, a short cammed 383 that makes peak HP at 5400 RPM (small heads again) with an induction length of 11.5" (valve to intake runner entry in the single plane plenum) will have tuned values of 6400 HP and 5000 TQ. Add an inch and a half to that length, for 13" total, and the RPM peaks shift to 5700 HP and 4400 TQ.
You can see the benefit of the longer induction being better aligned with the cam duration.
How long is the TPI induction altogether? I'd think 13" and counting? (Taking into account that an SBC port is about 5.25")
IIRC TPI is 17" plus the heads intake runner. So about 22-23" all together.
I'm only vaguely familiar with the OEM TPI. I had a TPI 305 in the 86 IROC when I first got it but that lasted all of a year until the engine let go. Back to my (ancient) roots with a carburetor ever since.
Doesn't it have two plenums? One on top behind the throttle body and the other in the base? The runners obviously joining the two. If that's the case isn't the tuned length going to be that of the runner? That in itself can't be 17" long can it?
I only bring this up because, as I understand it, the reflected pulses, like with open headers, are created where the volume changes substantially. Thinking about it, this would create all kinds of interesting events in the intake with two changes in volume.. Unless my understanding of the science is wrong (entirely likely) and the pulses carry across the lower plenum from the runner to the intake port to the valve.
Its got one plenum on top fed by a dual 48mm throttle body. From there the air makes a 90 degree turn into 8 separate runners that are roughly 1.5" 180 degree tubes into a base intake manifold where it runs back the other direction under the plenum into the adjacent cylinder head. Imagine an old school cross ram intake that goes up and turns into a plenum instead of 2 carburetors on the ends...
Exactly as I thought.
So, the question is: How do you calculate induction length in that particular scenario? The individual runner length is easy enough but what do you do with the lower plenum? How are the reflected pulses generated and distributed?
I've an old copy of PipeMax although I can't say I've experimented with the intake side of things. My exhaust lengths are based on PipeMax calculations but not the topside.
Exactly as I thought.
So, the question is: How do you calculate induction length in that particular scenario? The individual runner length is easy enough but what do you do with the lower plenum? How are the reflected pulses generated and distributed?
I've an old copy of PipeMax although I can't say I've experimented with the intake side of things. My exhaust lengths are based on PipeMax calculations but not the topside.
The lower manifold base has 8 individual runners and is thus an extension of each runner. The interesting part to me is just the base runner length stops making power at ~5,500 rpm. Also found it interesting that GM reduced the center runner divider down about 1" between 1&3 and 6&8 where it meets the plenum. 2&4 and 5&7 are not cut down. Was GM trying to broaden the torque curve?
So, given that extended length, how does our OP tune for that?
There's also something to the different harmonics that will realize intensities at RPM's up and down the rev range. It's no wonder that at 17" the tuning window is as low as it is.
I haven't looked into PipeMax for this however I'm tempted to tap into the 90 day trial of Torque Master for the umpteenth time. Through the cam selection program there's a data entry point to move the induction length around as well as the level of harmonics seen. Might be worth the 15 bucks yet again. SBC specific now though. (It covered a broader range before but now that's gone).
That runner length enhances torque at ~3200 RPM, and hurts it to an equal extent during the opposite phase/frequency. At ~5000 RPM it's hurting tq by a similar magnitude.
The OP (or anyone building TPI) can:
*exploit power below 4500 RPM,
*try to band-aid power above 4500 with large diameter runners more cam etc, Or
*just ignore it and enjoy whatever you get out of it and it's looks when you open the hood.
Actually the final option is to change the intake to a design with a shorter runner length.
That runner length enhances torque at ~3200 RPM, and hurts it to an equal extent during the opposite phase/frequency. At ~5000 RPM it's hurting tq by a similar magnitude.
Interesting.
On a similar note, I was having a discussion with Larry (PipeMax) Meaux about my particular exhaust tuning. Quick version was that when I incorporate the collector cutouts and keep the rest of the muffler/tailpipe attached, will I still benefit from the open collector? The short answer was "only if the full exhaust length produces a pulse that's in sync with short collector pulse". That is, not a pulse in opposition to the beneficial one. I can see how the TPI might make this difficult.
A file photo I have but something similar to my proposed exhaust build.
04-06-2024, 04:01 PM
