sinistervette85

I've been working on my 85 vette now for the past 14 months just experimenting with TPI mods all homedone by myself. I am fortunate enough to work in a machine shop with cnc and welding capabilties, and also have a stock car sponsored by a racing engine shop with engine and a chassis dyno. To make this short I'll skip most all of my prior tests and details and cut right to the final(best) results for my TPI.
Final details are this: 1987 GM base with extensive mods. I used a mill to cut the top side of the intake runners, to siamese them and also enlarge them as much as possible. I then welded alum strips back top of the intake over runners. They are siamesed all the way to1/4" above the injectors. The injectors are 36lb Accels. I then cut the stock runners through the center of each tube and flanges, welded alum strips to the outsides of them creating a single(siamesed) runner out of two. I then proceeded to cut a stock plenum in two halves upper and lower, allowing me to fully machine the inside of the plenum, then welded it back together. I machined my own single blade throttle body from a stock body, this was probably the worst idea of all, but I wanted to use "stock" gm componants to see just how much I could wring out of it.
This setup has been by far the best of about 4-5 previous attempts at "stock" modified TPI parts that I've built, and it looks like it is stock with the exception of siamesed runner tubes! The engine in my 85 is 379 ci, 4.155 bore, 3.50 stroke,Crower 5.7 rods, 12.8-1 Ross pistons, TFS twisted wedge heads massively ported, 2.08int./1.60exh manly raceflow valves,ISKY solid flat tappet cam .550int/.530exh lift, 262int/272exh dur@.050. The oil pan does have crank scraper, windage tray and baffles in it. The headers started out as Hedman long tubes, 1 5/8" but I've cut them off at 6" of length from the flange that bolts to the heads and made my own "stepped" headers from them. They are steped up to 1 3/4" for 8" then final step is to 1 7/8" down to a 3 1/2" collector. Exhaust is very crude.....3 1/2" pipes back 33" with 12" long augers in them(stock car stuff!)., and VERY LOUD. I am running mass air flow sensor, custom built that is 4" inside and capable of flowing upwards of 1300cfm at 28" H2O. We ran 7 different pulls over time period of 3 weeks allowing for chip burning and tuning of this package.
The final results of this modified "stock" TPI were 418rwhp@6500rpm and 374rwtq@5000rpm. The average hp from 2500rpm up to 6500rpm was 299hp and the average torque from same rpm range was 343lbs/ft. After 2 more weeks of street driving, engine developed a miss and started blowing white smoke. After lots of searching found 2 cracks in manifold base, allowing coolant to leak through into intake runners. After all the time spent on this TPI, having it brake was just too much to take so off it came and on when carburated set-up. I removed the cylinder heads while checking for the smoke/miss problems, but they were reinstalled. The only changes were new head gaskets, intake manifold, carburator, and air cleaner/filter assembly. I went with a GM 1103 bowtie aluminum intake with the runners extended 5/8" into the plenum and extensive porting. The carburator started out as a Holley 4781, I modified it to a 4 corner idle circuit, thinned throttle shafts, custom stepped the boosters, milled air horn and radiused the top and added adjustable air bleeds. Final air flow through this carb was 1030cfm.
We made 4 dyno runs over two week period with this setup and the final results were 524rwhp@7500rpm and 421rwtq@6000rpm! The average hp from 2500rpm up to 7500rpm was 358hp and average touque over the same rpm range was 364lbs/ft. The carburated version was worth +106hp, but only 47lbs/ft of torque! Peak power went from 6500 rpm(TPI) to 7500rpm(Carb) and the peak torque went from 5000 rpm(TPI) up to 6000rpm(carb). Ready for the good news/bad news!?! The weekend after the dyno tests was going to take the vette to the strip, thursday evening we are expecting a storm so I decide to put the vette in the garage because of a huge beach tree alongside the driveway usually drops small limbs and sticks when it gets windy......guess what.....tree was struck by lightning and fell on the garage!!! OK...that was the bad news! The good news you ask....well after the insurance adjuster came out and inspected the damage I decided to pull the engine out of the vette, and put it into something I don't like(I've built a 66 mustang with a 302(small block chevy) for my wife) so maybe I can drive it for a while and show the ford guys how to make a mustang really fast!!
The owner of the engine shop that has been working with me on this project heard about all my fun I've been having and asked me if I'd care to put my motor on his engine dyno so we could see what the engine puts out compared to it being in the car....great idea for a test on drivetrain loss I thought, so we loaded the engine and my vette headers and exhaust into my truck and headed for the engine shop again. We got it all hooked up and made two pulls without touching anything at all. 596hp@7500rpm and 479lbs/ft of torque@6000 rpm. So with this we took our numbers and found out that I've got an equal 12%loss in hp and torque in my vette! 596hp engine only, 524rwhp and 479lbs/ft torque engine only,421rwtq. So for overall performance carb was much better than a highly modified "stock" tpi, and my 85 vette with 4+3 manual trans, 3.42 gear dana 44 rear, and 295-50-16 Dunlop GTZ tires has 12% drivetrain loss. Hopefully sometime next year I will be able to give you some dragstrip times....if I feel lucky enough to put my vette back together.

Zix

Paragraphs are your friend!!

Nice write-up though, just hard to read!

Upstate

sinistervette85

Sorry for the lack of grammar, I did edit them in although I'm not sure if they are correct!!!....I'm not that great of a typer nor writer...heck man it's hard enuff to spell wright!!! Just thought I'd share some of my findings and hardships. Thanks for not ******* me yet for having a ford on my property too!!!

jmrl98

Nice job bro'!!

rick lambert

Thoughs going for the serious seem to all run carbs-but, I do admire all the experimentation you went through.Hope your insurance company
helps you get that motor back where it belongs And I hope you go out and take on a few Mustangs

Redeasysport

Very interesting.What kind of A/F readings did you get on the dyno with each?What do you contribute the carb gain to?Better flow?

jburnett

Just goes to show that a TPI, even an extensively modded one is NOT ideal for power production. Nobody seems to remember that this induction system was designed around a 305 with its tiny 3.8" bore.

You've given the TPI absolutely no chance whatsoever... You've handicapped it with a destroked, large-bore motor that HAS to breathe deeply at high rpms utilizing a camshaft that has 50 degrees more duration than is anywhere near optimum for a long runner induction system. You used heads that have large valves and assuming by your definition of "lots of port work), I would say they also have a ton more intake than a TPI could ever take advantage of. By doing this you've guaranteed it failure.

Now, had you built a mild 350 cammed more in agreeance to what would be seen on a typical street vehicle (whether EFI or carbed) the variance would not have been nearly the same. I'm not surprised at your results in the least... Throw an EFI single plane and a 4bbl t.b. on it and you'll equal the carb and probably best it in torque/average power numbers.
-Jeb

DonBecker

First thanks for the write up.

I have to ask though, did you adjust the carb when you put it on?

Why would anyone assume that you can modify a TPI setup and not change anything about the computer config. and make power is beyond me.

Diesel68

Awesome writeup. It sounds like the new intake was able to let that engine finally breathe.

It was also very interesting to see that the drivetrain loss was only at 12%. I have to assume that a ZF6 should be close to that. Using that number for LT1's and LT4's, stock dyno numbers don't seem to be off by that much.

AZC4Guy

Waaaahhhhhh!

mike 1985

don't worry about the paragraphs, thanks for sharing the results of all your time and hard work.

How do you plan to hook this car up at the track ?

Zix

Like I said, you did a great job on the write-up, and I really appreciate the time you took to put it there! It was just a little hard on the eyes, thanks for the edit, and thanks again for taking the time to type all that out!

65Z01

Hmmm, I might take those findings to mean that a good TBI setup would be much better than TPI.

Of course we have to remember that the L98, LT1, LS1, etc are all street engines that would not live long in the 7k+ RPM region nor would power up there be so useful on the street.

In any case, very interesting work; thanks for sharing.

Alvin

I'll bet if you woud have conducted the test with a miniram, or EFI retroed carb intake (same verison perferablly) You would have seen the same results.

The TPI intake or TPI style (including high flow bases, different runners, etc) is not productive in a situation like this.

GeosFun

Good job! real information is so much better than theory and speculation even when a configuration might not be optimized. I am sure we all get some bit of information that is useful.

sinistervette85

I just got back from some car shows this past weekend....will post the A/F ratios when I go to my shop and get the sheets. The gain is most definiatly from much more flow. I was just trying to see how far I could go to improve flow with the stock chevy tpi parts. I scraped 2 bases and several sets of runners during the past year and a half trying ideas and finding lots of them to not really help at all.
I do plan on fixing my current tpi base that has the cracks in it and doing a buildup of a 302 ci (4"bore X 3" stroke) to compare the tpi against a cross ram the late 60-s ealry 70's that I just picked up this weekend. Should make for an interesting test/comparison.

sinistervette85

Jeb, I had origionally been doing all my testing on a 9-1 350 that had a very mild flat tappet cam and the same heads on it, unfotunately after over 10 months and more than 100 dyno pulls it suffered from a severe case on unraveling. Not it's fault...it should have been torn down and inspected more often than never. I had the 379 together awaiting a top end, so I repaired the damage on the heads and put the tpi on the 379. I know it isn't fair to compare the tired 350 to a fresh 379, but there was a gain of more tham 40 hp and 30 lb/ft of torque. I do not remember the exact numbers, but it was a great improvement from any totals that the 350 ever produced with the same tpi setup on it.
As for the cam and duration...I'm basing my camshaft coices on what I've run over the years when I was drag racing and running tunnel ramd and cross ram intake setups. I know..they did not have the runner length that the tpi does, but the actual "individual" runner length is longer in both my tunnel ram and cross ram setups. The siamed runners are also not an ideal choice, but they are far better than truely individual runners. The engine shop is working on setting up his flow bench so we can play with flowing the complete assembly one and two runners at a time just to see how much airflow we have through the tpi and my carb setup that way we can really compare total airflow/air flow velosity/runner lengths etc. to maybe find more ways to get extra from all the intake set ups.
I've been porting cylinder heads and intakes for the past 15 years and doing race carbs for 18 years, and I've done extensive flow testing on many differet porting ideas on the same intake runnes(welding them back up and porting some more) to find ways to create the best airflow with a give port size. Velocity is the bigget key for making power. I've made more horsepower and torque with heads that have 20-30cc smaller intake runners only because the velosity that was created/carried through the runners helped fill the cylinders better. Size is not always the best...ok turbo and blower guys can argue this, but not for naturally aspirated.
Hopefully if things go well in the next year or so I'm planning for a test on a 302 with my tpi setup and then a cross ram carb setup to see how the smaller cubic inch works and to get the runner lenthg up on both. If the cross ram fails miserably I do have a tunnel ram that will be used in it's place. Once I've done this I'm going to try and get some 4bbl tbi setups to test against my carb setups.....same exact intake manifolds and engines, just replace carbs with tbi units. I hope to keep the cfm flow of the carbs and the tbi units as close to the same as possible so the results should be as accurate as they can be.
In those tests I do not expect my carbs to be as efficient or able to out perform the computer controlled efi/tbi stuff. Hopefully we will find out.

sinistervette85

Yes I did do two jet changes and 1 change to the air bleeds on the carb. Countless hours had gone into the tpi setup working on the right program in the chip to make it work to it's best possible ability. I'm not relly big into the programming of the tpi stuff, so it was handles by a guy that worked at a dealership and also runs tpi setups on his camaro drag car and streerods here in town. It is amazing how much can be done with programming to either screw up or mprove the performance on these setups. To deep for me to ever worry about....that is what friends are for!!!

sinistervette85

Well...if I do decide to rebuild the vette(all depends on the insurance company) I will be running it on Cooper Cobra GTZ radials and will bo whatever it takes to get the most from a true street setup. I do have a set of Hoosier Quick Times that are on a 70 Nova that are serious traction tires. There should be no problem hooking up the vette in "race" trim, but I do expect problems breaking my vette. I hope to have my rear axleshafts done and pro gears in the Dana44 when and if the vette goes back together. If the insurance company totals the vette, I've talked with my wife and we do plan on buying it back....then it will be built according to SCCA rules/guidelines so I can race it on the roadcoarse that is nearby.