I was looking at third gen tech articles and it said that the 92 5.0L TPI's had the same HP as the 88 5.7L TPI. I thought that the 5.0's were alot weeker, thats why people never make much power out of them and are always looking for more power. But if these #'s are true then the 5.0L were pretty good. can someone please explain to me it these Numbers are true. because if so then wuts so bad about having the 5.0L???

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

I have the LB9 with peanut cam and some mods in my '86 IROC auto 3.42 posi; the L98 with some mods in my '88 Vette auto 2.59 posi. The IROC is about 350lbs heavier but still the Vette is over 1.0 sec quicker in the 1/4mi in similar weather and the IROC has a hi-stall TC.

I cannot believe that, even with the better cam, the late LB9 is stronger than the L98. The extra torque from that 45cid is the difference.

BTW, though it has less potential than the L98, I don't think there's anything bad about having a LB9. I love driving the IROC.

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1986 IROCZ-28 Site
Best Times:
60'=1.92sec, 1/4mi=14.42sec @93.99mph in 65deg temp

 

When I first bought my car I raced my friends slightly supped up 92' 305 TPI 5-speed (Air Foil, K&N filter and 8.0 spark wires) And my car beat his every time, the only thing that I had up on him was about 20,000 MI less on the motor.

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88 Formula 350
Upper and Lower SuperRam, 1000 CFM Accel Throttle Body, 24# Motorsport Injectors, Custom Burned PROM, Larger Gutted Mass Sensor, MSD 6a box, Flowmaster Muffler, Homemade Cold Air induction, TB Bypass, B&M shift Kit, 160* Thermostat

 

Chevy has a rep for under-rating their performance motors. Partly to keep the 'Vette as the top dog, partly to keep the buyer's insurance costs down. I'd say the '88 L98 is actually making about 240 hp stock(based on magazine tests of the day, and some engine simulations I've run), whereas the '92 LB9's might make 230 hp on a good day(based on the same criteria). The '88 L98 also has an advantage in peak torque that'll keep it ahead of an LB9 with the same peak hp.

I think the advertised output was kept closer than it actually is to sell more LB9's(good for CAFE ratings).

 

Actually, from real world experience comparing f-bodies (no fair talking about vettes, totally different animal), speed density 305s tend to run pretty close to the MAF 350s.
Take my vert for example. With just a ported plenum and dual cats added to it i am running 14.8 @ 93.1 , which is a respectable time for a 2.77 geared MAF 350. And my vert is heavier with worse aerodynamics to boot (and also has horrid 2.73s) It's not even fair to call the dual cats a mod since my stock exhaust was the TBI sized small outlet manifolds w/ the 2" T pipe and 2.25" cat. The ****ty exhaust is why the speed density A4 305s are rated at less power than the G92 305s. The cams are the same, period. No stock peanut cam car ever ran 93mph, especially with so much working against it.

So what's so bad about the 305. Well, depends on your definition of bad. Even though i am obviously making about the same power as a MAF 350, i have a noticeable lack of bottom end torque, my car comes off the line like a slug. The extra 45 ci of a 350 would come in handy there.
Beyond that, they can be made to run great. Tim burgess has built a few pretty stock style TPI 305s that run in the 12s. Preston Smith had a vortech blown 305 running in the 9s (with a stock TPI/runners on it to boot) Obviously, with some planning and know how you can make a 305 run.
BUT, no matter what you do to a 305 to make it fast, if you do the same mods to a 350 it will gain more and always be faster. Especially NA there is a point of dimishing returns when trying to make power w/ a 305s small bore. There are NO great flowing heads made for a 305. And even if there were, you would start getting into ridiculous RPMs to make a 305 make power with them.

In short, depending on what your goals are, a 305 can prolly do it (i.e. you can make a nearly stock TPI 305 faster than 97% of the cars on this site, ala tim burgess) But a similarly prepped 350 will still make more power and have a lot more torque.

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.8 @ 93.1
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

The speeds density 305's that are rated at 230 HP are as fast as many of the 350 TPI cars. In 1991 the 305 SD with the 5 sp had a faster trap speed and lower ET then the L-98 cars. I can not remember what magazine was testing the paticular car's that I am refering to but I do remember the final outcome.

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1988 Formula 5L/5sp 3.45 gears, SLP cold air kit, MAS gutted, TPIS air foil, TPIS AFPR, MAC headers, Mac under drive pulleys, MAC cat back, Relocated MAT.
Best ET street tires 13.85
Best 60 FT street tires 1.930
Best MPH street tires 99.29

 

wasnt TPI designed for the 305 and that is why it is so restrictive on the 350? Or is that just a rumor?

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*1989 RS
*Red, Daytona Turbo fiberglass hood, chrome 16x8 IROC wheels
*355 CID
*TPI ported plenum, SLP siamesed runners, Edelbrock high flow intake
*Edelbrock TES Headers (getting SLP 1 3/4 this summer)
*Richmond 3.73, Auburn Posi
*Modded 700-R4, 2800 stall converter
*NO recent time slips.

 

YES! No rumor! ...and having said that, if GM had made the 350TPI with parts(intake, cam, TB, etc.) that were actually designed for a 350 instead of a 305, there would have been a much greater difference is power between the two. Something like this - 305TPI /230HP& 300TQ -- 350TPI /290HP& 390TQ instead of 245HP& 345TQ. ...02



[This message has been edited by whiteroc (edited September 19, 2001).]

 

Considering the LT1 was rated at 275-285 horsepower, I really doubt GM would have made the TPI 290 HP.

What was the rating of the L98 with the SLP package on it? If I remember it had the SLP runners, cold-air intake, and maybe the headers too. Something like 265-270?

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-