my 89 formula has a 305 5speed, its all sock except for i put a 80 series flowmaster on it. anyways whenever i am driving it after like 4k rpms it like falls on its face and makes no more power,i'll down shift and it doesn't go much faster, this normal weak performance from a 305?

 

I've tuned a Stock Cadillac 305 TBI that was put into a 1987 chevy shortbed truck. The stock peanut cam and 187 heads combined with headers, ultimate TBI mods, and an open element, let that engine keep pulling strong until about 5,300 rpm. Your TPI with the better heads and L98 cam should keep motoring right on up to 5,500 without too much difficulty, providing it is in a good shape of tune, don't have a worn out engine, you have good fuel pressure/flow, and decent valvesprings. Perhaps you are in the early stage of either a catalytic converter plugging up or a fuel pump getting weak. Don't forget to check the air filter and change the fuel filter.

 

i am thinking its prolly the air filter, its a brand new crate motor with 4,000 miles on it, fuel filter is new, i think its just its got the stock airfilter so it doesn't breath too well to pull in the upper rpms.

thanks for the help man

 

Yeah,, falling off at 4K is really weird. On a side note, people make crate 305s?

 

well at 4k it feels like its not makeing power like it was when i was at like 2. the 305 was just a stock replacement bought from gm

 

Its not your air filter. Its the LTR TPI system and they was its designed. Most stock TPI's fall off @4k-4.5k rpms b/c of the LTR design. Plus the combination of your stock cam, stock springs and stock heads doesnt help any either.

 

thanks man what exactly is ltr? and how does tpi differ from newer mpfi?

 

shorter runners allow you to make more hp higher up in the rpm band.
With the HSR on my car, it now pulls to 5K. May pull more after I put the headers on, I still have the stock manifolds/y-pipe/i-pipe on the car.

 

LTR is long tube runner.. TPI has long tube runners which makes power band stop pulling at 4500rpms or so.

obviously your not gonna pull like u do at 2k rpms at 4K and up rpms. just not gonna happen with stock heads/cam/intake. TPI torque down low from 2-3K rpms is peaking and thus gives u that strong pull feeling. after 4K, torque is dropping quck and hp is peaking and ready to fall.

TPI in a 305 should pull to 4500-5000rpms.. my L98 350 pulls to 4500rpms and its only got exhaust.

but i do recommend gutting ur air intake box and getting some headers, and a full catback exhaust with bigger 3inch tubing..... best mods to do

 

yah i have some shorty headers i am waiting to put on from a friend, i thought about getting the 350 tpi but didn't know if it was worth it. i was looking into either the lt1 or if i have enough money the ls1. is it gonna take alot of work to get the 350tpi to preform? is it more cost effective to go with the lt1?

 

It is more cost effective to stay with the sbc 350.
heads/cam/intake 355 can be built for under $2K and will be cheaper to maintain than the LT1.
I've got 3 friends with sbc 406's with minirams all running in the high to low 11's with the 165ecm.

 

yah but are you talking about the 350 tpi's or just a sbc with the tpi top end or what.

 

any small block 350-355 chevy with the TPI topend will work fine. doesnt have to be the L98

 

thanks for clearing that up that was something i wasn't sure on. cause one of my shop teacher hooks up students pretty good for about 800 for a 383 built decently, then i could just put some 350 tpi heads on and get a chip to accomadate for the added power correct?

 

Personally, I'd look for a MiniRam (LT1 clone) or converted LT1 intake. Use the existing ECM and burn a custom PROM. The detuned runner intake will cost you a few ft/lb of torque below 2,800 RPM, but you likely won't notice. Most cars don't need 350 ft/lb at low RPM - The wheels will spin and lose traction at a much lower level. The difference on the higher RPM end is very noticable. A 383 will run out of air under a TPI at an even lower RPM.

 

There's a little misinformation floating around in here. Someone earlier mentioned that TPI cars normally fall on their face between 4000 and 4500 RPM, this is NOT true. The falloff on a good running motor will occur at 4500+ rpm. Peak horsepower output on both 305 5 speed cars and L98 cars will occur around 4700 to 4900 rpm. You do get significant fall off at 5000+, but if its occuring at 4000rpm you've got other problems. Fuel pump, fuel filter, distributor or maybe a clogged catalytic converter. 4000 is WAY too early even for a TPI car.

edit: Correction there are several cam variations on TPI cars. The 5 speed 305 cars have power peaks at 4200 and 4400 depending on options. Which is somewhat strange since my buddies in stock trim peaked at just above 4600 rpm

 

i picked up a few tenths from shifting at 4600rpms from previous 4900-5000rpms... so i would say there is some fall off past 4400-4500rpms

 

There is on the 305 cars...stock vehicles at least no matter which cam peak at a max of 4400 rpms...the L98 cars its a bit higher.

 

305 with same L98 cam theoretically should peak higher than L98 cars. TPI doesnt feed alot of air.. especially for motors over 350 cubic inches. a 383 will be lucky to see over 4000rpms and still may only peak 4500 with fully aftermarket ported systems. 305 with 45 less cubes will need less air and thus the tpi being a good intake for smaller motors. it should run to 5000 rpm no problem.

my L98 seems to like shift points around 4600rpm. that might be abit too high. i might try 4400-4500 next time out.

 

Check the tech section here, it shows peak L98 power at 4750 rpm...I'd imagine thats accurate based on the dyno results I've seen.

 

so it sounds like tpi is junk,or there is just no hope.i will try and find most liekly just a lt1 over the winter. ls1 is outa the question looking at all the money people have spent doing the swap.

i have a spare cone filter sitting around i am gonna slap that on there and see how much that helps, i already gutted the maf screens

thanks again guys

 

TPI isn't junk at all, there's lots of guys deep in the 13's on 305's with factory intakes with a port/polish job. Its definately not a high revving motor setup, but switching intakes alone will yield big benefits in shifting the power north and decreasing the falloff above 5000rpm.

 

for the money u spend on a 305 to get it into the deep 13's u could have a 350 in the mid 12's. just depends on what will satisfy you

can u link me to that tech section.. cuz the only tech data i see shows 4400rpms. i have seen a few stock and near stock dynos and they show about the same

 

https://www.thirdgen.org/newdesign/faq/thirdgen.shtml


scroll down about 1/3 of the way where they talk about an AFPR on an L98 car. They have dyno numbers...


edit: I should say I know they're rated at a peak of 4400 or 4500 I can't remember on the L98 but the ratings and real world numbers are different.

 

13's is nice but i want something more with my f-body, i have two turbo vehicles that are pretty decent i want this one to be all a all out *** stomper

is the 350 intakes the same as the 305's do they interchange?

 

all i know is that it doesnt seem normal for a 305 to stop pulling decent after 4k rpms. i would say u should be somewhat strong to 5k rpms.

if u want a *** stomper.. ditch both tpi and 305. get urself a nice forged 355-383 and procharge it with a stealth ram on top. it'll get u 11's easy and make nice power

 

i would like 12's or 11's all motor hoprfully, i will most likely ditch the tpi

 

The intakes are interchangeable they're the same intake. The TPI intake was originally designed for a 305. If you want an all out *** stomper from the reading I've done this weekend the stealth ram is the way to go. You can get into the upper 11's with a stealth ram without forced induction if you do your homework.

 

my 91 gta(305 5-speed) used to die at 4000. i changed the fuel filter and it helped it out to about 4200-4400. i changed the injectors to 22lb and added fuel pressure regulator and picked up 4 tenths of a second and it started pulling past 4700 strongly.

 

It's stunning the difference that a clogged cat can make. On my dad's oldmobile, obviously not a beast of a car, but it started robbing the car of like 30-40% of it's power. Couldn't belive how much of a difference there was.