Just built up a new motor with comp cam 495, 503 lift 218 224 duration, corvette heads, roller rockers, eldelbrock runners cut the center top about 2" in, ported penlum, stock 48mm TB, stock base, home made cold air intake....

Now the engine falls flat on its face at 4500rpm..... 230hp at the wheels....

Help, why wont it pull further, what do you recomend..... I know TPI is renound for this but I still thought it would go a little higher. Would it be the throttle body?

 

From what I have heard so far from this website is this That with a cammed 350 with stock runners,plenum,baseplate, and thorottle body is impossible I would try a high flow base plate (intake manifold) next. Look at message board Engine swap and then find 305 to 350 vortec and read the whole thing it might help.

 

problem is you're using TPI

 

The TPI was not meant to be a high revving motor, it was meant for hellatious torque and was made to fall flat after 4500RPM. You need to upgrade the runners and baseplate, or better yet get a different TPI intake in general (miniram, stealthram, ect.). TPI is very restrictive in stock form, so don't expect any higher numbers with all the upgrades.

 

If it's truly a "fall on it's face" or "hits a brick wall" kinda situation I'd make sure you're not outrunning your fuel system.

Having a fuel pressure gague with a long hose on it helps considerably. You need to have a fuel pressure gague mounted where you can actually see it while driving (I temporarily duck tape the gague to the windshield and make a few runs). If you're outrunning the fuel system it will be obvious- fuel pressure will nose-dive at the top of every gear, especially 1 and 2, followed by the motor just about shutting off until the tranny upshifts at which point fuel pressure will immediately recover and off you go again until the top of the next gear.

 

i have the same sort of problam with my 87. it used to have a 305 with an exhust. now its a 350 with heads, cam, roller rockers. now it has a 52mm tb and slp runners that i havent put on yet. the only thing is is that im still using the 305 e-prom chip. ive been told on here that that is restricting all the work i have had done and will notice a significant gain in power as soon as the new chip arrives. however id definatly recomend the 52mm tb, really wakens it up further up the rpm range.

 

Port your base and heads. You still have a bottleneck at this point. No need for a bigger TB. The stock 48mm flows enough to support what youve done. Unless your trying to make 500HP the stock one is fine.

 

A rather ignorant statement, considering the detail of his post.

What heads do you run? run a AFPR? what size injectors?
stock PROM? Where's your timing set at? All this and much
more should be considered before ripping your car apart..

A inproperly tuned F.I. system will never perform no matter
how many parts you throw at it.

Nevertheless..I agree with damon, sounds like its starving for fuel.

 

yeah ok lol.

He's got a hopped up motor, and is using a tpi intake (which is designed to die off at 4500rpms) and *gasp* his motor is dying off at 4500 rpms!

Seems simple to me

 

Did you degree your cam when you installed it? I agree it should pull higher.

 

I think your missing the point of his post. Yes a TPI does drop off at 4500 rpms. But, w/ proper mods and proper tuning you can increase that drop off point a bit. A reprogrammed PROM, to match the mods and tuning, would give him the best results.

cutnsick: Pick up a copy of TPiS Insider Hints book, if you havent gotten it already. The most important thing you can buy, other than this site, if your a TPI owner. Its loaded w/ easy mods to do to a stock TPI system b4 bolting anything on to it.

 

Just asking,,, did you get spark plugs for the Corvette aluminum heads? Using plugs for the old iron short thread heads in the long reach thread heads is rather common and causes this type "problem". A "brick-wall" at 4500 is not because you're running TPI or a stock T/B. - most likely it'll be fuel or ignition related.

 

Thanks for the backup gentlemen,

I know my car doesnt "hit a wall" at 4500rpm
with my TPI build. Again, Im not stock.. & I do
have a solid tune on it, so I expect it. You cant
just place blame blindly, the car should perform
to an extent at 4500-5k even if its stock or near stock condition..regardless of the induction system.

 

Thanks for all your input...... Im thinking something is fundermentally wrong as the car seemed to pull harder longer before the mods... Ill check my plug reach as i probably just replaced them and didnt double check.... The cam has been degreed correctly. I have eldelbrock runners and have hogged out the base and plenum as well as cutting 1.5-2" into the top of the runners...... I know TPI doesnt support high RPM but are sure it should make power till 5500... The AFR:P was fine at about 12.7. If I can get it to pull another 1000rpm ill be happy. As long as i know its not the TB yet so I can try to fix the situation without spending heaps more $.

 

Dont spend money on a bigger TB thats not your problem. A stock TB flows well. Enough for 400 HP. Have you ported the head at all?

 

The heads were supposably ported. The gaskets matched correctly and everything looked smoothed out so i guess someone had stuffed with them.... I checked my plugs they are not the long reach ones....... "**** Head Me" Can you give me a plug number to suit the alloy heads also a plug gap if you know it.
Thanks heaps

 

Go to your parts store and ask for plugs for the heads you have. They will be able to tell you the gap. This could be your problem. Remember to start small first b4 ripping into it.

 

OK here it is....

 

Yeah, I thought i would have a relatively simple problem like this... Shame i just got a custom chip burnt... I think the guy should have known soon as i saw the dyno graph I knew something was not right...... Hopefully Hell do the right thing by me if it changes things too much. Dont know how ill tell if it is still ok? Thanks too all, this site is a god send for me as only a small number of people in my city know anything about these cars....