my girlfriend's son has a 91 z28,he bought an assembled long block , it is a '77 block with the correct heads.the car originally had a 305.after installing it,it wouldn't idle,ran very rough(if at all). after swearing to me that it was"pretty much" stock,he then tells me it has 10:1 compression and a comp cam#286h cam!according to everyone ,this is way too big for the tpi. i upgraded to 24lb injectors when installing and no adj fuel pressure regulator( i thought this was a stock 350). i know the cam is too big so my two questions are:what cam do you recommend to keep this setup(tpi) and is the compression too much for the tpi? he wants"the biggest cam possible that will still work right". this motor is not a roller engine so i need one that will work right be it a stock equivalent or maybe a little larger but one that will do the job properly for everyday driving and weekend trips to the strip. emissions are not a consideration nor is fuel economy.i just don't want to have to keep tearing this motor down guessing what it needs. the kid is fresh out of marine basic training,but i'm more afraid of mom(she's paying for all this). helllllppppp!!!!

 

From what i understand, a good chip burner can burn a custom chip that will allow that motor to run better.....You have alot of mods on that car that the computer does not know about.

Sombody correct me if im wrong.

 

You can tune just about anything to work, but that depends alot on the tuner and how much time and energy you want to dedicate to the project. In my opinion, the CR is okay for a TPI, I used to run a tad over 11:1... That cam has got to go though. For one thing, it is not working with the rest of the engine. I assume the heads and TPI is stock because there was no mention of any further modification. I would look at the Comp Cams web catalog for something more suitable. Keep the duration at no more that 220* @.050. Get as much lift as will fit. Also try to find a cam with the tightest LSA. That keeps the valves from being open together longer. Wide LSAs do provide that choppy idle sound we all love so much, but on untuned FI engines that aren't all that great. You could tune it so it would run fine, but I don' know if you want to do that. Also the wider LSAs bled off vacuum at idle, not only do this affect things like power brakes, but this makes computer think its engine is under load. Not to mentions with the bigger cam in there now, it is designed for higher RPM operation that the TPI is not going to support, airflow wise. I am sure if you go with lesser cam you will be rewarded with better drivablilty but more usable torque and power. Good luck...

 

http://www.compcams.com/catalog/056_057.html

XE256H-12 looks good

 

Correct me if im wrong but

when a cams lobe sepertion is up like 115 or 114 then youll prolly have a smooth idle or smoother and the valves dont stay open together as long but if its at lower like 110 then youll have a choppier idle because the valves are open together longer, and 108 is just real rouph.

I think thats right,

just a quick question though, would 110 pull enough vacum for tpi???? just curious cause the cam i already installed has 110 for my 383.

 

I have a comp Xtreme Energy 110 in my 383 and its working fine but I have heard some of the Crane 110s dont pull enuff vacume. Might just be hersay, as I dont know anyone with one to ask for sure.

badjuju342 I'll second Joshua on the XE256H 10 or 12 should work fine on that car, the 110 giving abit more HP and 112 giving a smoother idle.

 

Yep,,, 92 has what the lobe spreads do backward in his post – everything else is sound. The wider lobe spreads (114) have less valve overlap (overlap causes the lope) than the narrow lobe spreads (108). Depending on the duration, the tighter spreads can give you vacuum / idle troubles in a TPI and won't run right with the stock chip. As you mentioned the 286 Comp (236/236-110?) is way too large for your application and stock programming and would require major chip programming to work.

The cam Joshua recommended (212/218 – 112) is similar to the largest I’ve installed in a stock 350 speed density TPI car (like your 1991) – with an adjustable fuel pressure regulator. This should work fairly well in the 350 you described, since the engine in it now has just a little more compression and very little if any head flow advantage to the stock 350 TPIs.

You have a compound problem though. The stock 305 chip has a 19# injector constant. The computer still thinks it has 19# injectors and is telling the injector to open X amount of time,,, the larger 24# injectors flow more and puts more fuel in the engine for the same amount of time opened (pulse width). Add in the fact that the engine thinks it’s under load with the low vacuum reading from that large cam and is adding even more fuel. You’re dumping a ton of fuel in the engine and you stand a chance of washing / glazing the cylinder walls and either never gaining,, or loosing ring seal. I’ve seen it happen. You would be better off putting the 305 injectors back in it,,,, but I still would not try and crank the engine again until the cam swap.

You MIGHT be able run the 24# injectors (if they’re not the 24# SVO injectors that are like 26# rating for a GM application) and a stock 1992 350 chip which has a 22# injector constant. Porting the plenum, adding an air-foil, and K&N filters to increase air flow would help compensate for the added fuel the 24# injectors will give with 22# injector constant. However, I don’t know for sure if it will work good enough or not, so I’ll defer to the guys that have tried this to say for sure - I know they're out there.

 

thanks guys,the heads&tpi are totally stock,i was told the cam in it has a 110 degree lobe separation ,the vacuum is very low. i disconnected the map sensor and it did run better. i really appreciate the help,i was about to pull out the rest of my remaining hair.:hail: :hail: :hail: