i have a 388 built sbc efi motor that's in my 91 camaro. i'm using a comp cam hydra roller with the duration @ .050 230 intake 246 exhaust.

the problem is tunning is a bitch and start up seems to be impossible without holding the pedal to the floor. i was told by the tunner that this was because of lack of vacum.

anyone know what the proper range that a cam for my setup should be in? this was supposedly comp cams choice according to the engine builder but maybe someone screwed up so i need to know since i can barely start my car.

 

Put a degree wheel on the cam and verify the thing is ground as the card states.
Ya have to start here first.

 

so i have to tear the motor apart to find out if my cam is right for my application then no matter what?

i can get the car to run but i'm having trouble with start up specifically. i've been told by 3 separate shops that it could be a vacum problem so i'm trying to narrow it down.

 

What is the lobe separation angle?

 

the only number i have on my comp cam car for lobe separation is 111.0

?

unfortunately i really don't know enough about motors or i probably wouldn't need to ask. i had it put together for me but the shop isn't helping me at all so i'm trying to track down the problem on my own.

i'm wondering if i'm not getting enough vacum because the cam duration is so high....

 

Check your valve adjustment and adjust them 1/4 turn down past "0".

 

well it runs fine on the tune, it's the startup that's the issue. it currently quit running so nice because the tunner didn't tighten the distributor.

still doesn't solve the start issue though, i'm looking to find out about the cam to see wether or not this theory that my car doesn't have enough vacuum to start is bs or not.

 

What is your real static compression ratio and what is the initial timing set at?

Bret

 

Is this engine SPEED DENSITY?
The cam sounds ok.If you think you have a vacuum issue put a guage on it and FIND OUT.If the valves are to tight it will cause a vacuum issue.
Did it ever start and run right?
Is the timing set back right after the dist moved?
Is the chip in the CPU tuned for the cam?
What is your compression ratio?
Small things like these have to be answered before anything can be said. OTHERWISE it is just a guess!!

 

i don't know....



timing was set at 12* until it was taken to the tuner at which point he set it at 4*. the odd thing is when i brought it home the car ran fine (except for starting). didn't try to start it til the next day and i had difficulty. found out the distributor was loose so i set it to 12* had same problems at start up but at least i could drive it down the block with minimal backfire. tried to bring it to 4* and it was harder to start and could not drive it down the street without it backfiring......

i don't know how to find static compression but i could ask the shop tomorrow morning. i didn't put the motor together and they aren't helping me find the problem.

 

ecm is a 730(speed density)

no vacuum leaks if that's what you mean by putting a guage on it???

valves could be tight, i didn't do it....it's something i'll ask about and try to check tomorrow though.

no it has never started right with the new motor....yes the old 383 and original 350 both started right with no problems.

the chip is supposedly tuned to make the car run right.....is it tuned for the cam? i have no idea....it should be since the car ran fine until i shut it off and the distributor went out of wack.

compression is 10.8 to 1

i'll take all the help and suggestions i can get since no one i've delt with directly will help me i'm having a real hard time....

 

If the valves are to tight that in itself is a HUGE vacuum leak.

 

thank you for the suggestion....i'll have that checked out right away then.

any other suggestions or ideas?

 

Just be sure the valves and timing are right and after that put a vacuum guage on it and see what the reading is.Then go from there. Reading should be around 9-10 inches or higher.

 

just curious, how do i know if the timing is right? what can i do to make sure? i know how to set timing, check it, etc. but how do i know its the right number besides trial and error?