A friend of mine has been running a street avanger VS (750 I think) on his 350 with the Performer RPM "Power Package".

His car a street-only 2nd gen Camaro (a little heavier than ours?) automatic, 3.73:1 in the diff. He has been complaining that the car doesn't quite make the power he was expecting and is convinced he needs to switch to a carb with mech secondaries.

He dropped the car with a "perfomance mechanic" for a dyno tuning over the weekend who told him that the secondaries are barely opening (I'm assuming he's not just reving the engine while in park).

Is the carb just too big such that the motor doesn't create enough "demand" to open the secondaries any further? Can there be so much overlap that vacuum is insufficient all through out the rpm range?

Would the tall gears and overall weight of the car point more to a double pumper despite the auto tranny for a street car?

Yeah I know, lots questions without sufficient info the answer them. Still, thoughts, theories and conjecture are all welcome. Thanks,
Jon

JSD MOD 02/08/08

 

750 CFM on a 350? We have a 7.5L Ford V8 with a 750, he needs to down tune to a 650 Holley..

 

Edelbrock's marketing department is probably the biggest reason he's not making the power he expected.

 

Good. Were on the same page then. Thanks,
Jon

 

Yeah, for sure he won't see the 400+ horses Edelbrock quoted in the catalog. If memory serves, he peaks out in the 350-360HP range which is pretty respectable for the relatively small amount of money he's put into the project so far.

I think his beef is more with throttle response as he goes to WOT.
Thanks for the input,
Jon

 

If he's complaining about throttle response, the smaller carb might help.

 

I just got my 750 DP straight today (bad 6.5 PV) and I'm running an 82 Z with a 4 speed behind a .40 350 and a race cam, I'd say run a 650 or a 670 DP and play with the jets. He most likely will get what he's after

 

750cfm vacuum secondary is fine on a decent 350, thats not the problem. If the secondaries are barely opening, he should be buying a secondary diaphragm spring set and experimenting with those... he'd want the lightest spring possible without creating a bog (indicating they are opening too fast). That spring kit can make a HUGE difference.

 

I'd wondered about that but then discounted it thinking that that would only affect the opening rate and not the amount that the secondaries are opening. Then again, if they are only partially opening because that's all the engine needs a quicker opening rate might well give him the responsiveness he's looking for. I'll pass it along. Thanks!Jon

 

Just some food for thought. I had an edelbroke POS 600cfm carb on the 305 when i bought it and a street demon 750cfm on the 350 i built. my car ran fine just had a bit of laggy response but i really never noticed untill i put the HSR on ( the car always had carbs since bought it) The demon was fun, the secondaries opened kinda late so the car would jump hard from a roll and then bam even more power and she was side ways going into 2nd.

It's always best for power to default larger tho... too large and u lose crispy throttle, too small and you hurt power

 

A lighter spring will make them open sooner, faster, and possibly more as well (if its necessary, depending on demand). But if he goes too light, it will open too soon and/or too fast and create a bog - so he'll need to experiment a bit with the kit.

 

yea i would get him to work with the springs, and in no way is a 750 to big for a 350