Ok,here's my setup so far...

350 bored 30 over 4bolt 70's block
Decent forged pistons 10to1-4 valve relief?
062 Vortec heads with Z-28 springs
Xtreme Energy Cam and Lifter Kit - Grind: XE274H ; Lift: Intake .487", Exhaust .490"; RPM Range: 1800-6000
Edlebrock Performer Vortec Intake
New timing chain/cover oil pump and oil pan and harmonic balancer
New Holley 670 street avenger
underdrive pulleys
Proform HEI
Stewart stage 2 pump


My question is....how much actual horsepower am I losing by going with a Performer Vortec instead of a Vortec RPM? I already have the new Performer on the new motor on a stand out of the car so if it makes a big enough difference,I should change it now and try to sell the still new/but installed Performer.Also,is the 670 avenger enough carb for this setup?My motor builder recomended these,and I'm not experienced enough to know if there is a marked difference.I also have just stock rockers on the heads...would roller rockers be worth the cash?Thanks

Don

 

you might have problems closing the hood if you use the RPM... the performer will probably produce more low-end torque then the RPM... if you already have that one, I'd go with it, you're not losing much...

 

The RPM is a much better intake for performence its probably costing you a good 10hp on your motor also Roller rockers are a must on a performence engine your probably losing 10 there aswell. You will have problems with the stock hood with the RPM. If your going to get a new hood I would go with the performer RPM air gap Ive heard about pretty big gains with this intake. Super Chevy got 25 more hp than the weind stealth intake with the RPM air gap so i would say its a pretty sweet manifold. If you already have the performer on now it all just depends on if you want to go through the hassle of taking it off and buying a new one,but your engine will defenetely like the RPM better especially with a cam thats ran is 1800-6000 and the RPMs range is 1500-6500. The performer is for idle-5500 so it defenetly doesnt match your cam. Good Luck.

 

or you could change your cam to match the performer manifold, that is if you like that sort of setup. but the rpm is a great intake and would match your current setup better. Oh wait, you would have hood clearance problems though.

 

You will not encounter any hood clearance problems with the superior Performer RPM manifold.

 

I see where some people say I would have hood clearance issues and others say I wouldn't.I wish I knew for sure because I really don't want a new hood.Anyone else have experience with this?

 

It will fit under the stock hood, but you will need a special air cleaner. I dont have a cleaner on mine yet so I dont know which one you need. My 14x3 almost fit so I assume you need a drop base 14x2 cleaner but you will need a different cleaner than stock thats all. Good Luck.

 

What would be a good choice for full roller rockers?1.5 or 1.6?3/8 or 7/16?I do have the tall centerbolt valve covers

 

the rpm requires a very low ac to clear the hood, in fact on my car there was so little room between the hood and carb i was losing plenty of top end. I put my dual snorkel AC in a hydraulic press to get clearance. i also modified the lid. you will also lose clearance if you run urethane motor mounts, they usually raise the motor some. i was running a quadrajet, i do not know if the holley ia any shorter.

 

I would definitely ditch the Performer, about the only dyno numbers I've got on a weak 305 where the RPM was worth 15hp over the Performer, put it on a much hotter 350 and it's going to be significant... The Performer is more like a stock replacement manifold.... I would not even think of running that with the XE274 cam...

I'm running the standard Vortec Performer RPM under my 87Z's hood with no problems, just using a 14x3" drop base open element I got for cheap somewhere. No biggie. I don't know if the Air gap RPM is any taller than the standard or not. I'm running the XE262 (218/224 dur .462/.469 lift) on the untouched Vortecs BTW.