Not your Basic Intake Spacer Question

Piston

Founding Member
Aug 1, 2001
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Chicago Suburbs
Ok. What is the main purpose of these spacers that go between the upper and lower plenum? If I recall some say it will cool the upper better therefore your engine will gain in performance from cooler air. I also know sometimes you may want to run them if your valve covers are to tall. Now the question I have is how does a longer runner effect the intake RPM range? You see currently I have an stage II ported edelbrock performer that flows ~275cfm (if I remember correctly) and was using it with an anderson b2 cam. Now however with my new 331 and the n-91 cam which is a high rev cam up to 6900rpms my intake will be running out of steam at about 6000rpms maybe more because of the port work. So I was thinking of picking up a Holley Systemax intake and getting the lower ported to match the Stage II ported TFS heads. However, if a spacer and longer runners help out the rpm problem I may save myself some money and try it. However, I'm thinking that the upper plenum is probably very much involved in determining the RPM range not just the just the lenght of the runners on the lower. If the longer runners from a spacer do help, how much? Am I just better off in getting the Holley? You see I'm trying to make a 500HP N/A 331.
 
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no, the longer the runners the worse your condition will get...the shorter the runners the better upper RPM breathing..... that is apparent in the design of the Edelbrock intakes...if you notice the runners on the RPM are much shorter than the runners on the normal Performer...based on the fact that the shorter runners allow for breathing up top.....id look into possibly swapping to an RPM upper (and having that ported like your performer is) or look into the RPM II manifold....



Anthony
 
I don't see how an intake spacer would drastically change the RPM range, if any change at all. The upper manifold and lower manifold are equally important in determining RPM range. Look at Edelbrocks, the lowers are the same. The only difference are the uppers, and switching to a RPM upper intake gives you 1000 more RPM of room, if not more. Also, with a spacer, you run into hood clearance problems (if you still have the stock hood). Don't even go for the Holley, it won't be enough. Look into something like a Vic Jr. Not to be negative, but it is going to be extremely hard to see 500 RWHP out of a 331 that is not an all out race motor. I would love to see you do it, but I doubt it can be done with EFI. A carb would make it much easier.

Joe
 
Thanks Viper I wasn't sure which way that goes.

Joe. I was referring to fly wheel HP. I was told that even though the edelbrock lowers all look the same they are not. Otherwise I will try to find an RPM II Upper (anyone sell just uppers) which I was advised againts doing that because the lower will not match. I was also told that the Holley's are ideal for the situation and the victor's are a bit much. Looks like I got to do some more research.
 
An intake runner has a ram effect at a certain rpm. The stock intake was designed for good low rpm torque.

It is tuned the same way as a pipe organ. High pitch=short pipe: high rpm=short runner. Cross sectional area is also a factor, as the area increases, you need a longer pipe to tume for the same pitch/rpm. You want to choose the cross section of your intake so that your intake charge is traveling at a certain velocity at your power peak, I believe it's about 100 meters per second.

A spacer can only shift your torque curve down to a lower rpm. To shift the curve up, you need either shorter runners, or runners with a larger cross section.

The plenum volume is another variable. I don't think you will find much power there, I remember tests of cobra intakes that were cut open, ported and had there plenum volume increased and made less power than a stock intake. However, since the edelbrock's have that removable plate on the plenum, it should be pretty easy to make a spacer that will increase the volume.
 
Piston said:
Joe. I was referring to fly wheel HP. I was told that even though the edelbrock lowers all look the same they are not. Otherwise I will try to find an RPM II Upper (anyone sell just uppers) which I was advised againts doing that because the lower will not match. I was also told that the Holley's are ideal for the situation and the victor's are a bit much. Looks like I got to do some more research.
Your cam is going to rev up to 7000, and the Holley is going to start running out of breath around 6500 RPM. Sure, it will rev to 7000, but it will not produce as much power as a Vic Jr. will. The Holley will have much better street manners than the Vic. Jr. There might only be a 10 HP difference between the two manifolds, but the street manners lost by the Vic. Jr might not make the extra power worth it. If the car is going to be driven on the street, I would definitely go with the Holley.

BTW, all Performer and RPM manifolds have the same lower.

Joe
 
How much more RPM's will I get out of porting the lower holley Intake? I was defintely thinking of porting the lower holley to match the heads and leaving the upper untouched.

What's a better intake RPMII or Holley? Anyone seen those compared on a dyno someplace? It seems the RPMII runs out of steam at 7k that might be better for my application. Although, the Holley was recommended to me?!?

I defintely think the Victor is a little out there. That motor is wild but not that wild.
 
Piston said:
How much more RPM's will I get out of porting the lower holley Intake? I was defintely thinking of porting the lower holley to match the heads and leaving the upper untouched.

What's a better intake RPMII or Holley? Anyone seen those compared on a dyno someplace? It seems the RPMII runs out of steam at 7k that might be better for my application. Although, the Holley was recommended to me?!?

I defintely think the Victor is a little out there. That motor is wild but not that wild.
I haven't seen any tests with the new RPM II, so excluding that, the Holley is the best intake for your situation. There are guys running low 10's in a 306 with a slightly ported Holley. The Holley and RPM II are going to operate in the same RPM range as eachother, so don't base your comparison on that. I would go with the Holley because it is tried and true.

Joe