I thinking more and more about running an Edlebrock on my Streetport 12a. Do i want the proformer or Thunder. I'm going to go 500 CFM. What fuel pump and regulator would you recommend? Also I've read you need a spacer. How thick do i want? 1/2"? 1"? 2"!? Also 4 hole? Open? Or Split Divided wall?

 

I have 2 holleys and edelbrock and a demon. the edelbrock is soooo tunable and by far the smoothest running carb (I haven't dialed in the big holley yet though). No issues with it what-so-ever! Definitely go with a thunder series, the secondaries are so easily adjusted! You get mechanical secondaries with control over the opening with an easy adjustment. A 1" (or better yet 1 1/2" if you have clearance" 4 hole spacer is necessary. You with need to join the 2 primary holes to make one though (primaries only). You will not find a more user friendly carb to work with (sorry sterling). Only thing is you need to go premix or fabricate your own omp actuator. I run premix now, just wires the omp part way before. Man premix is so much better. Sure it's a little inconvenient, but remember these is no guage telling you your omp is working. Just mix 100:1, no smoking at the lights and the right lube is always there.

 

I personally like Mallory pumps, so for yours I'd run a Mallory Comp 110. It's internally regulated at 6psi I believe, so that should be just about pefect for your Edelbrock, but you can run a Holley 4-9psi FPR and a ReSpeed gauge if you want to be very accurate about it. It flows 110gph so that should be plenty for a SP12a

I'd run the Split Divided Wall, since that's how Carl's ported manifolds for the modded Nikkis look. Honestly I don't have any *real* knowledge or reason behind my suggestion other than that, so if someone else has a reason to run a different type of spacer I'd say listen to them.

But for the spacer, I don't know if you even need one, depends on the manifold you use. Mainly you want to make sure that your carb and airbox don't hit the hood I'd think. My ISCRacing airbox on my modded nikki rubs on the underside of the hood with the stock spacer, so I know there's not a lot of room there. IIRC the RB Holley manifold can be used with Edelbrocks, but again I don't have personal experience so I could be wrong on all accounts.

Jon

 

There's something I don't understand about the spacer.

84stock says to join both primaries together. I've always thought you were supposed to join both secondaries together. What am I supposed to do?

 

Like just drill a hole though the spacer to join the 2 primaries or secondaries? Witch ever it maybe. Speaking of, witch is it?

 

The primaries!!! The Edelbrock needs this for it to get a proper signal for the idle! The spacer will also help with throttle response and low end torque. I prefer not to join the secondaries, since they do not affect idle and only get opened with full throttle. Do not join primaries and secondaries, keeping these separate helps maintain good port velocity to the primaries and helps with throttle response and economy. There is no reason why a 500 cfm Edelbrock cannot produce equal economy to the nikki if driven easily while still providing more topend power.

 

So just drill a hole or cut out the wall of the spacer that divide the two primaries? Also any other suggestions for fuel pump and regulators, i don't want to spend a lot, but I'm willing to spend for quality. Is there anything else i will need/need to do.
1. Edlebrock 500CMF Thunder Series
2. ~1" 4 hoe spacer with primaries connected
3. RB Streetport intake manifold
4. Premix
5. Some sort of better fuel pump and regulator
6. ?
7. ?

 

Remove the divider between the primaries. The best pressure regulator I have come across is a Barry Grant regulator and it has a port for a fuel pressure gauge in it.

 

Everybody has a different answer. Call or email the tech guys at Racing Beat if you want an answer based on actual dyno testing. Or look at one of their Holley 4 barrel installations. The laws of physics will be similar for the Edelbrock and the Holley. The small connecting passage on the Holley is NOT the same as removing the divider.

 

I'm working on a 1" spacer today and I need to know whether to cut a channel to connect both primaries. The manifold already has channels like a '79 manifold so that's one strike against it according to 84stock.

My theory is channels connecting primaries and secondaries is a good thing on a stock manifold with a stock carb because whenever I've added them to an older seperarate runner manifold, the engine always runs better, regardless of the carb (all stock but different years had various differences in idle circuit, fuel jets and air bleed sizes). The latest 'proof' is my white REPU in which I cut some channels at the top to mimic a typical '79 manifold and the idle quality, primary power and secondary power all showed improvement.

The carb spacer I'm working on will go on PercentSevenC's GLC with an Edelbrock 600 which has the same channeled (by me) manifold as the white REPU with the same size channels. It's streetported and does ok with a stock carb. If this works out I'll look into adding my Edlebrock 600 to my recently rebuilt '74 spec engine in my red REPU. I'll break it in on a stock carb for now.

84stock says you shouldn't join primary to secondary in the spacer. Am I right? So then what if they're joined at the top of a stock manifold like a '79? How does this screw up flow? I've only ever seen improvements in driveability. Of course all my testing has been with stock or rejetted stock carbs.

As for the mods I'm doing to the spacer, it came with runner holes that are almost large enough for the Edelbrock to fit, so I've gotta hog them out a little. They squeeze down a bit to almost fit a stock manifold with only a slight edge (this is tons better than a typical spacer you could find at an auto parts store hehehe). While I'm doing that, I will cut a channel to connect either both primaries or both secondaries...

Since 84stock has had plenty of success dialing in his Edelbrock on an NA engine before (I assume) and he cut a channel only between the primaries, I think I will do that. My only problem here is that there is a recent thread where I asked the same question and the answer was to cut a channel connecting both secondaries only. Huh? Check out post #6 https://www.rx7club.com/forum/showth...ight=edelbrock

I'd really like a confirmation on which set of runners to join. Both primaries together? Or both secondaries? Thanks.

 

Jeff, isn't the edlebrock carb a "Square bore", so the spacer would be reversible? Try it with the primaries joined, then flip 180* and try with the secondaries joined.
That should give you the definitive "Real world" answer you really want/need.

 

The spacer was made to fit on a stock manifold. It has runner holes that closely match the top of a stock manifold. In other words, it has definite primaries and definite secondaries. No flipping allowed.

Now if I crammed a regular square bore spacer between them, it would be possible to test in this way. But then the air cleaner wouldn't fit under the hood. Then again it could be tested without one...

 

Oh, my bad. I thought you had a holley-style intake, not a stocker.

Yup, you could test with a generic spacer added, thereby protecting the custom job till after you see what works bestest.

 

*laughs*

I love how the laws of physics change with different carburetors! Now if only I could get ahold of the new "frictionless surface" for my rotor housing, then I'd really be set.

Jon

 

It is "okay" to have a passage between primaries and secondaries. I just prefer the alternate. If you wanna keep it real simple just use a 1/2" open spacer.

 

84stock, so I should just cut a channel in primaries only?

 

yep, that would be preferred

 

I would use a wood phenolic spacer and cut the channel

 

make your lives easier and run a 48 IDA.....

 

Don't use wood. When Rx7Carl was testing different things with his flowbench, he used wood, then found out how porous it is when he mounted it on his car. I can't remember what the specific result was, but I remember a resounding "wood spacer = bad idea even for testing" message coming out of the whole thing.

Jon

 

I tried both style spacers w/ my Edelbrock and honestly didnt notice any difference on performance. I'm now going to run one of those damned Holley's again on my 6 port 13b. A friend of mine is running a "NEW" style Holley 600 or 650 not sure but he said tunning was simple and so far she's running like a champ. I'll see what carb it is when I go visit him this weekend and post some info for you.

 

Okay, how about this, Do i want the one calibrated for Dual quad applications or single quad of the 500 CMF thunder series?

 

thunder

 

Ok, I'll cut the channel in the primary and leave the secondaries seperate.

 

uh, what? I know i want thunder series but there are two different carbs in 500cfm with a manual choke, one "Calibrated For Dual-Quad Applications" and the other for "Calibrated For Single-Quad Applications" but i not sure witch one to get. or what that really even means.