Carb Spacer - Airflow Test

I have some interesting airflow data. The Team at Jomar (John A and John B) asked us to flow test the leading carburetor spacer plates against their Powercone. Some of you may have already experienced these results but I thought that I would share them with the members of this forum. (with Jomar's approval).
The spacers used for the comparison were the 1" Wilson Tapered Spacer, 1" Super-Sucker, 1" Jomar (4) hole, 1" Jomar open spacer and the 1" Jomar Powercone. A standard 850 cfm Holly carburetor at full throttle position was placed on a special carburetor stand attached to a Superflow 1020 flow bench with a set pressure drop of 20.2" of water which equaled 851 cfm. This was the baseline flow setting used for all the testing. Each spacer was installed on the stand with the same carburetor and the same pressure drop (20.2" of water). An increase in airflow was reported for all the spacers, the Jomar Powercone demonstrated the greatest increase of 10.93%. The test was repeated with all the 1" spacer and a second 1" open spacer. Again, the Jomar Powercone showed the greatest gain with an increase of 14.34%. The test was repeated for a third time with the same 1" carburetor spacers and 2" of open spacer. Again, the Jomar Powercone demonstrated the highest gain with a 16.33% increase which equals 990 cfm. The total increase from the baseline was 139 cfm while maintaining the same pressure drop of 20.2" of water. Afterwards, the baseline carburetor was installed on the test stand and repeated original baseline flow of 851 cfm. Listed below are the results:

Height Carburetor Spacer Type Flow Percent Change
(in) (cfm)
0.0 Baseline 850 cfm Holley carb 851 0.0%
1.0 (4) Holes Spacer 868 2.00%
1.0 Open Spacer 921 8.23%
1.0 Super Sucker 931 9.40%
1.0 Wilson Tapered 937 10.11%
1.0 Jomar Powercone 944 10.93%
2.0 Open Spacer - 2.0" total 945 11.05%
2.0 Super Sucker w/ 1.0" open spacer 966 13.51%
2.0 Wilson Tapered w/ 1.0" open spacer 969 13.87%
2.0 Jomar Powercone w/ 1.0" open spacer 973 14.34%
3.0 Open Spacer - 3.0" total 948 11.40%
3.0 Super Sucker w/ 2.0" open spacer 976 14.69%
3.0 Wilson Tapered w/ 2.0" open spacer 986 15.86%
3.0 Jomar Powercone w/ 2.0" open spacer 990 16.33%

Thanks,
Jay

Thank you for sharing those results Jay

The power cones are good stuff and J.A. & J.B. are quality guys

Thanks to Jay for the testing - and developing a meaningful test matrix! Given these results, perhaps we should raise the prices!!

We appreciate the kind words too.... (from Lem et al.)

The results confirm reports from our engine builder customers and verify the HP gains relative to competitive spacers.

JB

great info! I had already bought a 1" Jomar Powercone from Lem last year! I have yet to try it out!

Jay,

I understand,,, I understand,,, and then I don't understand. We know that the industry standard for flow testing four barrel carbs is 1.5" Hg. Then the conversion factor for changing Hg to H2O is 13.5962. When you do the math, that equals 20.3943" H2O. Most people round that off to 20.4" H2O. That's what I enter into the computer when I'm flow testing carbs and I think many other people do also. However, you used 20.2", why didn't you use 20.4"?

Nice test by the way, and thanks for posting the good info.

Charlie Evans

Have a 2" open spacer and 1" alum spacer with a poly insert. I ground the insert to 'match' the super sucker. Noticed you tested the reverse. Just wonder how the 1" SS w/ 2" spacer would work? Any plans to do that kind of test? Thanks for the great info.

Charlie's Question
The carburetor used for the test was a Holley 4781 (850 cfm) that had the choke plate / shaft removed but maintained the choke hone. It was my discussion to match the carburetor airflow rating (850 cfm) and not a standard pressure drop because of the choke plate / shaft removal.

Also note; no bell mouth or radius entrance was used on the inlet side of the carburetor. No other airflow modifications were performed to the carburetor. The carburetor spacer installation order remained the same.

GT300TD's Question
Each one inch tapered style spacer was always installed closest to the carburetor base plate then followed by a one inch or two inch open spacer plate. The one inch Super Sucker (SS) with a one inch open spacer flowed 966 cfm. The one inch Super Sucker (SS) with a two inch open spacer flowed 976 cfm. The first column in the above chart is the overall height. If there is another test you wish for me to perform please let me know.

Thanks,

Jay

We've been thinking of doing the Power Cone in 1.5" when we get the time. Also offering aluminum versions for those who want that option, although the insulation benefit of phenolic is still a valid consideration.

JB

rmcomprandy wrote:

GT300TD wrote:

Have a 2" open spacer and 1" alum spacer with a poly insert. I ground the insert to 'match' the super sucker. Noticed you tested the reverse. Just wonder how the 1" SS w/ 2" spacer would work? Any plans to do that kind of test? Thanks for the great info.

The way I read it, 3.0" inches total spacer with a 2" open spacer and a 1" Super Sucker on top WAS tested.

Randy,
YEP, you are right, I misread it as a 3" SS w/2" open spacer, 5"?!! DUUUUH. Thanks for straightening me out, sure wasn't the first time, haha.

Jay,
You too!

Jay,
Was figuring % with my 750 (3310-3) Holley using your chart and at 14.69% equals 860 CFM + -. I realize it might me proportionally lower with less CFM to start with? According to a formula I used, my 466 should need roughly a 898 CFM carb. I'm not ready to sell my BG 775RS Race Demon yet...but it sure might perform better on the street?!!
Thanks again guys!

IDTJay wrote:Charlie's Question
The carburetor used for the test was a Holley 4781 (850 cfm) that had the choke plate / shaft removed but maintained the choke hone. It was my discussion to match the carburetor airflow rating (850 cfm) and not a standard pressure drop because of the choke plate / shaft removal.

Also note; no bell mouth or radius entrance was used on the inlet side of the carburetor. No other airflow modifications were performed to the carburetor. The carburetor spacer installation order remained the same.

GT300TD's Question
Each one inch tapered style spacer was always installed closest to the carburetor base plate then followed by a one inch or two inch open spacer plate. The one inch Super Sucker (SS) with a one inch open spacer flowed 966 cfm. The one inch Super Sucker (SS) with a two inch open spacer flowed 976 cfm. The first column in the above chart is the overall height. If there is another test you wish for me to perform please let me know.

Thanks,

Jay

HMMM, since you offered...BG 775 RS Race Demon, hint, hint.
When "BGTech" was on the forum he told me it wasn't the carb he would recommend...but if I removed the jet extensions it would be close.
I had already purchased it (before they went out of business), but for $500 I don't think I got hurt too bad. He said it would actually be closer to 900 CFM than 775.
Thanks.

GT300TD,

Yesterday afternoon, John B. from Jomar and I had this coversation. He wanted to test a 750 cfm carburetor with the appropriate tapered spacers. When we are ready to test the 750 cfm tapered spacer; if you are willing, we can use your carb for the testing. We can test at different volumetric flow rates and see the differences. Let us know.

Jay

Nice Test Jay, Thanks for Posting the Results.

Jay, I have a 750 holley vac.sec. you can try

Keith

IDTJay wrote:GT300TD,

Yesterday afternoon, John B. from Jomar and I had this coversation. He wanted to test a 750 cfm carburetor with the appropriate tapered spacers. When we are ready to test the 750 cfm tapered spacer; if you are willing, we can use your carb for the testing. We can test at different volumetric flow rates and see the differences. Let us know.

Jay

Jay,
You just may have made me an offer I CAN NOT refuse.
Would it be OK if I sent you both the 750 and the 775 and my spacers?
I'll send you a copy of my build, and my future intentions, if that would help you determine what is best.
Thanks,
T.Smith

IDTJay,

PM sent

T.Smith

Jay,

Thanks for the explanation. That's the only plausible reason I could think of, for your testing at 20.2" H2O. Again, nice test and it's appreciated.

Note to the guys, we've been running Jomar Power Cones for a few years now, and sometimes the carb pad on the manifold needs to be opened up (or ported), to match the exit of the Jomar. IMO pad to manifold "matching" is required.

Charlie Evans

c.evans wrote:Jay,

Thanks for the explanation. That's the only plausible reason I could think of, for your testing at 20.2" H2O. Again, nice test and it's appreciated.

Note to the guys, we've been running Jomar Power Cones for a few years now, and sometimes the carb pad on the manifold needs to be opened up (or ported), to match the exit of the Jomar. IMO pad to manifold "matching" is required.

Charlie Evans

To put some context to this post.....Charlie's statement is mostly relavant to the powercone spacers for the big bore 1250 & 1450 dominators.

bruno wrote:Thank you for sharing those results Jay

Nick, you should make this one a Sticky ! This subject about different spacers pops up from time to time.

so does this have similar results with nos plate engines or is this for n/a engines? Was just wondering if the plate would effect the flow

Jimmy ,

good question, i know from my experience we lost around 14hp with the big shot plate deal , i will look at my paper work this morning to make sure

Thanks Nick ,I figured it would thats why we push that button (more flow)