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Discussion Starter · #1 · (Edited)
This was a really nice back-to-back comparison between one of my ported Vic Jr intakes with a Pro Systems 950, and an out of the box RPM AirGap with the same carb. The engine is a 10.5:1 pump gas 540ci BB Chev with AFR 315cnc heads and a Straub custom HR. The customer had me build the top end for him which included disassembly and inspection of the heads, correcting guide clearances as necessary, surfacing to pick up a little compression, and reassembling the heads with the HR springs and Ti retainers. Once done, the heads were flowed and the numbers were given to CStraub for his magic. I also assembled the valve train and measured for proper rocker geometry and push rod length. I Once done, the top end was shipped to the customer and once completed, the engine was dyno'd at RWR Racing Engines in Glendale AZ.
The results are interesting. Here are the two dyno results and I'll let them speak for themselves.

First is the ported Vic Jr:


Next the AirGap:



Note: you can't compare the averages since the rpm ranges are not the same. If someone wants to compute the averages within the same rpm range it would be interesting.

Comments?? I see some things that are thought provoking.
 

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Peaks are at just about the same rpm for both manifolds,and predictably the air gap makes more torque down lower and the single plane makes more HP up higher,oil temp 20 degree spread from test to test.Peak torque number is very close 3 ft lbs.Nice combo either way.Bill C.
 

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Discussion Starter · #3 ·
Peaks are at just about the same rpm for both manifolds,and predictably the air gap makes more torque down lower and the single plane makes more HP up higher,oil temp 20 degree spread from test to test.Peak torque number is very close 3 ft lbs.Nice combo either way.Bill C.
Thanks Bill. I thought it was interesting that both intakes peaked at near identical rpm's and that peak tq was as close. The results were expected and the owner was willing to give up the 30hp for the lower rpm torque. I saw the oil temps...pretty sure they didn't do too many pulls with the Air Gap. Maybe just one or two. Never got the oil warm.
 

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Thanks Bill. I thought it was interesting that both intakes peaked at near identical rpm's and that peak tq was as close. The results were expected and the owner was willing to give up the 30hp for the lower rpm torque. I saw the oil temps...pretty sure they didn't do too many pulls with the Air Gap. Maybe just one or two. Never got the oil warm.
I do not understand the thinking behind giving up top end for the added low end with pump gas engines at this level. Unless in a marine application, in a typical street application, as soon as you hit the gas you are past the low end.:p Nice build.
 

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Whichever gives best hood clearance/more room for bigger air cleaner...is my choice. Jr usually wins that contest.

Buuut if you have room for an air gap, you have room for a SuperVic..
 

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Single or dual, that's nasty for a hydraulic roller street engine. Any info in the cam and lifters used? Knowing the effort Scott puts into intakes, I'd say the most interesting part of this test is how well a box-stock airgap stands up to a fully ported single plane. Impressive. But I agree, much better to give up a little bottom end for 30 up top at this level. Put the power where the traction is. Much more fun.
 

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Discussion Starter · #13 ·
I do not understand the thinking behind giving up top end for the added low end with pump gas engines at this level. Unless in a marine application, in a typical street application, as soon as you hit the gas you are past the low end.:p Nice build.
The Air Gap was the customer's doing and I can see his point. Street cars like this tend to spend way more of thier life below 3500rpm than above. This is a 3500lb back-halved w/sliders '69 Camaro with a 3.90 gear and a 29" tire, 3000rpm stall. On the strip, it's a no brainer. Stall it for the power and get as much as you can.
I very seldom recommend an Airgap in a marine app.
 

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Discussion Starter · #14 ·
confused:Both sheets are averaged from 4500 to 6500. Notice the asterisks.:confused: The bsfc was.5 difference between the two pulls.
That was my mistake on the averages. I don't know how much tuning they did for the Air Gap or how many pulls. By the oil temp, I'd say it didn't spend much time on the dyno.
 

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Discussion Starter · #15 ·
Single or dual, that's nasty for a hydraulic roller street engine. Any info in the cam and lifters used? Knowing the effort Scott puts into intakes, I'd say the most interesting part of this test is how well a box-stock airgap stands up to a fully ported single plane. Impressive. But I agree, much better to give up a little bottom end for 30 up top at this level. Put the power where the traction is. Much more fun.
I was pretty surprised at this myself. I had a pretty good idea what the trend would be, but I didn't expect the 'Gap to make as much power as it did. A ported 'Gap would be an interesting test.
 
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