2-bbl vs 4-bbl carb test - Team Camaro Tech
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post #1 of 9 (permalink) Old Apr 15th, 05, 08:46 PM Thread Starter
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2-bbl vs 4-bbl carb test

We recently installed a 4-bbl carb on the Durango Deuce 331" motor, and today I took a little time to run some chassis dyno tests.

The old setup - a Vic.Jr Sportsman 2901 2-bbl manifold, AED 4412 500 cfm 2-bbl carb, 1" 2-hole spacer, carb hat and a 14" x 3" air cleaner. 354 rwhp @ 6700 rpm on a mix of 91 and 110 octane.

The new setup - A Vic.Jr Tall 2999 4-bbl manifold with a Brodix DT-105 turtle, AED 4779 750 cfm 4-bbl carb, 1" 4-hole spacer, K&N Flow Control air cleaner base and the same air cleaner. 399 rwhp @ 6900 rpm on straight 91 octane.

I expected maybe a 25-30 hp gain, but not 45. I'll be trying some mixed gas tomorrow, with a little more timing and jet swapping. My dyno partner is bound and determined to get it over 400.
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post #2 of 9 (permalink) Old Apr 15th, 05, 09:20 PM
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Re: 2-bbl vs 4-bbl carb test

cool, since the most of the cars i know kill 3-5 tenths by unhooking the secondaries, 45 HP sounds resonable to me.

Thanks for posting the results!

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post #3 of 9 (permalink) Old Apr 16th, 05, 06:07 AM
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Re: 2-bbl vs 4-bbl carb test

I'd guess with 399 rwhp the engine is more like 470-500 HP at the flywheel. I can see how a 500 cfm carb would drop 50 HP . . .

Just curious, did you measure manifold vacuum during your testing? I'm curious what kind of vacuum the engine pulled at 6700 with the two barrell vs. the 4 barrell.

Interesting test results . . . thanks for posting

E85 racer and E85 carb builder
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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #4 of 9 (permalink) Old Apr 16th, 05, 06:30 AM Thread Starter
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Re: 2-bbl vs 4-bbl carb test

No vacuum data, but you can see where the 2-bbl starts flattening out about 5800 rpm.

I did a similar test on a 355" circle track motor with a Performer RPM manifold and we picked up about 30 rwhp, from 305 to 335. It had a 4412 on a Brzezinski spacer and he bolted on a 4779 with no spacer.

This same racer got interested in our vacuum pump setup and put one on his car. He called the other day and said he lost the belt for the pump in the qualifier and it felt like he was running on 7 cylinders. He went on to win the main event, and says his new setup makes much more torque coming out of the corners.
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post #5 of 9 (permalink) Old Apr 16th, 05, 09:51 AM
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Re: 2-bbl vs 4-bbl carb test

Good info,
Did you run the 4-bbl with and without the turtle, it may have contributed to some if the power gain.

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post #6 of 9 (permalink) Old Apr 16th, 05, 03:26 PM
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Re: 2-bbl vs 4-bbl carb test

Quote:
Originally Posted by onovakind67
No vacuum data, but you can see where the 2-bbl starts flattening out about 5800 rpm.
Hmm. Interesting. Remember the old Holley formula -- rpm x cid / 3456 * VE ?

[(331 x 5800) / 3456] * .95 = 526 cfm

Looks like that formula agrees that a 500 cfm carb is starting to get small at 5800 rpm on a 331" motor . . .

E85 racer and E85 carb builder
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68 Camaro, E85 powered 427" small block. 9.96 @ 133 MPH, 1.319 sixty foot on motor. 5.92 eighth @ 116 with a 1.42 sixty breaking beams with back tire on the bottle
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post #7 of 9 (permalink) Old Apr 17th, 05, 09:12 AM
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Re: 2-bbl vs 4-bbl carb test

Interesting info. Where in the powerband did the 4bbl setup start making significant power increases? Or was there power increases across the board? I know you have posted the engines specs before...care to post them again?

I am curious about the measured vacuum too. Seems that holley rates their 2bbl carbs at 3" vac drop vs. 1.5" for 4bbl's. Seems like the 500cfm 2bbl was equivalent to a 350-400cfm 4bbl@1.5" vac drop.

It would be cool if you could get your hands on one of the old 650cfm 2bbl holleys, but I think they quit making those years ago. I do believe Jet still makes a 560cfm rochester 2G though for 2bbl racing applications.
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post #8 of 9 (permalink) Old Apr 17th, 05, 12:00 PM Thread Starter
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Re: 2-bbl vs 4-bbl carb test

331" SBC
1130 GM forged crank
Eagle featherweight 550g H-beam 6.125" rods
SRP 138085 444g pistons with Casidiam coated pins
Camcraft Cams solid roller cam 269/269 advertised, 240/240 @ .05, .410 lobe lift, 110 LSA, 106 ICL, Isky Red Zone lifters, 210 3/8" pushrods
old AFR 195's angle milled to 56cc with 1.5 Jesel Sportsman rockers
GZM vacuum pump, 8" vacuum in the crankcase
MSD 6AL, 31 total timing on 91 octane, up to 40 at 8000'
1-5/8" x 40" headers with 2-1/4" merge collector
2-1/2" Dr. Gas X-pipe with Magnaflow mufflers, over the axle tailpipes


We've tested the 2-bbl setup with a JDR 2-bbl with 1-3/4" throttle plates, and with a C&S Specialties 890 cfm 2-bbl. The C&S carb requires the Vic-2V intake to be enlarged, as the throttle bores are larger than the intake. The JDR carb was a high altitude setup, so it didn't do much better than the 4412 on a sea level dyno, about 355 rwhp.

The C&S is also set up to run from 6000 to 8000' and is quite lean on the dyno, but managed 365 rwhp. At altitude it really runs well, we always get compliments on how clean and crisp the car runs while other guys are having mixture problems and blowing black smoke.

The 4-bbl makes more power at all rpm's, but really starts to separate above 5000 compared to the 4412.
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post #9 of 9 (permalink) Old Apr 17th, 05, 05:02 PM Thread Starter
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Re: 2-bbl vs 4-bbl carb test

I added about 30% 110 octane to the gas tank, stepped the timing up 3 to 34 total and got 406 SAE corrected rwhp, 417 uncorrected.
I lashed the valves for the first time since October and they were about 0.001" loose all around.
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