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Which yields more horsepower?
All things being equal on a Windsor block which of the following intake manifolds yields more horsepower. Victor Jr. or Air Gap?
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Just like Anthony said...what rpm range are you referring to? I'd say if the engine was built for the Victor Jr and then you changed it to an RPM Air Gap, horsepower would go down, but torque would go up.
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Just like bly and Anthony said...
On a mid size 9.5 deck from 351-371 ci this holds true. For bigger Windsors, 427 and up, the Super Victor works very well from 3500 to 7000. |
OK, let me try this again. On a stock 351W block which makes the most horsepower at any rpm? Another words, if a guy had an Air Gap manifold and just changed to a Victor Jr. would he get more or less horsepower in general. I was told a Victor Jr. would develop about 10% more horsepower at maximum power (what rpm I don't know). Earlier I was told the Air Gap held an advantage. So which is correct? If you must have an rpm range, then how about 5000.
Skip |
There are trade-offs to manifold design. The Victor Jr manifold is a single plane open plenum design and will develop more HP, however that HP will be up the RPM scale a little further than with a dual plane Air gap Design. A dual plane will generally have a little better distribution at lower speeds due to the smaller cross section of the port runners. The dual plane is a little more flexable and will provide more torque at a lower RPM but looses out to the Victor Jr as the RPMs rise. The open plenun of the Victor JR will support more airflow at higher speed but the fuel will tend to fall out of suspension as rpms drop (at part throttle) and therefore at low speed has poor fuel distibution and an irradic idle.
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I addition to what Rick said, the intake has to be matched to the flow of the heads (among other things). The Victor makes great high rpm hp, but only if you have the heads to use it. If you had a motor with good heads, the Victor will make more hp at a higher rpm, trading off hp in the mid range compared to the Air Gap. If you don't have the heads to support the Victor and you install it, the motor will not make more hp, and you'll still be giving up the midrange power. The car will be overall slower.
You need to look at your combination, and decide if you need a manifold like the Victor. Chances are, you don't. |
Skip,
You seem to want to just boil it down, so here goes. The single plane design, (Jr.) will make a generally higher figure at generally higher RPM. The dual plane (Air Gap) will be generally superior lower-down up to an RPM point when the Jr. will make a bigger number and go higher up in the RPM range. (Assuming your engine can.) If you were told this about your spec engine, you haven't told us what the specs are, so we can only generalize here. If you have say a 9.5-1, 351 that goes to 5200 with a dual plane, you'd waste money going to a single plane because it generally won't make a superior HP number until after your valve train quits at 5200. If you had a 7500 RPM valvetrain with a dual plane, you'd be choking the engine 2000 RPM before the valvetrain quit. The dual plane will feel much better (torque) in the 5200 RPM operating range described, with a probably higher HP number than the Jr. The Jr. allows you to install more cam, heads and carb to fully take advantage of the breathing. The gap under the runners means nothing in this comparison as both types have one. To make a wise choice and not waste money, you can't simplify so much-you have to look at the whole combination and RPM envelope you want make the most power in. It's a compromise. Manowar |
Thanks guys!
I am sorry my original question was so vague. There are obviously many factors involved. But, I think the answers you all gave me make sense and settle the argument. The engine we are talking about is a pretty mild 351W with Edelbrock RPM heads and a Holley 670 carb. The cam is a Ford Motorsport "E" (that is all I can find on the spec sheet) and the engine is not a hi revver. So, I think the Air Gap is an OK manifold for this engine. I am thinking about upgrading to get more power. (about 385hp now and would like 75-100 more hp) I assume I will have to stroke it, change the cam, possibly the intake and carburetor. Any other ideas? Thanks, SkipB |
Just bolt on AFR 185 heads. No other changes-should net at least 50 HP alone. The B303 cam might get you the 25 more to make your "window".
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Skip:
For what it is worth, I think I have the same engine as you, except I still have the 770 cfm Holley Street Avenger. I took the car to a chassis dyno about a year ago and found that peak hp was at about 6200 rpm. |
ERA,
Thanks for the ideas. I will check into AFR 185s. Who makes the B303, is that Ford Motorsport or some other brand. Sorry my background is Porsche and BMW engines, so number alone don't always mean too much to me yet! Sledge, I had a Barry Grant 750 on mine an it didn't run so well. I was told it was too much carb. So I switched to a Holley 670 and it runs great. Maybe a tuning issue? I could never get it to idle at all. The guys at California Cobra were stumped by the Barry Grant running so poorly, as they had installed quite a few without problems. Could be I had a defective one as well? I think if I make the changes I am thinking about then a Holley 770 might be in order. SkipB |
Within reason, you can make almost any carb work on an engine. Your problem was undoubtedly not the CFM (size) of the carb, but the jetting. The jetting is everything. I think the Boss 302 with old iron Cleveland heads came from the factory with a 750 or 780. Get the jetting right and it will be fine.
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Yes and they ran like pigs under 3000 rpm. CFM is very important. Too much cfm and the motor falls on its face at low and mid-range rpm. Too little cfm and the motor is choking and nosing over at higher rpm. In this case, fairly mild engine for street use, lean to the smaller carb like the 670 cfm. You will have more low and mid-range along with better throttle response. And as CobraEd says, get the jetting right. John |
I agree with John, you need velocity, not more cfm, especially with your small cam and heads. Your 670 is fine and feels sharper with the dual plane.
Yes the B303 is from FMS. |
Skip:
for what it is worth I have car 168 with the standard CA Cobra 351W setup for that time frame. When I went to the dyno I mentioned to the dyno guy that I had the 770 CFM carb and that pretty much everyone was telling me that it was too big. He said not necessarily so, let's give it a try. The dyno runs, once the car was checked for proper jets, with air cleaner on, and leaking and poorly-matched slip-fit headers and sidepipes, still gave me 320+ RWHP @ 6200 rpm and 330+ lb-ft RW torque @ 3000 rpm. Both curves were pretty smooth from 1500 rpm on up. We took it all the way to 6800 rpm on one run but there wasn't any real payoff. The car idles fine at about 1000 rpm but it spits a little until about 2500 rpm at partial throttle, then it really takes off. Overall I'm happy but I sometimes wonder if I'd find nirvana with a slightly smaller carb. The dyno guy said he didn't see much point in going to a smaller carb. When I find myself with some of that pesky excess income I may try a slightly smaller carb. In the meantime I am (perhaps ignorantly so) reasonably happy. Cheers |
Skip B,
I have the Smeding 351W Extreme in my BDR with the Holly Street Avenger 770. Probably the same Edelbrock RPM heads and Air Gap intake as you and Sledge have. May be a different cam than yours, not sure. Mine idles at 800 RPM and runs smooth thru the RPMs with no hesitations at all. Has been running great since day one. Maybe it's because I am below sea level, but it still runs good in the San Diego/mountain areas. |
I also agree you should stay with the smaller carb until you decide to upgrade for more power. Advice by CHAS to go with AFR 185's is probably the most valuable so far as the heads will be a major power making component . Since you have objectives now you may consider ordering the AFR's already milled to 58cc's .That would give you another .75 points compression over the stock 64cc's. For 500HP you'd probably want 10-10:5:1 compression, later considering the V-Jr intake port matched to your AFR heads, getting the larger carb, then select a matching cam that's a more aggressive profile than the B303. You can consult www.bennettracing.com for a Comp cam custom grind that would get you where you want to be with your components peaking HP around 6K.
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Squirrel:
Is your engine the 385 hp 351W? If so, do you have any kind of data or specifications for it? Despite repeated requests I never could get any info on the engine from Armond. |
Sledge,
I have a specification sheet from Smeding Performance on the 351W Extreme. I got it from Ben Smeding a while back. I have a scanned copy of it, I can email it to you, if you wish. Ben says this engine @ 357 cubic inches is capable of 405 HP @ 5800 RPM & 410 ft-lbs TQ @ 4600 RPM. |
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