FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: e philpott on November 18, 2011, 09:09:36 PM
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on a 550 horse FE with meduim riser 2x4 with 600's compared to 750's ???...or is the carb size not a big difference at that HP level with the med 2x4 ?? ...also , are meduim riser intakes supposed to have casting numbers ???...mine doesn't and was just wondering
thanks, Eric
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Great to see you here, Eric. On the casting numbers, the factory MR 2X4 intake I tested for my book had the C7ZX 9425 A number on it. I don't know if some of the manifolds came without casting numbers, but it wouldn't surprise me if they did, especially if they came on 65 or 66 2X4 427s. The manifold I tested was from a 67 Shelby Mustang, hence the casting number.
As far as the carbs go, on a 550 HP engine I don't think you would see a big increase in power with a change to the bigger carbs, maybe 10 HP or so. However, you are in the horsepower range where the dual plane design of that intake can start to become a limitation. I think you would get a bigger horsepower boost out of a switch to the tunnel wedge intake, keeping the 600 carbs, than you would with switching to the 750 carbs on the existing intake.
One other point, though, is that if the 750 carbs are mechanical secondary and the 600s are the vacuum secondary carbs, you may get more of a boost in power. Seems like the mechanical secondary carbs make more power with equivalent airflow than the vacuum secondary carbs (usually at the cost of fuel economy).
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vaccum secondaries are what I was refuring too .... this time around low end HP and fuel mileage was a consideration on this purchase , going from a 5K stall C6 dove spider 1000 HP double pumper annular booster to wide ratio stick 2x4 vaccum secondary meant I was loosing the stall to get into the power band in any gear on street with the touch of the gas pedal , so low rpm behavier edged out the tunnel wedge on this purchase (based on your 445 tunnel wedge verses 2x4 med riser email), I may even drop in a dura spark in place of the MSD dizzy to gain vaccum advance for fuel mileage , for 10 horse I'll stick with the 600's and stop by Jegs after the Columbus swap meet next weekend for some quick fuel metering blocks , secondary plates , vaccum diaprhams and a few extra's ..... one more question , on the vaccum secondaries is it necessary/or better to connect the vaccum housings with a balance tube/hose ??
thanks , Eric
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Since the C7 has a common plenum between the front/rear carbs, you don't really need a balance tube. Interesting what your doing in gaining low end and better mileage. If you already have a Duraspark with a vacuum advance pot handy, you'd be wise to install it for better part/closed throttle mileage.
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You are probably OK without the balance tube, but I think I'd be inclined to install it anyway. The vacuum level inside the intake is pretty dynamic, and you could potentially see some variations at the two carbs. The balance tube can't hurt, it's an easy install, and it would eliminate any possibility of one set of secondaries opening just before the other (assuming everything else is the same between the two carbs).
I remember running some dyno tests on different vacuum sources on a Streetmaster intake several years ago. The test that sticks out in my mind is how the vacuum level differed depending on whether the vacuum reading was taken from a fitting at the rear of the 1" carb spacer, from a fitting drilled and tapped into the plenum itself at the front, from the vacuum fitting on the carb base at the front, or from a fitting drilled and tapped 3" down one of the runners. There was about 2" of vacuum variation between these points. This seemed to indicate that pressure waves were moving around inside the manifold when the engine was running.
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my original equipment MR intake only has the FOMOCO and firing order on it.
on my upcoming dyno run I was hoping to compare the 600 BJ/BK carbs with my 780 BU/BT carbs on my pump gas 427 build....
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Hear that Eric? Stay tuned, Dean's motor will be on my dyno on December 10...
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FWIW, I agree with Jay. Ford didn't go to the trouble to dream-up the secondary balance set-up because they didn't have anything else to do. They must have found it necessary during their testing or they wouldn't have gone to the extra complication and expense to put it there.
KS
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Thanks jay , I will get some pop corn on the 9th :) ... thanks , Dean thats what I was wanting to hear , I knew it was a medium riser , it just had no numbers ... Machoneman in the past I raced and drove street some before parking the car to race my two youngest kids in jr dragsters , "now" after 10 years of jr dragster racing the kids aged out I now plan on driving street and then drag racing some so the mileage and low rpm power was a consideration , with 266/276 at .050 solid on 108 lobe centers it probably don't have much low end ??... with the 5 K stall speed it didn't matter on low end but now with a stick on street it will matter , fuel mileage wise I know the 5k stall and doubler pumper 4.11 gear 28 tall tire was terrible on mileage , I now will have a stick , 3.70 gear 29 inch tall 255/70/15 along with vaccum secondaries , was thinking maybe 8 mpg before to maybe 12 ish now , thats like a 50 percent increase in fuel mileage :) who wouldn't want that ??...lol
as far as the question on balance tube the carbs have it now but I would like to tune on the fly and not wrisk snagging the diaghram on the go , the quick change housing from Holley doesn't show provisions for balance tube in the picts and Quick fuels doesn't seem to have it either in the picts . also major tuning strategy difference between Holley and Quick fuel , the Holley requires a spring change where Quick Fuel use a constant spring tension but has a adjustable vaccum source for adjustment/tuning , so the QF might be hard to get equal with out a balance tube and spring change adjustment .... I will call QF on monday , maybe they can custom make me one out of there custom shop
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I'm eagerly awaiting the dyno results too! Thanks! :)
Not meaning to hijack, BUT would using single plane common plenum intake like a tunnel wedge make a difference compared to the dual plane MR 2X4? Would two 600's effectively flow more on the single plane tunnel wedge?
thanks,
paulie
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when Jay emailed me the dyno charts on his 445 with comp 306s , medium 2x4 verses tunnel wedge , the meduim riser beat it every where except the last 500 rpm in the power band .... I will have a tunnel wedge someday , but its hard to beat the meduim riser on a street driven vehicle , either way the Ford engineers knew what they were doing when they designed those two intakes .... I wonder how a FAST TBI 2x4 system would work on a tunnel wedge ??
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when Jay emailed me the dyno charts on his 445 with comp 306s , medium 2x4 verses tunnel wedge , the meduim riser beat it every where except the last 500 rpm in the power band .... I will have a tunnel wedge someday , but its hard to beat the meduim riser on a street driven vehicle , either way the Ford engineers knew what they were doing when they designed those two intakes .... I wonder how a FAST TBI 2x4 system would work on a tunnel wedge ??
I agree. I underestimated how good the MR 2x4 intake was until I read Jay's book. I had already bought a Tunnel Wedge and had it ported before I read the book. I don't regret it, but had I known how good the MR 2x4's are it would have been a tough decision for me.
The MR 2x4 intake, be it factory or Blue Thunder, is an AMAZINGLY good intake, over a huge power/rpm range.
JMO,
paulie
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took me over a year to decide after that email , plus I have always wanted a tunnel wedge , that made it even tougher ... I will have one someday , sooner than later :) .... one things for sure , the carbs and linkage will bolt up to either so no-back track there
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took me over a year to decide after that email , plus I have always wanted a tunnel wedge , that made it even tougher ... I will have one someday , sooner than later :) .... one things for sure , the carbs and linkage will bolt up to either so no-back track there
Maybe we could swap intakes sometime, Tunnel Wedge and MR 2x4, just to experiment? ;D
paulie
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we probably could :), I'm starting to accumilate some good intakes , I have a "like" brand new perfect condition street master with plenum mods all ready done , a Joe Crane ported dove spider in perfect condition (Ibought this new in 1997) and now med 2x4 with 600's ... carbs are HP series 1000 annular booster for the Dove and a nice 428 735 with milled horn and quick change vaccum housing for the street master , the 600's have milled horns and getting quick fuel metering blocks , QF metering plates , QF .130 seats and quick change vaccum housings , the 600's should be sweet when I'm done
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As for those balance tubes, have you seen these?
http://www.allcarbs.com/detail.php?pid=781&mfgn=1&ctgn=13&stt=0&gb=2
I fully agree they can't hurt (allebit they may not help either :) ) and will add that one could easily drill and tap the standard cover(s) to accept a right angle brass fitting with a small hose nipple. I've seen it done before.
Heck, even the newer style plastic quick change covers could be carefully drilled/tapped in the same manner.
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I see it now on Holley's web site :-[ .... I missed it somehow , I saw the 1x4 housing but not the quick change 2x4 , thats what I get saturday from Jegs
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Ummmm - OK?
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LOL, those spammers sure are sneaky. I deleted the message...
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Eric, you can drill a standard set of covers, I`ve done it several times. I used brake tubing and drilled the hole undersize . Just tapped the tube in and never had any problem, you could also Loctite it in for added security.