Modifying factory hipo manifolds

[moparsr2fast]

 Hey gang!

  I am a fan of the F.A.S.T. series cars, but am not looking to compete ( at least not at this time).  I am building a 493 that I want to mimic a factory 440 6 pack in every aspect except power output. The biggest bottle neck  IMO, would be the factory hipo manifolds. Giving them up in lieu of headers is not an option. What I would love to get, are proven suggestions for modifying the manifolds for better air flow. Can anyone point out some ideas? 

[Mike DC]

     
You could have them extrude-honed.  It means pumping a sort of abrasive toothpaste through the part.  I'm not sure who does it though and the gains are most likely pretty small. 

You're right that the iron manifolds will be a major choke-point but there's no way to really fix it.  Just step back and look at the manifolds versus a set of full length headers - the sheer size of the items alone should tell you what a losing proposition it is trying to improve the flow of manifolds.

[moparsr2fast]

 I was wondering if I couldn't bore from the flange back into the rest of it. Even an 1/8" in diameter would help. I have heard that extrude honing will help with the exhaust velocity. It would be great if someone did it, and had an actual flow chart showing the gains.

  I also realize it is an uphill battle, but even some improvement is better then straight up stock.

[tan top]

 remember  one of the mopar mags  done feature on a 440 build up & dyno etc one of the things they were trying  was , extrude honed parts !!  back to back dyno camparisions  between extrude honed intakes & hp manifolds ,  that particular motor combo , did not make  any more HP with extrude honed , HP manifolds , but did increase torque  1 foot pound of torque !! from memory  

was thinking  of getting my  HP manifoilds done till I read that article

[moparsr2fast]

 Yes, I would say that isn't the best way to spend money. I was hoping for porting tips or something..

[Cooter]

IMO, A 493 C.I. engine breathing through manifolds, even modded ones, is like taking a shower with your raincoat on.

[firefighter3931]

Dwayne @ Porter Racing Heads is a good friend of mine and  he builds a lot of the FAST engine combinations and does a lot of headwork on factory iron. During our conversations the subject of exhaust manifolds has come up a few times. He's done extensive dyno work and used (expensive) extrude honed manifolds and stock stuff. He hasn't seen significant gains with the extrude work. He told me that he didn't feel it was worth the expense and said point blank that if he was building a FAST combo for himself the manifolds would remain stock with maybe a flashing cleanup. 

The real magic in a FAST build is in the cam and cylinder heads. I would call him and discuss the parameters of your build and have him custom grind a cam for you. His shop number is : 802-951-1955

Bob, have a look at Mark's build....another good example of excellent power being made with HP manifolds. Dwayne had his hand in this build & it shows in the dyno results. 

http://www.dodgecharger.com/forum/index.php/topic,64302.0.html



Ron

[BSB67]

Open the port window so that it is dimensionally slightly larger than the head.  Be sure to align the head to manifold so that the manifold does not sit below the roof of the head port window.  Then you are done.

[moparsr2fast]

Being a machinist for the better part of 30 years, this is a very easy mod BSB. I will do this, amd call em good. Thanks again 

[moparsr2fast]

IMO, A 493 C.I. engine breathing through manifolds, even modded ones, is like taking a shower with your raincoat on.

  While I wholeheartedly agree with your assessment  Cooter, you have to admit, if you are in that shower long enough, you are still going to end up wet from head to toe 

[Ghoste]

Ed Cook, who is a member here runs a couple of cars in FAST and likely has good advice to offer as well.

[Chryco Psycho]

Open the port window so that it is dimensionally slightly larger than the head.  Be sure to align the head to manifold so that the manifold does not sit below the roof of the head port window.  Then you are done.

I agree enlarge the opening at the head so there is no restriction there , open the flange as well so it is the same size as the pipe or as much as possible without making it large than the pipe causing a flow restriction , cam design has a lot to do with oit as well , long overlap duration cams do not work as well with manifolds as you cannot create the scavenging of a long tube header

[74Rallye]

I'm sure you've already thought to take out the heat riser hardware inside the manifold as well.