Inliners International Forums General Discussion Hi Performance 250/292 intake port comparison with a 4200 Vortec.

The other day I was cleaning out some stuff and found the turbo intake/exhaust flanges for the my defunct 292 turbo project and then got out my intake flange for the 4200.

Just for giggles I lined the 292 intake flange up with 4200 intake flange.... and well the individual 4200 runner ( 2.74" x 1.38" about 3.39 in ^2 area)are really close in size of the 292 shared runner (2.45" x 1.48" rect. about 3.25 in ^2).

This info would be nice w/pics.

MBHD

EFI-DIY Nice pics, I expect the middle pic is the 292 flange above the 4.2L Flange. I tried blowing it up, but Image Shack gives me a box w/ a red X, problem may very well be on my end though (probably is).

Thanks for providing the data. I was able to view the full-sized images ok. At his technical session at the convention in Iowa, Jerry Weigt said that the 4200 intake would flow 300 scfm at 28" H2O.

Am I assuming that someone is making a 4200 flange, or is that a one-off?

Jerry W. had some made up, you would have to ask Jerry if there are any left.

The head on this motor makes all the other task involved in the swap worthwhile. Self Racing is making real power with this motor and so are a bunch of other folks. All the motor needs to wake it up is some port work on the exhaust side, header and camshafts.

efi-diy,
what does the stock head flow?
Also, what do they flow after porting?

MBHD

Jerry W. mentioned 300 cfm on the intake, I haven't flowed my head yet - still working on it. I've heard rumors that ported close to 400 on the intake.... but again I haven't seen hard data so take this as such - but its seem reasonable if the stock head flows the numbers Jerry discussed.

Last night a buddy dropped by and we got talkin..

He runs BBC in all his vehicles and was amazed at the valve area on the 4200.

area = pi * R^2

BBC intake valve.. 2.19 == 3.76 in^2 filling a 4.25" bore

4200 intake valve 1.52 == 1.81 in^2 x 2 (2 intake valves) 3.62 in^2 filling about a 3.6" bore....

Anyone coming to B'ville... I have something interesting in the works..... and its not for the 4200.....

jerry also said the 2006 and newer used a much larger exhaust port. please correct me if i am wrong on the year.
sounds like the head will be able to support lots of power (as is). tom

Tom,

Yes the 2006 and up have a much better exhaust port. All the heads though have a casting fault (kind of like flash) that sticks up into the port. 10 min's worth of blending really helps.

Even a junk 4 valve head will out flow the best 2 valve head, valve area is the most limiting factor on heads. That is why on the latest V8 heads they keep making the intake valve larger and the exhaust valve smaller on N/A motors. Next most important is short side radius and port shape, then the valve angle.

On a turbo motor the flows need to be more equal to each other.

The Z06 Corvette heads flow 360-380 CFM on the intake.
Not bad for a 2 valve.
The All Pro heads for LS2 based engines are flowing over 400 CFM

MBHD

See what I mean, after 53 years they flow what a supra, Quad4, 4200, ecotec flow STOCK !!

Don't get me wrong I'm a two valve guy to the end. With pushrods too!!!

I'll get back w/you on that one. :-)
I really do not think that those 4 valves flow that well "stock"
The bores are too small to flow that well,,,but I could be wrong.

MBHD