L48 Project: Ported Chevy 450 heads vs. Bowtie vortec heads

[Carnut1]

Sneak up on the bigger Exh throat real real slow!

The bigger you make the throat in a port that has a low / minimal short turn height for its given size valve, the deeper the throat will end up in the bowl, and this may not be what you want to do .
Most times with ports like this it's better to get your high lift flow by means of a good functioning Venturi which does take time and careful rework !

I will watch it. Thanks

[Carnut1]

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Just about fed up looking at these! Damn close to 250 cfm with a 2" valve. I think that will make good steam on a 355 if I can get a low rise intake to feed it. Slight increase on throat ratio to 88.95% little blending and just a bit of chamber work with a quick sanding of ssr. Now I just need to do this on all the other ports.

[Carnut1]

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Critique welcome.

[Carnut1]

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While the head was bolted to the bench I thought I could do a very rough estimate how bad the quadrajet manifold is vs. a good high rise dual plane. Horrible. I will do more accurate tests when I get the 750 cfm quadrajet from Kenny.

[Carnut1]

0711161855a.jpg

Far left quadrajet flow and swirl far right Weiand Air strike with minor porting, flow and swirl, no carb on either. I thought it would be much closer than this. Stock quadrajet is horrible! I will,do some work to the quadrajet and see if I can even it up.

[Bob Hollinshead]

Cams: Comp cams street mechanicals 12-676-4 XS268s or 12-677-4 or XS274s (with flat top pistons)
Can install at 104 in C/L for a bit extra torque and vary valve lash +/- to suite.
Excellent with 1.6 rockers on intake side. Room to grow with if /when more gear and converter.
but fine with auto stock converter and 3.08's in 10:1cr motor.
Sweet versatile running street cams. Better than hyds. Use he Summit SBC spring kit or Isky 235D

Rule the street with either of these and 125-180hp NOS,,, Won't come up short as a hyd cam will.
Yet daily driver.

The CC xs268s we put in my son's 10-1 331 sure runs good-no complaints

[ap72]

Cams: Comp cams street mechanicals 12-676-4 XS268s or 12-677-4 or XS274s (with flat top pistons)
Can install at 104 in C/L for a bit extra torque and vary valve lash +/- to suite.
Excellent with 1.6 rockers on intake side. Room to grow with if /when more gear and converter.
but fine with auto stock converter and 3.08's in 10:1cr motor.
Sweet versatile running street cams. Better than hyds. Use he Summit SBC spring kit or Isky 235D

Rule the street with either of these and 125-180hp NOS,,, Won't come up short as a hyd cam will.
Yet daily driver.

The CC xs268s we put in my son's 10-1 331 sure runs good-no complaints

It's not a bad grind. Be sure to use face oiling lifters if you go that route though, I also always give a quick clean up to the lifter bores when running a flat tappet cam. It seems there's always a lifter or two that doesn't quite spin right until you do.

[mag2555]

Have your buddy pick up another manifold and then save up to send it out to Brezezinsky to get big time worked on as there is 60 hp still to be had!

Your gonna convert the heads to screw in studs still I would guess?

[Carnut1]

Have your buddy pick up another manifold and then save up to send it out to Brezezinsky to get big time worked on as there is 60 hp still to be had!

Your gonna convert the heads to screw in studs still I would guess?

I was going to pin them. Looks like I found a crack that I missed when I magged them on an intake seat so I may not waste any more time on these. It was late after a long day so I will take another look today. I have been known to do up manifolds like Brzenzski. Lots of work and not for a cheapie build! Thanks Charlie

[novadude]

Thanks for sharing all of this information. I always wondered if there was really a lot of difference between various dual plane manifolds. Apparently there is. Would love to see a basic performer intake compared to the air strike, but I'll be happy to just take the free information you've already shared.

[Carnut1]

Thanks for sharing all of this information. I always wondered if there was really a lot of difference between various dual plane manifolds. Apparently there is. Would love to see a basic performer intake compared to the air strike, but I'll be happy to just take the free information you've already shared.

Check out my Sf600 learning curve thread. I think at the end I have three intakes heads up. A David Vizard copy quadrajet, Holley medium rise and Weiand air strike.

[Bob Hollinshead]

Don't forget that while your are grinding and going for a given pinch area / port choke size to max out HP ,the pinch point on most heads destine for this type of useage needs the choke point to be as close to one stroke lenght up stream from the back side of the Intake valve as you can get it.
Also the inlet side and outlet side of the pinch point need to transition slowly so you do not end up with a very peaky power band !
Start thinking about these things along with cfm Numbers and you will be far closer to maxing out what you have to work with in terms of production heads.

A smooth transition is a good idea to have the flow accelerate and decelerate smoothly but I am not sure what you mean by one stroke length. Please explain. Thanks Charlie

I've heard this before, so if it's a 3.48" stroke the MCSA in the port should be 3.48" upstream from the valve. If the velocity is high in that area I can guess it might help the column of air with momentum at and after BDC? Is that the theory here?

[Carnut1]

Don't forget that while your are grinding and going for a given pinch area / port choke size to max out HP ,the pinch point on most heads destine for this type of useage needs the choke point to be as close to one stroke lenght up stream from the back side of the Intake valve as you can get it.
Also the inlet side and outlet side of the pinch point need to transition slowly so you do not end up with a very peaky power band !
Start thinking about these things along with cfm Numbers and you will be far closer to maxing out what you have to work with in terms of production heads.

A smooth transition is a good idea to have the flow accelerate and decelerate smoothly but I am not sure what you mean by one stroke length. Please explain. Thanks Charlie

I've heard this before, so if it's a 3.48" stroke the MCSA in the port should be 3.48" upstream from the valve. If the velocity is high in that area I can guess it might help the column of air with momentum at and after BDC? Is that the theory here?

Interesting, never heard of that before. Thanks!

[novadude]

I've heard this before, so if it's a 3.48" stroke the MCSA in the port should be 3.48" upstream from the valve. If the velocity is high in that area I can guess it might help the column of air with momentum at and after BDC? Is that the theory here?

What's the science behind the "one stroke length" thing? I am trying to understand why position of the MCSA should be fixed for an engine that operates over a wide RPM range (with corresponding changes in air speed), has a valve curtain area that changes with piston position, etc. Is this just some empirical rule that has been found to work in most cases?

[novadude]

Thanks for sharing all of this information. I always wondered if there was really a lot of difference between various dual plane manifolds. Apparently there is. Would love to see a basic performer intake compared to the air strike, but I'll be happy to just take the free information you've already shared.

Check out my Sf600 learning curve thread. I think at the end I have three intakes heads up. A David Vizard copy quadrajet, Holley medium rise and Weiand air strike.

Just found it. Looks like the Holley low-rise would be similar to a performer. Not a whole lot of difference between the three manifolds tested. I'm surprised the stock Q-jet manifold is so much worse.