Crossram manifold

[JohnSlack]

Here you go...


Frank Dihartce photo

Thank you,
Do you know if that cam has three steps on the action? The first step would be primary actuation only, the second step would slowly bring the secondary butterflies along with the primaries open, followed by a third step that would be the change visible in the picture that would rapidly finishing opening both sets of butterflies. Do you know if that describes the action?
John

[Jon Mello]

No, it does not have three distinct steps.

[JohnSlack]

No, it does not have three distinct steps.

Jon,
Thank you.
John

[crossboss]

Here you go...


Frank Dihartce photo

Thank you,
Do you know if that cam has three steps on the action? The first step would be primary actuation only, the second step would slowly bring the secondary butterflies along with the primaries open, followed by a third step that would be the change visible in the picture that would rapidly finishing opening both sets of butterflies. Do you know if that describes the action?
John

Hey John,
Are you thinking this type of carb linkage for the 'unicorn' intake?

[JohnSlack]

Here you go...


Frank Dihartce photo

Thank you,
Do you know if that cam has three steps on the action? The first step would be primary actuation only, the second step would slowly bring the secondary butterflies along with the primaries open, followed by a third step that would be the change visible in the picture that would rapidly finishing opening both sets of butterflies. Do you know if that describes the action?
John

Hey John,
Are you thinking this type of carb linkage for the 'unicorn' intake?

No the carburetors on that intake are in line with each other. The Crossram linkage layout is absolutely not useable in that configuration. I was reading with interest on this site the development between the List 4210 and the list 4295 carburetors. As a result I asked about the cam slot timing on the 4295. With Jon's picture I can see a defined two step shape on the cam slot, my two carburetors have a definite three step cam slot. The cam slot on mine is not someone's regrind but a Holley part made that way for the 302 Tunnelport engine racing program. I was just wanting to compare and Jon kindly helped me out.
John

[PHAT69AMX]

? Possibly post a pic of the 3-Step style for reference ?
I do not have real parts or carbs on hand, just past Holley experience.
? 1st Design 4210 had "1:1" basically constant radius slot, except a slight primary tip-in ?
? 2nd Design 4295 2-Step "W" Slot is a "staged" design, primaries 1st x degrees, then secondaries ?
I myself have not seen a 3-Step, would be interesting to see.
My grandiose ideas, lol, "I'll make a nice 3D Model animation of the 3 styles"... LOL 

[JohnSlack]

? Possibly post a pic of the 3-Step style for reference ?
I do not have real parts or carbs on hand, just past Holley experience.
? 1st Design 4210 had "1:1" basically constant radius slot, except a slight primary tip-in ?
? 2nd Design 4295 2-Step "W" Slot is a "staged" design, primaries 1st x degrees, then secondaries ?
I myself have not seen a 3-Step, would be interesting to see.
My grandiose ideas, lol, "I'll make a nice 3D Model animation of the 3 styles"... LOL

I just took a nice picture of the 3 step cam yesterday. It was too large to attach here, so I'll resize it and post it here.
John

[Jon Mello]

John, what is the Holley LIST # for your Tunnelport carburetor(s)?

If you have trouble posting the pic let me know and I can help.

[JohnSlack]

John, what is the Holley LIST # for your Tunnelport carburetor(s)?

If you have trouble posting the pic let me know and I can help.

It is not a Holley list # carburetor, it is one of the special carburetors that FoMoCo had Holley make for the 302 Tunnelport engine program, as such it is a race only item. I have done a lot of searching on the internet and you guys were the only source I had seen of a good picture of the 2 step cam. (Thanks to you Jon.) I had been wondering about the cam on the 4295 and now I know that. But I feel it's only fair to share my side of the story, even if it is Brand X Blue. You guys seem really open to looking at both sides of the story of what was going on with T/A.
John

[Jon Mello]

Good info, John.  Yes, we are really open to learning about all sides on this forum because that paints a whole picture and not just a single facet.

[PHAT69AMX]

Am I seeing things ?...
Looks to me like that maybe the GM Mold Maker got things turned around out of place ?...
See picture, on the left is the claimed prototype Crossram that Bill Howell laid "wet flow guide ridges" in
using strips of solder and epoxy as one of the final stages of development to equalize exhaust gas temperatures.
Pictured on the right is the plenum floor of a production GM Crossram...  ?  notice the difference ?...
The plenum floor "wet flow guide ridge" pattern is not symmetrical left-to-right or front-to-back, and...
it appears the Mold Maker got it incorrectly turned around backwards when modifying the production mold ?...
Or am I seeing things ?....

And it looks like Offenhauser took the "safe route" and made the "wet flow guide ridge" pattern symmetrical...
And Edelbrock left out the plenum floor "wet flow guide ridge" pattern all together.

[Jon Mello]

Yes, the factory did make a mistake which they corrected.

[crossboss]

Jon,
It appears the Edelbrock Cross-Ram would be the better performer, as I see it. However, I have zero experience with a Chevy Cross-Ram intake. I DO have experience with the Boss 302 'Cross-Boss' Cross-Ram intake, and Inline carb. That said, the smoother runners, and less restriction will run better, no doubt. The 'bumps' on the inside will lead to fuel puddling, and can quite possibly make cylinder to cylinder air/fuel distribution non consistent aka some cylinders will run lean, while some may run rich. Yes, its a passionate and timely hobby with determination to make these things run.

[TangoBravo]

The runners on the bottom of the manifolds were to direct fuel toward cylinders that were running leaner. The fuel comes out of suspension easily and form rivers that puddle and trickle down the long runner tubes. The channels were an attempt to even the fuel mixture on cylinders that tended to run lean and guide it away from the rich ones. Chevrolet engineering and folks like Smokey Yunick found this out and re-routed the fuel to try to improve things. Smokey even built a clear top to view when revved up full song on a dynamometer when he was investigating this. Hope he was wearing some Kevlar where it counted!

[crossboss]

The runners on the bottom of the manifolds were to direct fuel toward cylinders that were running leaner. The fuel comes out of suspension easily and form rivers that puddle and trickle down the long runner tubes. The channels were an attempt to even the fuel mixture on cylinders that tended to run lean and guide it away from the rich ones. Chevrolet engineering and folks like Smokey Yunick found this out and re-routed the fuel to try to improve things. Smokey even built a clear top to view when revved up full song on a dynamometer when he was investigating this. Hope he was wearing some Kevlar where it counted!

Correct. On my intake, using a not so scientific approach when it was off the engine, and the lid removed I would use a garden hose to 'see' where the water would go. As I mentioned, some cylinders ran lean, some ran rich. Removing the 'bumps' and 'dividers', and filling some areas with Devcon made all the difference in the world! Remember, this was a trial and error effort. Once I hit the sweet spot, the engine ran smoother, revved quicker, and most important, cylinder to cylinder distribution was optimized. Granted this was on a Boss 302 engine, not a small block Chevy. However, the 'theory' of air/fuel filling each cylinder equally as possible works the same on any engine.