48mm inlet valves on CE heads, 94mm bore?

[Jonny Grigg]

There is no doubt that the heads on my engine are ultimately going to hold it back. At the moment I am not brave enough to suggest to my wife that it would be a good idea to switch out my Comp Elim heads to Component Development/ Strip Dominator type castings, so for now I am looking at how I get the most out of what in have- unless I break it of course!

So, at the moment my motor is 2442, using a Webcam 251, 14:1 compression and a pair of comp elims. These have 46*40 valves, but I am using a pair of Terminator carbs, which we had to vent down to 44s to get the thing jetted sensibly. Clearly we are not getting the best out of the carbs right now.....

So, whilst sat on my sofa I have been thinking about a number of potential changes.... I originally chose 46mm valves as i had read that 48s on a 94 bore put the valve too close to the chamber wall, detrimentally affecting flow and swirl into the chamber. In effect, the 46mm  valve was better than the 48. Did I get this wrong? Would a 48 valve flow better than the 46?

The motor is nitroused, but at the moment I would like to run near to or into the 10s normally aspirated if possible.....

I would appreciate any comments to my ramble.

Thanks,

Jonny.

[K-Roc]

A motor of your size should definitely benefit from the larger intake valve,  HOWEVER just increasing the valve size without also modifying the port and chamber probably will not make any difference, or you may even loose power. ( most likely the latter)
Your discharge Co-efficient will most likely nose dive... ( flow CFM per sq. inch of valve size)

Think of it this way....The valve head is the biggest restriction in the port... So if you go from a 46 to a 48 valve with no other changes, you have put a larger blockage in the port  the air has to get around a bigger valve head as it enters the chamber...... Now you have increased the seat throat size as you increase the valve size when you do your valve job,... This is why you need to perform extra port work  above and below the valve seat to get your co-efficient back to where it was, or better. You may even need to lift the 48mm valve higher... It all depends on the port,seat, chamber...

Cheers. K-Roc,

[Mike Lawless]

Bigger is better.

Way too big is just about right

[Udo]

I have used 50's in a 94 bore . If you ask Pat Downs he will get some for you ..

Udo

[K-Roc]

I have used 50's in a 94 bore . If you ask Pat Downs he will get some for you ..

Udo

With a 40mm Exhaust ?   

[BeetleBug]

I have used 50's in a 94 bore . If you ask Pat Downs he will get some for you ..

Udo

With a 40mm Exhaust ?   

51 x 40 valves - 94 bore - 286hp - 2386ccm

[Taylor]

I have used 50's in a 94 bore . If you ask Pat Downs he will get some for you ..

Udo

With a 40mm Exhaust ?   

51 x 40 valves - 94 bore - 286hp - 2386ccm

Did you move the valves over towards the exhaust or just notch the cylinders?

[goose]

just curious
what kind of horsepower are you getting n/a ie without the nitrous?

[BeetleBug]

Did you move the valves over towards the exhaust or just notch the cylinders?

Angle flow heads and it was (is) tight. No nitrous, NA. High compression and not for the street.

[Udo]

I have used 50's in a 94 bore . If you ask Pat Downs he will get some for you ..

Udo

With a 40mm Exhaust ?  

No 39

But more important is the port work


Udo