6 replies to this topic

[IainStallard]

For my college project, Stiggytoo and I have been studying into the difference between cylinder head castings and what can be modified to achieve better air flow into the head.

 

First of all, we flow tested 3 different head castings which included a standard 998 head (CAM4180), a standard 1275 head (12G940) and a standard 12G295 head. We also tested our modified CAM4180 casting which we enlarged the inlet port slightly and ground away the valve guide boss and smoothed it all out.

 

All of our tests were carried out with a standard twin carb manifold, the reason being will become clear later on...

 

And the results were in:

 

 

There is a clear difference between the CAM4180 head and the other two heads we tested. However with out slight modifications, we made a small improvement on the CAM4180 head across all valve lift, a result for us.

 

Now as we also found out, when using a standard single carb metro manifold, the outside port is biased hugely throughout the valve lift as show here:

 

 

When we performed the same test with a standard twin carb manifold, the values were pretty much the same. However, we do not have a graph for this test unfortunately.

 

I hope our results are helpful to anybody as they show how restrictive the standard 998 head is compared to say a 1275 head

[Wright&Wright]

It's interesting to see just how well the 12G295 compares to the 12G940. 

Smaller valves and ports but very well designed. Even outflows it at lower lift where the valve spends most of its time.

 

Did you take the lift any higher than 7mm? I know some higher spec 'Fast road cams' go into the .370" valve lift region.

 

I'm assuming that you've corrected for temperature etc. or did you not need to delve that far?

[IainStallard]

Unfortunately we didn't go further than 7mm valve lift as we are on time constraints

And none of our readings have been corrected for air temperature and seeing that we are 2 of the only people who actually know how to use the Flow Bench, I think our lecturers will see past that mistake for now. We taught ourselves how to use the equipment using the internet and other sources. We have had very little help from the college however we are the first students to actually produce some results for many many years.

Out of interest, how would you correct the results for differences in air temperature?

Edited by IainStallard, 08 April 2014 - 08:28 PM.

[ACDodd]

The good thing about your test on the cam head is that you have highlighted the areas that make little difference to actual flow. It is entirely possible to match the 295 with a smaller intake port. Steady on with the statement on smaller ports the intake of the 295 is almost identical to a 940. Too big for a small bore engine.

Ac

Edited by ACDodd, 08 April 2014 - 09:08 PM.

[IainStallard]

The good thing about your test on the cam head is that you have highlighted the areas that make little difference to actual flow. It is entirely possible to match the 295 with a smaller intake port. Steady on with the statement on smaller ports the intake of the 295 is almost identical to a 940. Too big for a small bore engine.
Ac

Out of interest, which bit of the head needs modifying to make the most difference to flow?

[Wright&Wright]

I imagine that the area needing the most attention would be the area around the valve seat and the valve itself.

 

Seems to me to be the most constrictive part of the head. 

[ACDodd]

On the cam head the limiting factor is the shear size of the intake valve. You need a much larger intake valve together with a 3 or 5 angle valve seat. The chambers will also need significant mods to get this new larger intake valve to flow.

Ac

Edited by ACDodd, 09 April 2014 - 06:30 PM.