Race Engine Forum UK

Hi Guy
just a reminder about the exhaust temp testing you were going to post after the 1438 build. Any results yet? I'm interested in differences between individual cylinders using a stock intake.

Mark, hi

it will be flowbench testing one port to another with manifold on, not temp testing as such although the airflow variance (if it exists) one cylinder to another may be relevant.

The head I am going to test on (just happens to be the only clean one around) is having a bit of welding done but I imagine I will publish the results here this week..

GC

Guy
the airflow variance will be helpful. Of course, trying to find a decent compromise on jetting is the problem and as a result the exhaust temps in the various cylinders. Trying to keep the end cylinders from a lean condition without going overrich in the middle cyls is the problem I'm trying to sort out.
I'm curious if you experimented with carb spacers or floor dividers to try and even out flow rates between cylinders?

Hi Mark

I've been testing today a 124 AC TC 8V head (stock) with OE manifold, details to follow. But - I can tell you for sure, the flow loss on 4 and 1 ports relative to direct fed 2 & 3 is only 2.5% with manifold fitted, ie: 89cfm without man and 86.7cfm with. That's nothing in flow terms.

NO loss at all on ports 2&3 - 90.6cfm at 10" with and without.

That's out of the box unmodified anything, except for the 15mm guides removed (in case you notice a guide in no 1 inlet it is just a trial GC race guide - retracted). This would, FWIW give some 5-7cfm increase over having them in their original place. I just happen to have previously removed the old guides but it doesn't affect the validity of the test.

So the reason for temperature variance is definitely not airflow, but could well be fuel pooling in the runners causing starvation or adverse negative/positive pressure wave effects during valve event (because of course the outer runners are longer).
We'll talk again on this I'm sure. The effect of turbulence on fuel distribution or airflow in the plenum region (see vector trace below) on a running engine I cannot test or comment on, but it could be quite severe.

A snapshot of the tests below.

GC

Guy
very interesting. I'm not too surprised that airflow is very similar between ports. On your last picture you state that elsewhere there is lots of turbulence. You have positioned the indicator about where the secondary throttle plate would be. I'll assume that running on only the primary would result in lots of turbulence in the plenum.
In my testing I've found that the exhaust temp is highest at cruise conditions; light throttle between 3700-4000 rpm. Going full throttle lowers the exhaust temp substantially on # 4 ( I can only test one cylinder at a time). Could it be due to turbulence in the plenum that 1 and 4 lean out?
With your picture showing the draw into #2, I'd tend to think that more fuel from the secondary would be drawn into 2 and 3 than 1 and 4.
If you do any dyno testing I'd be interested to see what temps you get between cylinders.