Don Terrill’s Speed-Talk

I have a question on cam selection for an alcohol fueled 565 BBC drag engine. One well known cam company recommends keeping the exhaust duration on the short side to keep heat in the chamber (290@.050-320@.020). While a well known drag race engine builder with experience in alcohol fueled engines recommends the opposite, he wants exhaust duration around 305@.050-335@.020. This motor has conventional heads and 14.5 CR and is injected (Rons) in a dragster. Any thoughts?

I used a similar cam as the cam grinder recommends,application was blown 468 bbc,set record with it.

Dirrerent deal with a blower.

We find we can normally run about 4 degrees less with alcohol.
I believe that since the exhaust temp is down with the alcohol, the exhaust gasses do not need as much time(duration) to evacuate the cylinder.

Thank you Mike, I just can't see running 15deg. less duration because of using alcohol for fuel.

Does some of this go back to a magazine article a few yrs back? Dragster 555cu in? Alky carb-big Duke heads. Engine wouldnt pull and or had HS miss. Thay crutched it up by adding Ex duration. And Every one went home happy!

A related question to the original posters set up, dose the mechanical fuel injection system have any influence on the cam design?

Thanks
Tom

I just got camshaft specs on Ed Pink Toyota and Mopar Midget Engine Camshafts as well as a Roush Engineered Cam for a Ford SC1 Headed Midget Engine. All of the above were virtually identical although speced by different folks. For what it's worth, the Intake/Exhaust spread is 11*to13* on all of them. I thought that if the exhaust gases were colder they move slower therefore requiring more exhaust duration? Also with Injection the fuel curve tends to get rich on the top, even with a high speed bypass cooling exhaust gasses and slowing them more?

Think about what's going on.
The mass going into the cylinder is the same, but it's not heating up as much.
What's different about a pound of air at 1,200 degrees compared to a pound of air at 1450 degrees?

BTW, I just looked at a bunch of midget and Sprint car cams, both my designs, and other cam companies designs. The biggest spread I found was 8 degrees at the seat(SB2 headed midget). The shortest was a zero spread(D3 headed midget).
The mopar sprint engine I was looking at had a 2 degree split from another cam company, and I mine was a 4 degree split.

Ahhhhhhhh, SEAT! I was looking at .050". I will look at the files again when I get home. I had the Roush one ground by LSM for my -12 engine a month or so ago. I was in a rush and when I got in touch with you Mike the timeline didn't fit. I did just buy a Ford SC1 headed engine an have no idea what cam is in it........

Mike, I just E Mailed you the TRD/Toyota cam chart........

looking for cam specs on 565 bbc with sv1 carb 1180 cfm . head flow 470 and 335 . on methenal . car weighs 3100 w driver ,glide 4.11 gears. : 14/1 comp