What NOT to do..............

PKRWUD · 03-17-2002, 08:36 AM

Okay. let me elaborate and simplify at the same time. In short, a carbed engine in 1/4 mile racing runs optimal with long runners. Straight or curved, it really doesn't matter at WOT. They just need to be long.

EFI engines optimal setup seems to be short runners.

I understand that the air/fuel is mixed differently, but that still doesn't explain it. The a/f mixture could be easily atomized perfectly with 10 inch runners, but it will run faster with 14 inch runners (carb applications). I have always presumed that velocity was the whole reason this was true, but why then wouldn't high velocity benefit an EFI engine?

Even in circle track racing, carbed engines perform better with longer runners. They also require a large plenum, which 1/4 mile engines do not.

The only thing I can think of is that if the velocity in an EFI engine was too high, it would "blow out" the fuel spray, reducing atomization. That can't be true, though, because if it were, EFI engines wouldn't be able to surpass 3000 rpms.

So why do carbed engines prefer high velocity, while EFI engines prefer low velocity? I don't get it.

03-17-2002, 08:36 AM	#19
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Okay. let me elaborate and simplify at the same time. In short, a carbed engine in 1/4 mile racing runs optimal with long runners. Straight or curved, it really doesn't matter at WOT. They just need to be long. EFI engines optimal setup seems to be short runners. I understand that the air/fuel is mixed differently, but that still doesn't explain it. The a/f mixture could be easily atomized perfectly with 10 inch runners, but it will run faster with 14 inch runners (carb applications). I have always presumed that velocity was the whole reason this was true, but why then wouldn't high velocity benefit an EFI engine? Even in circle track racing, carbed engines perform better with longer runners. They also require a large plenum, which 1/4 mile engines do not. The only thing I can think of is that if the velocity in an EFI engine was too high, it would "blow out" the fuel spray, reducing atomization. That can't be true, though, because if it were, EFI engines wouldn't be able to surpass 3000 rpms. So why do carbed engines prefer high velocity, while EFI engines prefer low velocity? I don't get it. __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!