Would you rather?

[The Badger]

So brought up a hypothetical question to some of my engine builder friends and no one could really make a good guess so figured get the boards guesses.

This is assuming that there is no restrictions anywhere else in engine design. Also saying that mid lift and everything else would be inline with top flow

What would be better?

A 185cc head flowing 270 at .600 and good flow thru out comparative with top flow with a way more agresive camshaft (ramp rate).

A 205cc head flowing 300 at .600 but with a more mild camshaft.

Someone was going on about lighter valves in smaller cc heads due to less diameter and got me on this question.

[randy331]

What would be better?

The combination that makes the most average power on the dyno.

Randy

[MadBill]

The one whose minimum port CSA best matched the RPM range that other major components trended towards.

But in general, better the right port size with the right cam than a smaller port crutched with a big cam.

[CGT]

The one with the biggest intake valve

[Casper393W]

What CI is this Hypothetical engine?

[The Badger]

Lets say it has 363 ci.

[modok]

Carb or port FI?
Roller or flat tappet?
Street or race?

[The Badger]

Carb or port FI?
Roller or flat tappet?
Street or race?

Lets say carb. To give the smaller head a chance I say lets go with roller. And ideas with both street and race?

[The Badger]

But wait. If I remember reading up on flat vs roller on here the roller doesn't start to help much until after .600. So speedtalkers choice!

[KnightEngines]

Required rpm range?
Required peak HP rpm?
Required over-rev?

Application?
Stall speed?
Diff gears?

Question is too vauge, what I'd choose for a road race engine running in the 3500-6500rpm range with a manual trans is quite a lot different to what I'd choose for a drag engine turning 8000rpm through the traps with a 5000 converter...........

[modok]

Carb or port FI?
Roller or flat tappet?
Street or race?

Lets say carb. To give the smaller head a chance I say lets go with roller. And ideas with both street and race?

HA! Tough call then. I was thinking....carb, then we have wet flow, and more concern to keep the velocity up in the runners.

Port FI and roller cam then I'd say the bigger head wins, with carburetor....I don't know, it would be down into the specifics, like the valve job, which might be different to optimize each.

A bigger valve has bigger low lift flow, bigger runner moves the peak torque up, both meaning you almost HAVE TO shorten the duration, and open and close the valve more rapidly to make the powerband the same. If you can, you gained overall, if you can't....then you just moved the powerband UP, is all.

Maybe with a steep valve job and a radical cam you can make a small valve do the job of a larger one and gin overall, but that doesen't tell you what port size to run.

So....can of worms opened, good luck.

[Frankshaft]

So brought up a hypothetical question to some of my engine builder friends and no one could really make a good guess so figured get the boards guesses.

This is assuming that there is no restrictions anywhere else in engine design. Also saying that mid lift and everything else would be inline with top flow

What would be better?

A 185cc head flowing 270 at .600 and good flow thru out comparative with top flow with a way more agresive camshaft (ramp rate).

A 205cc head flowing 300 at .600 but with a more mild camshaft.

Someone was going on about lighter valves in smaller cc heads due to less diameter and got me on this question.

Food for thought, the 205cc head has likely very similar velocity, and, quite possibly more, which will wash the difference in port volume, and the engine will likely make more power everywhere, depending on the application of course. We need those details. But as a dynamics standpoint, the difference in cross section, which if these are similar heads, just one is bigger by 20cc, the extra air flow makes up for the bigger area, and the velocity is the same, or more. In that port size range, from my testing, I would choose the 205cc head, even for a smaller lower rpm engine, within reason. The only advantage the smaller head will have, will likely be below the tq converter stall speed.