max rpm for a 2.4 cross section?

bc · Post by bc » Tue Mar 15, 2005 9:57 am

Just put a 406 on the dyno 4.155 bore, 3.75 stroke. Its the first engine of mine to go on a dyno. The thing that Im surprised about is it made peak hp at 6500 with a head that has a minimum cross section of 2.4" (at the pushrod) and 250cfm. I really thought it would go flat around 5800 or so. Can cam timing delay the choke effect? The cam used was a solid 246-254 at .050, lobe seperation was 106 and center line was 102.

Bos's5.0 · Post by **Bos's5.0** » Tue Mar 15, 2005 10:06 am

wow.. i wanna hear about this as well.

LilRacr · Post by **LilRacr** » Tue Mar 15, 2005 10:56 am

What head was used, anything done to it? What compression is the motor?

I am very curious about all the CSA vs choke effect on power and RPM.

bc · Post by bc » Tue Mar 15, 2005 11:02 am

This was on a Pontiac and the head did have some porting done to it. The compression was 10.5:1.

Post by **maxracesoftware** » Tue Mar 15, 2005 11:36 am

Just put a 406 on the dyno 4.155 bore, 3.75 stroke. Its the first engine of mine to go on a dyno. The thing that Im surprised about is it made peak hp at 6500 with a head that has a minimum cross section of 2.4" (at the pushrod) and 250cfm. I really thought it would go flat around 5800 or so.

RPM = ( 614 * 2.4) / ( 4.155 * 4.155 * 3.750 * .00353 )

RPM = 6448 at .55 Mach .... =>6500 RPM on your Combo

RPM = 7032 at .60 Mach

RPM = 7618 at .65 Mach

your peak HP is occuring near .55 Mach
its possible to see .60 or better Mach depending on Port shape
and you have to also account for the Exh side Mach number
which is close to same on the Intake side, but actually much higher FPS
because of Exh temperature's effect on speed of sound.

it also takes about 253 CFM of Flow @ 28" to go 6500 RPM
so you are pretty close

and your Cam specs are a little conservative to match the
250 CFM Flow and 2.400" CSA