408 Stroker

[wade]

do it all at once and if your gonna use rpm heads have them gone through and worked over

 

[AJ/FormS]

Thx B3422.
I am quoting from "Performance With Economy", by David Vizard (1981), p49
I agree with you.
I don't build V8s for a living, and have no dyno. But experience with the few engines I have engineered, I'd have to imagine that a point of compression is worth at least a half a cam size in absolute power, and way more at the bottom.
To that end; I'd rather build an 11/1 268 cammed 360, than a 280* cammed 8/1 360. The 280 engine may make more absolute power which is what a track car wants, but the 268 is gonna be way more fun at the bottom where streeters live.

Here is the 268 engine with an ICA of 60*
Static compression ratio of 11:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 9.04:1 .
Your dynamic cranking pressure is 187.21 PSI.
V/P (Volume to Pressure Index) is 165.................................................165

And the 280 engine with an ICA of 66*
Static compression ratio of 8.0:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 6.36:1 .
Your dynamic cranking pressure is 118.17 PSI.
V/P (Volume to Pressure Index) is 99...................................................99

That 12* extra degrees for the 280,is about 1.5 cam sizes. The power-peak has moved up about 250/300*, and in an 8/1 engine this might be what, 20/25 hp.So that might be 8% hp increase, on a 300hp job.
But check out the bottom end as revealed by the VP. The 268 will be 67% stronger from idle diminishing to near zero by maybe 3000rpm! I'll take that 268 anyday!

Obviously I stacked the deck in favor of my thinking, cuz neither combo would typically be built. The exercise is just for demonstration Purposes.
OH wait, I sorta built the first one; 270* and 10.9Scr. What a Funtastic combo!

I also believe in aluminum heads on a streeter, for the thermal efficiency reason you mention;But with a twist.
In my thinking the aluminum robs a lot of heat from the chambers and puts it elsewhere. This allows the 11/1 compression ratio to not detonate while driving normally. But when you stand on it,in the typical 3 to 5 second blasts a streeter does, there is not enough time for the heat to escape, and that is when the 11/1 makes the power.
Your thoughts?

 

[doogievlg]

I want to have the option of driving it 100 miles if need be. I also want to flatten it from a dead stop and just lay rubber. I really would like to see 12’s but I need to be realistic at the same time.

12 seconds is a vey obtainable goal without striking as I stated before.

 

[B3422w5]

Thx B3422.
I am quoting from "Performance With Economy", by David Vizard (1981), p49
I agree with you.
I don't build V8s for a living, and have no dyno. But experience with the few engines I have engineered, I'd have to imagine that a point of compression is worth at least a half a cam size in absolute power, and way more at the bottom.
To that end; I'd rather build an 11/1 268 cammed 360, than a 280* cammed 8/1 360. The 280 engine may make more absolute power which is what a track car wants, but the 268 is gonna be way more fun at the bottom where streeters live.

Here is the 268 engine with an ICA of 60*
Static compression ratio of 11:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 9.04:1 .
Your dynamic cranking pressure is 187.21 PSI.
V/P (Volume to Pressure Index) is 165.................................................165

And the 280 engine with an ICA of 66*
Static compression ratio of 8.0:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 6.36:1 .
Your dynamic cranking pressure is 118.17 PSI.
V/P (Volume to Pressure Index) is 99...................................................99

That 12* extra degrees for the 280,is about 1.5 cam sizes. The power-peak has moved up about 250/300*, and in an 8/1 engine this might be what, 20/25 hp.So that might be 8% hp increase, on a 300hp job.
But check out the bottom end as revealed by the VP. The 268 will be 67% stronger from idle diminishing to near zero by maybe 3000rpm! I'll take that 268 anyday!

Obviously I stacked the deck in favor of my thinking, cuz neither combo would typically be built. The exercise is just for demonstration Purposes.
OH wait, I sorta built the first one; 270* and 10.9Scr. What a Funtastic combo!

I also believe in aluminum heads on a streeter, for the thermal efficiency reason you mention;But with a twist.
In my thinking the aluminum robs a lot of heat from the chambers and puts it elsewhere. This allows the 11/1 compression ratio to not detonate while driving normally. But when you stand on it,in the typical 3 to 5 second blasts a streeter does, there is not enough time for the heat to escape, and that is when the 11/1 makes the power.
Your thoughts?

Yea. Most anybody i have asked/ talked to that I trust to know what they are talking about says 3-5% per point in compression( at the low compression numbers you are using)
For instance, going from 13 to 14 compression wont net as much gain.8-9... 9-10..... 10-11...... sizeable differences
I just went from a little over 9 to 10.5 compression on my 360. With a swap up several sizes in cam, intake change, and mild port job on heads, i picked up 9/10ths in ET. Nothing else was changed.Over 9 mph gain. I attribute a good bit of it to the extra compression

 

[rumblefish360]

B3422W5 is correct for sure but in addition to what he mentioned is the cam and compression ratio working together or not. This can cause a larger swing in how much the compression ratio will add power but even more so how it reacts in actual useage on the street or strip.

The first and most talked about issue with these Scenari scenario is is to big of a cam on a low compression engine (as AJ made mention to.)

I do believe Steve Dulcich did a compression ratio tests series where he used head gaskets to alter the ratio around. While I thought it a good tech point to write about and show readers, it would also be great to see various cams used from the mello grind to a fairly heavy hitter on the street.

I see that 3% as a low gain on easier builds and a 5% gain in more radical builds. With a wider spread still yet when limits are pushed rather than being safe.

Safe is fine... just sayin, that’s all.

Jim had already shown the head flow trumps compression and the NASCAR truck series was limited though 9.0-1 IIRC. The MoPar trucks still made over 700hp.

AJ, I think your compression vs. cam idea is off. “A point of compression is worth half a cam size.” Ummmm, I’m not sure I’d go with that unless the balance of the package is wacked out. Like really out of place.

A lot of mills that I have built over the years have always been pump gas friendly by a nice margin because when the bad gas tank fill comes in, well, it’s baby it time until there’s a half tank and the. Refill with decent gas. I know it’s power left on the table but sometimes pump swill really sucks.

I’d rather the ratio be a slight low and head flow bitchin rather than the other way around.

 

[crackedback]

Paralysis by Analysis...

There's a good recipe that will get either a 360 or 408 well into the 11's, maybe 10's, in a good chassis. AutoX posted a nice synopsis.