endeavour32

iTrader: (4)

I agree that would have been interesting. I know some say it makes a difference and others say no noticeable difference. I'm in the "it matters" camp. If time was on my side I would like to get my new engines on the dyno and see exactly what they make. I was told 650-675 hp. Either way, great info- thanks for sharing.

bck

I will get to know the difference in the half point when they go back on. Unfortunately it will be too late then to use the info to make a decision. The engine builder swears half a point will be unnoticeable, or within the standard range of variance from engine to engine/ pull to pull. He is in the "doesn't matter" camp.

MILD THUNDER

iTrader: (3)

Thanks for sharing the info BCK.

As far as compression goes,
My thoughts are, if everything is equal, higher compression is typically going outperform lower compression. But, things are often not equal. Rarely is a combo absolutely perfect by design, and I myself, would not trade off static compression, for cylinder head flow, cam timing, intake tuning, exhaust tuning, etc. Also, jacking up the static compression, was the key to making power decades ago, when guys typically had factory heads to work with, limited camshaft designs, limited induction designs, and so on. Its a no brainer that a 540ci with 9:1 static , afr cnc heads, good induction and exhaust, would walk all over a 10:1 , factory headed, crappy cam combo build.

An example I find interesting, is some guys will completely tear an engine apart, to get 1/4 to 1/2 point of static on their build, and then install a set of "average" marine exhaust manifolds, or a general induction combo. Often discussed are cams, heads, carbs, intakes, and rarely, is exhaust design a topic in our group. Most tend to just assume that if its not a stock iron merc manifold, its fine for about any engine, any power level, etc.

It be interesting to see a series of tests like BCK did with his induction, with a series of different exhaust styles. Manifolds vs headers, header size, length, collector length, and so on. I have a series of dyno tests here from a buddy, who just from swapping from one style of CMI's, to another, saw a difference of over 20 peak HP, and 15 ft lbs of peak torque. This was on a 750ish hp N/A engine. While 20hp isn't a ton, thats just an example of two similiar, but different header styles. I'd bet the difference would have been much greater, if comparing a set of 2.25" tuned for the engine headers, and a set of basic GILS, stainless marine, imco, etc, would have been compared back to back.

bck

I've been told just using the cat pans that I have will make the engines different from one another because of the extra room for the oil to sling off the crank on the one engine. We will hopefully be testing the exhaust if it is at all possible to fit it on the dyno, so hopefully we'll get some more info to share at least about CMI big tubes vs automotive style. M/T have your friend that needs the t-stat give me a part # if he has them apart. I have someone that claims he can get them from the manufacturer, but needs a part # or any other info.

hogie roll

All things being equal .5 point of compression will yield 1.5-2% more power. So 10-15hp in your case.

The Otto cycle is well known and has been mathematically modeled. The torque potential can be calculated from the engine specs and derived from BMEP. The only tricky part is when using high overlap cams and tuned exhaust systems that can improve scavenging and create higher than 100% volumetric efficiencies at some engine speeds.

bck

That's about what I thought. It wasn't cheap to get a 15hp gain on these motors so I wouldn't be thrilled about losing 15 by being down .5 as small as it sounds. I can't believe I didn't just buy blowers.

hogie roll

Yeah people say 15hp isn't significant, but 15 here and 15 there adds up!

Sounds like there may be some HP in controlling the oil in your pan depending on your current setup.

SB

iTrader: (1)

I missed something(s) in all of this.

Why all this parts testing and now compression change going down ? The starting out 670hp was really pretty good and the ending 700hp is really good.

bck

We intended to check the best combo (700hp) at both compression levels to see how much of a difference there was. If significant we'd set them both up at 9.7 or if running the 4150 at a slightly higher compression gave power numbers I was satisfied with we would not have swapped intakes / carbs and saved me some cash. We had multiple setbacks on the dyno that made that impossible.

bck

The engines were originally going in a different boat that needed the cat pans. There are the usual trap doors and such in the pans but the kickouts are on opposite sides of each pan. I was told that alone can have a noticeable effect