quote:

Originally posted by TOP38:

quote:

Originally posted by wideopen231:
In a post about gaskets another memeber mentioned he thought that going from 12.5 to 15 would only be about 12 hp. I disagree and figure lot more.

I figure lets see what other have found, just to give both opinions a chance.

So if you have increased compression in a engine with little to no other mods .What was gain, what was increase and if other mods what do you feel was main contribution of compression increase.

While we are at it lets here from anyone on bore size increase. Reason I will be going up .125 bore and 2.5:1 on compression. Well maybe few other things that will better increase coming first. Some for power, some consistency and some because I damn well want them.

Yes I know it is bracket engine and power not issue. That is why half of guys here are running 600 plus cubic inch stuff.Me I am just trying to get as much as possible with cheap as Hemi stuff and yes its all made in America.

Do you understand what your asking vs basically no specific information given???

The answer is , it depends on what your starting with and I am not just talking about C.R. The entire combo matters and will impact the results.

Such as, if your cam is too big for your combo now, an increase in compression would show a much larger increase vs if you had the right cam to start with...

Sometimes more compression from a larger dome can hurt performance

the list goes on and on!

So it depends on your specific combo to start with...…...

Holy crap, just give him a broad average answer. He has a friggin normal hemi, it has a frigging dome.
That is what I get for clicking on show post.

Correction it has a lot of dome. LOL

It also has a plug dead center the chamber at very top where as Chevy has plug more to side and lower in chamber. Totally different flame front.

Guess you can't ask a general question anymore. It has to be specific to your engine , trans or what ever part.

You asked a question and we answered it, you just did not like the answer.

Yes yours is different than most everyone else runs but I would not expect to see any huge differences in your combination with higher compression.

So what are you expecting? Raise compression 1 point and pick up two tenths? Nope. Not unless you have some other major problem such as mismatched cam. From my experience there was no noticeable change in ET by lowering compression from 15.9 to 14.7. Yours may be different but I simply would not expect much difference. You have already said you think it would be much more. Okay.

To go along with cpl reply's here. I ha ve 3 pms all are seeing roughly what I was thinking. A running average of 25 to 50 per point. I was figuring on 20 for my combo.So maybe I am being conservative or will be happily surprised .Only way to know will be if I can talk a buddy into some cheap dynu runs.If I do it will be a first.

For shyts and giggles I ran it thru desktop dyno and it showed 45 lbs tq and 48 hp for 2.5 increase. Similar BBC showed 75 gain for same jump. Proving numbers I got from other pretty close. Again it combo thing.

WALLACE CCALCULATOR shows .07 and 3 mph improvement. Almost afraid to aske if anyone compred it to their cars runs for accuract .

quote:

Originally posted by Curly1:
You asked a question and we answered it, you just did not like the answer.

Yes yours is different than most everyone else runs but I would not expect to see any huge differences in your combination with higher compression.

So what are you expecting? Raise compression 1 point and pick up two tenths? Nope. Not unless you have some other major problem such as mismatched cam. From my experience there was no noticeable change in ET by lowering compression from 15.9 to 14.7. Yours may be different but I simply would not expect much difference. You have already said you think it would be much more. Okay.

I never said I had problem with answer as to what you had seen with your stuff. I never asked what mine would do. I never asked about cam.Hell I knew 4 years ago cam was too big for this.Not rocket since that a cam designed for blown motor making 50 lbs boost is not best choice for NA motor.


I never argued with anyone findings. Close I came was when is when td 6591 said he had 50 hp change and then In stated I was surprised it would be that much. I did say I would expect more than 12 hp You stated,but never said your statement was incorrect for your combo.Just that I nhave never seen anyone estimate that low. You did not like that apparently, said I expected .2 change either. Wouildn't mind it but figure kre more inline with .07 to .1 for cam and compression. Also never said anything abbout .1 increase. Going from 12.5 to 15 is little more than one point. I can get almost 1 point from gasket change. Actually expect most of gains will be in getting more low end to get more wheel speed at hit. A Cam and compression together might do it.gain I never asked what to expect on my combo.

Cam AND Compression change is totally different as they work together. But back to question I think the difference from compression change ALONE is minor.

On a 375 hp circle track 2bbl engine, it was 16 hp going from 10.8 to 11.8.

Chris, FWIW, on a "little" BBC, 468, Increased compression from 12.5 to 13.7, (actual, as measured with fluid and calculated), dyno results showed a gain of 41 HP.
*BUT* I also changed cams, (minor change), +2* on Int, +4* Exh, +.014"I/+.010"E on Lift. So how much of the improvement was cam vs squeeze I have no idea.

This message has been edited. Last edited by: FootbrakeJim,

rule number 1. 1 change at a time. Yea have brokent that one more times then can count osn two set of hands and feet.

Thanks.

quote:

Originally posted by wideopen231:
rule number 1. 1 change at a time. Yea have brokent that one more times then can count osn two set of hands and feet.

Thanks.

Hail Mary tuneup.
Line comes off the pod in 3rd, go figure the rest. Parts is Parts.
Different short, different heads,different intake, same blower. Different fuel curve, different compression. Same R296 cam, 42 psi as I remember.
Lots of changes, still went 6.10

BAd news,

That sounds too familar. Maybe not to same extreme but have done almost that much and still run close. Number one reason in your reply. Same blower. A alky car will run as long as the blower is good and everything stays inside for 1321'. Some old guy named Bob Told me that at Rockingham about 1992 or 93.

Ironically after reading thru post one thing stood out and totally oppisite what I would have thought. Chnging compression had more effect on bigger engines than it did smaller. Maybe because its easier to gain compression with bigger cylinder

As others have stated for the best results the camshaft, ect needs to work with the compression.

However, I have a real life example where nothing was changed except head gasket thickness.

I ended up with a cracked cylinder head a few days before a big 4th of July race week. I had another engine in the works but the short block wasn't done. The cracked head was an old cast iron "292" head(nascar take offs bitd). The heads for the new engine were aluminum bowtie Nascar take offs with bigger valves. I attempted to put the bowtie heads on the engine that had the 292 but had less than no piston to valve clearance. I didn't have time to fly cut the pistons, or complete the other engine before the races I wanted to go to. I ended up with 5 .020" steel shim head gaskets on each side. I ran the engine that way from July until late October. The best it ran was a 6.01. I never ran in 1/4 mile with those head gaskets. In late October I took it apart, freshened everything and fly cut the pistons. (~1cc per piston, clearance problem was radial) and put the "correct" .041" thick head gaskets. (1 per side. LOL) The best 1/8 mile run was 5.69, but that was in Florida in November. It ran a bunch of 5.75's in the Carolinas the next year. So.... that was ~.025 1/8 mile for ~2.2 points in compression. Methanol, 360 CID SBC, 2400 pounds. 11.6 to 1 with the stacked gaskets. (Probably the worlds first MLS head gaskets. LOL) 13.8 to 1 with the correct gaskets. Same everything else.


Every combination is different but above 14 to 1 with methanol is asking for a small tuning window, and not much more power.

I totally agree cam is first thing to be changed in my combo.That I why I have one ordered,if they ever get in cores to grind.If not before Christmas I will yank the one in car out and have reground. If quicker turn around I would have done so already.

Like I statedthere seems to be a pattern of small motor mainly sbc not gaining much but the bbc's are getting decent gain for most part.Maybe just looks that way because of those combo's. If I cam get to 15:1 I can easily drop back to 13.6 with nothing but gasket change. Cost me no more cash for 15 than it does 13 or 14.Maybe little time on mill work fly cutting. Right nowe pistons in it have butt load piston to valve almost enough to get me to 15:1.All I need is to fill them and machine back(joking guys).

Read woody b's post. His typo of .025 instead of 0.25 threw me for second. a .1 per point that bad.

woody B,
question about .100 of gaskets and intake sealing up and ports matching. Anywhere near close with that setup? I would imagine NO since you basically made block .060 taller and mover heads apart in doing so. Asking because I had to set intake up in midrange of gaskets to get best fit on upper and lower range of the gaskets I might want to use.

I had stacked up intake gaskets, as well as thicker, homemade end rail gaskets, and silicone.

some times you just have to make what you have work.