Kf3

I have this engine built because I plan on installing an APS TT kit. Would it be best to install the kit before I put the new motor in the car?

sabrefanpc

iTrader: (4)

depends on the block but most likely wait for the kit as the block will probably have lowered compression. Also, this will make install a ton easier (save $$$)

Kf3

what do you mean by lowered compression?

Zexy

iTrader: (55)

Uh oh..

Kf3

Can you help me out instead of just saying "uh oh"

johnoppa

If you had your engine build for the turbo you probably got lower compression. Sabre was saying you probably shouldn't put the built engine in w/out the turbo... if you do have a build engine that is.

sabrefanpc

iTrader: (4)

basically it is a measure of how much the air in the cylinder is compressed. A high compression NA engine may be around 11 or 12:1. Turbos force air into the cylinder and thus work better with lower ratios like 8 or 9:1. This is a safety measure for a turbo engine but a performance killer for NA

rocks

iTrader: (1)

LoL you people make me laugh. Going from 10.3:1 too 9.1:1 will only lose maybe 3-4hp at the wheels. I have built engine with no turbo and it runs damn good, from increased displacement and cams.

Alberto

iTrader: (14)

Wrong. All things being equal-no addition of cams or other power adders you will see more of a power loss than that.

OP-I dont believe you have a built motor, to be honest you sound like a dumb newb who claimed something and got caught, who in the world would have a built block already and not know the specs of it, or know what lower compression is?

rocks

iTrader: (1)

with the .20" overbore you will gain power back albeit a small amount but it helps so the power loss is negligable and you can also use low octane gas untill you turbo the car. The crank being balanced also frees up power. So at the most you would lose maybe 7-10 horsepower total. I once ask an old man engine builder about milling the heads on a V6 engine i had once to increase the compression from 9.1 to like 11.1 he said it would be pointless and maybe gain 10-15 horsepower and it wasnt worth it.

Anyway i would like you prove me wrong alberto you fall in the same camp as all the other people that tried to tell me my car would be sluggish. I wouldnt run a 12.5:1 NA either because 90 octane gas wouldnt be enough for it.

I had a friend with a 8.5:1 compression v6 with heads a huge cam in a firebird run a 13.0.

Check this out
http://www.bgsoflex.com/crchange.html
http://www.bgsoflex.com/cgi-bin/crch...10.3&newcr=9.1

Engine Horsepower (peak) is 300
Old Compression Ratio is 10.3
New Compression Ratio is 9.1
Computation Results:
Computed New Engine HP is 290, a -3 percent change

Now that is at the crank so its what 3-4 hp at the wheels lol. Your ricer math doesnt work on me.

Wired 24/7

iTrader: (2)

+1

It's not like someone just gives you a built motor like a best buy gift card.

Alberto

iTrader: (14)

No-you prove yourself correct and in turn prove me wrong. You dropped comp, but went with a normal overbore and did cams and other mods, so of course its possible in your situation your at stock power levels. Congratulations, now please re-read my original response and tell me how I could possibly be wrong in that if all things are equal, dropping compression in a motor will result in more than 3-4whp loss.

2TH PWR

iTrader: (21)

I saw someone on this board was selling his built short block for $2200.
Very cheap. I was thinking of snatching it up, even though I hadn't really researched it. I mean come on it was $2200. Perhaps that is what the OP did.

rocks

iTrader: (1)

Compression wont result in more of a loss than that. Its not going to happen. If it does happen you can advance timing due to lower compression and be back at the same power level you were before. These are simple facts of engine tuning. Hell I used to run unprocessed gas i got for free by retarding the timing on a v8. It was probably 80 octane. Of course to put pump gas back in it i had to advance the timing so it would run right. Going up one whole number is like a 10hp crank gain.

Also due to lighter forged components i have less rotational mass.

Wired 24/7

iTrader: (2)

1st of all, rocks, no one appreciates the name calling and generally offensive attitude.

2nd, how is someone going to prove your speculations wrong? Why dont you go get a dyno of your built motor and post it up... a dyno costs what, $30?



Just because adding compression doesn't necessarily give you much horsepower (most likely due to octane/detonation considerations), doesn't mean reducing compression will have an equivalent effect. And it doesn't mean you can just add timing to make up for it. Timing and compression ratio are engine tuning and building parameters that need to be optimized. Everytime you stray away from the optimum, you lose power overall. So you can't necessarily dial back in more power by adding timing. Because you might start to stray away from the optimal timing.

You sound very naive and defensive about your engine. So if you want to put everyone in their place, get a dyno and stop posting garbage.

undrgnd

iTrader: (2)

In my experience, rocks is more correct than wrong on this. The effect of compression ratio on horsepower, all else being equal, is no more than 2%HP per point CR. Many articles are available on this, and most are in agreement. Here's an example. http://www.442.com/oldsfaq/ofcrc.htm
This next article specifically states that the effect of compression ratio on high octane engines is negligible (discussing turbos). http://www.sdsefi.com/techocta.htm. I suspect there is a formula floating around somewhere, but real world results have shown that even though higher compression ratios will yield higher horsepower, the effect is not that pronounced.

Wired 24/7

iTrader: (2)

See, at least you back it up with something. Now I'm more willing to believe what rocks is saying, but he never came up with anything other than "this mechanic told me..." or "an engine builder I know said that..."

thanks undrgrnd

rocks

iTrader: (1)

Basic rule of thumb is 3% at the crank. I have posted stuff on it before and i posted a calculator from the megasquirt site that gives you a general idea. Ill have it dynoed thursday hopefully heh.

sabrefanpc

iTrader: (4)

to OP:

Basic idea, not really worth it, just wait for the turbos. Otherwise you are paying for a tune you don't need and a lot extra on the install. Also, power (though possibly only a small bit) will be lost.

overZealous1

iTrader: (27)

it isn't really all hp figures that change that much. it is more pronounced in the torque. i did 2 motors in my vette, one with 10.3/1 and one 12/1 comp. the 12/1 motor (same motor, just different pistons, so all is perfectly equal) was very noticeably stronger than the 10.3 motor on bottom end.
btw- most all aftermarket forged piston rod combo's are going to be heavier than the stock stuff.

i recently had my charge pipe pop off on my Z, so i was running basically "all motor" at 8.6/1 comp with cams and major head porting. the car was a frigging dog! i got to drive my friends basically stock G35 right after i drove mine, her car would have whipped me badly!