High Compression

[Lextreme II]

What do u guys think about getting some custom pistons with high compresson like 12:1. I was reading an article from Hot Rod Mag and one of the articles talked about a big block Ford with 13:1 Compression ratio and made 800+ hp. What do you guys thinking about a 5.3 Liters with 12:1 N/A application?

 

[cribbj]

David, my 5.5 litre BMW motor will be built for 12:1 compression, too.

The only downside to running a high compression motor is ensuring it has enough octane to keep it happy. You can't feed a 12:1 motor the 89 and 91 octane oxygenated swill that's at the pumps these days.

I'd be willing to bet that many of the under 30 crowd here have never experienced the responsiveness of a high compression NA engine, but IMO they're as much or more fun to drive than a turbo motor, but in a different way. The power is just there "now".

 

[Lextreme II]

John,

If you have a dyno software, would you please do some testing with 5.3 Liter with 12:1 compression ratio running on 3uzfe heads? I think octane and timing would be an issue.

 

[Anaema]

not if you run alcohol

 

[Lextreme II]

I think the 12:1 compression can be fun for street. Great lower end with responsiveness.

 

[bango]

Well That was the whole point of FI..even with 8.5 to 1 but with FI.it will end up as high compression am i right? Just that you get so much more air/fuel mixture in,but ultimately when the Piston hit TDC its high comp in FI...
But Your right ,it be fun to drive,as thats what iv got now,11.5 to 1 comp in a 308 Cu motor..but u will start to want more,Im on the thought that SC for low down,TT for up top..lol

 

[cribbj]

paging MWP....

John,

If you have a dyno software, would you please do some testing with 5.3 Liter with 12:1 compression ratio running on 3uzfe heads? I think octane and timing would be an issue.

David, I'd be happy to, but MWP seems to be our resident EA Pro "pro". Me, I only installed the program for the first time yesterday, and am just now learning to play with it.

I'd have a lot more confidence in someone who's had some experience with this program. Perhaps he'll jump in here, otherwise you can PM him.

 

[MWP]

I would, but i have none of the 3UZ stats.
To get anything close to an accurate result ill need bore, stroke, head flow nums, cam timing info, etc.

 

[BARRY]

4cylinders easily can run 12.5:1 on the street with 91 octane. in specialty built motors even higher due to dynamic compression.

i don't know how well a v8 will be with 91 octane though. i would liek to try a 12:1 comp ratio on a v8. i think it'll work greeeat!

 

[bango]

Well V8's are 2 banks of 4's?Should be NP,but why run 91 octane,that fuel is rubbished,well in Australia anyway,I know of a mate with 355 Cu V8 that runs 12.5 comp making 600 HP NA..but on 98 octane.
On the pump fuel note,on a trip once ,I filled up with 95 octane(we call it premium here)and my Van got 500 k,filled up with 91 oct(regular) and barely made 350 k on the same driving conditions,so im never going to use 90-91 again, pure rubbish !I recon there's a bit of fuel mixing goes on ,heaps less power too with lower oct..

 

[BARRY]

lol, yeah your ignition timing has to be correct for the speicific octane you expect to run.

then again octane figures are different from USDM to JDM ratings. its a different RON scale if i recall correctly. they're measured differently giving a different end octane rating.

my 4age 20v in japan uses premium gas in japan, but i run fine with 91 octane. actually i don't gain much power using a higher octane fuel. ignition timing plays a key role in all this.

but my 4cyl does get better milage on 91 octane verses 87 octane on the same tune though. i have not tried adjusting the timing to be perfectly optimal on 87 octane its pointless anyways. for the power i have lost i gained in gas milage? not worth it for such a little motor.

oh in california we are limited to 91 octane from gas pumps. there is a 100 octane gas pump about 5-10 miles from my house though.

 

[Tomo]

i am doing mine for my hilux 4x4 build. ordered 0.020 MLS headgaskets from Cometic, then shave the head, from what i have worked out, 60 though will take it to 11:1. i am not sure how much the heads can be milled before there are probs. I can get hi comp pistons which take it up .5 but for $1100 depends what condition the current ones are in.
Would 11:1 or 11.5:1 CR run fine on stock ecu with bigger fuel pump and adj fuel reg. I need all the low down torque i can get so. Will run it on 98 octane unleaded
There is a thread here about the engine and probs http://www.outerlimits4x4.com/PHP_Modules/phpBB2/viewtopic.php?t=71929
LS400 engine

 

[Zuffen]

Tomo,

Just remember as you mill the heads you change the cam timing in relation to the crank. Also both sides of the engine don't change at the same rate.

 

[Lextreme II]

I think the best way is to get high compression pistons. Increasing or decreasing gaskets height will not only alter the timing but also the heads position in relationship with the V (valley) If i can get around 450 to 475 bhp from a 5.3 liters then i will be very happy.

 

[bango]

I think the best way is to get high compression pistons. Increasing or decreasing gaskets height will not only alter the timing but also the heads position in relationship with the V (valley) If i can get around 450 to 475 bhp from a 5.3 liters then i will be very happy.

Hmm..I don't quite get the timing being altered with different thickness gaskets..can that be explained?

 

[Anaema]

Hmm..I don't quite get the timing being altered with different thickness gaskets..can that be explained?

i can only guess, but... i think it has something to do with taking the extra slack out of the belt by moving the tensioner.... which(i think) woul move the cam gears a few degrees. which wouldnt be a problem if you had adjustable cam gears.

 

[BARRY]

it is very possible to push 100hp per liter for any race built engine. headporting shape and cam design will aid in power production.

 

[laine etwell]

12:1 compression ratio is very achieveable as i run 13.8:1 in my 1UZ with custom made ross pistons and carbon fibre head gaskets. My engine has also been bored and sleeved out to 4.3 ltr is dry sumped , lightened and balenced crank and rods ,ported and polished heads with 8 throttle bodies.plus a full set of arp bolts. A must if you want it to hold together at 9000 rpm

 

[bango]

Have there been any report of orginal bolts breaking or stretching and failing ?If so what HP did they failed on?

 

[laine etwell]

they havent failed as such with the horse power but i blew headgaskets because the bolts stretch and dont tourqe up enough so i would change them to save you the hassle .This is also a recognised problem in stockcar racing to