compression, how high is too high on 98fuel.

[af300e]

I'f your tuner is shit, you'll either be rich and it will last with shit power, or lean and it will burn out. Regardless of CR, shit tuner=shit job

I'd have to say, the tuning is the single most important variable. Get a good tuner.

[Sam_Q]

if I was getting an engine tuned I would be more worried that the bad tuner would do more than just a bad a/r, but instead causing broken internals through detonation.

Continuing from what AF300e said; another thing to keep in mind is that the combustion chamber design has a big effect on the maximum dynamic comp that can be run. Modern pent roof quick burn chambers with good squish areas work wonders compared to some of the older detonation inducing engines. Thats why the old holden 5 litre engines sopposedly ran an 8:1 comp (8.3:1 advertised)

Piston size again changes everything, in direct comparasin if two identical engines are compared and one has half the diplacement then it can have a higher CR.

So it is not possible to have an overall chart of maximum static compression ratios because all head models burn different and also have different cams. All this even before tuning even comes into the picture.

I dont know if it would help anyone but I wrote an article on working out the static CR of engines, its based around the 4A engine but the concepts are all the same. I have checked it many times and no-one has gotten back to me saying its wrong but I could be as I had to work it out for myself. So if you see something you dont like then let me know ok?

http://www.ae86drivingclub.com.au/fa...ression-ratios

[JustCallMeOrlando]

Dynamic compression ratio on that bitch would be mind blowing!

Factory cams too.

[rms]

So where are you going to get 11 to 1 or higher pistons for the 1UZ ?
They have to be custom made with a bump shaped to suit your combustion chamber !

Have been down this path, using 13.5 to 1 Wiseco.

[Duk]

if I was getting an engine tuned I would be more worried that the bad tuner would do more than just a bad a/r, but instead causing broken internals through detonation.

There was an article in Zoom quite a while ago about detonation. According to Nizpro's Simon Gishus, ignition timing is the major factor to control detonation for any given set up.
I know that sounds like a huge statement of the obvious, but in the article Gishus gave an example of a LeMans 24hr Nissan twin turbo V8 engines that ran AFRs for hours on end, that 99.9% of us would instantly assume would destroy a high powered engine (espescially a turbo'd engine) in only a few seconds.
Another example was an XR6 turbo engine running technically lean (14.7:1 type) AFSs on boost, with detonation kept in check by ignition timing. With more standard richer AFRs and advance timing, the engine made more power at the same boost, but not massive amounts more.
Big doofus engines like the LS1/2/76 and what ever the other numbers and codes are, use some impressive CRs even with their technically inferior combustion chamber designs (are starting to make decent power too ).

And those graphs that claim to show max safe compression ratios for a given fuel octane are as helpful as a graph trying to state maximum potential power output from a given engine capacity

[big_zop]

There was an article in Zoom quite a while ago about detonation. According to Nizpro's Simon Gishus, ignition timing is the major factor to control detonation for any given set up.
I know that sounds like a huge statement of the obvious, but in the article Gishus gave an example of a LeMans 24hr Nissan twin turbo V8 engines that ran AFRs for hours on end, that 99.9% of us would instantly assume would destroy a high powered engine (espescially a turbo'd engine) in only a few seconds.
Another example was an XR6 turbo engine running technically lean (14.7:1 type) AFSs on boost, with detonation kept in check by ignition timing. With more standard richer AFRs and advance timing, the engine made more power at the same boost, but not massive amounts more.
Big doofus engines like the LS1/2/76 and what ever the other numbers and codes are, use some impressive CRs even with their technically inferior combustion chamber designs (are starting to make decent power too ).

And those graphs that claim to show max safe compression ratios for a given fuel octane are as helpful as a graph trying to state maximum potential power output from a given engine capacity

Got that article, and it wasnt quite 14.7:1 - more like 13-13.5 instead of the usual 12.5:1 for a full power run.

As you say, it was definitely lower on power but not by as much as expected.

It was actually more aimed towards the comparison of the resultant lap times, with the time lost due to the lower power output counteracted far greater by the time saved by less fuel stops.

Will put it up if interested.

[JustenGT8]

Yeah but the retarded timing you need to run takes it's toll as your exhaust gas temps go thru the roof......fine for a race car that just has to survive the race, not so good for the longevity required on a road car.

Still, timing is the key to survival, far more so than A:F

[big_zop]

Yeah but the retarded timing you need to run takes it's toll as your exhaust gas temps go thru the roof......fine for a race car that just has to survive the race, not so good for the longevity required on a road car.

You must spread some Reputation around before giving it to JustenGT8 again.

True, that was the drawback to running it on a street car. Knew i forgot something!

[DenZel]

So where are you going to get 11 to 1 or higher pistons for the 1UZ ?
They have to be custom made with a bump shaped to suit your combustion chamber !

Have been down this path, using 13.5 to 1 Wiseco.

internet forums is your friend, i cant get what ever i ask. what fuel are you planning on using with the 13.5:1 pistons?



and guys i know factors like tuning and timing can/will be a issue, but doesnt really help me when saying get a good tuner,

just want to know what people have run, and for how long..and experiences, and what they you think is safe on a good tune. is 11.5:1 pushing the limits? or it sounds like it should be fine on 98 fuel.

cheers.

[oldcorollas]

if you are running a 300 deg cam, then 11.5 might be too low....

so, what cam, what rpm?

[DenZel]

im looking at these 2 choices

207-E Lexus / 1UZFE stage 2 race cams, suits good exhaust, raised compression, eight throttles USD$1,320.00 3000-7500 286 286 246 246 9.50mm 9.45mm 104 108

207-F Lexus / 1UZFE stage 3 race cams, suits good exhaust, raised compression, eight throttles, ported head, good exhaust USD$1,320.00 3500-8000 294 294 250 250 10.10mm 10.05mm 102 108

[Gavatron]

Hefty Hefty Hefty

[rms]

internet forums is your friend, i cant get what ever i ask. what fuel are you planning on using with the 13.5:1 pistons?


cheers.

Please enlighten me !
We ARE running premium unleaded.
What about piston/valve clearance ? 1UZ's are not 'free spinners' when you run big cams and compression.

[DenZel]

pm sent, you are running just premium leaded on 13.5:1 ......wow.

[jeffro ra28]

Some good first hand examples as you asked.

2008 YZ250F 14:1cp piston, 98 unleaded . Jetted 6 sizes leaner then stock. Stock cams, ported head. Been racing for 4 months since build. 8hp increase in power

2TG, 10.5:1 ACL duralite pistons(cast cheapies), 98 unleaded. 15 degrees static ignition timing. 256 @ .050 cams 110 lobe seperation. Ran fine for me, and as far as i know is still going well.

18RG, 11:1 custom JE pistons. Not yet built but going to be run on 98 unleaded.

430 cubic inch V8 chev, custom built engine throughout, 28 psi manifold pressure and 12:1compression, alcohol fuel, 28 degrees total ignition timing(magneto), 118 lobe serperation, [email protected] duration camshafts. 2090hp or 1500 ft/lb of torque.
Lasts long enough for a race engine. Very large and flat torque curve.

366 cubic inch V8 chev, custom built throughout, 16:1 Compression, alcohol fuel. 32-34 degrees total ignition timing(magneto) 790hp. 600 ft/lb torque. Lasts a few race meetings!