E85 petrol

[MWP]

I got a tank of Caltex EFlex for 92c/L here last week.
Should be about that price today too.

Im only getting ~350km out of a 60L tank though
More tuning needed.

[GU11TY]

thats still ok fuel economy
with some of my cars i only get 250-300 from a 65-70l tank on 98 premium

[MWP]

My average over the last year on ULP98 was 12.19L / 100KM.
Will need a few more tanks of E85 and more tune tweaking to get a decent comparison.

Since ill be aiming to run E85 on my new 5S-GTE built engine, i was considering running higher comp pistons (ie 10:1).
But my engine builder (Tony Knight) insists that higher comp isnt advantageous and to go with the normal 8.5:1 pistons.

[trdee]

depends on whether you are aiming for power or fuel efficiency, and since you're building a 5SGTE im guessing you want power. so use the lower CR pistons and pump even more boost in instead

[MWP]

No, actually i would like to build a very torquey engine, so i thought high CR, low boost would be best.
TK said that with E85, low end torque and quick spool can be easily attained with low CR & lots of ignition advance.

[JustenGT8]

No, actually i would like to build a very torquey engine, so i thought high CR, low boost would be best.
TK said that with E85, low end torque and quick spool can be easily attained with low CR & lots of ignition advance.

Interesting as TK (Tony, head porting guy i assume?) is a smart guy. My take is that ignition advance doesn't really help spool much, well not directly? Weirdly, ignition retard, which hugely increases exhaust gas temps can help spool (hurts power though). E85 also combusts a fair bit cooler which hurts spool.

High comp definitely helps spool. Also helps with off boost performance. I've been nothing but impressed with my high comp turbo...hence going to higher comp again with the built engine (11.5:1 )

I'm not guessing either. WRC cars progressively went higher and higher in comp ratio as regs allowed them too. Check out what any factory turbo track car uses...they go the highest comp ratio they can under the limitations the regs cause eg fuel type, boost limit. Porsche went 13:1 at one stage

I reckon you should aim for the highest comp ratio you can get that will support the power you want. With a 5SGTE, i'd be looking at 10:1 if it's easy but if not go with the highest comp ratio that is.

Still keen to hear TK's thoughts as i highly rate his work.

[MWP]

Yeah, it is that same TK.
Everyone seems to rate him highly which is why ill take his word for it.
... but like you, it doesnt make much sense to me?

Anything other than 8.5:1 (or 9:1 depending on HG) requires custom pistons.
Though, this why i have been considering the 5S offset crank grind idea. Gain stroke, and gain compression using the same easily available 8.5:1 pistons.
I have mentioned this idea to TK, but he dismissed it pretty quickly as not being worth the effort.

There is a 5S-GTE 10.5:1 MR2 in the USA somewhere getting good results (ie >700hp) on E85.
I wouldnt go that high comp ratio though as i will also want to be able to run ULP95 if required (obviously with a very conservative ignition map and zip boost).

[JustenGT8]

I seem to recall that the forged pistons you can get for the 5S crank etc will give you 9:1?

I chase the high comp stuff but not to the point where you are spending silly dollars. 8.5:1 will still work fine. I only went 11.5:1 'cause they were already done, i wouldn't go ordering custom sets at mega bucks for the level of modding i'm at

[MWP]

Well there are only CP and JE pistons readily available.
JE state theirs are 9:1.
CP state 8.5:1, but a lot of sites for the same part number say 9:1.

[JustenGT8]

There you go then, 9:1 it is

[trdee]

rally cars have increased CR because they have limits on the amount of boost they can run. if they could run more boost, the CR would be appreciably lower as well. but that is just common sense really

But yeh. For a street driven car which you want good torque/response from, higher compression and lower boost (for the same peak cylinder pressure) will indeed be what you're after.

[JustenGT8]

rally cars have increased CR because they have limits on the amount of boost they can run. if they could run more boost, the CR would be appreciably lower as well. but that is just common sense really

But yeh. For a street driven car which you want good torque/response from, higher compression and lower boost (for the same peak cylinder pressure) will indeed be what you're after.

No, WRC cars ran the highest CR allowed by the regs As the regs allowed them to run higher CR they did.

Nothing common sense about it at all sorry. The only limit to CR and boost limit is det resistance......more CR and/or more boost and more det resistance required. With the appropriate fuel there's no need to drop CR with increased boost so why would you?

[trdee]

The only limit to CR and boost limit is det resistance......

exactly.

Assuming everything else is equal, then you can only run X boost at Y compression ratio before you start getting knock. if you lower the compression ratio, then you can increase boost to get back to the same peak cylinder pressures before knock, and thus you will make more power, as you now have a denser charge (more air/fuel) for the same given peak cylinder pressures

[JustenGT8]

Your logic is arse about If the situation allows you to increase your CR you would, why on earth wouldn't you (bar having to buy stupidly expensive pistons)? That's all i'm saying

That's where MWP is at. For the power he will make, it makes sense to go for the highest CR he sensibly can (just like the WRC did). A 10:1 4 cyl will make 300rwkw easy peasy, it'll do it at lower boost than a lower CR setup and shit all over it for response.

If you start chasing 400, 500rwkw then sure the boost/CR/Det equation gets trickier and you need to 'compromise' somewhere.

Turbos are no different to n/a, the engine is just a pump, it doesn't know there's a turbo bolted on, just that there's more air getting stuffed in. Know of any n/a cars where they drop CR to make power?

[dangdang]

If you run water/alky injection you can run unGodly amounts of boost with quite high static C/R. With this and Tolulene some engines run 5 bars boost and make 1000HP per litre if the engine internals are strong enough. I guess its all about avoiding detonation. I'm going with a 8.0 static, just what I'm comfortable with.