E85 + Rb30det + High Comp = ?

[Endless26/30]

Sorry to bring up such an old thread but im currently in the process of building a RB30DET (Forged 3.0l Bottom end, RB26 Head, GTX45, E85, Built C4). My engine builder has told me we want a 11.5:1 compression ratio because we are using E85. ill be looking to run 30+psi with this. Ive contacted Brad @ Spool Imports to see what pistons he can get his hands on that would get close to this CR. He reckons that they (CP Pistons) wont be able to fit enough Dome on the piston to achieve that. Another issue im looking at is, ill be running fairly high lift cams (between 9-11mm lift) so with such High compression im assuming ill have to fly cut the pistons which would lower the compression again surely. So what CR have people running high boost and E85 run and how did you achieve that CR (original CR of piston, work to block, HG thickness etc)?

[Blackkers]

you're really in unknown territory there mate. I don't think anyone could give you advice having been in a similar situation. 11.5 CR is stupidly high for a 30+psi goal Internal cylinder pressure is going to be incredible, hope you've got strong internals.

Cam wise I'm sure someone could weigh in, you can measure the valve movement and height of the piston so surely clearance can be worked out beforehand

[Endless26/30]

Yea the motor is being built to go for the 850+rwkw so alot of people seem to be very quiet in regards to advice. my builder has a lot of experiance building High HP and high boost motors, and to my knowledge hes built 2 RB30DETs and both went 600+kw for years so i trust what hes doing. just interesting to see that no one else has gone big power with high comp on E85.

[AngryRB]

If you were located in brissy, id be trying to talk to the guys with the R32 HTR skyline that's going to the Jamboree, saw it do a 7.5 Quarter at 198 last week.

[Simon-S14]

Yea the motor is being built to go for the 850+rwkw so alot of people seem to be very quiet in regards to advice. my builder has a lot of experiance building High HP and high boost motors, and to my knowledge hes built 2 RB30DETs and both went 600+kw for years so i trust what hes doing. just interesting to see that no one else has gone big power with high comp on E85.

is your builder from tas by any chance

[KiwiRS4T]

Yea the motor is being built to go for the 850+rwkw so alot of people seem to be very quiet in regards to advice. my builder has a lot of experiance building High HP and high boost motors, and to my knowledge hes built 2 RB30DETs and both went 600+kw for years so i trust what hes doing. just interesting to see that no one else has gone big power with high comp on E85.

You would think there has to be a good reason for that.

I take it your engine builder has not used astronomical compression ratios in his previous 600w builds otherwise you wouldn't be asking how to acheive it.

[GTRPSI]

I be questioning the engine builder how he is going to run 11.5, over 30psi and achive it with removing the squish pads from both sides of the combustion chamber to handle those power levels and DET and still remain at 11.5.

Oh hell, did i just drop a spanner in all the works by saying that?

There is someone in the US from memory who has a CNC machined open cumbustion chamber design with a custom domed piston to suit, still not near where your engine builder wants to be compression wise.

Most builds in your power bracket are running flat tops with open chambers, so very low compression then winding copious amounts of boost into them, usually in the low 8 compression ratio.

If your engine builder wants 11.5, ask him for the piston part number or to organize to get it custom made......

[NYTSKY]

My mates 26 has 11.7:1CR on E85 and 35psi. Made 650awkw. Has 290 11.5mm cams too.

[bigmikespec]

I don't know why you would do it just to get a handful more hp off boost; you are fuel constrained (or more specifically octane constrained).

More info on NYTSKY's mate would be interesting!

[GTSBoy]

I don't know why you would do it just to get a handful more hp off boost; you are fuel constrained (or more specifically octane constrained).

More info on NYTSKY's mate would be interesting!

I'm not sure I agree. I reckon that no-one really ever gets close to using up all the anti-knock property of E85 just by winding up the boost and adding timing. You have to stop adding timing a fair way before you can make most E85 engine knock simply because you stop making power.

Trying to use up the knock margin by taking the easy option of just piling in massive boost is unlikely to be better than starting with a more capable base engine (more compression) and adding less boost. Boost is bad. Every psi you pump the air up adds heat that you have to cool out of the air. Every psi that you add to the air is also pretty much added into the exhaust manifold. That adds exhaust contamination back into the cylinder that doesn't have to be there.

I reckon it is smart to try to find how high you can run static comp + boost on E85, still get realistic ignition advance numbers, etc. More static comp is going to make the engine more willing to work off boost and very much improve the boost threshold. What's not to like?

[KiwiRS4T]

My mates 26 has 11.7:1CR on E85 and 35psi. Made 650awkw. Has 290 11.5mm cams too.

Only 650kw? OP is going for 850!

[NYTSKY]

Custom Nitto pistons fly cut to the max, head work for the cams to work.

[bigmikespec]

I'm not sure I agree. I reckon that no-one really ever gets close to using up all the anti-knock property of E85 just by winding up the boost and adding timing. You have to stop adding timing a fair way before you can make most E85 engine knock simply because you stop making power.

Trying to use up the knock margin by taking the easy option of just piling in massive boost is unlikely to be better than starting with a more capable base engine (more compression) and adding less boost. Boost is bad. Every psi you pump the air up adds heat that you have to cool out of the air. Every psi that you add to the air is also pretty much added into the exhaust manifold. That adds exhaust contamination back into the cylinder that doesn't have to be there.

I reckon it is smart to try to find how high you can run static comp + boost on E85, still get realistic ignition advance numbers, etc. More static comp is going to make the engine more willing to work off boost and very much improve the boost threshold. What's not to like?

That is the same thoughtI had up until I talked to some serious enginer builders; I explained exactly that and all dismissed it stating their experiences. It makes the engine more prone to issues with excessive squish velocity and the handful of hp made off boost was offset by the much larger increase in performance by increasing boost pressure.

I agree there is a balance, but it would be dependant on application as with most of these decisions.

[discopotato03]

There is a simpler way to get the static CR up and it's as simple as using an RB25 Neo turbo head - smaller volume combustion chamber .

It involves changing manifolds or fixing points but if you want super power it can be done .

I agree that extra fuel octane is great but the point of it is to have the optimum ignition firing point for most power rather than finding the limits of the fuel .

As per boost thresholds I'm not sure higher static CRs will bring them down , more likely increase the pre and just post positive pressure torque .

My mentors taught me that there are two benefits of high static CRs .

First , the only way to increase an engines power other than FI revs and capacity increase is the static CR .

second , it's the way to reduce the torque loss (reduced dynamic compression) on an engine with long duration cams .

Thing is that really high cylinder pressure and power loads means having the engine structure more like a diesel though if anything they are worse off because they make comparatively big torque at low revs . It may not be silly to search what Nissan did to RD28s to make them a reliable diesel .

A .

[AngryRB]

Has anyone had failures from using E85, from what ive read, E85 being an alcohol cleans and washes the cylinders so with a lot of compression/boost and increasing piston clearances from forged pistons or worn stock pistons I wonder if there could be an increased heat and friction build up to cause a piston failure. Could this be possible on an RB30 piston that doesn't have the oil

squirter to help cool the pistons or does the amount of oil outweigh the ethanol content in the cylinders.

Edited August 28, 2014 by AngryRB

[GTSBoy]

E85 engines run MUCH cooler than petrol engines. So your worries about heat issues are unfounded.

E85 does clean up all the crap in the combustion chamber and so on.....but not from "washing" as in wet fuel washing like you appear to be worried about. If it was wet fuel washing the bores then you might worry about reduced lubrication, but the cleaning action is actually from steam. So I wouldn't fret there.

There is a concern with old tired engines or engines with forgies that have been built too loose (as in they don't actually need to be built as loose as a lot of people think they do, and if you make the mistake of building it very loose, then yes, it will be loose enough to possibly permit this concern to occur) then you can get a lot of blowby into the oil, and E85 blowby is full of water. So that can upset the lubrication and possibly lead to failures. But it's not because of heat. The absence of an oil squirter probably not an issue given the lower heat issues with E85 - but any potential lubrication issues from water in the oil are a separate issue that may or may not be assisted by having a squirter - as in, I think if the oil has enough water in it to be a problem, the a squirter probably won't help anyway.

Edited August 28, 2014 by GTSBoy

[NYTSKY]

My car gets driven once every couple of months, gets raped, then put back in the garage.

Has been like that for years.

No issues.

[AngryRB]

I know that engines run cooler, my point was more that if lubrication was being lost from the alcohol's cleaning effect then there would be increased heat build up around the top comp ring as friction increases with boost/comp.

What piston to wall clearance would you suggest if dedicated E85? I was thinking a 4thou could allow washing down the skirts on cold start?

[GTSBoy]

I I was thinking a 4thou could allow washing down the skirts on cold start?

But what does it matter? Run it until it is hot and boils the light stuff out of the oil before parking it up. This HAS to be standard practice for any E85 engine, surely.

[NYTSKY]

^^^This.

Also, the engines are slow to come up to temp. I always let it warm until the thermo kicks in before I drive it.