E85 + Rb30det + High Comp = ?

[zebra]

Hey Guys,

Been thinking, and throwing some calculations around.

Im thinking of maybe building a high comp Rb30det using 11.5cc dome rb25 forged pistons and using a 1.0mm head gasket.

But there is a 0.7mm difference between comp heighs so the 25 pistons should sit .7 lower in the bores of an rb30.

By my calculations it would have a comp ratio of 9.2:1 so its not that bad comp wise as the 11.5cc dome gives 8.5:1 in a rb25det.

Any ideas if this would work or not...I think it would be a good thing for E85/race gas.

[Simon-S14]

not sure about your calculations as i havent sat down and gone thro them. However 9.2:1 is hardly high comp these days. Pump fuel will do that no worries... even 10:1 wouldnt be too much of an issue.

[R31Nismoid]

9.5 is pretty standard these days i would have thought.

So less than that should be fine.

[Simon-S14]

lots of euro turbo petrols are running 10.5:1 to 11:1 CR's these days.

fuel quality and tuning has come a long way in the last 10 or so years

[zebra]

Good to hear, When I started writing this post id forgotten to adjust the comp height so it would have been about 9.8:1, which as you say isnt all that much by todays standards.

I know you can buy 9:1 rb30det slugs off the shelf but every little bit helps, as it makes the cars much more responsive to timing changes, my 8.5:1 comp rb25 was a bitch to tune compared the the 9:1 version in the car now.

So with a Belly full of E85 and say 9.5:1 comp (after the block and head are machined a bit) should be hugely responsive.

Now all I need to do is find just 2 ACL rb25 forgies and im set

[NYTSKY]

My mate has 9.5:1 in his 25/30. E85 and 700rwhp.

Unbelievable torque! Pulls up Mt White 5th gear no boost and hardly touching the throttle, its quite funny actually.

[zebra]

what pistons is he using dave? 25 ones?

[NYTSKY]

Rb30 i think. CP pistons.

[PM-R33]

My mate has 9.5:1 in his 25/30. E85 and 700rwhp.

Unbelievable torque! Pulls up Mt White 5th gear no boost and hardly touching the throttle, its quite funny actually.

*drools* Thats awesome.

[discopotato03]

If I was doing a twin cam RB30 turbo engine 9.0 would be absolute minimum I'd run and preferably the as mentioned 9.5 to 1 .

The extra 500cc or + 20% should be good for in theory 20% more torque and most people say you get more out of each pound of boost with the higher CR .

It possibly means that you may not be able to run real high boost numbers but IMO airflow is what makes the power anyway not a boost gauge number .

Some may not agree but I think the idea of running E85 permanently is a bit premature at this stage , so many water and corrosion problems there may not be long term answers to just yet .

Short term I'd like to see E10 or E15 that was based on 90% 98 ULP at the pump .

Over 9 and under 10 CR for today's turbo road engines , IMO cheers A .

[zebra]

The water absorbison issue doesnt really worry me as it would be for a track car, so the oil would be dropped after each rae meeting,

Being that I'm a poor bugger atm my dirty 30 will have 8.2:1 comp using cast pistons and pump gas, so I need somthing that is det resistant and the low comp gives me that security i need, so that I dont ping the engine to bits if the intake air temp skyrockets from being tucked in behind another car for 4 or 5 laps.

But the high comp E85 engine will come

[Dale FZ1]

my 8.5:1 comp rb25 was a bitch to tune compared the the 9:1 version in the car now.

Being that I'm a poor bugger atm my dirty 30 will have 8.2:1 comp using cast pistons and pump gas, so I need somthing that is det resistant and the low comp gives me that security i need, so that I dont ping the engine to bits if the intake air temp skyrockets

So exactly what spec are you running - 8.2, 8.5, or 9.0?

Not sure why a 0.5 change in CR would make the thing any more/less difficult to tune. Run to your target AFR, and develop an ignition map that doesn't allow the engine to knock. The lower static CR should allow for greater knock resistance at a given boost pressure, maybe at a cost of overall engine efficiency/output.

Also good tuning would/should provide suitable correction for changes in IAT. If you were in someone's draft for 4-5 laps everything would be hot, especially coolant temps?

[zebra]

the rb25 thats in the car now has 9:1, the previous 25 to that had 8.5:1

it just felt that small timing changes made more of a difference in the way the motor responds in the 9:1 comp motor.

Ill be running the 8.2:1 comp rb30det rather rich and retarded, capping power in the mid 200s atw, so it wont be taking full advantaage of the 500cc extra capacity, but i will mean the overall level of tune will be less stressful compared to a 250rwkw rb25 and run cooler, needing less revs etc.

[TiTAN]

As no one else seems to be aware of it. ARIAS make off the shelf highish comp forged pistons for the 25/30.

These are the ones i have in my engine.

Suit RB26/30, 25/30

p/n= AP332104

10.6cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.2-9.4

They also make these with even higher compression

Suit RB26/30, 25/30

p/n= AP332105

13cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.5-9.8

No need to mess about with RB25 pistons and what not.

[MBS206]

the rb25 thats in the car now has 9:1, the previous 25 to that had 8.5:1

it just felt that small timing changes made more of a difference in the way the motor responds in the 9:1 comp motor.

Ill be running the 8.2:1 comp rb30det rather rich and retarded, capping power in the mid 200s atw, so it wont be taking full advantaage of the 500cc extra capacity, but i will mean the overall level of tune will be less stressful compared to a 250rwkw rb25 and run cooler, needing less revs etc.

Sounds like the tune mine has... LOL

Fouls plugs if you let it idle for 20 - 30 minutes...

[zebra]

As no one else seems to be aware of it. ARIAS make off the shelf highish comp forged pistons for the 25/30.

These are the ones i have in my engine.

Suit RB26/30, 25/30

p/n= AP332104

10.6cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.2-9.4

They also make these with even higher compression

Suit RB26/30, 25/30

p/n= AP332105

13cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.5-9.8

No need to mess about with RB25 pistons and what not.

That is very handy to know Thanks mate

if they are only stocked in +20 then i may just leave the standard pistons in the 30 for now if they are in good nick, rather than bore it out now

[Dale FZ1]

lots of euro turbo petrols are running 10.5:1 to 11:1 CR's these days.

fuel quality and tuning has come a long way in the last 10 or so years

There's a big difference between what can be done with direct petrol injection setups and the port injection setup we have with the RB. Even so, those factory setups aren't running much if any further than 10:1.

My mate has 9.5:1 in his 25/30. E85 and 700rwhp.

The fuel is the secret ingredient there - looking through competition history books shows what has been achieved with high quality blends and rocket fuels. General availability puts a dampener on my enthusiasm for E85.

If I was doing a twin cam RB30 turbo engine 9.0 would be absolute minimum I'd run and preferably the as mentioned 9.5 to 1 .

Over 9 and under 10 CR for today's turbo road engines , IMO cheers A .

Considering what the likely pressure ratio (say 12psi) is required to hit a streetable 350rwhp, I agree that perhaps up to 9.5:1 would strike a very good balance for output and fuel efficiency. I don't think I'd like its chances of surviving a hard day at the track though, unless it was running some sort of special fuel.

As no one else seems to be aware of it. ARIAS make off the shelf highish comp forged pistons for the 25/30.

These are the ones i have in my engine.

Suit RB26/30, 25/30

p/n= AP332104

10.6cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.2-9.4

Be a bit interesting to see/hear more on the results of this combination.

Sounds like the tune mine has... LOL

Fouls plugs if you let it idle for 20 - 30 minutes...

Running a tune very rich (say 11.2:1 AFR) at high load does not mean it has to be rich at idle also. Time for a proper tune?

[Dale FZ1]

Keeping on-thread, and checking out zebra's build thread, I'll differentiate between the intended uses.

For an occasional track machine it would be hard to deny the benefits of E85, and what Dave's mate achieved should be repeatable. The number of hours use it would realistically see during a year means E85 and >9.0:1 CR would bear serious thought. Good tuning would determine how well it lives.

Keep us posted with progress.

[twinvl]

E85 is amazing stuff.

One of the guys at work is playing around with a SR20DET on the engine dyno. Is was a completely standard engine, it made an extra 40hp just by switching from 98 to e85, same boost, 40% more fuel, 15 degrees more timing, where it was pinging a little on the 98, not a hint of a ping on e85.

The rest of the work has been done with a different turbo and 36mm restrictor. He needs 10.5:1 so he can run it to the knock limit again in the higher end where it will be raced. Has 26psi of boost at 4000rpm dropping off from there with the restrictor.

I'm putting together a RB30DETT for my r32 and i will be building the engine for e85, 10.5:1. The fuel system isn't that difficult to make survive e85. Rules are simple, no bare aluminium, anodised is fine. Most bosch fuel pumps are fine, they just say the life of the pump is halved. Steel lines/ rails are ok but the water e85 soaks up can rust them. Zink phosphate coating (like on factory fuel rails) will eventually fall off. Stainless lines are the go. Compatible rubber hoses are available. Steel tank might rust out eventually, meh!

[R31Nismoid]

Only 40hp from E85 with 15 extra degree's of timing with 40% fuel extra?

That doesn't sound right at all. Generally people are getting 35-50rwkw gains, not 15-20