Recommended Static Cr Target For Full Time E85 Street Car.

[Blackkers]

Hey guys I'm starting a twin cam RB30 build; picking up a S2 block this weekend with 240,000kms on it. I'm not sure if it's ever been opened or if the motor was swapped at any time, but 240 was on the tacho of the VL it came out of.

I plan to fit the RB25det neo head with an MLS gasket.

Seeing as I'm going to be running full time e85, what CR do you think I should aim for? I believe somewhere between 9.0-9.5:1 would be ideal. I don't plan to exceed 20psi on a hypergear 21u highflow IWG.

I also plan to use the stock pistons and rods. But I plan on fitting fresh piston rings and giving the bore a quick hone. I also want to check bearings for abnormal wear but I'm not sure whether to just swap them all out and call it a day. Oil pump will be coming from a twin cam motor. Are the DE oil pumps the same as the DET models? And is it worth fitting a crank collar for 95% street use? None of this is set in stone so if you think I should hunt around for a lower KM's engine and leave it untouched please weigh in!

Any input or suggestions would be welcomed. I'll be posting photos etc as the build progesses and I'm really looking forward to getting started. thanks guys

[The Mafia]

At those sort of kms, I'd be getting the bores checked. They will most likely be mushroomed.

Also, why that turbo? There are much better options out there. The kando range are cheap and brilliant.

[KiwiRS4T]

Facts are few on the ground re compression ratios - nobody seems to actually measure them. If you are going to stick with stock pistons and put a Neo head on top then that doesn't really leave you much ability to affect the outcome but hopefully it will be nearer 9:1 than 8:1

After 240,000km I would be inclined to do bearings and if you are not going to replace big end bolts you should probably use a 6,500 rev limit.

Mine is a cheapo job - rings, bearings and big end bolts (no balancing) and with stock pistons probably some where around 8:1 (less than ideal). I have an N1 pump and have been revving it to 7000 for about 3 years.

[Blackkers]

The turbo is on my 25 at the moment. I think its a good option for response and if it means I won't have to spin the absolute shit out of the unbalanced 30 bottom end then that's a bonus too. If I was changing turbo I'd look at something a fair bit bigger, maybe towards SS3-4 territory seeing as 3L +VCT will help with off boost driveability.

anyway as far as the bores go, If they are mushroomed does that mean I need to have the block bored to 86.5? If that's the case I might as well throw the block away and look for another with decent bores. Hmm making me think that I should probably look for a lower KMs RB30 to start with..

[Blackkers]

Facts are few on the ground re compression ratios - nobody seems to actually measure them. If you are going to stick with stock pistons and put a Neo head on top then that doesn't really leave you much ability to affect the outcome but hopefully it will be nearer 9:1 than 8:1

After 240,000km I would be inclined to do bearings and if you are not going to replace big end bolts you should probably use a 6,500 rev limit.

Mine is a cheapo job - rings, bearings and big end bolts (no balancing) and with stock pistons probably some where around 8:1 (less than ideal). I have an N1 pump and have been revving it to 7000 for about 3 years.

Did you use the R33 head? Also did you get the head or deck skimmed? or just clean it up and slap it together? how much power are you making and do you think I should buy ARP headstuds? Did you change all the bottom end bolts including rod bolts and I forget the name of the other but the bolts that hold the big end bearing caps down too? thanks

[Dale FZ1]

I'd consult with Stao about his recommendations for turbo. The 3 litre will require a fair bit more turbine capacity otherwise it will choke. You've got to let those gases out and get the engine breathing especially if you plan on pushing 20psi boost into it.

Decent quality cast pistons won't cost much and will be more than adequate for street use. Get the block bored .020" over and be happy that you aren't using old slugs that are fatigued.

If you are 100% committed to E85 then you could probably use a thin head gasket to bump CR up a touch. Bob's suggestion is good; you could physically measure the chamber volume and cylinder volume at BDC. Then you work out what HG you want. 9.5:1 is right up there but shouldn't be a problem with E85 if it's tuned right.

[R32Abuser]

FWIW

I'm running BP98 with somewhere around 9:1. Off boost response is fantastic (~230RWKW @ 4000RPM) with a GT3076R (0.82 A/R) and no VCT. Dyno sheet is in the RB30 dyno thread.

E85 + NEO Head + VCT + 9:1 + Static CR + similar sized turbo would make a weapon of a street car.

Edited May 30, 2014 by R32Abuser

[Blackkers]

Thanks guys. Yeah I'm thinking the 21U is a bit small. It is pushing around 300rwkw on 20psi on the 25det with the stock manifold and IWG; it seems to nose over the top of the power curve towards 7000-7100ish. I'm happy for now not revving that hard.

I'll have to inspect the block once I've pulled it apart before I make any final decisions. Thanks for the help guys

[iruvyouskyrine]

E85 + NEO Head + VCT + 9:1 + Static CR + similar sized turbo would make a weapon of a street car.

[KiwiRS4T]

Did you use the R33 head? Also did you get the head or deck skimmed? or just clean it up and slap it together? how much power are you making and do you think I should buy ARP headstuds? Did you change all the bottom end bolts including rod bolts and I forget the name of the other but the bolts that hold the big end bearing caps down too? thanks

Yes R33 head - just cleaned up. Making just over 300AWKW. Stock head bolts and main bearing cap bolts just better rod bolts. You'll do better with a Neo head and suitable turbo.

[AngryRB]

Im gonna get the neo head skimmed for hopefully 9.5-1 on E85, why fall short if its a street engine, need all that bottom/mid range poke,

how much should be skimmed to have 9.5ish on E85 ???? guessing a couple of thou would be a good thing?

Edited May 30, 2014 by AngryRB

[GTRPSI]

9.5 Should be a walk in the park for E85, there are engines out there running more compression and boost with that fuel.

You will need to calculate your compression ratio, take some measurements of your deck height, piston dome volume, head gasket thickness and cc your combustion chambers, then just do the maths.

[hypergear]

If you are using a standard RB30 NA buttom end with a Rb25det R33 engine head it should give you an compression ratio of 8.3:1, roughly 135psi per CYC. I think its a good compression ratio. With the ignition angles, its about where the engine produced the best torque, with E85 fuel and lower compression it allows you to have it set at optimum angles and run heaps of boost without pining.

Then you might want to go for an .82 turbine housing for the high flow, or some thing like an ATR45SS-1 that can supporting around 450rwkws mark.

[Ben C34]

He is using a NEO head.

Just bolt together.

You get the comp the engine decides!

(Which will be what you want)

[jet_r31]

you'll need the .82,at the least ... thats a given

cheers

darren

[KiwiRS4T]

If you are using a standard RB30 NA buttom end with a Rb25det R33 engine head it should give you an compression ratio of 8.3:1, roughly 135psi per CYC. I think its a good compression ratio. With the ignition angles, its about where the engine produced the best torque, with E85 fuel and lower compression it allows you to have it set at optimum angles and run heaps of boost without pining.

Then you might want to go for an .82 turbine housing for the high flow, or some thing like an ATR45SS-1 that can supporting around 450rwkws mark.

This is what I have and its far too low (compressions are in the range 130 - 132 psi). OP is going to use the Neo head which will give better CR (and be better all round).

[Blackkers]

That's the idea. I'm aware my turbo is too small to be efficient in the top end but I'll be happy with a midrange monster at the moment.

I figure I want the engine done properly and get the car running and tuned nicely before I go thinking of turbo upgrades. I could swap out the turbo now but I'd rather do it properly with a highmount manifold from ETM or 6boost with an external gate + a turbo like the FP3582 or something from the hypergear SS range; haven't decided yet. One thing at a time.

And who knows, this new highflow profile flows really well in the top end on my 25 so I think it will surpass expectations. If I end up with the same top end power figure as I've got now at lower RPM with a high~ish comp 3L + VCT then I have nothing to complain about! In 4th gear currently it builds 20psi by 3400rpm on a flat road with minor boost leaks. Can't imagine what it would be like with the planned setup

[iruvyouskyrine]

Give me 2-3 months and I will let you know

[Blackkers]

Okay I can't actually move forward with this build until I sell the superkart. I've got to move on this trailer and kart for garage space and now that the 25 is running again I'm not rushed for this build.

If anyone knows anyone that is interested in a superkart that is capable of getting into the 61 second laps at Wakefield let me know. I've personally done 1:02.3 but that was it's only race event ever and there's still more fine tuning to do.

[chairman]

cp flat tops 8.1