High Comp And E85

[kitto]

Hmm swore standard RB25 was 8.5:1.

CP pistons for the Neo are now an off the shelf stocked item.

[Simon-S14]

Nah all 25's are 9:1

[JustinP]

CP pistons for the Neo are now an off the shelf stocked item.

Damn it! I must have been one of the last people to order them when they were still a custom item (and much more expensive!)

[kitto]

Haha yeah, i paid $880 or something

[bradsm87]

I wouldn't go higher than about 10:1 with a .63 housing because higher C/R and small housing both contribute to the detonation threshold.

I'd go with 10.5:1 comp and chuck a .82 housing on and it'll probably make full boost about the same as before but make a shit load more torque off boost, as it's coming on to boost and on boost, so EVERYWHERE.

Even for me going from 8.5:1 with a GT2871R .64 to 9:1 and a .86 housing, I only lost about 100rpm spool threshold but it just felt better everywhere, especially off boost and coming on to boost.

[STATUS]

More comp and bigger housing... do it.

We did a SR autech NA engine plus t67 10cm... was fantastic.

Beams engine from altezza (11.5:1) plus turbo also a massive winner.

[RRob]

Rb25's are 9.0:1. Neo engines have a smaller piston crown and a smaller chamber in the head but have the same CR.

If you want big CR 2.6 crank, rods, pistons and a neo head on a 1.2mm gasket works out to about 10.7:1 from memory.

[SS8_Gohan]

in comparison to a 2.8, how would 10.7:1 CR go? still a long way off what you'd get with a 2.8 in terms of response?

maybe a good cheap option would be, 2.6, N/A Neo head keeping VCT, high comp and running E85 - surely that would be competition for a 2.8 stroker?

[STATUS]

in comparison to a 2.8, how would 10.7:1 CR go? still a long way off what you'd get with a 2.8 in terms of response?

maybe a good cheap option would be, 2.6, N/A Neo head keeping VCT, high comp and running E85 - surely that would be competition for a 2.8 stroker?

That is a combo i have thought about allot lately

[Roy]

What plug gaps do people run with E85?

[Simon-S14]

.8

[StevenCJR31]

RB20 DET 8.5 to 1 CR RB25DET 9.0 to 1 CR

[Dose Pipe Sutututu]

funny how not long ago I suggested upping the static compression ratio to around 10:1 on a RB25 and got totally shot down by a few forum members (not mentioning names) and now there's a thread that's dedicated to it and there are all positive comments... I don't get SAU at times

Yes RB25DETs are 9:1, most people "think" they're 8.5:1 because most piston kits reduce the static CR to 8.5:1, being 86mm stock bore or 86.5mm oversize bore.

I am planning to also go down the high comp path, but yet to work out the right combination of parts & head shaving

Edited May 27, 2012 by johnnilicte

[discopotato03]

I regret not knowing a few years back that RB25 Neo heads had more compact chambers because I spent good movey improving an R33 era one .

Nissan obviously changed the later 25DETs for a reason and since the satatic CR is the same I have to assume they were trying to reduce detonation in leaner burning (possibly ULEV) engines .

I reckon having smaller chambers and a deeper dish in the middle of the piston crown allows them to have good quench abilities and not having a large aluminium mountain across the middle would make them breathe and scavange better .

If I was doing an RB25 that was a pure E85 engine I would go up half a ratio to say 9.5-9.75 to improve the off boost performance and still have it low enough to run sensible timing at a sane boost level . Since I don't think too many have played with higher CR turbo Neos and E85 the CR is something that would take a bit of trial and error to get it right . My conservative reasoning is that its less of a problem if its a tad lower than perfect than if its a bit too high a gives detonation grief .

That aside I wonder what the CR ends up being when you bolt a Neo head onto a stock standard RB30 NA , if it's around 9.0 - 9.5 that a pretty cheap dirty 30 build .

A .

[bradsm87]

Is is all Neo's or just the N/A ones?

[GTScotT]

Someone sponsor me and Jez to put some ethanol in my SR.

My current SR is 10:1 and very det prone. I wouldnt mind letting jez see if the pineapple juice makes it a monster, would be good for everyone to see.

For science

[Simon-S14]

What turbo? Small turbo on sr with high comp like DE with t makes them wanna ping

[bigmikespec]

funny how not long ago I suggested upping the static compression ratio to around 10:1 on a RB25 and got totally shot down by a few forum members (not mentioning names) and now there's a thread that's dedicated to it and there are all positive comments... I don't get SAU at times

Yes RB25DETs are 9:1, most people "think" they're 8.5:1 because most piston kits reduce the static CR to 8.5:1, being 86mm stock bore or 86.5mm oversize bore.

I am planning to also go down the high comp path, but yet to work out the right combination of parts & head shaving

I dont know who shot you down but I can say, I have asked a few big engine builders in the USA about raising the compression in my RB26 to 9:1 or higher and their comments were (in short)... "What for? What is the point all you will do is generate more heat and it will detonate with increasing boost levels"

Depends what engine, fuel and what you want to achieve. But for my goals, lower compression and no quench is right for me.

[GTScotT]

What turbo? Small turbo on sr with high comp like DE with t makes them wanna ping

Rekon something bigger will work well?

Ive done T28 (works good on 9.5:1), 28RS disco, TD05H 18G. The Disco was very fail, I suspect due to cams, the 18G has gone over 200kw but pings with any more than 15 pounds.

My 10:1 motor has been shit from word go, all other 9.5 motors Ive done have at least always been fast. Im currently rebuilding my old DET to make way for an FP30, unless you rekon the 10:1 motor will take to the FP30 as is ? lol, id try it if there was merit (want to stay 98 though).

[discopotato03]

David Buschur in the US usually says that increasing the CR in 4G engines usually makes them feel better off boost but nothing much changes boost threshold wise .

I think you need to look at any engine as a combination of parts making it a specific package . There are good and bad ways to increase the static CR and bad ways tend to promote detonation . Leaving piston and chambers for a moment turbo systems are sometimes done differently on higher CR engines . For example if the raised CR engine makes better part throttle torque off boost you can probably increase the turbine housing size because you may not need boost as early , the reduced turbine inlet pressure should help reduce a higher CR engines tendency to detonate . I think effective intercooling becomes more important because lower charge temps ideally means lower combustion temps .

Ultimately I think the secret is keeping a handle on combustion temperatures and pressures in the rev ranges tend to detonate in which is usually the low to mid range . I'm told the reason for this is because at low revs the compressed charge has more time to absorb heat from engine components and finds it easier to "auto ignite" .

Tuning would be very important and not being too greedy with boost pressure for its own sake would help .

My take with any of these performance enhancements is first can I make the engine any bigger because its the same as it was 40 years ago , extra inches (cubic ones) make the easiest horses . Not necessarily the cheapest but more often the easiest .

A .