Rb26 And Higher Compression

[Duncan]

while we are chatting about CR instead of turbos for a moment...

stock 26 deck height is 0.5mm above the deck

a few i have heard of are custom cp's.

a fresh decked head will come in around 64cc. (just measured one at work)

I just checked old v new paperwork. I have had heads cc'ed at 63.5cc and 64.5cc.

Had the one today been decked? It was the lower cc at 63.5 so higher CR.

BTW overall CR will be affected by chamber size, gasket thickness, piston style, block height and even bore. lots of variables....

[rob82]

oh yeah forgot bout that .

just said it on the "smaller chamber" side of things

if it was goin single turb there is no shortage of manifolds . and nothing a plazmaman on the intake wont fix .

can someone say if a neo head has a realistic chamber size for a 26 ? as in does it achieve a higher comp ratio in a way that is beneficial ?

The neo is the pick of the heads IMO - you've got narrow valve angles, smallcombustion chamber, vct, mechanical heads. Can't see why it wouldn't go on the rb26 - just need to do the same mods as the rb30/25.

[Sidwysracr]

Yes.. -9 and -5 are both on table. No VTC is not an option. From reading one with 11 to 12:1 can run E85 all day boosted. But I am more concern with pump fuel because it's more common.

[bradsm87]

about 9.7:1 and 18psi would be the highest I'd go on pump 98.

I know a guy who runs an 11:1 SR20 running 23psi on E85!!!

[Sidwysracr]

The OP is also talking about a built motor, that again would easily make 320rwkw out of -9's like everyone else does

I agree -5's on a built motor would be good - however ONLY if you are chasing 600hp+, and not the 500hp stated here.

I read a lot about -9's and -5's. -9's fit a perfect to street car for what most people say, but once it reaches the upper rpms it runs out of it's puff, this is where the -5's shine.

Here's a dyno graph with a comparison of -9 and -5's, the taller line is obviously -5s, but you can see that the -9's match the description as above.. and notice that the -5's are only 300 rpms behind. But notice the torque curve... even though not sooner, but it allows you to say in gear longer before it dives down.

They follow nearly nearly identical paths on the up climb (the difference noted above), the -5's does it more efficiently. I plotted both the -9's and -5's compressor maps. Like I said 77% over 74%, less hot air the better. Tuning and cams can make the -5 spin sooner.

I am after a track build, what ever gets me around the corners faster and have enough top end to keep up in the straights. Raising CR will allow more off-boost power, which for a tracker that means a fatter power band to be used. My differential ratio is 4.363, so naturally in the higher rpms...with this...it would make the -5 spin sooner...and in the end I would have a lot of top end too. A bit of tuning can make the -5's respond sooner as well.

Edited July 13, 2010 by Sidwysracr

[R31Nismoid]

Everything you said about -5s, can be said for -9's as well remember.

Anyway aside from that there is one major flaw with what you have just posted mate...

Things are not equal!!!

As I've been saying all along, they need to be if you are going to compare.

The -5 setup you are comparing to is not making 500hp, its 600hp+.

-5 setup 380rwkw

-9 setup 340rwkw

It is not an even comparison at all!!!

If you pulled the boost out of the -5s to back them down 40rwkw to the same output as the -9s then the different would be very signifigant, and the -9s would piss on the -5s in every single respect.

There is also no boost plots to check out, it looks as if the -9 setup is almost certainly falling off in the top end (you are losing over 25rwkw with another 500rpm to go yet)

I'll say again (before people jump up and down), for 600hp+ you want -5s and I would be suggestion as such without question.

So are you after 600hp now? Or 500hp? You need to decide I think so we can offer the best advice

[Sidwysracr]

First... whatever mindset/chip in your shoulder about the heated -5/-9 debate... leave it in that debate thread.

I never said they were equal, where ever you get that from.

I already stated reasons why the -5 are good to have still on the table and it has potential to deliver more power if needed.

Finally,

This thread is about running higher compression with boost, I am seeking knowledge from ones who have done it.

Edited July 13, 2010 by Sidwysracr

[R31Nismoid]

From your first post mate!

Not even worried about that other thread, plenty of discussion going on there & I know it's stemmed away from CR, just trying to keep accurate discussion to points

I would like to get up to 10:1 CR (I can settle with less down to 9:1 min) and eventually roll with gt2860-5s.. maybe -9s.. making around 500 hp, goal is to make a super responsive machine.

1. Your requirements stated 500hp & super responsive.

2. People then tried to say that -5's were the better choice for this goal - which they are not.

You then said…

^ I been thinking about it a lot actually. I been stuck. The reason why -5 stays in the fight... is because it has more top end.

Just going by what you said mate, nothing more, nothing less.

I'm certainly not having a go @ you in my last post - Just trying to keep accurate discussion running here as suddenly you are comparing 500hp & 600hp+ setups.

Hence my saying the info was not really comparable based on your initial post about what your requirements of 500hp/super response…

I suspect the results you are basing the better "top end" on above, are not quite setup correctly also, separate issue in some ways

End of the day I'm trying to give you enough information and challenging your idea so you can make a solid decision.

Which your decision seems as though you want 600hp+ in reality?

Anyway 9.5:1 will be fine, 20psi and off you go on PULP, most people are doing that with builds.

Both my motors have been @ that.

[rob82]

From your first post mate!

Not even worried about that other thread, plenty of discussion going on there & I know it's stemmed away from CR, just trying to keep accurate discussion to points

1. Your requirements stated 500hp & super responsive.

2. People then tried to say that -5's were the better choice for this goal - which they are not.

You then said…

Just going by what you said mate, nothing more, nothing less.

I'm certainly not having a go @ you in my last post - Just trying to keep accurate discussion running here as suddenly you are comparing 500hp & 600hp+ setups.

Hence my saying the info was not really comparable based on your initial post about what your requirements of 500hp/super response…

I suspect the results you are basing the better "top end" on above, are not quite setup correctly also, separate issue in some ways

End of the day I'm trying to give you enough information and challenging your idea so you can make a solid decision.

Which your decision seems as though you want 600hp+ in reality?

Anyway 9.5:1 will be fine, 20psi and off you go on PULP, most people are doing that with builds.

Both my motors have been @ that.

How were your motors built? Was the reduction in combustion chamber volume bias more toward pisotn design or cylinder head design? What size cams were you using at that compression ratio? What was the cranking compression? What timing numbers were you running on 20psi on pump? What was the propensity to knock like? Did you use the factory CAS or were you using a crank trigger?

I think these are the type of question you need answered.

[R31Nismoid]

I don't build my motor - that's the job for Racepace

I just know basic final details! Factory cams, factory CAS as well.

I doubt i'll get answers to such questions anyways even if did ask.

[Sidwysracr]

I don't build my motor - that's the job for Racepace

I just know basic final details! Factory cams, factory CAS as well.

I doubt i'll get answers to such questions anyways even if did ask.

Bump

[T04GTR]

head decking only to get a new gasket surface. not to raise comp. ie its not a red motor....

[T04GTR]

why not just use -5's instead of -9's. why screw 20+psi out of -9's and have limited to end. when you can run less boost on -5's and have more top end to the same hp

i dont know about you guys but i dont dribble around the track at 3000rpm.... and in contrast instead of just breaking loose when it hits boost the extra (minimal) lag of the -5's will make for a smoother corner exit.

and if you can have 600hp for the same price as 500hp... why not!!

[bigmikespec]

That Racepace hocus pocus is really annoying; but from what Nismoid mentioned stock cams and 9.5 static compression will give pretty high dynamic compression. Hence good results for a street car with -9's and stock stroke.

Advantage in going higher compression allows you run longer duration cams without causing such a loss in dynamic compression.

[T04GTR]

very good point. i hadnt thought of it that way. 9:1 is is the new 8:1.

[Sidwysracr]

From your first post mate!

Not even worried about that other thread, plenty of discussion going on there & I know it's stemmed away from CR, just trying to keep accurate discussion to points

1. Your requirements stated 500hp & super responsive.

2. People then tried to say that -5's were the better choice for this goal - which they are not.

You then said…

Just going by what you said mate, nothing more, nothing less.

I'm certainly not having a go @ you in my last post - Just trying to keep accurate discussion running here as suddenly you are comparing 500hp & 600hp+ setups.

Hence my saying the info was not really comparable based on your initial post about what your requirements of 500hp/super response…

I suspect the results you are basing the better "top end" on above, are not quite setup correctly also, separate issue in some ways

End of the day I'm trying to give you enough information and challenging your idea so you can make a solid decision.

Which your decision seems as though you want 600hp+ in reality?

Anyway 9.5:1 will be fine, 20psi and off you go on PULP, most people are doing that with builds.

Both my motors have been @ that.

To be honest. I am looking at a 500 to 600 range of power. I will be hooking up on rw only.

The engine goodies will be replaced forged internals (2lbs of reciprocating weight reduced), I am going to do minor head work. Possibly spring and valve replacement to support higher revs. I am looking at tomei 260in 10.25 lift and 252ex 9.15 lifts.

9.5:1 to 10:1 seems to be a magic number, considering that good number of turbo cars are coming out 9:1 from factory. I can reason this is due to better electronic modulation. And I would assume a AEM ECU unit would be a fair bit better than current stock ecu's to modulate the engine.

As I mentioned before I'll be running a 4.363 final drive over my recent 4.1's. this is roughly 400 to 500 rpm per speed. I believe this will reduce the variance between the turbos. And I am running a 6-speed which the ratios are :

3.794

2.324

1.624

1.271

1

0.794

which calculating the end of all of the gears at a 9000 rev limit, is 40.1 MPH, 65.5 MPH, 93.8 MPH, 119.8 MPH, 152.3 MPH and 191.8 MPH, respectively. I honestly believe that there shouldn't be a drop of 3000 rpm per shift. Which put you somewhere above 6000 rpm. This is my dilemma in thought, even if I make 500 hp with -9's it won't have the poof before 9000 rpm; this would effectively reduce my boosting time and time in gear. Including that I am not likely to fall under 4000 rpm as well. The -5 have an efficiency island of 77% and the -9's are 75%. Comparing the range that engine will be running though from the compressor charts the -5's will be running cooler. With those parameters, how much response difference would there be with the -9's and -5's even if I opt to push only 500 hp? How long can I stay in gear if I choose the -9's how about the -5's? I am sure to recon that the one that stay's in gear at a longer rpm range will be quicker, especially when your rpms are climbing like hellfire due to the larger final drive.

And btw, I am looking at 2500 to 2800 lb vehicle.

Edited December 17, 2010 by Sidwysracr

[STATUS]

increase to 10:1 on pump your crazy... on E85 then your talking.

AEM ecu is awesome providing its the version 2. My favourite plug in ecu atm behind PFC.

[bradsm87]

increase to 10:1 on pump your crazy... on E85 then your talking.

AEM ecu is awesome providing its the version 2. My favourite plug in ecu atm behind PFC.

What about running a highly efficient turbo, 12psi, really good intercooling and a big turbine housing? That's my plan until E85 comes to the pump here then will re-tune on about 17psi.

Edited December 17, 2010 by bradsm87

[zebra]

What about running a highly efficient turbo, 12psi, really good intercooling and a big turbine housing? That's my plan until E85 comes to the pump here then will re-tune on about 17psi.

What if its a really hot day, or you have low vehicle speed so no air passing through the cooler core etc.

Sure you could do it, but I would be shit scared of giving it a hit without checking intake temps every 2 seconds

[bradsm87]

It'll be a water to air intercooler. The water stays cool for a fair while after u slow down. 12psi is pretty low tho. Hottest days here in Tas are about 35 degrees at the very most and i won't have air con or anything. Also I'll be running a Haltech with air temp compensation set up to run richer once air temps get too high for my liking.

Edited December 17, 2010 by bradsm87