Cr Advice For My 30/25 Build,

[DaveO74]

Hey Peeps,

Well I have decided to give "GR33DD" a big makeover as the old 25 is getting a bit tired and the little scratches and rattles etc etc are driving me crazy. So after 10 years of ownership its time for the full rebuild with a respray and some nice interior goodies

I have been doing my homework and I am about 110pages into the R33 Sticky and have been in touch with a couple of forum members (Thanks Al) and most of you guys seem to like a compression ratio of between 8.5-9:1 for response and to aviod the "doughy" feeling that can be associated with lower compression. Soooooo anyway I decided I would give a reputable engine builder in SA (Im not sure wether its right to name him) the task of building the new engine as he does the whole thing including head work (porting, cams, springs blah blah) is very well priced and seems to know what he is talking about.

I am after a nice responsive package running a 3076r on e85 and i'm aiming for between 300-350rwkw which I reckon will be achievable on jungle juice. I decided to go with what the builder calls his "Torque Monster" build, fully forged, balanced and blueprinted, but I am adding forged rods.

The main reasons I was planning on using him is with a young family time is limited nowadays and I will be spending enough of that running around getting resprays and eng certs and what not so I thought it will be good to not have to worry about the engine and just wait for the truck to turn up with the 30 on the pallet ready to bolt in and turn the key after I bolt on all the ancillaries.

I quized him last night about what CR he will build the 30 to going by what I have said I want to use it for (mainly street with a couple of track days a year) and he insists on a 8:1 CR!

I sent him another email respectfully asking what was his reasoning behind such a low compression as the standard RB25 sit at around 9:1 and the 26 around 8.5:1 and he replied:

"Hi david. Its nice to run a bunch of static comp to get the engine to feel responsive, in the real world a turbo charged engine is a compromise in either top end or bottom /mid/ I prefer to stick with 8 to 1 comp as it is more user friendly. When giving static comp to get engine to be responsive it is either wrong turbo choice or gearing issues etc. the turbo charger is giving the engine its compression as it pumps . the highish static comp will then have you removing timing unusually on boost and its false economy in my mind. Basically what I say to people is why do you want the response? I then follow up with youre turbo charger is too large !! then they say ‘’ it makes 300rwkw and it has no response . truth is it will never be responsive , invest in a good ogura clutch that you can kick theres youre response !... sorry for the rave hope it helps.."

Now I am in no way an expert and quite franky get a little lost at times but to me this does not seem right???????

Could some of you guys in the know give me a bit of advice on wether I should go ahead with the build at this CR or should I look around again

What are some more of the pros and cons of running a CR of 8:1

Im not planning on doing the build next week or anything and have a timeframe of 1yr for the ENTIRE rebuild of the car but I was going to send the engine over in the new year.

Thanks in advance

[TiTAN]

Fuel these days is pretty good and 9:1-10:1 isnt uncommon for factory turbo engines, if you intend to run on E85 you could even go higher without any real dramas. Off boost (which really, most street cars do 90% of the time) the higher compression makes it a much nicer car to drive every day.

A few members on here have had their engines built by Greg (ProEngines) as they do lots of RB30's and know what needs to be done, they are also a lot closer than SA.

[DaveO74]

Yeah I have sent Greg an email so I'll see what he has to say. So my guess of 8:1 being way to low is on the money?

I'm learning as I go

[N1GTR]

All I'll say is this; I hope you didnt send any money

[R31Nismoid]

lol 8:1

[Adriano]

So he is saying you can have a resposive 8:1 engine by giving the clutch a kick, wonder how long 3rd would last in my gtr gearbox if i drove it like that.

[DaveO74]

All I'll say is this; I hope you didnt send any money

Nah Steveo even I'm not that silly mate. I was going to get him to do the build but by the sounds of things I should reconsider it me thinks.

I've tried to get hold of one of the ones you told me about but jeez he is hard to track down.......in a way a good sign cause it shows how busy he must be.

And yeh Adriano apparently all my troubles will go away with a good old clutch kick!

Plus I didn't think a 3076 would be in any way too big a turbo for a thirty

[Al]

Fark Dave. If you don't need response just throw in a stock RB20 with a TD06 off the side. Whole project will cost you $1000.

This guy sounds like he's still using 1970's theories on forced induction.

Just reply "thanks but NO THANKS!"

[StealthX]

It's your money at the end of the day, you're the customer!

His theory has grounds, i.e. less compression and more timing, but in reality, higher compression gives a much better feel when cruising around in vacuum...

[DaveO74]

Fark Dave. If you don't need response just throw in a stock RB20 with a TD06 off the side. Whole project will cost you $1000.

This guy sounds like he's still using 1970's theories on forced induction.

Just reply "thanks but NO THANKS!"

I reckon you are right Al, you know who it is we were talking about it the other day. Just goes to show it dosent hurt to ask lots of questions.....couldve been a very expensive lessen

ah well looks like I'm on the hunt for a builder again, I've knocked two off the list so I'll get there.

[TiTAN]

Nah Steveo even I'm not that silly mate. I was going to get him to do the build but by the sounds of things I should reconsider it me thinks.

I've tried to get hold of one of the ones you told me about but jeez he is hard to track down.......in a way a good sign cause it shows how busy he must be.

And yeh Adriano apparently all my troubles will go away with a good old clutch kick!

Plus I didn't think a 3076 would be in any way too big a turbo for a thirty

anything smaller than a GT30 is TOO SMALL for a 3L, as it is the GT30 will be well into boost at 2500.

[Al]

anything smaller than a GT30 is TOO SMALL for a 3L, as it is the GT30 will be well into boost at 2500.

100rwkw @ 9psi @ 2500rpm

150rwkw @ 17psi @ 3100rpm

220rwkw @ 21psi @ 3600rpm

Then steadily increases to

335rwkw @ 21psi @ 5800rpm

I just love the rb30/gt30 combo

Let's not also forget the 900N of tractive torque

[DaveO74]

Sounds nice Al, can you PM me your dyno sheet when you get a chance?

Still haven't heard back from proengines, and I have toldthe original builder that I'll "think about it" and get back to him. I was pretty sure 8:1 was too low.

Thanks guys

[TiTAN]

Al's dyno sheet and mods list is in the RB30 dyno results thread.

It may be easier to give greg a call.

[Al]

Al's dyno sheet and mods list is in the RB30 dyno results thread.

It may be easier to give greg a call.

just fitted a wastegate and had a retune. Better response (again) and more torque. Updates yet to be posted.

[BoostdR]

8.8:1 works well with E85 (lower comp may slightly effect cold start on E85)

6boost Manifold

CP pistons

Tomei oil Pump

1.2mm oil Restrictor

NEO head and keep the VCT

PM me the name of the workshop and I will point you in the right direction. Having a builder with a level head is not such a bad thing. If he does't know you want to run E85, that may change his thinking.

The builder sounds to be playing it safe. Low comp gives an easier tune and less chance of detonation. The lower comp also gives a larger chamber volume which effects fuel economy in a negative way.

Matt

[DCIEVE]

Pretty obvious it's Darren. Those bagging the builder are jumping the gun a little I think... if he doesn't know what fuel is being used or how competent the tuner will be it's more than reasonable to keep the static cr low.

[DaveO74]

Thanks Matt I'll PM you tomorrow.

And just to clear things up, I did tell the builder it will be run on E85........the clutch kick comment threw me though

[Al]

How many rb dohc engines are running 8.5+:1 comp without detonation, on pump fuel?

The need for low comp forced induction engines is old school, unless setting up a drag car with huge boost and NOS.

Whoever the builder is, hasn't listened to Dave and his intended use of his car and new setup. He is after a responsive 330+rwkw, running E85, with 22psi max. I have acheived that on pump fuel, using 9:1cr and no issues with detonation. Why the need to "clutch kick" when the engine is capable of producing the figures, if built properly.

[STATUS]

^^^ OR SR20 they hate high comp, ive had a few lately that have been raised and wont take more than 2 degrees up top and are limited to 16-17psi... Perfect for E85 but when they were told they were to suit bp98 its no good... engines have since had head modified (quench pads removed) and are now back to 12-15 degrees of timing and 22 odd psi and another 30-40rwkw more with no discernible loss in tractability.

9:1 no issues on a rb though and on E85 should be even less of a worry, we are using 13.5:1 in NA e85 applications.