Rb30/26 (Suicide Is An Option)

[GTRNUR]

How about some maths.

RB30ET pistons have a 10cc dish. Assuming a 87mm bore, standard stroke, standard head gasket and zero deck height on the block, the HIGHEST your compression ratio will be is 7.37:1. That is assuming your head's combustion chamber hasn't been re-worked.

Now factor in the head work. Considering its a RACE PORT head, which doesnt really elaborate on what has been done, the head CC's are really an unknown. But for calculation sake, lets assume that one of the quench pads has been machined out, then the head CC will be near on 68cc. This puts the compression ratio down to 6.93:1.

But wait, it gets worse. Those camshafts with their combined overlap and duration will lower your dynamic compression to at least 6.5:1.

What all this means is, your cylinder pressures are all pretty much spot on for how the engine is setup. Compression ratios directly effect the cranking compression of the compression test.

With standard cams a 3lt motor: (also depending on how they are dialed in)

8.0:1 will net about 115-120 psi

8.3:1 will be about 140-145 psi

8.5:1 will be around 150-160 psi

Compression ratio is your main issue.

Your options?

Well you if you aren't disapointed with the off-boost drivability of the car, there really is nothing stopping you from really cranking some serious boost into the engine. Around 30psi at least would be where I'd start the re-tune at. With this level of boost you should be seeing at least 625-650hp at the tyres. You will have to watch the fuel closely though as the injectors will me maxed if your reving 7500-8000. It could really do with a set of ID1000's or bigger.

Once you up the fuel injectors a little, you should be able to crank it up to 40psi. Keep in mind that I have said this with no idea what the engine has been built for. If your builder understood that you would be leaning on the engine a lot to make some big numbers and the bearing clearences are setup accordingly then you should be fine.

You will pickup a little more dynamic compression and off boost drivability by advancing your intake cam a few degrees, but this should be done with great care and only after consulting your engine builder. Lest you end up bending valves. Short of swapping out the pistons for flat tops or domed pistons you won't pickup more off boost drivability any other way.

This engine will not tune even remotely like a normal RB. It will tolerate considerably more ignition while under load/boost than an 8.5:1 cr engine. So much so that if you run values that would work in an 8.5:1 engine your combustion temps will be elevated and will induce knocking early. (making the tuner put in a soft tune) At 20lb boost this engine will still have at least 24-25 degrees of advance at peak torque(6000-6500 rpm or so). That would kill most RB's instantly, but not yours.

Making this motor work will be all in the tune.

[Gerg_R31]

well i was more thinking the common thing that we see at work (which is chrome molly rings not sealing due to wrong bore finish)

but yeah i agree with everything GTRNUR said

[Joe_89]

Ok so i spoke to mark from godzilla motorsports today. He said that even if the cams were out it wouldnt affect that much power.

He also said the low compresion isn't a problem just means i have to double the boost to make the same power as other motors on 20psi

But he did say to f****** the microtech off cause they really dont work well at all and timing is always out or to much. (mine is set to 50 deg)

And he also said a smaller turbo to max out around 600hp and 1000cc injectors and then it will be mental. Said making 500hp on a smaller

turbo will fell like a 1000hp compared to 500hp with the turbo im using now.

Well if you go down the road of a different ECU, go and see Mark about a Vipec, I have one and they are fantastic.

He also uses one in his R32 drag car currently running 7 second passes

[NYTSKY]

My mates RB25/30 has a comp of 9.5:1 and with the same turbo makes 750hp at the wheels on E85

[Harey]

Great post GTRNUR! Wow compression ratio of 6.5 thats crazy!

Who designed this engine? I personally would want the person building the engine ideally to be tuning it or at least in contact so the tuner knows how it should be tuned.

This is far from a standard engine build and not the sort of thing you should just be booking in for a tune (with someone who doesnt know the engine) and dropping it down.

It must drive like a pig off boost? NYTSKY 9.5 compression is what I would go for too especially with E85 fuel, that car must be mental!

[NYTSKY]

It has a CR of 9.5:1. Engine built for E85 fuel.

[Zorro]

Beside the obvious that the comp ratio is way low, the 38mm gate is far too small for a 1000hp turbo! Then i would also question the reliability of the std rods with that kind of power!

[Harey]

It has a CR of 9.5:1. Engine built for E85 fuel.

Woops yeah the "It must drive like a pig off boost?" was directed to the thread owner and the "NYTSKY 9.5 compression is what I would go for too especially with E85 fuel, that car must be mental!" was directed to you. 9.5 CR would be awesome off boost!

[monty_r33]

Beside the obvious that the comp ratio is way low, the 38mm gate is far too small for a 1000hp turbo! Then i would also question the reliability of the std rods with that kind of power!

So what effect will the gate being to small be. The expensive turbonetics one was shit and i didnt have much cash at the point of time and fould the tail 38mm for a good price and needed it asap

[monty_r33]

Great post GTRNUR! Wow compression ratio of 6.5 thats crazy!

Who designed this engine? I personally would want the person building the engine ideally to be tuning it or at least in contact so the tuner knows how it should be tuned.

This is far from a standard engine build and not the sort of thing you should just be booking in for a tune (with someone who doesnt know the engine) and dropping it down.

It must drive like a pig off boost? NYTSKY 9.5 compression is what I would go for too especially with E85 fuel, that car must be mental!

Marty white from white brothers racing in brisbane buit the motor for the owner befor me withch had a rb25 head on it with mild porting stock cams and cam gears and stock valves. A rip of garret gt45 a ebay manifold and a greddy rip off plenum and f**k knows what the injectors were. but it went realy realy f****** hard. It would come on boost in 3rd at 120km and peel smoke off the tires that are 22in rims on the rear. That was rolling in 3rd at 80km and holding it flat waiting for boost to come on at at 120 km. So thats when i thought i wonder what it will do with a 26head big cams a 6boost manifold and a good turbo. ( turbonetics gtk1000) Its was worse then the ebay special. This was 2 yrs ago and i was only just starting to lean all about this stuff. I didnt even think twice about changing the pistons when i saw there were still freash hone marks and the way it performed with the 25 head.

[monty_r33]

How about some maths.

RB30ET pistons have a 10cc dish. Assuming a 87mm bore, standard stroke, standard head gasket and zero deck height on the block, the HIGHEST your compression ratio will be is 7.37:1. That is assuming your head's combustion chamber hasn't been re-worked.

Now factor in the head work. Considering its a RACE PORT head, which doesnt really elaborate on what has been done, the head CC's are really an unknown. But for calculation sake, lets assume that one of the quench pads has been machined out, then the head CC will be near on 68cc. This puts the compression ratio down to 6.93:1.

But wait, it gets worse. Those camshafts with their combined overlap and duration will lower your dynamic compression to at least 6.5:1.

What all this means is, your cylinder pressures are all pretty much spot on for how the engine is setup. Compression ratios directly effect the cranking compression of the compression test.

With standard cams a 3lt motor: (also depending on how they are dialed in)

8.0:1 will net about 115-120 psi

8.3:1 will be about 140-145 psi

8.5:1 will be around 150-160 psi

Compression ratio is your main issue.

Your options?

Well you if you aren't disapointed with the off-boost drivability of the car, there really is nothing stopping you from really cranking some serious boost into the engine. Around 30psi at least would be where I'd start the re-tune at. With this level of boost you should be seeing at least 625-650hp at the tyres. You will have to watch the fuel closely though as the injectors will me maxed if your reving 7500-8000. It could really do with a set of ID1000's or bigger.

Once you up the fuel injectors a little, you should be able to crank it up to 40psi. Keep in mind that I have said this with no idea what the engine has been built for. If your builder understood that you would be leaning on the engine a lot to make some big numbers and the bearing clearences are setup accordingly then you should be fine.

You will pickup a little more dynamic compression and off boost drivability by advancing your intake cam a few degrees, but this should be done with great care and only after consulting your engine builder. Lest you end up bending valves. Short of swapping out the pistons for flat tops or domed pistons you won't pickup more off boost drivability any other way.

This engine will not tune even remotely like a normal RB. It will tolerate considerably more ignition while under load/boost than an 8.5:1 cr engine. So much so that if you run values that would work in an 8.5:1 engine your combustion temps will be elevated and will induce knocking early. (making the tuner put in a soft tune) At 20lb boost this engine will still have at least 24-25 degrees of advance at peak torque(6000-6500 rpm or so). That would kill most RB's instantly, but not yours.

Making this motor work will be all in the tune.

Hey thanks GTRNUR so much for sharing your knowledge and experiance. As far as the head goes i got it from spool and paid top dollar for it and was told it was a full race prep head with over sized valves and hks 272cams. it has been poted that i can see easily. But a few weeks ago when i had the head off i thought i would have a close look at the valves and to my suprise they have the nissan logo on them. To me that mean there standard valves and i guess the chanber hasnt been touched. Do you tune. If so how much would it cost for you to come tune this thing. I have access to a awd dino. Also would the microtech be holding this motor back from full abillity.

[GTRNUR]

In my opinion getting a good result that will last more than 5 minutes after you drive it off the dyno is going to take a little more than just a tune. There are too many unknowns.

I only just noticed the stock rods that were spotted by someone else. That alone raises questions over the quality of the rest of the build. The engine is going to need to rev to 8000 with 35-40lb boost get the most out of it, yet only some of what is needed to make it reliable at that speed is there. And especially there is a question mark over what the clearences the engine is setup with too. Clearences will determine if it spins a rod bearing 5 minutes after the dyno tune.

The small wastegate will present run-away boost control issues when the boost is cranked up. It will potentially climb out of control as it won't be able to flow enough exhaust gas despite being wide open. This will only present as an issue once the boost is really cranked up. It should have something around the 45mm size minimum, with at least 25psi of springs in it so it can have a hope of holding boost pressures once your boost controller starts regulating the valve.

Regarding the head and the combustion chamber. This is a standard combustion chamber:

This is has had both pads removed:

Less pads = more head cc's and less compression.

The Microtech isn't technically holding back the capability of the engine, but it does limit which SKILLED tunners will be willing to tune the car.

My recommendation is to have the engine pulled down and re-assembled by someone that can set it all up the way it should be. That same person will be responsible for tuning the engine (or at least be able to communicate well with the tuner). The tuner will be the one that will determine what ECU you should be working with as well. Link or Vipec would be the most common and no doubt the best way to go for the big power setup you are after.

You are going to have to take your time and be patient with sorting this out as well, or it will cost a packet load more money. If you come up short trying to find a builder that you can trust, I would recommend contacting Paul at Red R racing and send the engine to him to have it rebuilt. He could do the forensic strip down and reassembly of the motor and set it up specifically to make the power you are after reliably. Once that is done you could have confidence that it isnt going to turn into an expensive bomb when you least expect it.

As it is at the moment, anyone that tunes it can only tune it to be safe. Least they begin to lean on it hard and something might fail, and then the have to face the expensive repair bill potentially caused by the builder.

[Gerg_R31]

what 25 head was it? 32/33 or neo?

if you can get the long motor to my shop in western sydney ill be happy to strip it down in my spare time and report everything no charge

[monty_r33]

]here are on of the performance shops that screwed me. The car had a minor runnig problem. They were told to find the problem call me and then fix it. Instead they done what they wanted and gave the car back making less power and running worse. they refused to test drive it and said there was no problem with it on the dyno. I found the problem my self it turned out to be the intank pump cutting in and out of power with filled the surge tank enough for a ramp on the dyno but not enough for on the street. So a $60 intank pump was the problem all along and this is what they done.

[Harey]

Marty white from white brothers racing in brisbane buit the motor for the owner befor me withch had a rb25 head on it with mild porting stock cams and cam gears and stock valves. A rip of garret gt45 a ebay manifold and a greddy rip off plenum and f**k knows what the injectors were. but it went realy realy f****** hard. It would come on boost in 3rd at 120km and peel smoke off the tires that are 22in rims on the rear. That was rolling in 3rd at 80km and holding it flat waiting for boost to come on at at 120 km. So thats when i thought i wonder what it will do with a 26head big cams a 6boost manifold and a good turbo. ( turbonetics gtk1000) Its was worse then the ebay special. This was 2 yrs ago and i was only just starting to lean all about this stuff. I didnt even think twice about changing the pistons when i saw there were still freash hone marks and the way it performed with the 25 head.

Do you know what boost it was running before with the rb25 head? I guarantee a crapload more than 18psi.

[monty_r33]

I think it was 21psi making 450. It used to be awesome

[monty_r33]

what 25 head was it? 32/33 or neo?

if you can get the long motor to my shop in western sydney ill be happy to strip it down in my spare time and report everything no charge

I didn't know 32 had rb25 heads. Thought they rb20. I guess since it was a r33 and the old owner build the car from scratch it would of been the original head

[TiTAN]

Woops yeah the "It must drive like a pig off boost?" was directed to the thread owner and the "NYTSKY 9.5 compression is what I would go for too especially with E85 fuel, that car must be mental!" was directed to you. 9.5 CR would be awesome off boost!

my car runs 9.3:1 and is on 98, if its dedicated E85 10:1-11:1 shouldnt be an issue. the engine would be a monster off boost and all that compression is going to bring even a big turbo on earlier.

[Super Drager]

Yeah quite a few supra's in the US doing 24-25psi of boost with 10:1 comp on E85.

[045HOW]

Was reading through this thread like "what the hell is going on, why has no one picked up the most probable possibility in this story??????????" and then GTRNUR brang the ruckus.

Low Compressions is Low lol.

I didn't know 32 had rb25 heads. Thought they rb20. I guess since it was a r33 and the old owner build the car from scratch it would of been the original head

There were late model R32 GTS25. Running a non-VCT N/A RB25DE.