Few quick questions guys, as I am planning this conversion soon 1. I will be retaining my current RB30 NA bottom end (8.3:1), with Hiflo'd VLT T3/4, decent cooler....what rwHP realistically acheivable...i'm doing 280rwHP atm with Turbo'd NA RB30. 2. What cams do people use with the head....the standard NA items? 3. Injectors....RB25DET's?.....& what rwHP would they max at? 4. Will my VLT bolt straight up to the RB25DET Manifold? 5. Or, If there is a thread on this already do you have a link Cheers Lindsay Some original photos have not been recovered yet.

If fitting the RB25 head to a RB30 block can you still run the power steering without any fouling problems?

Hey TwinVL, can you do that calc for an RB25 head on an RB30 with standard RB30ET pistons. I have read it is about 7.3:1.

Hey, Yeah can do no probs! If you work it out from the standard comp ratios of 9.0:1 and 7.8:1 and use all the same figures it can be done. 0.97cc n/a piston + 5.94cc headgasket + 55cc sohc head = 61.91cc 493.7cc piston displacement + 61.91cc total @tdc = 555.61cc @ bdc 555.61cc / 61.91cc = 8.97 8.97:1 comp ratio for na So if i make the ratio = 7.8 and the piston volume = PV, i can work it out. 493.7+PV / PV = 7.8 493.7+PV = 7.8PV 493.7 = 7.8PV - PV 493.7 = 6.8PV PV = 72.6cc piston dish = 72.6cc - 5.94cc head gasket - 55cc head = 11.66cc piston dish So no if i add up the piston volume 11.66cc with the head gasket 5.94cc and the twincam head of 63cc = 80.6cc volume @tdc And again add displacement of 493.7cc and tdc vol of 80.6cc = 574.3cc voulme @bdc Comp ratio is 574.3 / 80.6 = 7.13 7.13:1 comp ratio, RB30ET pistons with RB25DE head! I think thats too low, it would be ok if u wanted to pump in about 2bar of boost but then the standard pistons wouldn't cope with that for to long.... Cheers.

hey people, sorry to ressurect a bit of an old thread, BI5HOP, higher compression is a much better thing that high boost. a high compression engine will probably (in most cases) make more power than a low compression engine with high boost. kinda puzzles me why people go for low compression pistons like 7:1 and such, makes the car a pig off boost, and will make your support systems work much harder(intercooler etc., because you using higher boost to make the same power) maybe they are still used to old engines with poor head clamping and poor cylinder sealing... you shouldn't have any of those probs with the RB's, so long as you use good fuel. compression is your friend, boost is not. the reason why the stocker has low compression,. no intercooler, poor fuel, simple as that. am into racing nitro r/c cars,, 20:1+ CR, 35000 rpm... -jimmy Some original photos have not been recovered yet.

An r/c cars engine is slightly different to a car engine... Generly 2 stroke and compression ignition arn't they, or do they have 4 strokes and spark plugs these days?? But yeah your right, higher comp is better simply from a drivability POV, but low comp has it's advantage. u can make alot more power out of a low comp engine for the simple fact u can put ALOT more boost into it. And it's more to do with better combustion chamber design as to why the comp ratio is going up and up with newer engines.

yeh, true about the better chamber design. but i still disagree about more boost is better, depends on your compressor efficiency though. higher boost doesnt always net you bigger power, and it lessens reliability. RB's dont have a prob at all handling high cylinder pressures, the low compression thinking stems from the old days when engines had crap head clamping and cylinder sealing. btw, rc cars are four strokes nowdays, still use glow plugs though. -jimmy

So to get a high compression of 9:1CR you would need dome pistons instead of dish pistons. With a negative displacement of 7cc each... Wouldn't it be easier to shave the block? And what is the volume when using n/a RB25 pistons?

Didn't bother to read the whole thread so I appoligize if this was mentioned before but ACL is about the make low price forgies for the VL turbo, thought you guys might be interested.

Just CC'd my motor. Using stock, original bottom end form an NA and a VVT RB25 head, it came out to 8.8:1. Bummer. Now I have to buy forgies. Be careful what you do with your motors, cause I believed what everyone else said and the comp. ratio was too high for a turbo motor. It just won't have enough timing in it to be a decent motor.

Hey luke, what figures did u get when u CC'd it??? I did the same and got 8.06:1 not 8.8?

hi there i have a friend who works at sps pistons and there are a few ppl on this site which are personal friends who use them. one which ran a 10.5 at 125 mph last weekend at calder. HSVSUX: i beleive your engine builder didnt tell sps exactly what he required obviously as your the only person i have seen with bad reports about them. oh and for wanting to throw them in the bin, thats silly ill have em Some original photos have not been recovered yet.

Cylinder head with spark plug - 61cc 1cc dome on the NA pistons I got around 8.5 with this method, but when I torqued the head down and cc'd it as a unit, it came out to 8.8:1.

My final figure is 8.48:1. Sorry about the confusion. Thats with an Rb25 head (VVT if it makes any difference), nissan gasket and NA psitons.

RB30 pistons I guess?

yes mate, na RB30 stockers

in the skylines australia forums several ppl have done the conversion using the rb25de head and rb25det head. there has been alot of discussion into the finer details in the thread. http://www.skylinesaustralia.com/for...ad.php?t=15420 (http://www.skylinesaustralia.com/forums/showthread.php?t=15420)

is the rb20 head the same as rb25. 'cause you can pick up 20's cheap as.

No they are very different, rb20's have smaller bores.

and bore is about 10mm smaller. back to the rb25.....