Which Rb Engine Combo?

[The Ant]

Hi

I'm looking at building a performance RB motor out of the bits and engines that I already own.

Here is the list;

RB30 engine (non turbo) complete

RB25DET complete (worn rings)

RB26DET rods and pistons (only)

Do I start with my RB25DET engine and work it or the RB30 and work it and say put the RB25DET head on it? Surely I dont have to use the RB25DET head on the RB30 to get 300plus rwkw? I know the RB26DET rods and pistons fit into the RB25DET but do they also fit into the RB30 crank and block as they are all the same bore size? Im not wanting to spend to much money but prepared to spend some money of course for extra performance bits. I'm wanting to get as much hp as possible and still use pump fuel and have boost under 20 psi.

Any other suggestions?

The engine will be going into a 1970 fibreglass car that has no loom for these motors so I may consider a carburrettor version of the above or obtain the appropriate loom/computer.

Edited May 4, 2008 by The Ant

[Adriano]

Your options really are: 25 head, 30 block N/A, big cams, may make engineering easier, due to the weight of the car.

25 head, 30 block turbo, forged pistons.Will make heaps of torque, great way IMO to make 300rwkw

25 motor compete, with 26 rods, and forged pistons, will need more revs than option #2 to make the 300rwkw

Edited May 4, 2008 by Adriano

[tm_r33]

yer cant argue with adriano.

the gtr rods and pistons will be a good way to strengthen the standard rb25 but u will need a few mods and good reving to make 300rwkw

the 25 head on the 30 bottom end with a decent turbo (doesnt have to be huge) and supporting mods will see u easily making 300rwkw.

the 3 litre bottom end will spool a turbo quicker (more exhaust gas) and will have a bit more torque

[The Ant]

OK thanks for the input. I must be able though to get 300rwkw from a turboed RB30 and standard head with out having to put the RB25 Turbo head on?

Also does the RB26 GTR rods and pistons fit into the RB30 and and crank?

Edited May 4, 2008 by The Ant

[Sydneykid]

OK thanks for the input. I must be able though to get 300rwkw from a turboed RB30 and standard head with out having to put the RB25 Turbo head on?

Also does the RB26 GTR rods and pistons fit into the RB30 and and crank?

Pistons yes, rods no, they are too short.

Cheers

gary

[tm_r33]

you could keep the single cam head but i wouldnt bother. chuck the 25 twin cam head on mate.

yup pistons will fit but gtr rods are a lot shorter. the rb30 gets its extra capacity from a longer stroke.

[The Ant]

If I did keep the RB30 head on it what rwkw would I expect? If the RB30 was completely standard, I dont care how much boost I run through it and blow it cause they are so cheap to buy.

[tm_r33]

well its an NA rb30 so its high compression. chuck a turbo on it and they are pretty nuts lol. they just dont last long.

[Adriano]

How long is a piece of string? LOL what ecu and bolt on's

[DECIM8]

Out of interest how much would this conversion cost on a Neo head? Id most likely get forged internals keep the standard rb30 rods forged pistons and so on and want 350rwkw. Is this conversion a direct bolt on? Ive heard head studs are different or somthing for a rb30 vrs 25?

Have not looked deeply into the matter just interested.

Im looking into my other toy... either a rx2 rx3 and rx7 series 6-8 Im leaning towards the rx7 for reliablity and the rx2 and rx3 for value appreciation.

What would you guys say do, rb3o bottom or new car? keeping the line too.

[tm_r33]

well its completely up 2 u mate. many people get 350kw out of 25/30 motors. do u want to build up a motor from scratch or do u want to buy another car. im building a 25/30 as we speak so thats what i chose but if u dont have the knowledge and resources building a motor will become very expensive

[infamous_t]

Sorry to go a little of topic, but what CR would using rb26 pistons result in?

I realize the standard rb30e pistons give around 8.5:1, but does the 26 give higher/lower CR, or is it purely that they are stronger?

[The Ant]

Ok...After doing some research, I hear that if you put the turbo RB25 head on the RB30 block it becomes very unreliable because of the modification of the oil hose connected from the block to the head can leak or malfunction. If this is the case and my source seems reliable, Im going to go for a complete RB30 engine with either lower comp pistons or RB30 turbo head. Either head will be ported with big exhaust cam lift.

Any comments?

[Adriano]

Ok...After doing some research, I hear that if you put the turbo RB25 head on the RB30 block it becomes very unreliable because of the modification of the oil hose connected from the block to the head can leak or malfunction. If this is the case and my source seems reliable, Im going to go for a complete RB30 engine with either lower comp pistons or RB30 turbo head. Either head will be ported with big exhaust cam lift.

Any comments?

Never heard of the external oil feed failing, anless it was done incorrectly, should be more reliable than the plumbing for an oil cooler, and you dont hear of them failing. An rb30 turbo head is the same as an rb30 head

[gtst25]

Mate,

Have you had a good read in this section?:

http://www.skylinesaustralia.com/forums/RB...sions-f184.html

There's tons on info here on building a bullet proof rb30.

Having driven high 200kw rb25's I'd go for a rb30 any day. You want as much torque as you can get. So use the rb30 block and rb25 head... Guys have made well over 300rwkw with stock rb30 bottom ends - have a look here there's a few fellas making high 300's at the tyres:

http://www.skylinesaustralia.com/forums/Rb...yn-t104332.html

I'd rebuild the engine properly though - it's up to you really. Maybe pull the rb30 down and measure it up - if it's ok chuck rings and bearings in and it'll probably last for ages.

Cheers

Cheers

[nizmonut]

i think i posted this somewhere else, but just for the record.

i used the r33 rb25de head with the vvt.

i had the engine rebuilder weld up the oil gallery on the front right hand corner of the head(looking at it as if it were in the car(drivers side)).

this is because it overlaps with the rb30 blocks front right water jacket outlet.

once this was done we took the intake cam pulley off and you can see the oil gallery running up to the horizontal gallery that feeds the hydraulic lifters.

drill a 11 ml hole and tap it with a .75 ml thread gap and fit a brass 1/4 inch fitting into it on a 80 degree angle from front(almost facing sideways)

this will allow you to refit the cam cover's with clearance for hose and hose clamp.

secondly get a brass T fitting to and screw it into the block where the oil pressure sender unit is.

fit the sender unit back to one end and run a 1/4 high pressure piece of fuel line from the T piece up to the fitting on the head.

this worked for me and never had any issues with it.

ive heard of people replacing the solenoid valve on the side of the head and doing via there aswell but this elemenates the ecu control and the hydraulic lifters are driven purely on oil pressure.

doing it this way the rb30 tended to stall some times or idle rough when you cam back down to idle.

this is due to the lifters still being open a little longer,

keeping the solenoid will allow the ecu to control the oil flow like it normally would if it were a R33 rb25 block.

Rb30 25de head, garret 35/40

[The Ant]

Ok...why cant I just use a standard rb30 head (maybe port the head a little) on my rb30 block? What benefit am I really going to get putting my rb25 vvt turbo head on to the rb30 block with all the head ache and modifications needed to do so?

Surely the rb30 head with some work done to it can do the job as well or better? The rb25 vvt turbo head is probably worth $700-800 at then I still have to change 2 cams in it costing probably $1500 plus in total. I only have to buy 1 cam for the rb30 head?

So...the rb26 turbo pistons fit on to the rb30 rods and can then be used into the rb30 block. What compression ratio will this give me using the rb30 head?

Edited May 11, 2008 by The Ant

[Simon-S14]

sure you cna use a shitty SOHC 30 year old design head... it will do the job, but the DOHC head will do the same job, but BETTER and more efficiently

[kessian]

Ok...why cant I just use a standard rb30 head (maybe port the head a little) on my rb30 block? What benefit am I really going to get putting my rb25 vvt turbo head on to the rb30 block with all the head ache and modifications needed to do so?

Surely the rb30 head with some work done to it can do the job as well or better? The rb25 vvt turbo head is probably worth $700-800 at then I still have to change 2 cams in it costing probably $1500 plus in total. I only have to buy 1 cam for the rb30 head?

So...the rb26 turbo pistons fit on to the rb30 rods and can then be used into the rb30 block. What compression ratio will this give me using the rb30 head?

You seem to only want people to confirm for you to use the rb30 head. Do what you want, but at the end of the day, the rb25 head will be better, which is what everyone else is telling you.

[gtst25]

Don't forget the SOHC heads tend to crack. There's not many VL turbo's on the planet that haven't had a cracked head - everyone I knew who had a VL 10 years ago when we use to muck around with them ended up cracking their head. And that was with cooling improvements and taking every measure in making sure they were bled properly. I've got a friend who builds big power sohc vl's - but he always sends the head off to get recoed and welded up in the weak spots before he starts. So there's your 600 or so bucks gone already. Sure you can make the power no worries but it'd be such a pain in the arse if you drove it for a week and ended up with water in the oil. To make 500+ at the tyres he runs a cam and standard head - so nothing special. You won't need cams to make your 300rwkw with the dohc head. Even 350rwkw if you want.

As for putting in the rb26 pistons you'd have to be someone really in the know to get the clearances right. If they measure up ok just use the rb30 pistons if you're doing it on the cheap.