R33 Rb30 Conversion

[Cubes]

Hi Joel (thanks for quoting me on which head to use in which chassis) and BobJones, I have used a RB30 bottom end with a RB25DE top end. The first one I ever buiit, it is still going 5 years later and making 500 bhp. So leave riceline alone, if you are doing it on a budget and want to sell a complete RB25DET, it's a perfectly acceptable solution.

Quoting u?!?!

I wasn't aware that was the idea behind riceline using the RB25DE head.

By the time you sold the RB25DET then bought the RB25DE head changed ecu, wiring etc is it really worth it to save maybe $500?!?

[Sydneykid]

Hi Joel, why would riceline have to change the wiring and ecu? So it doesn't have VVT, and there is a spare plug, that's not really a problem. The diff for me was over $1K, plus with the RB25DE you can use cheaper (top feed) injectors, another $500 saved.

I found the N/A cams worked very well with the 3 litre engine. I can't say that there were better than RB25DET cams would have been, because I didn't do a back to back. But they were certainly very effective. Plus I could use adj pulleys on both cams on the standard N/A cams. Best of all I knew that if I wanted to upgrade the cams later on, I could stick a set of standard GTR cams straight in and not have to worry about the VVT. If I wanted to go the next step, I could buy a pair of used HKS/Jun/Apexi/Toda upgraded GTR cams for 1/3 what new VVT cams would cost.

All up, I reckon I saved $2.5K by using the RB25DE top end and that paid for a nice new 550 bhp Garrett turbo.

But as I said it's not for everyone, you have to have your targets (power and use) well in mind before you go down that road.

Hope that clarifies.

Hi Joel, what compression ratio did you end up with? The domed piston and 62.2 cc combustion chambers would give over 9 to 1. Or did you use a thick head gasket?

PS; How many tooth cam belt?

[Cubes]

Apparently 8.5:1. I hope he did the math correct.

He was talking to Wiesco quite a bit, this is the combo they came up with after doing a dummy setup to get all the measurements required.

Apparently with the origional Wiesco non domed RB30DET piston the comp ratio was around 7.8:1.

I'll have to get the exact specs of the headgasket thickness etc when I pick the motor up. He's got everything written down.

Here's the part no on the box. I don't really understand it as of yet hence the compression height.

Note I said Apparently quite a bit.

I did say to him origionally I would prefer a 9:1 comp ratio.

If I ran in to problems, I would throw a thicker head gasket in there.

He didn't really want to go for a high comp ratio recommending 8-8.5:1.

Some thing to do with the fuel, how much boost you run and it making max power when everything is matched up.

Gary,

152 Teeth.

Dayco 94407.

I've fiddled with the comp. calc and tried to slap in some figures from what I have (also from the wiesco pdf)

Here's a couple of pics of workings plus the Wiesco RB25/30 & 26 Piston specs.

Problem is I have no Idea if I have the right values in the

Piston Down from TDC & Volume above piston.

I fiddled with the Volume above piston until the CR came up to around 8.5:1.

[Sydneykid]

Hi Joel, a few things interest me;

1. RB30 rods are 6" (152.5 mm), why do they quote 6.1"?

2. The head capacity, at 66.5 cc's, is way over what I have ever seen, 64 cc's is about the biggest.

3. Volume down from TDC means that the piston is not going to the top of the bore at TDC. This is achieved by machining the gudgeon pin in the piston to a point higher than it is in a standard piston (which does go to the top of the bore at TDC).

This means there is a portion of the bore (above the piston at TDC) which forms part of the combustion chamber. If you want to increase the compression ratio you simply machine the top of the block and reduce that volume above the piston. This is pretty standard practise when the piston maker only wants to have one piston capable of many different compression ratios. Saves them making a range of part numbers, when one will do.

We use a flat top piston that goes all the way to the top of the bore at TDC. It has a limited range of compression ratios (disadvantage) but does not expose the bore to combustion (advantage). I also suspect that the squish is better with the flat top design, as there is no gap between the top of the piston and the squish ramps in the head.

It is good to see someone else’s approach, thanks for posting it.

[Cubes]

Gary,

Andrew mentioned he had to take off 20thou from the block to get the comp. ratio I was after.

Something else to take in to account..

Peter,

You will have to get some one who knows what they are doing to know exactly what compression you will get by using certian pistons. In other words, don't believe what the piston manufactures tell u.

I don't understand why a set of pistons in a RB25DET will get say 9:1CR then in a RB30 the same pistons get a lower compression.

[GiJOr33]

You have to take into account the stroke of the engine. The 3.0lt sucks in more air/fuel so when the piston comes up into the combustion chamber with the RB25 head on it there is more air/fuel being squeezed into the same space as before so you get a higher compression ratio. I think that's how it works but am not 100% sure. You also need to take into account the size of the combustion chamber too, cos if it gets bigger by putting the RB25 head on the RB30 then the compression ratio drops so you'll need pistons that have a dome in them to take up some of the space and bring the size of the combustion chamber down and the compression ratio up.

[Sydneykid]

Gary,

 

Andrew mentioned he had to take off 20thou from the block to get the comp. ratio I was after.

 

Something else to take in to account..

Thanks, Joel, that's what I tought he would have to do. Otherwise you would end up with around 7 to1 based on those numbers.

GiJOr33 is right, more volume (3 litres / 6) sqeezed into the same space at (2.5 litres / 6). So if you used RB25DET pistons with an RB30 block crank and rods and a RB25DET cylinder head you would get a higher compression ratio. Well, as long as the block was machined so the piston came ot the same deck height as it did in the RB25DET.

Hope that helps

[RB20LagWagon]

Hey guys will r32 rb20det intake manifold bolt up to rb25det r33 head? or will they only bolt up to r32 rb25de head?

I have the rb25det manifolds but i want to use my topfeed injectors etc.

[riceline]

Rb20LagWagon

I know that the r32 rb25DE manifolds will not bolt onto the R33 RB25DET head

and the R33 DET manifolds (intake) will not bolt onto the R32 RB25DE head

Hope that helps you sus it out a little

BTW found a shop to send my car to - Goes in there in as soon as they call me....

Hopefully will have a car back soon

Take it easy guys.

[GiJOr33]

Does the RB25DE fuel rail use the same injector style as the GTR (i think it's top feed)?

I know the RB25DET uses different injectors to the GTR, but i'll be using the RB25DE fuel rail and inlet manifold. It would be good if i could chuck in some GTR injectors or at least the same style (as they are cheaper).

[Jaws]

Whoa!!! after reading all 42 pages my eyes are burning! :nowigetit

You guys can add another rb30/25 conversion to the list.

But this ones going into a VB commie( it's the VH lookalike in my avator), something different for a change.

Well what I have so far is a R33 GTST 2.5 top end and loom, the head has had a full machine with new springs,valves, porting and polishing.

Aiming for 300rwkw, mind you the Vb weighs around the same as a 32.

Will be purchasing a brand spanker GT30/40.

I am stiil to decide on motec or autronic (dont want an afm but still retain closed loop).

I am capable of doing everything myself except the bottom end, I live on the gold coast. Can anyone recommend an engine builder in the area that has experience with this kind of engine?.

The injectors and fuel pump will no doubt need upgrading, also would the pressure regulator need to be changed?.

I'm also using a standard VS tank and intank fuel pump, is there a suitable intank pump for this application?,also what injectors would suit?.

I've priced a set from Rocket and they come in at $1147 with floating pins and rings. These are an Aries piston for the 3lt with the 2.5lt head bringing the compression ratio to about 9:1

Do you have the part no/kit no. so it can be posted up here for future reference?.

No doubt i'll be needing that kind of info soon.

Sydkid:

As soon as you said oil spuirters arnt needed, ceramic coated pistons came to mind. later on you mentioned this which backed up my thoughts.

Do you have a idea $ on how much it would cost to get 6 forged pistons done?.

You also mention the use of a JUN adaptor with the r33 oil pump.

Where did u get this from, how much?, and any part numbers u have would be greatly appreciated.

Still waiting for all the info to sink in.

Thanks in advance. :wavey:

PS: I've just got hold of the r33 factory manual which i'll scan onto pdf and will put on the net for everyone to download. :kick:

[Cubes]

For every 2cc's less in the head you have roughly .2 of a CR less.

I said it before but I'll make it clearer.

My head CC'd up at 62.2cc's, it didn't appear to have been skimmed previously, the head was dead straight and didn't require a skim.

I used 87mm RB25 Dome K578M87 pistons

20thou was skimmed off the block to get a 8.2-8.3:1cr.

Which works out roughly right when you consider the RB30E pistons are also domed and with the RB25de head also gets around the 8.2-8.3:1 cr.

The RB25 piston dome is not as big as the RB30E piston hence why 20thou was most probably ripped off the block.

When the motor is run in I'll do a comp check and find out the exact comp ratio.

I have this problem where i tend to take alot of things with a pinch of salt when I am told. Guess it comes from so many bad experiences with mechanics.

Should be able to run some nice boost with the CR.

Not sure if it is worth going a slightly smaller turbo for quicker response and just pump more boost in to make the same/similiar power?!?!

I'm aware of a 2835 that has made around 280rwkw on ~1.3bar so with a little more boost maybe 1.6 it should make 300rwkw no problems.

I'm also aware of a 3037 that has made roughly 300rwkw on ~1.3bar.

The motor has been setup (clearances piston to bore) to run over 24psi.

[the phantom]

Hey Joel,

What piston clearance are you running? How are you going to measure compression ratio with a pressure guage...just curious! I haven't got the RB30 manual in front of me, but from memory the recommended decking is 20 thou max. Do people abide by this or are deeper deck cuts possible reliably?

[Cubes]

I can't remember what clearance the piston to bore is.. I know it is what wiesco recommend for over 24psi or race.

I asked andrew if the thing will need a rehone after so many thousands of kays due to the slightly bigger clearance. he said no, it all comes down to how you warm the car up in the mornings and how well it is run in.

I measure the compression ratio with a pressure guage by working out the psi to a cr. hence say for example if the stock RB20t compression is 8.5:1 and it gets 140psi then i do the math which isn't much. Gives me a decent idea. Appears to be pretty standard over every engine with psi to cr.

[Sydneykid]

Hi Jaws, I think the guys answered your questions. I have one though, why don't you want to run an AFM?

[Jaws]

Hi Jaws, I think the guys answered your questions.  I have one though, why don't you want to run an AFM?

After reading all 42 pages i can't recall anyone talking about the right injectors,fuel pump (intank) and pressure regulator for 300rwkw with a RB25det GTST top end.

No one has mentioned the cost of getting pistons ceramic coated nor an experienced engine builder in se qld.

AFM's restrict airflow, I don't have one atm - will be using an aftermarket comp.

Plus it would only add to the list of parts i need which already aint guna be cheap.

Then again the AFM gives more accurate readings so I may have to include it.

hrmmmm :blah:

With so many more engine choices than a skyline, the costs involved in this hybrid engine make a "400kw" 383 stroker look much more attractive.

Even tho I will probably go with forged pistons, hyperneutectic's(spelling) are looking good (they would be ceramic coated of coz) as ppl are achieving near 250rwkw's with cast pistons.

What's your thoughts on this?.

PS: just trying to cover every possible option.

[Sydneykid]

Hi Jaws, AFM restricting airflow on RB's is simply not true. All you have to do is have one (or two) the right size. I use my standard example, Apexi V Max makes 1,100 PS with AFMs and a Power FC. If you are really going to build a 300 rwkw RB then the cost of a Q45 AFM will go almost unnoticed.

Injectors are worked out by the formula, I think its on page 12. On a 6 cylinder injector cc = bhp. So if you want 300 rwkw (480 bhp) then 500 cc injectors or bigger are the go.

Fuel pumps are on page 10'ish, we use Bosch 044 in tank for up to 650 bhp. There is a table of Bosch sizes, pick the one for 500 bhp if the 044 is overkill.

With 480 bhp, 500 cc injectors and an 044 there is no need for anything other than the standard fuel pressure regulator. If you need to get a little more out of the injectors then a Nismo FPR is the go, fits on the standard rail. Nengun sell them for around $180.

Prices of ceramic coating pistons varies a lot depending on what else your are doing at the time, about $20 per piston is a good budget. Give you local guy a call.

I have only one thing to say about the 383 idea, pushrods belong in suspension not engines. In light of yours, I might have to change my sign off, how about ....

"Commondoors, like haemorrhoids, once you get rid of them you never want them back"

Perhaps some of the other guys might have a couple they want to share............

[Jaws]

Q45 afm it is then.

Thanks alot for clearing that up sydkid.

Perhaps some of the other guys might have a couple they want to share............

LoL, lets hear em.

[Cubes]

Jaws,

Really depends what you want out of the car?

A juice sucking 383 rumbling V8 or a fuel efficient RB30DET that packs around 650-700nm of torque around 3500-4000rpm (depending on turbo) then continues to rev on to 6000-7000rpm.

Can't beat the sound of the V8 but you also can't beat the fuel efficiency & torque the RB punches in the mid range.

SK,

Not going in to a RB vs V8 debate but which would make more torque earlier in the rev range? The V8 or the RB? Or should I say which would accelerate the car quicker in the mid range with similiar peak power? Just for curiosity's sake as I once saw a XR6t dyno compared to a LS1 dyno making the same rwkw figure. The XR6t actually had more torque in the mid range then towards the top end the V8 made a little more.

[Sydneykid]

SK,

 

Not going in to a RB vs V8 debate but which would make more torque earlier in the rev range? The V8 or the RB? Or should I say which would accelerate the car quicker in the mid range with similiar peak power? Just for curiosity's sake as I once saw a XR6t dyno compared to a LS1 dyno making the same rwkw figure. The XR6t actually had more torque in the mid range then towards the top end the V8 made a little more.

Hi Joel, totally depends on how you tune the RB and what size turbo/s you put on it. I saw an RB28, with a single T03 turbo on it, that made boost at high idle. Didn't make much power over 4,500 rpm but it sure had some torque at 2,000 rpm, where it made over 1.3 bar. Compare that to one of our Chevy big blocks that makes 900 bhp at 7,250 rpm, makes bugger all torque at 2,000 rpm. If fact it barely idles properly at 2,000 rpm, the cams, valves and ports are so big to enable it to make 900 bhp on carbies.

Ridiculously extreme examples of course, but it shows the advantage of a turbo engine, you can set it up to have power anywhere you want. The N/A engine is a bit more limited in the choices.

Hope that makes sense.