Rb30 cylinder head work

[Diko31]

So i plan on rebuilding the top end of my rb30e out of a 86 r31. I want to a bit more power and economy. Is it possible to achieve that by keeping the cam stock but replace valves and porting the head? I plan on getting the stock head flow tested so i compare the difference. Not sure how i should go about it. I plan on talking to an engine builder, aswell as reading forums and books for knowledge. Yes i am a rookie when it comes to internal work 

 

If im thinking to far ahead, let me know please 

Edited May 30, 2019 by Diko31

[GTSBoy]

You won't improve economy much by doing headwork. Decent valve angle job will help a little. You will make a little more power from porting alone, but porting is an expensive way to make power on its own.

[Diko31]

Yeah i thought that. I plan on upgrading fuel system and what not prior to doing headwork. I was just enquiring so i can start to get my head around what actually goes into getting better performance out of a head. I do plan on keeping stock cam, or possibly going a wee bit bigger if run out on the cam is out of spec. At the moment im just planning though! 

 

I am also not sure if a port is necessary when getting bigger valaves...

[GTSBoy]

There's no such thing as "necessary". Porting + valve sizing + compression choice + cam choice should all be application driven things. How much power do you want? At what RPM are you happy to operate? Fuel choice? Usage model for the car? Unless you go at it from that point of view, you stand a chance of going backwards compared to where you would like to be, and just generally wasting time and money.

I have no objection to a very mild clean up of ports and tidying the bowls and getting the valve seats set up nice. But taking metal out of the ports "just 'coz" is not a good idea.

[Diko31]

Thats why i need to read up alot, because i dont know what would be an ideal choice for valves and what not. It gonna be for road use mainly, but i do plan on attending powercruises and stuff once its ready. Maybe 350hp at 4.5-5k rpm, not sure if thats realisitic or not, but thats what ive got in my mind.

Im taking advice on as i go, so i can understand how i should go about it. i will be constantly referring back to this forum, because i know the point of veiw i have atm isnt a good point to start from 

 

So you're saying if im gonna port the head, its probably best to clean the head up, upgrade seats, valves, guides etc? 

 

[GTSBoy]

350 engine HP from a naturally aspirated 3L? That's a VERY highly strung engine. Big compression, big cam, lots of revs. Lots of revs.

They make less than 140 engine kW, call it 180 engine HP, standard. You're talking about doubling that.

[Diko31]

So not realistic...proof that ive got alot to learn. I dont plan on rushing, so when it happens, doesnt bother me. I do understand that upgrading fuel system, modding intake manifold and rebuilding the top end is only gonna get me so far, but as to how far it gets me, im entirely unsure. I say 350hp because i genuinely thought itd be achievable with out going to big in the top end, but obviously not. What do you think would be optimum power without running a massive cam and what not, or what do you think is acceptable for what i want to achieve, im staying open minded because compared to the info thats out there, i dont know shit...excuse the french ?

 

[Diko31]

Bottom end upgrades are out of question as i dont plan on touching the crank, conrods or pistons until i decide to boost it. I would like to supercharge, but a supercharger is obsolete if the power isnt already there...

 

[GTSBoy]

Note that I said "less than 140 kW". The S2 GTS motor made that much, the S1 made 130, the normal R31 make ~120 and the VL motor made 114 kW. At the engine. Starting from your likely, factory fresh 120 kW, adding 25 years of use, it might make a bit more than 100 kW now. Without freshening up the bottom end, most of that difference is unlikely to come back, even with a standard head rebuild. So, benefit of the doubt call the baseline 110kW if you have a fresh head on the old bottom end.

Now, if instead of the head being just reconditioned, you gave it a mild port job, just cleaning up the bowls, taking care of the guides, port matching to the inlet manifold and polishing up the exhaust side a bit, plus a decent set of extractors, you might give it an extra 25 kW. I would hesitate to suggest that you will get more. To make the most of any such work you would be well advised to put a Nistune board into the ECU and some fresh injectors and AFM so that you can tune it more aggressively. You'd probably make more power just with a tune than with a street port job on its own!

I must reiterate, porting does not equal diving into the ports with a jackhammer and making them as large as possible. You only get the head ported to the extent that it will not hurt performance in the intended operation model. For a streeter, just giving it a tickle is usually as much as you can do. A full race port job with many hours spent digging every last scrap of flow out of it will result in a head with low port velocity when you're driving around at road revs unless you keep it boiling away in the upper half of the rev range all the time, and that gets old VERY QUICKLY.

You need to find a head specialist near you that has experience with RB30s, who will know how much time and effort (and therefore $$) to put into a head. Spoiler alert. Porting takes many hours and costs many dollars. Turbos will return much more power per dollar spent.

[admS15]

Leave everything as is, add vl exhaust manifold, turbo, injectors, ecu and call it a day. Easy way out.

[Diko31]

I want to upgrade/mod everything besides the bottom end. I was planning on buy a nistune ECU aswell as a better fuel system as a whole. The intake was gonna be modded or replaced with a billet intake. I have spoken to otaku garage and they said that you cant run a billet intake with stock ECU, and the upgraded ECU is gonna have to be mapped to run a billet intake while staying NA.

 

Ive been reading engine tuning books, and i do understand that wider ports and bigger valves arent always ideal for road use, hence why i dont want big upgrades. But if i can only achieve a max of say 150kw with what you're mentioning, then so be it, ill be happy with that. 

 

@admS15 what numbers would that produce do you reckon? I would resort with that, but i do want to do somewhat extensive work to my wagon, it may be illogical, but i dont think thats gonna get me what im sort of aiming for, then again, who am i to say anything, i don't know much at the moment 

[Ben C34]

What you plan on doing is far beyond pointless and a waste of money. You will regret it.

[Birds]

Buy RB25 with electrics

Swap in

Live happy

[Diko31]

So just leave it stock and focus on doing my drift pig up?

[Ben C34]

12 minutes ago, Diko31 said:

So just leave it stock and focus on doing my drift pig up?

Yes

[Diko31]

Wouldnt mind getting some NA power though 

Its not like im gonna expecting to get as much power out of it like you would with a turbo. 

I guess if i have to ill upgrade the bottom end so i can get more power out of it while its NA

[Ben C34]

Nitrous.

[Diko31]

Thanks for the help everyone 

[admS15]

A stock vl turbo setup will make around 250 whp when tuned. Around 300hp at engine. Bigger injectors, turbo, more boost will make more + nitrous, dont forget the nos, 2 of the big ones.

[Diko31]

Id love to do that, but i dont really want to hop on the band wagon so soon

Im pretty sure im gonna need new valve springs soon so i might just rebuild the top end then, get slightly bigger valves and possibly cam. Give the head a wash in an acid bath, and if it doesnt cost too much, ill get it ported just a fraction (if machine shop reckons its necessary) and tidy the bowls up. Get nistune installed, new injectors, new fuel rail+pump. Get the intake machined and possibly chuck on vl turbo extractors 

I think thats the best way to go about it.