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RB25DE Head Work = Less Boost Same Power?

Cubes

By Cubes,
in Engines & Forced Induction

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Cubes Grand Master

Cubes

Posted
Posted

I'm getting my RB25DE (Non VCT) Head sent in to be reconditioned as soon as I make my mind up if I should get a little bit of work done to it.

I've been told that the most befinitial work is the first stage of work that is relatively cheap ($300). This cleans up the area around where the valves are to make it flow a bit smoother.

When performing head work it obviously increases the amount of flow and reduces the restriction.

SO.. would it be correct to assume that you could make as much power with slightly less boost as boost is a restriction to the flow of air?!?!?

Sydneykid Grand Master

Sydneykid

Posted
Posted

Yep Joel, plus the turbo will come onto boost earlier (lower rpm) and faster. Off boost performance will increase as well and fuel economy will improve (unless you use the extra power of course).

Cubes Grand Master

Cubes

Posted
  • Author
Posted

Thaaaankyou.. :) Just what I wanted to hear.

I'm getting Chris Milton Engineering to do the work as he was one of the nicest blokes to talk to and gave me 1 hr of his time explaining a little about heads and previous jobs they have done regarding the RB25/30 conversions etc.. :)

He said it is worth while working on both the inlet and exhaust ports around the valve area.

He also said that Port matching is mainly used on the older Dinosaur engines and wouldn't be required on the RB unless you are after every little bit of power.

Hence $$ to Performance ratio is bad. :P

Its amasing how many people actually bagged the Jap import motor, one bloke even stating that if it were up to him all of the Jap cars would be sitting at the wreckers.

Thanx Again Gary.. :D

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi Joel, whilst the standard Nissan stuff is pretty good (not perfect), I have seen some pretty average port alignment with aftermarket manifolds (both inlet and exhaust). They just don't line up properly and I reckon this may be the reason why some people get bad results from expensive bolt on manifolds.

I always check the alignement of the head, gaskets and manifolds, and in 5 out of 10 cases I have to get out the die grinder to tidy them up.

The ice age caught up with the dinosaurs and they are extinct, some people just don't know it yet.

JNR24 Proficient

JNR24

Posted
Posted

Joel,

I reckon i am neck to neck with you on your RB30/25 build!

i am dropping my heads off next wednesday (payday) at a place in melbourne to get built.

I have a couple of questions for you:

1. Are you replacing the factory RB25 valve springs with harder items?

2. how much are you spending on a complete end to end process? (for me including springs etc, i am puttting aside 1K?. should be getting some change)

3. what components of your head are you getting built? (re-seated?, new guides?, etc)

thanks Joel/sydneykid,

Trev,

Warpspeed Experienced

Warpspeed

Posted
Posted

Hello Sydneykid.

What is your approach port matching ? I have done it a couple of times, and have my own method, although it is a fair bit of work.

What I do is very carefully make a sheet metal template that just slides onto the manifold studs, and with a die grinder, match the metal template to the head ports. I then transfer the template to the inlet manifold, and remove minimum material from both, so template and manifold match exactly.

Then go back and check the head again. Eventually the metal template matches both exactly, so in theory the manifold should then match the head as well with a very smooth transition.

I am in the process of rebuilding and upgrading my flow-bench at the moment, and find all this particularly fascinating.

Cubes Grand Master

Cubes

Posted
  • Author
Posted

JNR.. Including a VRS kit the whole lot is costing around 1k.

I'm using the standard valve springs as it won't be reving super high so they don't need to be changed.

I'll ask Chris about valve springs when I drop the head off.

Although he didn't mention it so I gather the standards are fine.

Steve Grand Master

Steve

Posted
Posted

I dont know exactly, they told me that they didnt like quoting without seeing the car????

He just picked up a price sheet from another job and said it will be $1500 to remove the head, disassemble the head, mild port, reseat the valves (which he said had to be done because they couldnt guarantee they would seat after they had been in the port with a dremel tool) and to reassemble and fit.

I was under the impression that it would cost about $3-400 to remove and replace a head, and if the port is $300, then that is $8-900 to strip the head, do valves and refurbish. Not IMHO very good value.

EDIT: and that price included me providing a head gasket.

Cubes Grand Master

Cubes

Posted
  • Author
Posted

Yer I wasn't going to worry about porting as it really isn't that necessary.

The biggest restriction is apparently around where the valves are so that is what he recommended I do first.

Call it Stage 1 if you like.

I was quoted ~$400 for the head recondition including putting it all back together and then $300 for the head work.

I was quoted to replace a head gasket a while back steve and it was in the vicinity of $600+

Steve Grand Master

Steve

Posted
Posted
Originally posted by -Joel-

Yer I wasn't going to worry about porting as it really isn't that necessary.

The biggest restriction is apparently around where the valves are so that is what he recommended I do first.

Call it Stage 1 if you like.

I was quoted ~$400 for the head recondition including putting it all back together and then $300 for the head work.

I was quoted to replace a head gasket a while back steve and it was in the vicinity of $600+

Well I didnt want the head recoed, but anyway using your figures $400 + $300 + $600 = $1300 LESS the cost of head gasket which are around $150odd, so should be 1150 not 1500. Why is it that they quote me $350 more than you? And that was a rough quote, he said it could be more.

Cubes Grand Master

Cubes

Posted
  • Author
Posted

Yer not sure Steve.. ?!? So that $1500 was supplying the VRS Kit?

A VRS kit for me is $265 that comes with all the rocker cover gastets, cam gaskets i think it was?!, Head gasket, inlet manifold gasket, exhaust gasket, valve stem seals etc..

If you just want to buy the valve stem seals they cost $330 which. If you were to pull the head off you would want to do the valve stem seals obviously anyway.

Steve Grand Master

Steve

Posted
Posted

He didnt say.

Was a bit vague/cagey about giving out info. Just kept saying that he couldnt really say how much it would cost me, I'd have to bring the car in.

I got the impression that he didnt have much to do with headwork, or just didnt want to answer my questions.

dont know the name of the guy I spoke to...ah well, might just stick with AED:) Only that way I gotta remove the head myself:(

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