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Discussion Starter #1
it just occurs to me that I need to straighten out what it takes to build the ultimate head.

ok, starting with a raw head:
- port and polish the exhaust ports
- intake ports, port, but no polish? Knife-edge the wall between the pair of each intake ports? Not polishing would make the air tumble in rougher? Knife-edging, why or why not?

valves:
- polish the valves
- what about seating the valves? grinding out new valve seats? A. Bell details this procedure in his books, is this a critical step?
- how about widening the diameter of the valve openings? Aftermarket valves? (since stock valves seem pretty high-spec, with the exhaust valves sodium-filled, does anyone ever buy aftermarket valves?)
- phosphor-bronze valve guides. When I last rebuilt my engine, I think I had conflicting information on this - on the one hand, bronze guides would be smoother, but are softer and would wear faster than stock? Yet stock guides are brittle and can crack? There was something said about aftermarket valve guides that stopped me from buying a set, but can't remember what.

bowlwork:
- polish it out, maybe measure and equalize volume between all six?
- squish pads. This has been debated plenty. Nismo removes the intake side on the Z-tune. Some heads have had both removed. It's not a lot of material to take off really. How about not fully removing, but rounding off the edges (bowl volume check would still be required after rounding off some edge material).

valvetrain:
- hot cams, of course. For high lift cams, material has to be cut out for clearance, correct?
- valve buckets and shims: any mods other than ensuring proper clearance?
- valve springs: upgrade? do they wear out? if stock springs are good for 8250rpms, what do you get from uprated springs? Is this the key part of a valvetrain, where if it's not uprated, then spinning the engine too fast could bend a valve or otherwise create valve float?

other bits:
- skim the head if needed
- rear head oil drain, if desired
- ARP head bolts
- anything else I'm missing?
 

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I think the first thing you have to do before you even touch the head is decide ultimate what...

power?
economy?
mid range?
torque?
boost handling?

etc
 

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Be aware removing both squish lands from a chamber adds a LOT of chamber volume, and it'll be very hard to run a sensible CR without custom pistons. Whether removal of the squish land is good or bad has been debated before. I asked 2 really good engine designers this question and got two totally opposing answers..... :)
 

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I removed the inlet squish-pad on my 25 head.
I have to pull a few dgrees of timing at 5.5k rpm I think because of this...however...
It makes a LOT of power 500bhp+ is tame on the street, and has good economy driven off boost but spirtited.
I did a club day about 40 miles from my home last saturday (at Kemble airfield) filled with fuel as I left home, the car ran all day with 2 drivers, got home with 1/8-1/4 tank of petrol still....
I'm happy with my squish-pad removal. Std. valves, exhaust 'lumps' removed and polised, inlet std but matched to runners, Tomei cams.
 

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Discussion Starter #7
ok, getting away from the squish pad debate, I think that any head would benefit from RPM-proofing, and is that in the valvetrain? Springs and guides? More to that, or has anyone taken a stock head and spun it to 10,000rpm without throwing a valve?

On top of that, by application-specific, are you saying that big ports might be good for drag but turn the car into some kind of lumpy-idle lag monster? Then in what case would you leave the stock ports untouched?

I guess to be more specific, by "ultimate" I was thinking more along the lines of RPM than outright power, but if someone wants to enumerate what you'd do for a 600bhp street car versus a 1000bhp drag car (other than the squish pads), cause instinctually, flow is flow and isn't more better in any case? And 10,000rpm is still the same sort of strain on an engine in terms of parts moving, whether you're spinning 500bhp or a thousand?
 

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ok, getting away from the squish pad debate, I think that any head would benefit from RPM-proofing, and is that in the valvetrain? Springs and guides? More to that, or has anyone taken a stock head and spun it to 10,000rpm without throwing a valve?
You know Toby, that feels like a blow off to me re. the squish-pads.
I've followed your posts for years now and like your stories etc, but please do not underestimate what others have done with the mighty RB engine.
I was 2nd by .4mph over 1/3'd-ish mile to a 580bhp GTR (that was running consistent 3.7 0-60's against my 5.9's-massive wheelspin), Had the track been longer by even 50m I'd have killed everything there on top speed.
I've never dyno'd my car but it runs 1.5 kg/cm and makes big power even with it's 7.25k rpm limit.
I'm offering you proven DIY hard- earned experience, no BS.
 

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Discussion Starter #11
Definitely didn't mean to blow you off. I like the inlet squish pad removal mod. I'm jus fishing for more information regarding the other parts of the head that I haven't researched in depth.
 

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"dirtgarage" from Red R Racing has great experience with RB26 heads if he sees this thread I am sure his opinion would count for a lot.

And I think "utlimate" is a bit vague, is the the best flowing? Maybe but probably not, increase the flow too much and you sacrifice velocity at lower rpm...

I think you need to match the head with the bottom end you are using and more importantly turbo selection.

Mike
 

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im very interested in this thread but what is a squish pad? am i being a complete idiot?

kev
 

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I don't think it is a good thing to remove the squish pads as they are there for a reason the proper way to do it is put a slant squish band in there but you then need to start with a blank piston crown and machine the same angle on to the piston as you have on the head this mod works best with over size valves to remove the masked area by the old squish band it all so reduces the knock limit by a faster burning velocity over the stock rb one any way that's enough typing for me I hate it.
[email protected]
 

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Discussion Starter #17
Gary's 900hp on lowmounts engine runs the standard valves and still has the squish pads.
but what about the valvetrain - springs, buckets, guides?
 

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Just send it to these guys......

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By the way - has anyone here drilled the head to let the air bubbles bleed out from the jacket above the combustion chamber.

Naprec have been doing it for years and I've seen the same drillings on pictures of the group A heads. They drill into the rectangular water recesses between the inlet ports.
It looks like a diagonal drilling as it eats into the edge of hole at the outside edge. Fancy doing my cylinder head but it looks kinda scary drilling into the unknown.
 

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Yeah, its not hard to do, once you have the head off you can stick a straight o ring pick up into the area you are trying to reach and get a good idea of where you should be aiming for.
 
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