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Rb25Det Cylinder Head Porting?

ricardo.benin

By ricardo.benin,
in Engines & Forced Induction

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ricardo.benin Explorer

ricardo.benin

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Posted

Hi I recently have started my build on my rb25det and the block is at the machine shop. But I am now onto the cylinder head and that is were I am having problems, basically I am trying to find out if I should port the cylinder head. I want to make 450-500hp and I was wondering if I can do without porting. I was thinking about removing the humps in the exhaust ports but what about porting the bowls, should I leave it or make a better transition from valve seat to casting. Btw the machinist is going to use a 3 axis valve seat grinder. Also I found some engine manuals for the cylinder head but non of them for the rb25det has any info on valves and valve seat clearances just a basic cylinder head disassemble that does not include removing valves, so if any one has any tech sheets that would be great as the cylinder head is next to go to machine shop.

Thanks

Richard

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R31Nismoid Grand Master

R31Nismoid

Posted
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You can most certainly do without porting for that power figure. I made that power, as have many others before you - stock head and on PULP. If you plan on using E85 then it's a piece of piss.

All comes down to how deep your pockets are mate, and what the overall budget is. You can certainly save money on that if you need to spend it elsewhere.

discopotato03 Grand Master

discopotato03

Posted
Posted

I'd just do a quick clean up around the throat/seat area if keen .

You can fit slightly oversized exhaust valves with a bit of machining on the existing valve seats . All RB25 and 26 twin cam heads are a tad down on exhaust valve size and if you re do the exhaust valve seats they can be done for the OS valves in one go . Ferrea and one of the other mobs do them but I don't have part numbers .

I did this and had no power loss . The current trends with turbo engines is to do everything possible to free up the exhaust side so the engine runs more efficiently when on boost .

There is a supposed valve head area ratio exhaust to inlet and I can't remember accurately the numbers but the RBs end up being a tad small in the calc .

Doing this is a bit like having a very mild exhaust cam upgrade but no valve train geometry changes .

Works for me , cheers A .

ricardo.benin Explorer

ricardo.benin

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Hi guys thanks for all the info. Btw I forgot to mention that I do not have e85 were I live, we only have 92-93 octane fuel so I was thinking of maybe running water/meth injection. I was also planning on putting valve springs and retainers in as well and keep every thing else stock.

Thanks

GTRPSI Mentor

GTRPSI

Posted
Posted

The first cm into the exhaust and intake port is the most critical on the short side, remove a valve and run your finger in there, you will feel a sharpish ridge that needs to be smoothed.

Removing the exhaust lumps also helps.

Dont make the ports any bigger as it will reduce gas velocity. (unless its a all out drag engine)

A basic port cleanup can go a long way.

Sure you can make good power without all this, need more power, run more boost, then again wouldnt you prefer to make it with lower boost levels and a turbo coming on quicker and stronger ....

GTRPSI Mentor

GTRPSI

Posted
Posted

Thats the most critical area, its the first cm or 2 i spoke of near the valve.

On both intake and exhaust, concentrate on the short side, on the intake its all around near the valve seat that needs work to smoothen the transition to the vavle seat.

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