Head rebuild : Porting and parts question !!

[cobrAA]

Well, my forged RB26 skipped a few teeth and it's now stored for winter. For now, i want to focus on my head rebuild and I have a few questions.

Background : I wish to go BW EFR 83/74 IWG 0.92. Full-race said this should give me about 620-650whp on a dynapack. Rev limiter to 8k or 8.5k rpm. The car is mostly driven DOWNTOWN or 70km/h road. I wished to do some track, but it never happened yet.. so good idle and response is pretty important for me.

*Since I don't know anything about head, I searched for infos and based my rebuild on what RAWbrokerage and PHR offer as a head rebuild package.

Machine work : I wish to have it ported a bit, but jeez...through all the thread I read so far, you have 50% of the ppl who said it could hurt the response down-low while the 50% think its THE answer to extract another 50whp/40lbs out of your setup.. However, 100% agree on the fact that if you give your engine to the wrong machinist things will be worse... so, anyone went through all this and what was your outcome ? which shop did you go with ?

Shopping list : ( Feel free to recommand me other option/parts)

1. Mine's cam baffle 250$
2. Supertech OEM-size valve set with titanium retainer 720$ ( Should I go +1mm ? or Tomei/JDM brand?)
3. Bronze valve guide 170$
4. I already had ARP head bolt, can I re-use them or I should buy new one ?
5. Spring ( I'm totally lost here, should it be single or dual spring !?) 700$
6. valve stem seal 50$
7. reinforced timing belt tomei 170$

* I see tomei sell a variety of reinforced bolt, cam stud and such... they are quite pricey so not sure its needed for my application..

** I was also considering swapping my poncam type-b 9.15mm 260 for a set of procam, but then I'm unsure if the higher lift wouldn't ruin my low-down and idle.. maybe I should stick to my poncam.

I sincerly appreciate your help because I don't wish to rebuild a 3rd time and wish to make it right this time!

[caliber676]

No need to go with reinforced cap studs if your running poncams, I would only use if going over 10.25mm lift.

I would focus on cleaning up the casting marks, gasket matching and smoothing out the valve bowls. That will give you a little bit better flow and can be done yourself. There's no need to be knife edging your runners and the works for a street queen with minor track time, spend your money on something more useful.

Mines baffles are definitely a good investment, and oem valve sizes are better than oversized.

Look up the spring pressures for the cams you have, I think tomei suggests type A springs for your cams so buy the recommended tomei springs or cross reference the pressures to supertech or bc etc but you should most likely be using single springs

[Skym]

Porting, oversize valves, etc gives a mid to high rpm powerband and that requires using the gears to keep rpm needle in the powerband to take full advantage of the powerband. There can be up to 100hp more from those types of mods.

Talk to head or cam specialist who can flow test the head and workout what cams, turbo, etc work with your setup.

From what I understand, general rule of thumb is rough intake to help with fuel mixing with air, smooth exhaust ports and removing the bumps, etc.

Most people have their own opinion's on removing the quench pad around spark plug to help in preventing knock with high hp RB engines. Research this and talk to some professionals.

If that specialist claims that rwhp, find out what head mods they used with that turbo. Cams, head are matched to the intake, exhaust, turbo setup, etc you are running on the car. It's the whole package, not just one area of the car or engine.

The list of what a head specialist asks for is here (engine builder gives them this info) -

https://www.capella.co.nz/sites/kelford.co.nz/design-shop/

For a small fee they can tell you what works.

Be aware that more rpm = more inertial load on bottomend (snaps conrods). It's better to use higher boost level, lower rpm than more rpm to make the hp. More rpm requires very expensive parts to keep it in one piece.

From what I understand, more lift and duration creates a crossbow look at bottomend, but mid to peak hp, torque are increased.

Valve springs are rpm, lift rated and that rpm rating drops as they age.

[cobrAA]

Skym, I cant see any rpm max limit on spring's description ( beside the tomei one).

Thanks guys for your post, I wish to buy everything before school start over so i have one less distraction !

[Dragon Humper]

About the only things you can do is make sure that there are no casting irregularities (the head having some wierd looking steps right at the spot where the sand casts come together) and gasket match. You can also check the runners for any other junk that might be hanging in the stream but to be honest, I have never heard of any issues. The biggest gains are in the short radius area just before the valve and the port diameter in the guide area. Make a spoon out of tin with the big end the same dia. as the valve you are using and check the ports. If the spoon gets stuck anywhere then there is some restriction.

Unless you want to run nothing but race fuel dont remove the quench pads, they promote mixture in the chamber and are your biggest ally to fight detonation. Only the biggest dog race engines USED to do that because no-one made pistons that were only 7.5 - 1 comp. to go with 40psi of boost. Removing the pads drops the comp. at least .25 of a point...another thing you dont want in a street motor.

Same thing with a thicker head gasket...pointless. All it does is open up the quench area (thats bad) and lower the comp. Both of which kicks the "response" that everyone seems to be obsessive about right in the dingleberries.

Its OK to re-use the head studs and I would stick with the PONcams...thats all I got...wink wink.



Jon.

[cobrAA]

About the only things you can do is make sure that there are no casting irregularities (the head having some wierd looking steps right at the spot where the sand casts come together) and gasket match. You can also check the runners for any other junk that might be hanging in the stream but to be honest, I have never heard of any issues. The biggest gains are in the short radius area just before the valve and the port diameter in the guide area. Make a spoon out of tin with the big end the same dia. as the valve you are using and check the ports. If the spoon gets stuck anywhere then there is some restriction.

Unless you want to run nothing but race fuel dont remove the quench pads, they promote mixture in the chamber and are your biggest ally to fight detonation. Only the biggest dog race engines USED to do that because no-one made pistons that were only 7.5 - 1 comp. to go with 40psi of boost. Removing the pads drops the comp. at least .25 of a point...another thing you dont want in a street motor.

Same thing with a thicker head gasket...pointless. All it does is open up the quench area (thats bad) and lower the comp. Both of which kicks the "response" that everyone seems to be obsessive about right in the dingleberries.



Jon.

Jon, thanks for your input,

You opened another subject, headgasket thickness. which one is better ? keeping oem 8:5;1 ratio or getting higher to 9:5 ? Could you care to elaborea little more on the subject ? My thinking is higher compression = higher rev = more responsive engine but downside is the higher rev is the more chance you have to break parts.

EDIT: seems like its either i get +0.2 more for a 8:7 ratio or go with a 1.2mm which would keep it standard ratio. http://www.tomeiusa.com/_2003web-cat...26_gasket.html

[Dragon Humper]

Head gasket thickness boils down to quench clearence. Whatever pistons you end up using will have a specific distance from wrist pin to pad. You tailor the .040" quench spacing based on what you have to work with. If your quench is too tight, use a thicker gasket, too big, try and find a thinner one (than stock).

The .040" is a # I have settled on based on the bore dia. VS piston clearence (to account for piston rocking in the bore) and operating RPM vs rod length and material. The ultimate test is to run the motor for a bit and pull the head, if you see some very slight rub marks on the head from the piston just barely rubbing the carbon off...it's perfect.



Jon.

[cobrAA]

I'm using 86.5mm piston.. worst case, I will go 87mm if needs to be.. can a 87mm HG be ordered right away ? ( it will works with either a 86.5mm or 87mm piston ?)

[Dragon Humper]

Are you talking thickness or diameter? I dont think there is much of a difference between the 86.5mm and tbe 87mm gaskets as far as the fire-ring size (I think they just make them all for 87mm to save tooling costs). I would use a stock thickness gasket though.



Jon.

[cobrAA]

thats what i'm aiming jon, 87mm diameter and stock thickness. just want to make sure i can use a 87mm with a 86.5mm piston ( if we decide not to overbore to 87mm)

[nick-nismo]

I'm currently using a cometic 1.3mm headgasket in 87mm size. with 86.5 pistons. No problems there
After decking the head and block I figure I'm right back around 8.5:1 compression. Perfect for pump gas and sub 20 psi boost.
From everything I've heard, leaving the head untouched is the best thing you can do for a street driven/ response and driveability in mind
Since your already in there as well I would recommend the ARP timing tensioner stud ( AM3.350-1LB ) and the nut to go along with it ( AMN12-1 )
That's just about the cheapest 12$ insurance you can get.

[Dragon Humper]

The stud is a must for sure, I wouldnt trust the factory bolt at all...even a new one.

Honestly, you could get away with 9 to 1 on these motors with the bore size they have. There was a dude with an Acura running 9.5 to 1 on a totally stock setup save for the pistons (11-1 was stock comp.) and he was hosing 30 psi at it on pump gas (94) and trapping at 140mph @ Ashcroft a few years back. Its all in the tune....and the fact that the turbo wasnt coming in untill 5000rpm...that helps a bunch. The higher the compression and the tighter the quench the more low end torque you will make and the bigver grin you will have. The tune is the key though...a lazy tuner will turn even the best combo to poo.



Jon.

[Bruizer]

650whp? I'd go with tomei 280 procams, +1mm tomei valves, gasket matching on ports, mines baffles, tomei type c springs and up to 10,500 rpm.

Badass turbos need badass engines

[cobrAA]

650whp? I'd go with tomei 280 procams, +1mm tomei valves, gasket matching on ports, mines baffles, tomei type c springs and up to 10,500 rpm.

Badass turbos need badass engines

guess I'm not badass enough loll

Engine builder told me the money toward fitting +1mm is better spend on porting. And he prefer I buy everything from the same brand than different brands so i will go all Supertech stuff ( their dual spring is equivalent to the type c from tomei, well from what i gathered lol)

I'M still thinking about swapping my 260 type-b tho.. I don't know... I still drive the car downtown very often.. so if the idle will get even more lumpy than it is right now, it might not be a good idea.

[Bruizer]

The smaller cams like type b or R will help with spool up. Especially if you use a big turbo like that. If you went with an 7163, that would be even better response while using the turbo to the full capacity unlike only 550-600whp on that 8374