N12 Turbo Forums

I'm just about to rebuild my engine and i'm going to port and polish the head, add copper head gasket, ACL Pistons, balance the bottom end.

I was just woundering was there any point in getting double vavle spring and uprated cam as i'm going to do this rebuild right from word go.

I will be using an T25 ball bearing turbo running 20 psi, mappable ecu, uprated injector and trottle body.

Depends on the profile of the cam and the revs you intend to use M8.
You would be best to run this by your cam supplier. He will be able to advise you as to the rev range of the cam and whether double springs, or indeed tougher single springs are actually in order or not.
No point in fitting all that heavy clobber if the lift and revs wont require it.

20Psi from a T25???? Ummmm, I think you might be asking too big a question from such a small turbo M8. T25g turbos were only Juuuuust good enough for a stock or even slightly boosted 2 litre.
Im sure it will deliver that pressure but whether it becomes a "potato in the tailpipe" doing it and killing top end Hp is anybodies guess.

If you want to play right up there at the pointy end of the boost range and be reliable, youd be best to look at at least a T28 or something in the GT25 range of turbos.
Something that might flow the numbers efficiently in the first place.

Have a look at this dyno comparison.
Its the identical engine dynoed with 2 different turbos but both at the exact same boost pressure.
We are talking a difference of a whopping 100hp here at the identical boost pressure!
http://site.mawebcenters.com/evanstuning/comp1.html
OK this is obviously some very serious drag racing kit but it demonstrates that equal boost pressure nowhere near equals horsepower if the turbo is not matched correctly to the application.
The compressors on both turbos were up to the job as 32psi was reached easily, with insignificant lag difference but the exhaust turbine on the ("smaller") turbo is the culprit and its efficient flow rate has obviously been well exceeded so becoming a "potatato in the tailpipe" and effectively throttling the engine on the exhaust due to increased manifold back pressure.

Lastly, why do you want to fit a copper HG?

L8tr
E

iv'e also currentyl taken my head off my e15t and it had a crack in it which is getting fixed as we speak now im using a acl monotorque gasket which is supposed to be gr8 for up to 15psi, now what i want to know is WILL PORTING THE HEAD MAKE ANY DIFFERENCE AND SHOULD I PORT BOTH INLET AND EXHAUST PORTS OR JUST THE EXHAUST PORTS??? i will only be running max 14-15psi with a t25g and a 400x 300 cooler! also i wanted to do my pistons but the bores seem clean and DIDNT SEEM TO BLOW BY ANY OIL so i am not sure whether it would be a waste of money!!!!

any other info would be fantastic cheers, SAM!

If your going to bother having any porting done do the whole job the first time.
Get both inletas and zorsts done and have a good 3 angle valve job done. That 3 angle job alone is worth more than a quick port and polish and leaving the seats stock.
Stock gasket is fine up to engine banging boost pressures but guys seem to reckon the genyoowhine Nissan HG is a better gasket.

You have to ask yourself the question, are you just doing a top end tidy up with some mild head work or are you going to lift the engine and do a bottom end job as well in which case you might as well mic the crank and replace bearings, press in some new jack shaft bearings, bore it and fit new pistons, deck the block, chemically clean it, and so-on and so-on ad nauseum.

If you can justify at least 600 or 700 dollars on a bottom end freshen up on top of the 500 odd plus you are going to unload into the top end then go for it.
L8tr
E

Lurch wrote:I'm just about to rebuild my engine and i'm going to port and polish the head, add copper head gasket, ACL Pistons, balance the bottom end.

I was just woundering was there any point in getting double vavle spring and uprated cam as i'm going to do this rebuild right from word go.

I will be using an T25 ball bearing turbo running 20 psi, mappable ecu, uprated injector and trottle body.

so u will buying a new Gt25? cos t25's didnt come in ballbearing form 20psi should be fine witha Gt25 290hp version would be the go

Ye it's T25R i bought it new and now it has a T28 wheel in it. The turbo crowd that did it said the turbo will boost all day at 20 psi with no problems.

ok kewl its the GT25R gotya now mates putting one on his ET perfect size for it wil go well.

and by the way a copper hg is a pain in the ass lol goa stock one they do a great job. if u do go copper make sure u O-Ring the block and head otherwise u MAy have trouble with sealing

Yea you will have trouble sealing with a copper head gasket unless you o-ring it, or use a whole lot of copper gasket spray. I use one on my engine, only because when i first rebuilt it, i didnt have a great knowledge on turbocharged cars and figured to run more boost i needed a bit of a lower compression ratio. now i realise otherwise.