B5254S head into B5234T block

[thecheat]

Xb, your engine bay photos in your Facebook are absolute pornography.

[xb corp]

wow! should i censor them?

[xb corp]

i just got back my B5254S head from the machine shop the other day. They bored the combustion area to mate the piston clearance (81.5mm) and at 2.00mm depth. This is the maximum depth achievable before reaching the valve seat.

with this, i believe i am getting closer or similar to turbo head, at CR 8.5:1. but i want to achieve at least 8.0:1.
since no thicker metal head gasket is availble off the shelf, i dug out some more alum around the valve face....and estimated i have dug out enough...for another 8cc.

based on calculation, i am sitting at CR 7.64:1. would it be safe to run at this kinda CR?
what would i experience?

[xb corp]

i have fixed everything and painted some areas...my engine bay is in total flat black with red chillies in the center...heh.
will post the pictures when i figured out how to soon..

anyway. i have dynoed the motor and here are the results.
- B5254S head, with over-bored combustion chamber to 7.64:1 (too low anyway) + stock B5234T2 block (stock internals)
- Nissan 16V-11 turbo, external HKS wastegate, Fujitsubo exhaust with sports cat 3" from turbo downpiep all the way to the back (from Subaru Legacy), JASMA 600mm x 450mm x 80mm intercooler with samcos and 2.5" pipes.
- N/A cam and TB, K&N drop in filter. Stock orange injector + 5 sub orange injectors from S80 2.0t
- RON97 @ 33degree C ambient, no-load dyno

RESULTS:
- All above, with sub-injectors off @ 1.0bar = 257.7hp@4200rpm 44.4kg@4400rpm
- All above, with sub-injectors off @ 1.2bar = 287.7hp@4300rpm 48.9kg@4400rpm
- All above, with sub-injectors on (315cc + 295cc) = @ 1.4bar = 355.2hp@4000rpm 55.3kg@4800rpm + blue fire and intense smoke..

At condition 1, with all the rest of parameters are same except for the head, which was original but modifed B5234T2 head, i got 324hp + 53.4kgf-m...
Now, due to low compression i only got 257hp + 44.4kgf-m.
I have to compensate with higher boost pressure and additional fuel to get back where i was before i put in the N/A head.

So moral of the story..you may use the N/A head for its intake port curve angle, but please make very sure not to over bore the combustion chamber. Try to get around 8.6~9.0 CR. You will be good around 280hp. make sure use high octane fuel too..

[csbrianp]

The NA heads have bigger valves, bigger ports and if you mill the head a little increase compression just enough to increase the power at low RPM's to make the 850 turbo fast everywhere in the RPM range.

Don't worry about the valves not being sodium filled, Porsche, Audi, BMW, and Mercedes don't use them and they have no problem, and neither will you.

Brian

[precopster]

It's not the heads that are different between turbo and non turbo it's the pistons with a different dish in the tops.

What you may risk now is longevity of the aluminium head due to making it thinner. Cracking the head will now be the greater risk.

The turbo and non turbo heads are identical unless it is an NA VVIS head from the 1994 era.