Milling head vs new pistons-240SX

[handfulz28]

Wondering what everyone's thoughts are on the difference between milling the head (within the service limit of course) and installing the flat-top pistons.
I have no idea what's involved with correcting the timing for a shaved head (at .001 or whatever, is it necessary?)
Is there really a power difference with the flat-tops/overbore?
I've got the flat-top/overbore pistons in the motor now, but the head is bone-stock. Just getting ideas for the next motor...
Michael

[Banzai240]

Simply put... Milling the head raises compression, overboring increases the cubic inches AND the compression... If you get 9.5:1 compression in both cases, wouldn't you rather have the larger displacement engine? .... I would!

As for correcting the timing... it depends on how much you mill the head. I wouldn't expect that you would be milling a lot off if you expect to stay within the "service limit" of the head, but generally, timing is corrected by using an offset key at the crank pully, which I think is the only place it's legal (at least on the twin-cam motors...)

Hopefully I got that all correct... If not, I'm sure someone here would be happy to correct me.

Is this an S13 240SX (ITA) we are talking about here???

Good luck,


------------------
Darin E. Jordan
SCCA #273080, OR/NW Regions
Auburn, WA
ITS '97 240SX



[This message has been edited by Banzai240 (edited March 03, 2003).]

[dpc]

Michael, Call me -Dave -518-792-4986

[erlrich]

Michael - I'll be starting on my rebuild later this month, and I plan to do both. The GCR allows us a compression limit of 9.5:1, and the flat-top pistons for the SOHC engine have an advertised compression ratio of 9.1:1, so there is a little room for compression gain from shaving the head. And, I've never pulled an aluminum head that didn't need to be shaved anyway.

As far as the cam timing, its not that hard to do, and I'm guessing Dave can walk you through that when you call him. Nissan Motorsports has a cam sprocket to correct the timing on the SOHC engine, and it comes with a selection of offset keys. If you have the DOHC engine you'll have to correct the timing on the crank sprocket (per GCR).

------------------
Earl
ITA 240SX in process

[lateapex911]

Are the flat top pistons the same as the stock overbore replacement pistons? I didn't know you could change, but hey-I'm a rotary guy- just trying to learn a little!

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[erlrich]

Originally posted by lateapex911:


Are the flat top pistons the same as the stock overbore replacement pistons? I didn't know you could change, but hey-I'm a rotary guy- just trying to learn a little!

Jake - yes, in this case they are. A few (think I heard somewhere it was around 1,000) of the very first 240SXs to come over in 1989 had the higher compression flat-top pistons installed, so they are legal replacements for all SOHC engines.


------------------
Earl
ITA 240SX in process

[ITA240]

MIchael
Did the timing change make any difference? CAll or email me..

Jim

[handfulz28]

Banzai/Darin-it is an S13(ITA). I'm not convinced the overbore is necessary that's all. At .5-1.0mm over, is the displacement gain worth the cost/risk of drilling the motor to the limit?
And maybe I threw two considerations into one-I don't recall what's available, but can you get the "flat-tops" in a stock bore? Wasn't there a choice on which ones to get? So maybe you could use the flat-tops without boring? Hmmmm.

Jim, I don't think the timing change helped. It felt pretty flat up top.

Thanks,
Michael
[email protected]

[dpc]

How far did you advance the timing? Also have you ever put your car on a chasis dyno. I may have the opportunity to do so, but do not know what to look for or change when I do it. any help out there.

[erlrich]

Michael - I have only seen the flat-top pistons from Nissan Motorsports, and they only list the .5mm & 1.0mm overbore pistons, not the stock size.

I would also be interested to know how far you went with the timing advance. Are you using a stock ECU? (you don't mind us picking your brain, do you )

------------------
Earl
ITA 240SX in process

[ITA240]

Earl, DPC
Mine has been on a dyno...email me

[email protected]

Jim