bigben

Hey everyone, working on my motor this winter for some reliability/ cheap performance upgrades.
I have a 1995 stock engine in a 1990 car, and since I'm doing the head gasket, I want to shave the head to get a bit of performance. I did some research on this forum, and 0,060'' seems to be the most you can shave on stock cams and pistons (which I have). This would give a compression ratio close to 10.5, which would be nice.
My question is: Can I do this and keep stock cam gears, or will the cam timing be too severely changed.

I'm not running an aftermarket ecu at the moment, just the cheap rx7 maf modification to adjust afr. Car is mainly used for autox, and will be running on 91 octane pump gas.

If you need more info to answer, let me know!

Thanks for your help,

Ben

Savington

iTrader: (31)

Buy a '99-00 head.

bigben

Hi Sav,
I'm running in csp in autox, thus I wanted to keep the 94-97 head.
I'm aware that the 99 head has better flow, next motor I build will definitely be one of the newer design, but for this winter, the racecar budget is on the low side...
Thanks,

Ben

Leafy

iTrader: (1)

That much shave isnt legal in CSP. You'd be much better off buying an 01+ engine for that.

Savington

iTrader: (31)

The problem is that you'll never get a single penny back out of the money you put into a 94-97 head. You may as well just flush it down the toilet. If you can't afford an 01+ swap for CSP now, wait until you can and spend minimal money on your current powerplant.

bigben

Yeah, I know that, I just thought that since I'm doing the head gasket, and surfacing the head, I might as well ad a little compression. I'm racing in a local autox club, and I'm pretty sure that they won't measure the amount of shaving that was done to the head. If they kick me in SM, I'll go racing with the fast guys anytime, doing this for fun more than anything...
So, about my initial question, any answers?

Thanks,

Ben

Leafy

iTrader: (1)

The money it would cost you to do the head shave would get you like 1/3 of the way to a stand alone, or buy you 1 evo school. Both would make for faster times than the 2 hp from a head shave.

bigben

Thanks for the interest and the suggestions. However, I still need to do the head gasket. I haven't unbolted the head yet from the block, but I'm pretty sure I'll need to shave it to make sure it is straight.
Trust me, I don't want to spend my money for nothing, and I appreciate your inputs. I'm just looking for a technical answer.

Thanks,

Ben

Savington

iTrader: (31)

I have to ask why you're doing the head gasket. Did you overheat the motor?

bigben

Very good question...lol, yeah I overheated it in traffic at the beginning of the la summer (put the fan fuse in the wrong slot...). Compression is fine though (180-175-175-175), and it doesn't smoke or anything, more of a preventive maintenance while the engine is in my basement... Your replies make me think twice I have to admit. Would you just leave it like that?

Savington

iTrader: (31)

It's an MLS head gasket, so it doesn't wear. If it's not visibly leaking, don't change it.

spikes

I'm more interested at how the stock ECU and RX7 will handle the upped compression ratio, when you will have increased from 9.1 to 10.5

That much of shave will effect your cam belt timing, you will need adjustable cam gears as you will have retarded the static timing.

For every 10thou, you gain approx .25 points of compression, and for every 20thou you get 1 degree of timing

Also be aware that at 60thou, your motor will be interference. Quinn reckons he still could have gotten more, saying he would have done 80thou.

Read up on his thread over in clubroadster. He built quite an impressive NA monster on a budget.

bigben

Hey Spikes,
Thanks for the reply. I've already read Quinns thread, it's pretty much what motivated me to try to shave the head that much. I'm changing the timing belt and don't plan to rev over the stock rpm limit, so the interference issue doesn't scare me too much.
Leafy and Sav got me thinking twice about, since I want to be fast, without spending too much... I looked again at it last night, and there seem to be a small oil leak at the back of the head, but it is probably coming from when the CAS seal leaked pretty bad 2 years ago.

If I decide to not replace the head gasket, would you recommend checking the torque on the head bolts? My thinking is that it will more likely break the loctite that was put on there in the first place, which wouldn't be good.

Thanks,

Ben

Savington

iTrader: (31)

You must have owned a DSM or an MKIII Supra or something in the past. Forget about the head gasket/head bolts/etc, it's all fine and doesn't need anything.

bigben

Lol, perfect, I'll put the money on some helper springs for my koni race/gc setup instead!

bigben

Hey guys,
I listened to your advises, and decided to not do the head gasket. I'm saving money to get a proper ECU and wideband sensor, which won't be that much more expensive, and should yield to better results.
If I blow a head gasket this summer, I'll let you know...lol

Ben