Raising compression so to say

[78 280zcar]

I just have a question because I am still new to this. I have a question for all the people that have raised compression to 10.1:1. I was thinking about doing the mod that this guy has in his post.

http://www.geocities.com/zgarage2001/head.html

Buuut! What kind of rings would you have to use to keep them from blowing! And what kind of other mods besides header and more breathing through throttle body ETC. would you have to do to actually make it scream!

I know the difference between rings and how to crosshatch the cylinders for the right rings but do you have to get performance rings from say http://www.zcarparts.com/store/merchant.mvc? or can I just use stock rings.

I will just ask this question! Has anyone ever actually done this mod and what kind of performance did you get?

[olie05]

don't forget, this mod only works if you have a flat top pistoned car. I actually have an N42 head on a flat-top block, and I will blow my headgasket (on 93 octane) if I floor the throttle in 4th or 5th gear. (its like a blow-your-headgasket button) I would recommend staying just under 10:1, unless it is a full race car.

[Nigel1943]

don't forget, this mod only works if you have a flat top pistoned car. I actually have an N42 head on a flat-top block, and I will blow my headgasket (on 93 octane) if I floor the throttle in 4th or 5th gear. (its like a blow-your-headgasket button) I would recommend staying just under 10:1, unless it is a full race car.

Have you actually blown a gasket?

If your motors' put together right reliability shouldn't be a problem with an all stock parts engine. Don't go to the expense of special pistons/rings, they simply aren't necessary for a compression of up 10.5 to 1

[78 280zcar]

I was talking to a machine shop guy and he says that I will blow rings anything past 10.1:1! For a stock L28 what is the best rings, moly, cast iron or chrome, I know chrome ones are for off road but what about chrome steel top rings or this link says it all, is that the same thing as chrome rings?:lick: I am looking for ones that are good with a 30 degree crosshatch and street driving. But the price on these looked good!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8006348370&sspagename=STRK%3AMEWA%3AIT

[Nigel1943]

I was talking to a machine shop guy and he says that I will blow rings anything past 10.1:1! For a stock L28 what is the best rings, moly, cast iron or chrome, I know chrome ones are for off road but what about chrome steel top rings or this link says it all, is that the same thing as chrome rings?:lick: I am looking for ones that are good with a 30 degree crosshatch and street driving. But the price on these looked good!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8006348370&sspagename=STRK%3AMEWA%3AIT

Well all I can say is I built an L series 4 banger rally competion engine [10.5:1 compression] with 280 pistons and stock rings and never had a problem.

[78 280zcar]

So that machine shop guy was giving me a load of crap. What kind of gasket did you use? I am using this program Lengine.exe, how do you measure the cc's of a head so I can type that into the head cc's measurement?

[Virto]

So that machine shop guy was giving me a load of crap. What kind of gasket did you use? I am using this program Lengine.exe, how do you measure the cc's of a head so I can type that into the head cc's measurement?

I don't really think it's a load of crap. It's pretty widely accepted that you shouldn't run a 10:1 compression, and the book "How to rebuild your Nissan/Datsun Engine" covers it. From the few things I've read, 10:1 or over is a potential timebomb on L6 engines.

Sure it can be done, but it depends on if you're looking for everyday reliability or track day performance, when you have a trailer handy to get it home should it blow.

[78 280zcar]

Yeah that would bite, to blow it without a trailer out in the middle of nowhere. I could only find a set of cam tower shims at goodson for 15.00 but they are only .015 mm in height, you cant really get .080 out of those so I dont think I am going to go that route. But I will port it out a little or just sand it with cloth to get the imperfections out. How do you go about measuring the cc's of the head though?

[Nigel1943]

I don't really think it's a load of crap. It's pretty widely accepted that you shouldn't run a 10:1 compression, and the book "How to rebuild your Nissan/Datsun Engine" covers it. From the few things I've read, 10:1 or over is a potential timebomb on L6 engines.

Sure it can be done, but it depends on if you're looking for everyday reliability or track day performance, when you have a trailer handy to get it home should it blow.

Well if you have money to burn, get your fancy pistons/rings.I ran my engine for two seasons in anger and was only let down engine-wise once when a lashpad broke up all with stock parts including head gasket. As for measuring head cc's you need a piece of clear perspex with 2 holes in it big enough to cover the combustion chamber and an accurate fluid measuring device to fill with kerosene through one hole until the fluid is level with the bottom of the hole. Any excess air should have been expelled through the other hole. Measurement is then calculated by the amount of fluid you have put in depending on what measuring device you have used.

[78 280zcar]

I found a kit for measuring the cc's here.

http://www.cbperformance.com/catalog.asp?ProductID=1338

I dont really have alot of money to spend right now so I will just get whatever is cheap.

[jmortensen]

Yeah that would bite, to blow it without a trailer out in the middle of nowhere. I could only find a set of cam tower shims at goodson for 15.00 but they are only .015 mm in height, you cant really get .080 out of those so I dont think I am going to go that route. But I will port it out a little or just sand it with cloth to get the imperfections out. How do you go about measuring the cc's of the head though?

Stack the shims to .075.

As far as the cc'ing goes, I used a reasonably tall graduated cylinder. That syringe looking setup doesn't have enough space between the lines to be very accurate.

Phred also said in a previous post to use alcohol, I had used water and the surface tension made it difficult to get the air bubbles out. Also, I would put the inner valve spring on, then take it off, remove the valve, grind, then put the valve back in, put the valve spring on again, then test again. Phred's other piece of wisdom was to smear some white grease around the valve seats and on the spark plug threads, that way you don't need to keep installing the valve springs over and over.

I don't recall what kind of rings I have, but they seem to be holding at 11:1 compression just fine.

[78 280zcar]

Phred is the one that I bought the flat top pistons from:classic: . I also found this one set but it is a little expensive.

http://www.precisionmeasure.com/block15.htm