Increasing Compression Ratio

[DjB 0]

Clearly increasing CR on a NA motor is the best source for real power increase with the exception to a cam/cams.

 

With that in mind i've read that changing to 0.5 copper head gasket is a method for upper CRs. The problem with this is that after a while it will damage the deck of a block. So, is there a different head gasket that can be used to do the same job? Or do you have to start machining to get the same results without resorting to a copper head gasket? Is machine a costly exercise?

 

Also, Petert, your website has been fantastic. I've learned heaps from what you put up on there.

 

 

Chris

[petert1345402284 0]

Thanks in regards to the website, although we're having server problems at present.

 

Increasing the CR needs to be done in conjunction with other mods. For example, increasing to 12:1 with the standard inlet cam would more than likely result in detonation from excessive cylinder pressures. Increasing the CR inmproves volumetric efficiency but it is not the only way to do it. Our local V8 Supercar series for example, has a 10.5:1 max. rule, yet they make 600+hp from an eight valve 5L V8!

 

Cu head gaskets are great for track cars but I'd have reservations doing it to a street car. The likely hood of poor maintenance is high, leading to corrosion problems. Maximum time between rebuilds is 3 years, even with good coolant.

 

Also, the liner protrusion needs to be on the high side of the accetable limit, 0.0035-0.0045". You can't measure this reliably while the liners are still sitting on o-rings. So it needs to be measured during a dry, trial assembly. You can try, but there is a risk you will have gasket sealing problems.

 

Given most Mi16 engines are nearing rebuild time, I would be looking to optimise squish and compression during the rebuild process. Whilst the increase in CR will account for an improvement in efficiency, so will the reduction in squish height (piston-head distance). Throttle response is vastly improved. I'm built a few engines now with zero deck height, 10.8:1, Stage I inlet cam and std. management and they all sound and go really well. They have a very crisp note, which you don't get on a std. 10.4:1 engine, regardless of cams fitted.

 

It costs approx. AUS$400 to have the block decked and liners machined to suit. Machining liners is a tricky job with no margin for error. They have to be square to the vertical axis and of course, protrude the correct amount above the block.

 

In regards to coolant, stay away from mixed blends unless you live near the snow. I use distilled water plus Castrol anti-corrosion concentrate (small tin). It has no anti-freeze qualities.

 

Fitting a Cu gasket is a cheap and easy compression upgrade, but beware of the consequences!

Edited March 6, 2008 by petert

[JeffR 51]

The former Peter-Budge 406 SuperTourers used steel headgaskets along with a semi permanent sealer.

 

They ran around 13:1 CR, & I think the liner protusion was approx 0.008".

 

Jeff

[DjB 0]

Ok.....

 

With rebuilds in mind, bearings, rings and some machining... A top end rebuild might as well be done to while the engine is in bits. Peter, you mentioned that machining Mi16 motors is fairly specialized, so is there anyone you would recommend for these tasks? Even though I'm Melbourne I don't have a problem with traveling up to Sydney (thats where you are, correct?) to get machining done...

 

 

Chris

[Guest Dilan Valentinoff]

Hi all,

Just wanted to ask...

How about head grinding, lets say... about 0.8 mm and use std head gasket?

I'm talking about xu9j4z.

 

Thanks.