Savington

iTrader: (31)

Correct

andyfloyd

ManiacLachy

Do you guys base your compression ratio suggestions by the octane of the available fuel? I've heard the US, and California in particular, don't have good high octane pump fuel available. If the quality/octane of the available fuel was better would you go for a higher compression? Does E85 considerations have an impact on CR selection?

concealer404

iTrader: (3)

Yes. If you're running E85 most of the time, higher is good.

Mazdaspeed_Miata

I will only run 102 octane pump gas.

So your recommendation is also 8,6:1? Or then better 9:1?

And would you recommend Supertech or Wiseco?

And OEM head gasket as andyfloyd has written, or better a different one?

Thanks again

psyber_0ptix

iTrader: (4)

yes

konmo

iTrader: (2)

8.6 CR Supertech pistons 83.5 MM with OEM headgasket.

sixshooter

iTrader: (12)

Power you make is directly related to how many pounds of air engines can consume. When you're using pump gas you are detonation limited. You can cram more pounds of air into a low compression engine without detonation than you can a high-compression engine. Therefore you make more power buy trading compression ratio for detonation resistance. For instance. On a 10.5 to 1 compression engine you may not be able to add any additional air (and of course fuel) without detonation but you might be able to add 50% more air to an 8.5 to 1 engine without detonation. 50% more air and fuel is about 50% more power, generally.

There's plenty of information on the subject if you're willing to read books and articles. Forums are often full of people who I've never read any formal theory on engines so beware what information you take as gospel. Back when I first learned about it everything was in books and you had to actually go to the library to find it. Life used to be much more difficult for the car enthusiast.

Mazdaspeed_Miata

First question, what does MBT means?

Six, thanks for your explanation and advice to read some articles about theory of engines. Because of the fact that I learned that theories in my studies and read a lot of articles in addition to the studies, my knowledge in this regard should be ok.

A low CR got the disadvantages that the efficiency of the engine decreases. And in addition also the responsiveness decreases.

The most current stock 2l F/I engines are running CRs of ~9,6:1 (Civic Type R, Golf R, etc.). But of course they are using direct injection, which reduces the combustion chamber temps and so on the detonation problem.

Due to the fact theory and experience often vary I was asking what you guys would recommend, which have built several engines yet.

So I will go 8,6:1, thanks.

Till which bore diameter the stock head gasket can be used?
84mm should be still ok with OEM gasket, right?
I will go 83,5 or 84mm pistons, should be the same?

Some further questions.

I would like to purchase the Gates Racing Timing Belt. Is this belt recommandable?
Is it correct, that it squeaks that loud?
I am using my car only from april to september, so only very very rarely under an ambient temperature of 50°F.

And then the question depending oil squirters.
In combination with this 83,5/84mm 8,6 Supertech pistons, would you recommend to close them or leave them untouched?
I know that this topic was discussed often in the past, but what is the current opinion/recommendation about it?

Thanks so far
Bastian

psyber_0ptix

iTrader: (4)

Knows about engine theory. Doesn't know max brake torque....

j/k


Gates Racing Timing belt isn't squeaky or loud. Where did you hear that? Ancillary belts will be noisy if they are improperly tensioned of if your alternator/waterpump bearings are about to go. If I recall, stock head gasket will accept up to 84mm to accomodate the O/S OEM pistons available from factory. I may need to be corrected on this one so take it waith a grain of salt.

Squirts are controvertial. There is a camp that believes it does more good than harm by helping shed heat, which helps mitigate pre-ignition. The other camp wants more stable oil pressures and claim consumption reduction. This ideology might change with the type of pistons you have and it's placement of oil control ports. You also might find piston choice might dictate whether or not you can actually keep the the oil squirters due to physical clearance; Wiseco comes to mind, but I don't remember and don't care. Unless there was a breakthrough, I think that thread you read might be the most updated concensus which last I read, was 50/50.


I'm running squirters on 84mm supertechs, haven't had too many issues with knock/detonation. Leakdown is healthy after years over 300whp, though I suspect the bit of smoke I get randomly ~might~ be due to valve seals; but that's a whole other topic.

ryansmoneypit

iTrader: (6)

You can not compare engine dynamics of a miata to a new Honda. That's 30 years Honda had to improve over a miata. A lot has changed

a k24 makes 400hp on 9 psi boost. A miata makes 200 at that same boost level.