Miata Piston thread...revisited

[Gen1GT]

It all depends on how much it's shaved by. Try the numbers yourself.

http://www.rbracing-rsr.com/compstaticcalc.html

bore 3.346
stroke 3.268
head gasket thickness .040
deck height .030
piston volume 5cc
chamber volume 45cc

Those are approximations, but it works out. Now subtract how much you'd want to shave off the head from the deck height and/or head gasket thickness. You will come to the number you want, better than trying to figure out how much it'll change chamber volume from shaving. So if you do a .020" head shave, it'll raise compression from 8.8 to 9.2.....

In my case, my 11:1 pistons with an .020" head shave will raise compression to 11.89:1......

[zenilder]

Be aware that when you shave the head, you retard the cam timing. (You are lowering the head.)

[JesseSays]

also at a certain point, you'll have to do custom tensioners on the timing belt. I emailed Vaughn about that probably back in 2001, but forget the answer.

[JesseSays]

What are you scared to be smoked, all those forums dont know anything as well as this one. You only say it because you dont know crap, dont be blamin a forum for your ignorance.


Dont be afraid to accept yourself. DOnt blame others.

Instead of telling me to go talk to your posse or whatever, how about WE have an intelligent discussion?

*HOW* is low compression better for a turbo application?

Reduction in knock?

Using the same crappy heads and pistons that OEM's give you on most engines, this pretty close to the truth. This is the way of the MAJORITY of DSM tuners. How do I know? Read their forums, and friends/aquaitences with some of the faster street DSM guys, one trapping 131 and another at 127. The DSM way is to be fast, cheap, and deal with reliability later. The 4G63 is a remarkable engine that takes abuse like a desiel. However, it CAN be better, and if you look at what's in the all-out race DSMs these days, you'll see higher than oem 7.8:1 static CR pistons. Why???

However, using modern technology to build "soft heads" as Endyn puts it, you can great reduce knock via MECHANICAL ways. Shaping the heads and pistons and the rest of the combustion chamber to not allow for hotspots, to get rid of areas where gases will go unburnt, and to keep a very clean, dense mixture in the area of the chamber you want (by exhaust valve), you will have a VERY detonation resistent combustion chamber. That being the case, you can go other directions to get more power, such as raising the static compression ratios in order to give better spool up characteristics, as well as better efficiency across the board. Not only that, it'll be much more driveable. Controling the combustion process mechanically is the key. And not many people can do it correctly.

Oh, and I'm not usually smoked, as I don't often run at the drag strip. My car was and is built and maintained for a different racing application, and it does quite well there. As you might say, "I smoke most everyone else"

I await your reply...

[JesseSays]

Prostock, Diesel... complete different combo.

Like I said just contact the nearest forum, store and magazine and tell them that all they know about pistons is just nonsense because a diesel has hC pistons as well as NASCAR.

I'd offer to give you the links to the better forums, but one of the reasons why there's a lot of smart people on them is the LACK of people like you who can't keep their mouth shut and don't listen when someone trys to teach them.

[Gen1GT]

Back to our engines, and compression ratios. The BP has a short rod ratio. This means that there is very little dweel at TDC. Because of this, even if there is detonation, the piston is quickly on it's downward stroke before it can cause any damage. If you had a BP with 10:1 aluminum pistons, you'd have to be way outside the boundries of intelligence to be causing problems from detonation.

A car like a 350 Chevy on the other hand, with big heavy cast pistons, ineffecient combustion chambers, needs upward of 25 degrees and more of ignition timing to make power. Run high compression with boost on those, and it's a time bomb.

Just because some rules apply to some engines, doesn't mean all rules apply to all engines. Just because you wouldn't run high compression with a turbo on another car, doesn't mean the BP can't handle it.....

[zenilder]

Our engines put anywhere between 15-45 degrees of ignition advancement depending on how you set the distributor. Detonation will most commonly occur before ignition firing. If you are at full throttle at 6k rpms, and pre-ignition happens at 70 degrees BTDC, you are still going to break or bend something no matter what our pistons are made of. Our engines are not as bullet proof as you think. It certainly won't grenade like a 350, but internals will bend or break.

As Jesse said (haha JesseSays... get it? ), shaping the combustion chamber and eliminating hot spots helps immensely to prevent pre-ignition. Of course pre-ignition at earlier intervals will be seen in turbo applications over NA because of the pressure in the cylinder befor the piston even begins to move back up to TDC. The more pressure, the greater chance of pre-ignition.

Just because our engines have light-weight pistons and a low rod ratio does not mean our engines are impervious to pre-ignition.

[Gen1GT]

The BPs rod ratio is 1.56:1, and the FSs is a horrible 1.47:1. A Chev 350 with 5.7" rods has a ratio of 1.64:1. Edwin, the BP has an EXTREMELY fast piston speed compared to a 350. But since it's a strong, and relatively lightweight piston/rod combo with a short stroke, it can still rev. Rod ratio does not mean you're immune to detonation, but a low rod ratio means the detonation has less to cause havoc. Especially at high RPM. A guy on the msprotege board recently built and dynoed an FS-DE with 13:1 compression, and with pump gas, got 223hp. It wouldn't be possible without aluminum pistons, and the FSs short rod ratio.

zenilder, detonation can happen ANY time before ignition, and even DURING ignition. The more the intake charge is compressed, the closer it is to self-ignition. It can come from poor fuel self-igniting, from hot spots, which create a flame front just like the spark plug. Piston material DOES influence detonation characteristics, as aluminum transfer heat better, and is less prone to hotspots.

What everyone is confusing, is compression ratio, and compression pressure. As I've already pointed out with this chart...

http://members.aol.com/solomiata2/BoostCompRatio.gif

10:1 with 10psi, will give you the same compression pressure as an engine with 8:1 and 16psi. They will both have the same level of detonation proneness. When you compress air, it heats up. With enough compression, it can self ignite(like a diesel). That's detonation. Both examples will have the same amount of compression pressure. The difference? The 10:1 engine will have better fuel economy and better drivability. Did I mention higher compression engines are more fuel efficient? An engine with 11:1 compression, can use less fuel to make power than an engine with 9:1 compression. ie, a 1.6 with 11:1 compression would make as much power as a 1.8 with 10:1 compression.

[Gen1GT]

Our engines put anywhere between 15-45 degrees of ignition advancement depending on how you set the distributor.

Stock timing is 10 degrees advance, and at 5000RPM, the electronic advance adds 24 degrees of advance. So at 5000RPM, a stock engine runs 34 degrees of ignition advance. In my case, 42 degrees. I tried 20 degrees advance, and lost 2whp, although(just as I preach), there was absolutely no ping.

[Gen1GT]

but hey, the FS's rod ratio isn't as bad as the QR or probably the 1ZZ-FE

QR?

The 1ZZ-FE has a rod length of 146.55 and a 91.5mm stroke, which gives it a rod ratio of 1.6:1. I thought your research skills were better Edwin....

The BP had 133mm rods and of course, an 85mm stroke. As you can see, the 1ZZ-FE has some pretty long rods for a small 4 cyl.

The FS is a stroked FP-DE. It 135.2mm rods, with a rather long 92mm stroke. Because of the deck height of the FP, they couldn't make the FS rods any longer. Since they wanted to enhance torque over the FP, the short rod ratio was what they were looking for. With a longish stroke, and a horrible rod ratio, the FS is the last engine you'd want to make a screamer. I'd like to see an engine with a lower rod ratio, as I'm not sure one exists. There are ways around it of course, like makinng the rod journals smaller or lowering the compression hight of the pistons.

[Geovannie]

Stock timing is 10 degrees advance, and at 5000RPM, the electronic advance adds 24 degrees of advance. So at 5000RPM, a stock engine runs 34 degrees of ignition advance. In my case, 42 degrees. I tried 20 degrees advance, and lost 2whp, although(just as I preach), there was absolutely no ping.

Thanks for that info. I asked about that a while ago. Still have not figured out that one timing problem. Stuck at full advance. **** it it runs good that way and soon it will be solved with a stand alone.

[Gen1GT]

Proof you don't need lower compression to get power. Here's a Miata running stock 8.8:1 pistons....yes, that dyno chart says 462whp

http://www.cardomain.com/id/candrew

[Geovannie]

Proof you don't need lower compression to get power. Here's a Miata running stock 8.8:1 pistons....yes, that dyno chart says 462whp

http://www.cardomain.com/id/candrew

from that link

" JE 9.0:1 forged pistons, Crower billet connecting rods, ARP head studs, balanced/lightened/micropolished crankshaft, '01 Main Bearing Support Plate, everything balanced/blueprinted, swirl polished/oversized (1mm) stainless-steel intake valves, swirl polished/oversized (1mm) inconel exhaust valves, ported/polished/flowbenched cylinder head, dual valve springs, titanium retainers, '99 solid lifters, '99 camshafts, and Mazda Comp. adjustable cam gears.
"

[Gen1GT]

Sorry, I meant that he was running stock compression ratio, not stock pistons. And yes, Miata's stock compression is 9:1, not 8.8:1 like the Proteges....my bad

[charles]

94 Proteges supposedly got the true 9.0:1 pistons.