fyi, wiseco does not make a 9.0:1 piston
 

Many retailers advertise 9.0:1, but this is not what they sale. So now, I just sold my old 8.6:1 pistons because I wanted a higher compression, and I'm getting 8.5:1 pistons.

I guess I have to buy the FM 9.0:1 Wiseco pistons, since its a custom piston.

no... JE Pistons bro, I just ordered some a couple days ago. They come in 83.5, 84, and 84.5 mm for about $500 w/rings.
http://www.jepistons.com/cat/je/sport/mazda/bp.shtml

I still think you're retarded for selling the supertechs.

Why would you go through the trouble of selling your 8.6:1 ratio pistons and only upgrade to 9:1??? If your so worried about low compression ratio's as to sell your 8.6:1, you might as well go to 10:1. If you don't you'll probably be selling your 9:1's before long. JE makes 12:1 I believe, buy those. Buy something and install them and be happy.

I drove an 8.5:1 supercharged car, and it fucking sucked ass. I don't want to deal with the lower compression, on a motor that has too big of a turbo.

My vw was a fucking turd out of boost at 8.5:1.

yeah, spend $2000, and enjoy living with your fucked up mistake, shitty slow car which never spools.

More timing off of boost (used to run up to 60* off boost on a 3sgte with a 66mm turbo and C16, off boost was peppy). Or mill your head...

See I would have kept the 8.6:1 and had the head and/or block machined to get a more compression.

Do you seriously expect to be out of boost much driving the car on the track?

the slight bump in compression will get the car moving out of boost, and spool earlier. I want the turbo to spool before 4000.


I'm about to take the 8.6 supertechs to UPS anyway, I already accepted the paypal monies.

my jetta had 1500rpm of power with the big turbo, and I don't want to live with that in the miata.

You are so over thinking this.

its easy to say when its not your money, and your car driving like shit. I'd like to have more than 1500rpm of power.

It's easy to say because it is true. The silver lining is that y8s get's a good deal on some pistons.

So exactly how much earlier will your turbo spool because of the additional compression from the 9.0:1 over the 8.6:1? How much more power are you going to make?

I guess for piece of mind and the placebo it might be worth it for you.

So what are the pistons in my car. They're .020 over, all the documentation i've read says 9:1.

:rofl:
To each his own. You know what has 9.0:1 pistons? The stock motor. Just do it and be fucking done already.

#K533m835 is 8.5.

I just went and checked their catalog. Looks like 8.5-8.8:1 is what they say the .020 over pistons were.

My car is not slow out of boost and it spools my little turbo just fine. I'll let you know how the larger T3 setup spools when i swap it over.

what turbo and exhuast? Its going to take a lot more air to spool my gt2860rs with the low comp slugs. I want to see 12 psi by 4000rpm. I'd rather change pistons now, than try to sell this turbo and waste more money on a gt28r which I probably should have purchased in the first place.

Bore has nothing to do with compression. Look at "dish" and deck-height.


I'm so tired of the anxiety over this. I lose sleep over this crap.

Little Garrett T25 .80/.48 with a super shitty downpipe that has a crushbend in the bottom that necks it down to more like 1.8", the rest of the exhaust is 2.5" with some shitty generic baffled muffler.
Our engines aren't slow revving slugs, they rev fast and climb in RPMs fast. When you want to go fast you're going to be getting into the pedal deep anyway. THe GT2860rs is not a slow spooling turbo. Isn't that the whole reason people buy it, fast spool and big power.
Quit losing sleep about the pistons man they don't suck.

Hurm, my stock 1.6 spooled that size turbo to 10psi just a little past 4k. With no tuning done... and a damaged turbine wheel.

well, everyone aside from the guy who sold me the turbo thinks its too big or too small for 250whp. I think the 9.0:1 pistons can only help since I'm only going to put down 250whp, and I'd like to have 12psi at 4000rpm so I don't have to constantly slam gears on the track like I do at 94whp.

Hopefully I didn't fuck up by selling these pistons.

well, I'm hoping for 12 psi by that mark, so this supports my thoughts.

hopefully I don't have to mill too much off the head, so I then have to sell the pistons I have currently and buy another set of 8.6 pistons, and still be fucked in the long run with a car that is either going to pop the motor because of too high compression, or be sluggish off boost because of low compression.

:rofl: Welcome to the world of compromise.

Hustler,

Do you have a Megasquirt?

yes

Man, this is kind of exciting for me. Maybe i'll be able to run some serious timing when i get Jerry to tune the car.
Edit:
Just checked the paperwork on my pistons part #k553m835
Kind of weird that every website except wiseco's catalog says these pistons are 8.6-9.0:1 while wiseco's catalog is saying 8.5-8.8:1.

You obviously haven't seen my turbine wheel :p

now I kinda wish I wasn't selling these. I tried to not think about stuff so much, so I put the pistons up, and they sold. Now I'm feeling like I may have fucked up. lol, I'm a walking catastrophe of indecision.

I would say keep what you have and either

A. Increase off boost timing (you have low comp pistons, you can afford to). You could even have the water/alky injection that you have come on while in vacuum and add an enormous amount as in the example I gave above. We were running C16 and added between 18-25* of timing off of boost, this gave us an extra ~40whp while in vac, much more useful than 1-3rpm earlier spool as far as I'm concerned.

B. Retard your timing while off boost to spool the turbo earlier. I only did this a few times at the request of customers so I don't know about the long term effects on the turbine but short term it decreased lag about 500-1000rpm (talking 70+mm turbos). You could even make a separate map for this...

Just don't sell them, if they haven't shipped you can still give a refund?

MS table switching anyone?? Only one toggle away.

I did something similar on another MR2, I connected the two-step switch on a TECII to the upper clutch safety switch and gave the clutch enough free-play that you could press the pedal enough to activate it with out engaging the clutch. At any point you could lightly touch the clutch pedal and get a near instant 20-30psi (depending on rpm).

so i guess I should go ahead and pull the trigger on these 9.0:1 JE's. I hope they fit with the probe rods.

Its either the 2618 JE's, or the 4032 supertechs. I don't know if I want more strength, or less thermal expansion. I'm leaning toward the 2618 JE's since the 9.0 considering the higher compression.

If you want your turbo to spool sooner, do headwork. You could drop spool RPM by 5% by cleaning up the ports of casting marks and port matching the intake to the head. That's probably more difference than you'll see going from 8.6 to 9.0 compression pistons. If you were to unshroud the valves enough, reduce the shortside radius, blend the bowls into the throat and combustion chambers correctly, etc, etc, you could drop spool time closer to 20%. Not only would it drop spool time, but your getting 20% increase EVERYWHERE. The motor would make more power everywhere, which seems to be what your after. You want 250whp total, but you want a strong motot that's peppy not slugish. You would be MUCH better off improving the head to gain a 10% increase in power vs. upping compression to compensate for flow. The motor will have more potential for boost and you'll be less prone to detonation. Your way overthinking how important compression is. You should read some books about this stuff. There is a certain degree of science to it.

From Corky Bell's book 'Supercharged' "...Raising the compression ratio only increases the efficiency of burning the same amount of air/fuel ratio. The best to be hoped for in changing the compression ratio is about 4% more power per compression ratio point." (26 Bell)

Your already second guessing yourself about selling the 8.6's, so I wouldn't "go ahead and pull the trigger on these 9.0 JE's" Instead you need to read some shit and learn what your doing so you can make an informed decision, instead of this random spur-of-the-moment shit.

Edit: using Bell's numbers, you could see possible gains up to 1.6% in power going from 8.6:1 to 9:1 comression ratio pistons. Wow.

Keep your current 8.6:1 pistons and spend $35 and deck your head .020 and you will be at 9:1.

noooooooooooooooooooooooooooooooo

hey i run 10:1 compression on a turbo car. it feels like my old celica off-boost. celica was 8.5:1.

I'm familiar with the concept. However, that's 4% peak hp. There is no way to tell power levels at low rpm levels without doing more math than I know how. I do not want this car to drive how my old turbo corrado or jetta did. The corrado went from 130lb/ft to 460 in 700rpm. It was impossible to drive.

The car was impossible to drive.

if you hadn't sent the ching-dow last night, I would have held on to these.

This statement confirms to me that you don't know shit about motors....

That's what I was thinking. He should read up about engines as he's too critical. He would be better informed and happier in the end when his motor opperates as he wants it to.

This thread pisses me off....Compression has little to nothing to do with spooling a turbo. Displacement on the other hand has much to do with spooling a turbo. A 1.8L will most likely have a gt28rs in full boost well below 4k in any gear but first. My guess would be around 3.5k.

I spent a megaton of money on my turbo 2.9 vr6, and it was almost underivable with power delivery.

So you don't get your fucking queer as panties in a bunch look at this dyno. http://forum.miata.net/vb/showthread.php?t=258097

Hmmm, just like a thought....3.5k rpm. I must be a fucking genius, oh wait no, I just happen to know shit about motors...

wouldn't less higher compression create more heat, and more energy in exhaust gas means more spool.

this is what I want to avoid:
http://i23.tinypic.com/23lfw3c.jpg

I've seen enough dynos in my life to know that it will not make any tangible difference in spool. The only thing it will do is make the car a little more peppy off boost. Considering where that turbo will have full boost can you honestly tell me that fucking matters? Even on the highway you will have 250lbft of TQ at what I wouldn't even consider high boost whenever you want it.



edit:: The above post is just an example of a poorly put together setup. I would put 0% blame of that power curve on the pistons. ZERO PERCENT!!!!!

http://www.digthechick.com/FUN/crash-kick-in-nuts.gif


what turbo are you running?

Yes. I remember in the corrado how I had to change gears before boost because it would smoke the tires at 4500 rpm...but you had to rev it that high becuase it was such a slug off boost.

Also, on the actual thread topic, wiseco will make you a piston at any damn compression you want. They run their business based on one offs. Its just places like race engineering that buy large quantities of pistons so people like me can get them in 3days. If you ordered through Wiseco directly even to get an "off the shelf" piston you would have to wait the same 3 weeks as your custom piston. The reason being that they have no "off the shelf" pistons. They are all made to order.

gt2860rs

fuck!!!! I'm trying to get the motor built next week. Everything is rushed now because I'm moving.

I'm done man, you can do whatever the fuck you want with your motor. I've tried to help you in numerous threads of yours. You're just like a friend of mine, probably worse, in that you just don't trust anyones advice. Even when you ask someone else something, you don't trust their answer or experience. I'm done giving you any of my advice....

for one thing, your 1.8L will spool it well below 5K, for another, you can add timing advance to make up for the loss of compression. for a third, you're insane.

Sure, 9.0 over 8.6 is a 1.6% reduction in spool time. If you normally spooled at 4,000 RPM's, you would drop that number down to 3,936 RPM's. Energy is the key word. It takes energy to spool a turbo. Retarding the ingnition timing will reduce the power the engine is making, but increase the energy going into the exhaust and cooling system. That extra energy in the exhaust would help to spool the turbo. Makes since to me to retarding timing at certian times to help spool the turbo. Once it's spooled, then run as much timing as you can.

Rushing an engine together is the WRONG thing to do. Period. You need to do it once and do it right. I've already explained what's important on building and break-in so you know you can't rush this thing together. Let's stop beating that dead horse. I think the members of this forum are in agreement that you need to do some learning on your own. Quit whining.

Your advice is valued, but other people disagree. TDR swears up and down that he hated the 8.6 pistons in his car, and promptly switched them to 9.0. So far, that's the only real work experience I've heard of from miatas, and I've never seen a real comparison of static compression ratios.

I don't want my car to drive like an MSM, even though that car is at 9.0 and makes 8psi at 4500rpm.

I'm not moving in the miata. That would take a while with a 10-hour commute.

does anyone actually have experience with a low compression motor?

Not in a miata, but a VW. 8.5:1. It really isn't a slug off boost, it's all in the timing and fueling. If I can find it after work I'll post the dyno charts.

Currently I help with a 8.6:1 20V drag car running a SC61, which is a massive turbo for a VW motor. With a ton of advance down low and pulling some fuel we were able to get it to fully spool at ~5,000 rpm.

8.6:1 is not going to be a problem. I'd venture a guess you could drive two identically prepped cars; one with 8:1 and one with 9:1, and you'd be hard pressed to be able to differentiate.

So with a .4 bump in compression it would have gone from 135lb/ft to 465 in 690rpm. How has the situation been improved?