MX-3.com

From MX-3.com UBB (link is here ):

"In essence, a low compression motor is good to turbocharge, because it is just easier to do so...and not worry about it. But is that what we really want to do as enthusiasts? Do we want to just slap a turbocharger on a car, and call it a day? Absolutely not. With turbocharging, comes the responsibility of tuning and care. If you are just going to turbocharge your car, and call it a day, then frankly, you don't deserve the luxery of boost! As well, might I add...that simply because it is easy to slap a turbocharger on a low compression motor and not worry about it, does not mean that it is right. I can guarantee you, that if you turbocharge a low compression motor, and fail to tune it correctly, you will end up on the side of the road, with blue smoke coming from your exhaust pipe.

Generally, a lower compression motor affords you more margin of error, when tuning. A slightly imperfect a:f ratio probably won't lead to the demise of your motor...unless you drive like a total jerk.

Why should I consider a higher compression motor, while making my decision of what motor will suit my needs?

Different from a low compression motor, a higher compression motor will not give you a large margin of error, when tuning. As stated before, if you expect to slap on a turbocharger, and call it a day, well then stay away from the higher compression motors all together. A higher compression motor demands slightly more TLC than a lower compression motor. But oh, the rewards are plenty.

Bottom line...a higher compression motor, pound for pound, will make more power, than a low compression motor. This works along the same lines as naturally aspirated Honda motors. You never see an NA enthusiasts spouting off about low compression do you? No, one of the keys to NA performance is high compression. So, why should it be any differnt for turbocharged applications? Of course, the routes to high compression are different (NA uses lightweight rods and pistons, that a turbocharged application would simply tear to shreds), but the end goal is the same. "...

Hope it helps!

11:1 compression + boost would kill probably 98% of the you guys engines simply because of the TONS of dollars you would have to spend on a engine management and fuel system. Some Pro turbo cars run 10:1 or a little higher, but they are burning Methonol and NOT gasoline. To my knowlege C16 race gas doesn't even have a high enough Octane rating to run that kind of compression under decent boost! On a Methonol engine the Air/Fuel ratio has to be twice as rich as a Gas engine. For the majority of you I would recommend 8.5:1 up to maybe 9.5:1 on a well tuned moderatly boosted engine. The only time I'd recommend 10:1 or higher is if your car is a drag only car. Ofcoarse you can run 11:1 and MAJORLY retard timeing + use BIG injectors and a BIG fuel pump, but you would end up making less power than running a slightly lower compression w/ more timing advance!

My car will be running right at 9:1. When I get to crank up the boost and hit the Nitrous it's gonna take a Stand Alone (FINELY tuned!)w/ about 1000cc's of gas PER CYLINDER and either DUAL intank Whalboro 255 fuel pumps or a Aeromotive Tsunamie inline pump connected to 1/2" fuel lines! Now thats $h!ty gas milage!!!

<small>[ March 03, 2004, 07:10 AM: Message edited by: JWMotorsports ]</small>

Originally posted by mx-k:
I was just looking into stuff I can upgrade when I'm done my turbo project and came across a site saying that they have new Wiseco pistons coming soon for the miata 1.6l. They are listed as giving 11:1 compression ration. Now I know generally everyone here says if your running boost, lower compression is better. But if one was to put these pistons in with new rods and maybe some cams, wouldnt you see a huge increase in power per pound of boost?

For now this is just an idea, but I wanna look in to something to do next winter, and I've never rebuilt a whole motor before so I figure this would be a good project. Also with an 11:1 compression ration and like 10psi of boost, wouldnt the results be pretty wicked?

high compression + boost = less lag + more hp/psi. thats exactly correct. my ze has 10:1 comp running on 89 octane is fine. you will be fine with boost and 11:1 compression maybe more but you must have proper tuning and a good ems.

the only reason to lower compression when boosting is because you are need the extra margin of error because you are self tuning without a dyno or you want to boost more to get hp with the extra margin of error. with higher compression, tuning fuel maps and timing need to be more precise but the high compression will make more hp and have less lag.

if u all dont think high compression + boost mix perhaps you should look at the m5 engine compression ratios then the bolt on supercharger kits that they make for them that do not have any low comp pistons.

I don't know why everybody is scared about high CR on boost....you just got to have a very good intercooler and high octane
(probably going to need octane booster) to prevent detonation...you must make sure that you got all the fuel needed too...A healthy engine with a high CR BUT highly tuned will make it...just my 2 cents

It's all in the tuning....

Yes a lot of Hondas have high compression, but they aren't running but about 5-10psi on stock internals. If you turn up the boost much more than you could kiss the bottom end of that Honda motor good bye! You can run high compression but again, I'm telling most of you can't afford the fuel and engine management you need to run it. Low moderate boost with a large intercooler, big fuel injectors, Super AFC, and Whalboro 255 pump, colder plugs and high flow exhaust will work, but you better dyno tune it w/ a wide band O2 before you hammer it! If you tried running 11:1 with some health boost on pump gas with octane booster, I'm gonna be rolling when you start B!tching about a rod through the side of the block or a hole burt through your piston!!! Do some research and talk to some REPUTABLE tuning companies and you'll understand why I'm telling you this. I'll be praying for you, & your engine!


<small>[ March 04, 2004, 12:21 PM: Message edited by: JWMotorsports ]</small>