Re: 9-1 compression pistons w/ stock tune

Every time I check this thread I wince at my miss of the 9-1 when it should be 9:1.
Been doing a good bit of searching and reading over the last few days but have not found this particular question answered. Has nobody ever run into this question before?

 

Re: 9-1 compression pistons w/ stock tune

I can't give you any firsthand experience but I've always leaned towards 8.5:1 for the fact that you have a bit more leeway with tuning. Maybe one of our drag/high power experts can chime in with some real world knowledge.

 

Re: 9-1 compression pistons w/ stock tune

For the little extra hp that the increased compression ratio gives you, its not worth the derease in knock threshold, you will gain more power with the increased timing with the 8.5's

 

I run 10.5: 1 on one motor and 9.5-9.8:1 on another. No issues.

 

On the stock tune Gary?

 

You shouldn't have any problems running 9:1 cr on a STOCK tune. The stock tune is overly rich anyways and you should be perfectly fine

 

Thanks for all the suggestions guys. My original reasons for investigation 9:1 CR pistons is that the guy I am building the motor with said he was a fan of Mahle, which only seem to make 9:1 for the 2g, and the guy whom I am tuning with said he would go for 9:1. But, he is an evo tuner and is used to the higher stock compression. I have to run the motor on a stock tune for registration purposed before I can mess with it for track days.
Car is 99% a daily driver, and I don't have goals far beyond the 400ish hp and 11sec mark. Post researching and all the helpful comments I am leaning towards 8.5:1 and maybe Wiseco standards. Still a bit on the fence though. 9:1 on an economy tune might yield good commuting mpg, and is the extra .5 worth it for later and a larger turbo once the car is no longer a daily? Right now I am running FP68hta.

Thanks to the mods for fixing my original title! Now it makes so much more sense.

 

i would keep with the 9:1cr any lower is stupid in my opinion and not needed even for a daily driver. I Ran 9.1 on my first built motor and recently swapped to 10.5 on my current setup (Evo) and it is words different and i drive mine mostly on pump gas and e85 for the track.

Cons: Better off boost drive abilty, a couple hundred rpm increase in spool. and is a happy medium to use for pump gas, race gas or E85

 

Keep this in mind people before you go suggesting higher compression for him: his location is in California, they have nothing for octane there.

 

Good ole commiefornia!

 

I'm not sure why you'd want to go with a forged piston on a DD. Do you not put many miles on it or just not care about the lack of longevity?

 

Haha yes we do have horrible fuel here, and no E-85 in my town yet. Oh well.



I was concerned about just that though the guy who I am working with did not think there would be any issues. Should I be looking into evo VIII pistons, or spend the money to buy new OEM ones? My overall goal for the car is a reliable DD that I can take to the track occasionally.

I don't want to start a new thread but I guess I should be asking for suggestions here on build options. I could also look into getting a new stock short block and just getting the head rebuilt. Either way my goals stay the same.

 

Well, with the expansion rates of forged pistons you'll probably only get 30-50k miles. While there are exceptions, it is rare for them to last longer than that. If that's something you're fine with then no problem. The thing I've noticed is that there are far more people that know how to assemble an engine than people that actually understand what's going on and build an engine.

For your goals of a DD with around 400hp, I personally would go with a hyper eutectic piston. They run nice tight bores, don't expand much, and will last much longer. They'll just come apart quicker with too much detonation, and don't have ultimate power capabilities of forged.

 

That made for some good reading. Learned a lot about silicon content and how that translates into piston behavior. Correct me if I'm wrong, but stock 2g pistons are indeed hypereutectic, so all good there. So now I am at a pretty clear choice. Either buy a new oem shortblock and get the head rebuilt, or get the longblock rebuilt mostly stock but with arp rod bolts and maybe upgraded rods along with head work. Honestly I am kind of leaning towards just getting a new oem shortblock. A bit more expensive but only slightly when everything is considered. I would then have a spare block. What are the expert opinions on these two choices?

 

I'm not sure I qualify as an expert, but I personally would rebuild your shortblock with an NPR 2g piston, 6 bolt rods reconditioned, with arp's, and machined to use in the 7 bolt and just reface/back cut your valves, upgrade to a manley single coil spring, and call it a day.

At the end of it you'll have an engine that is a bit better than stock, will definitely hold the power you're looking for, and dead nuts reliable.

 

Thank you for the advice, it's appreciated. Now I need to decide if I can trust any engine assemblers around here to understand what I would be talking about. Sure wish I had the time and space to do it personally, but that is for another time.

 

I have similar goals to yours and from my research (a lot of research over years) I am going with the NPR 2G pistons/1G 6 bolt rods, ARP main, rod, and head hardware and I am expecting to push 350-400 horsepower with a Holset HX35, reliably. From everything I have read it is very possible.