question about stock versus 9:1 ratios on an NA block

[Chaotic_Warlord]

I have a question for anyone who's upgraded their pistons to aftermarket ones. I am looking to turbo my block so I am planning to do a 9:1 piston swapout with the reinforced rods. My question is two parts; first is there any real performance difference between a stock 89mm 9:1 piston vs a 90mm 9: piston with a .050 overbore? The second part is if I do this would I see a decrease in performance over stock without having a turbo system installed or will I see an increase in performance. I'd do a search but honestly I have no clue as to how to go about searching for this specific question(s). I understand that upgrading to a 10.5:1 compression ratio would give me added NA performcance but since the stock ratio is what like 9.5-10:1 I don't know if I would actually degrade or increase my NA performance with 9:1 ratio, so let me know.

IPP has ross 9:1 pistons in stock 89mm trim are these good or should I fork out the money to do the .050 overbore? Any help you guys can provide would be beneficial and much appreciated.

[:: orion ::]

Stock KA24DE ratio is 9.5:1 for all years...

And going to 9:1 will yeild very little difference...most accept 4% per compression point bump as a guide to HP increase. So if you drop half a compression point, you're looking at losing ~2% power...so ~3HP or so.

But you can make some of it back up by adding a little timing until you turbo it...it's all about cylinder pressure, and you can affect that with more timing.

- Brian

[:: orion ::]

Oh...and the diffference in displacement will be negligible...it's 3 cubic inches.

239Xcc versus 244Xcc...

[Chaotic_Warlord]

thanks you guys, I was looking at a smaller ratio but I can wait to do that until Im under boost. Plan on running stage 2 cams with reinforced valves and springs so the powerloss will probably not even come up. Wish my GI bill comes in so I can order the parts. Would I need to do anything with my ECU if I change my ratio, like would my fuel map change or anything.

[DjPantsSpecR]

nah, you'll be cool and the gang, just keep saving up for turbo parts. you dont need to mess with any fueling if you're just losing a few compression points. i might advance my dist in an attempt to gain back a little top end, but this is entirely unnecessary

are you sure you wanna use the lower compression pistons while you are saving up for a turbo, or is this jsut going to be a thing where you only gotta save up for a few weeks

[Chaotic_Warlord]

My engine currently has almost 240K on it so all the parts and tired and beat up anyways. So since I am in need of doing a rebuild anyways minus well get the heavy internal engine stuff out of the way. I am joping to have my turbo kit by the spring so a couple of months shouldnt hurt, going to do this in stages. Just waiting on my GI Bill to kick in so I can go ahead and order the parts.

[sunnys14]

if you got 9:1 compression ratio with a .20 overbore, wouldnt the overbore compensate for the compression ratio loss?

[SonyPete]

Damn double posts

[SonyPete]

Yea increase in bore will bump up compression. But when aftermarket pistons state a certain compression such as 9:! they have already compensated for the bigger bore with changes to the compression hieght or changes in the dome or dish on the top of the piston.