Best piston(type) boost and compression
Thread Starter
Melting Slicks
Joined: Apr 2018
Posts: 3,185
Likes: 779
Best piston(type) boost and compression
trying to get smarter on pistons and what each style will do for compression, which ones work well with factory connecting rods. Looks like I’m going to build the bottom end, another forum member “Mordeth” dropped a lot of science on me this evening! Just an awesome guy btw. He did suggest I do my own research on pistons and which ones work best with boost and figure out my ideal compression ration. He said he just wasn’t up to speed on boosted applications, he was on damn near everything else. So I’ve started my quest for knowledge, this forum has provided a bunch of good info for a new vette owner and I honestly can’t thank you guys enough. So my path to get smarter on pistons and compression had begun, googling and reading, figured I’d throw this post out and see where you fine gentlemen lead me. So if you take the time that read this and post your opinions or have some essential readings I thank you in advance. 🇺🇸
Thread Starter
Melting Slicks
Joined: Apr 2018
Posts: 3,185
Likes: 779
Oh yeah I stumbled across an article from LSX magazine and it mentioned a specific dished piston made for boost on LS7’s. RACEtec dished. It was a good read and mentioned why these dished pistons were ideal for boosted LS7. Link below. I could care less about which brand of forged piston I use, I don’t have any brand favorite or anything. Just looking for info,suggestions and real world use feedback.
LSX magazine link on RaceTec dished pistons
https://www.lsxmag.com/features/pri-...-boosted-ls7s/
LSX magazine link on RaceTec dished pistons
https://www.lsxmag.com/features/pri-...-boosted-ls7s/
Team Owner
Joined: Nov 2007
Posts: 24,035
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From: Gilbert AZ
There are tons of good ones. All depends on application. Talk to Mike@RES or Anthony@HPR and they can set you up. There is no "best", just what is ideal for your application. You may want to keep stock or higher compression and just do a nice forged piston, or you may want to drop compression. It depends on fuel, blower, power goals, etc. Then there is ring packs, ring sizes, coatings, etc etc etc etc.
Team Owner
Joined: Nov 2007
Posts: 24,035
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From: Gilbert AZ
Lower compression pistons are going to be dished, you need to decide what you are going to do. If the car is staying as is, or are you going for more power later? What fuel? Do you want to keep it snappy and responsive down low, or willing to give some of that up? How good is your tuner?
Thread Starter
Melting Slicks
Joined: Apr 2018
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So I’m going from a 6 rib system with 4.25 blower pulley to 8 rib system IW 10% OD crank pulley and 3.7” blower pulley(all parts on hand) AHP heads milled .0010 with chamber softening as well. New custom grind blower cam from cam motion and I’ll be doing E85. I don’t have new injectors on hand yet.
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Team Owner
Joined: Nov 2007
Posts: 24,035
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From: Gilbert AZ
Have you checked max blower speed? A 10% OD and 3.7" maybe way past what that blower can do.
Should not mill the heads, that is a bad bad idea. Not only does it not work as well for boost, it also weakens already poor castings.
ID 1050x, ID1300x for injectors. Don't settle for anything less.
Should not mill the heads, that is a bad bad idea. Not only does it not work as well for boost, it also weakens already poor castings.
ID 1050x, ID1300x for injectors. Don't settle for anything less.
Team Owner
Joined: Nov 2007
Posts: 24,035
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From: Gilbert AZ
8" lower, 3.7" upper, with a 4.10 step up ratio puts it at max RPM at ~7300rpm, so you have it tapped out pretty much.
If you are doing e85, or Flex fuel, I would target ~11:1 to max out the power, keep it efficient, drive the best, and fill in low end from the centri/cam.
If you are doing e85, or Flex fuel, I would target ~11:1 to max out the power, keep it efficient, drive the best, and fill in low end from the centri/cam.
Thread Starter
Melting Slicks
Joined: Apr 2018
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Ok that’s good **** right there now I have a target for my piston selection. I spoke with a engine builder a few minutes ago and liked what I heard so far, gonna bring what I’ve got to them Friday and get a better feel for these guys and their shop. I can always exchange the blower pulley for a larger diameter if I need to maybe 3.8/3.9”
Thread Starter
Melting Slicks
Joined: Apr 2018
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So I had a productive day with a couple a machine shops, still haven’t made a choice on who going to do the work but I have decided regardless of who does the work I will source all parts needed on my own. I’m liking these racetec dishes pistons. I could use some input or clarification though. These pistons will bring the compression rate down to the high 9’s. That’s a good thing correct? I know I was taking Unreals advice and shooting for under 11:1 or 11:1 max. 9.7-9.9:1 isn’t too low right?
Team Owner
Joined: Nov 2007
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From: Gilbert AZ
Depends on what you want. That opens up the tuning window, but you lose low end, efficiency, and power. If you have the octane, I would keep it high. If you are doing e85, no reason to go down into the 9s. Especially with a small blower. Now if you want to run a F series later and make 1000+, then dropping it can be ok. I personally can't stand low compression motors. After driving Joe@CPRs 11:1 blower car, I was sold. My old motor was a 9.7:1 and now I'm upping it because with good fuel, I rather have all the benefits of higher compression.
Thread Starter
Melting Slicks
Joined: Apr 2018
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Ok got it, so if I do run a dish I’ll need a custom piston, if the shelf @ .23.5 is gonna bring compression Way down, like 9.6:1, I honestly don’t know if I may go to a bigger blower, last week I would have said no way. Now that I’m building the bottom end property for boost I guess I could see a D1X-F1X in the future. So I guess I need to make that decision. So could I use a flat top piston? Again the heads were milled .010 so I do neee to account for that I’m assuming.
Drifting
Joined: Jun 2016
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From: Temecula, CA
My guess is that with a built bottom end, you will quickly want more power than the P1SC can deliver. The milled heads raised your compression so you will need a dished piston to bring the compression back down, especially if going to a bigger blower at some point. With e85, I would aim for 10.5 to 11:1 compression.
Team Owner
Joined: Nov 2007
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From: Gilbert AZ
If you ever go big power those heads have to come off anyways, and block needs to be sleeved, so keep that in mind. So without dumping a ton of money now, your choice is either throw in a ~11:1 with the milling will be ~11.1-11.2, which on E85 would be amazing, or throw in the dish ~9.5-9.8 and play the safe conservative route knowing you are giving up some power/efficiency/mpg/low end/etc
Thread Starter
Melting Slicks
Joined: Apr 2018
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Can I achieve 11:1 or 11:1.1(2) with out a custom dished piston? I’m 100% open to any and all suggestions. I kinda zoned in on those racetec’s because they were specifically designed to keep the titanium rod and have the same angle geometry, it’s kinda off set or canted a little bit same way the factory pistons connect to the factory rods.
Team Owner
Joined: Nov 2007
Posts: 24,035
Likes: 2,339
From: Gilbert AZ
Yes you can easily run a flat top or whatever size piston. Custom pistons are nothing strange or special. Takes a few days to cut them to shape/size. Plenty of other companies that make same type of pistons for stock rods as racetec. I would call RES or HPR and just have them order you the pistons that fit your goals. Almost all pistons are made in a few places these days anyways.