Poormans "LS7"
Thread Starter
Melting Slicks
Joined: Jul 2016
Posts: 2,521
Likes: 219
From: Los Angeles CA
Poormans "LS7"
I have an 99 FRC I bought for weekend road course and autocross events. I'd like to go dry sump while increasing torque, so I had an idea, however I am not experienced enough with what exists and what is capable with the LS series, but I can do about 75% of the machine work, I just need to know if it's possible. I believe the pro's outweigh the cons, if it will indeed work.
I'd like to grab some stock LS7 rods and an LS7 crank, run a forged piston in an LS2/LS3 block. The math makes sense, the only thing I can't find is aftermarket piston schematics to ensure there's proper pin placement. I'd also like to keep compression in the 11-11.5:1 range.
So on to the math
Crank 4" Stroke
Rods 6.064
Bore ~4.070 neighborhood
Deck height 9.240
Now assuming I cut a modest .010 the deck off any used block I buy, that leaves me with a piston that requires a compression height of ~1.165, which a quick search shows JE has, but I did not see any in a -5cc configuration, only domed.
So assuming the "shelf" pistons have the same pin placement as the stock LS7 piston, and if there's not, what is an acceptable deviation that would still allow for a reliable piston to rod configuration? And what other brands would have something in a valve relieved -4cc to -6cc configuration?
I'd like to grab some stock LS7 rods and an LS7 crank, run a forged piston in an LS2/LS3 block. The math makes sense, the only thing I can't find is aftermarket piston schematics to ensure there's proper pin placement. I'd also like to keep compression in the 11-11.5:1 range.
So on to the math
Crank 4" Stroke
Rods 6.064
Bore ~4.070 neighborhood
Deck height 9.240
Now assuming I cut a modest .010 the deck off any used block I buy, that leaves me with a piston that requires a compression height of ~1.165, which a quick search shows JE has, but I did not see any in a -5cc configuration, only domed.
So assuming the "shelf" pistons have the same pin placement as the stock LS7 piston, and if there's not, what is an acceptable deviation that would still allow for a reliable piston to rod configuration? And what other brands would have something in a valve relieved -4cc to -6cc configuration?
Melting Slicks
Joined: Jun 2006
Posts: 2,497
Likes: 261
From: Miami Florida
Call Texas speed about the pistons and any other questions they have several different pistons with different number cc.
Careful going over 0.030 on the ls2/3 block sleeves they are weak and thin.
The pistons are out of the deck already by 3 to 6 thous so you may not want to deck block.
May I suggest something?
Sense you seen to know your way around machining why not use oem crank and ls3 rods and put you machining effort on the block and re sleeve it to 4.185 and use a solid roller cam on e85 and crank compression up to 13.5 or 14?
Careful going over 0.030 on the ls2/3 block sleeves they are weak and thin.
The pistons are out of the deck already by 3 to 6 thous so you may not want to deck block.
May I suggest something?
Sense you seen to know your way around machining why not use oem crank and ls3 rods and put you machining effort on the block and re sleeve it to 4.185 and use a solid roller cam on e85 and crank compression up to 13.5 or 14?
Thread Starter
Melting Slicks
Joined: Jul 2016
Posts: 2,521
Likes: 219
From: Los Angeles CA
Call Texas speed about the pistons and any other questions they have several different pistons with different number cc.
Careful going over 0.030 on the ls2/3 block sleeves they are weak and thin.
The pistons are out of the deck already by 3 to 6 thous so you may not want to deck block.
May I suggest something?
Sense you seen to know your way around machining why not use oem crank and ls3 rods and put you machining effort on the block and re sleeve it to 4.185 and use a solid roller cam on e85 and crank compression up to 13.5 or 14?
Careful going over 0.030 on the ls2/3 block sleeves they are weak and thin.
The pistons are out of the deck already by 3 to 6 thous so you may not want to deck block.
May I suggest something?
Sense you seen to know your way around machining why not use oem crank and ls3 rods and put you machining effort on the block and re sleeve it to 4.185 and use a solid roller cam on e85 and crank compression up to 13.5 or 14?
I'm not building this engine for all out power, I need it to pass smog in CA and the idea to use the LS7 parts allows me to dry sump at the same time. 500ftlbs is more than plenty for road course work.
Melting Slicks
Joined: Jun 2006
Posts: 2,497
Likes: 261
From: Miami Florida
If i'm not mistaken 4.070 bore is only .005 over, not .030 over. With the LS7 stroke and rods it puts extended stroke length at 9.229 which is .011 in the hole, not above the deck.
I'm not building this engine for all out power, I need it to pass smog in CA and the idea to use the LS7 parts allows me to dry sump at the same time. 500ftlbs is more than plenty for road course work.
I'm not building this engine for all out power, I need it to pass smog in CA and the idea to use the LS7 parts allows me to dry sump at the same time. 500ftlbs is more than plenty for road course work.
If in the hole by .011 decking 15/.020 is fine with .051 compressed h/gaskets and makes easy to dial you compression of choice with a given piston.
1st Gear
Joined: Dec 2016
Posts: 1
Likes: 0
I have an 99 FRC I bought for weekend road course and autocross events. I'd like to go dry sump while increasing torque, so I had an idea, however I am not experienced enough with what exists and what is capable with the LS series, but I can do about 75% of the machine work, I just need to know if it's possible. I believe the pro's outweigh the cons, if it will indeed work.
I'd like to grab some stock LS7 rods and an LS7 crank, run a forged piston in an LS2/LS3 block. The math makes sense, the only thing I can't find is aftermarket piston schematics to ensure there's proper pin placement. I'd also like to keep compression in the 11-11.5:1 range.
So on to the math
Crank 4" Stroke
Rods 6.064
Bore ~4.070 neighborhood
Deck height 9.240
Now assuming I cut a modest .010 the deck off any used block I buy, that leaves me with a piston that requires a compression height of ~1.165, which a quick search shows JE has, but I did not see any in a -5cc configuration, only domed.
So assuming the "shelf" pistons have the same pin placement as the stock LS7 piston, and if there's not, what is an acceptable deviation that would still allow for a reliable piston to rod configuration? And what other brands would have something in a valve relieved -4cc to -6cc configuration?
I'd like to grab some stock LS7 rods and an LS7 crank, run a forged piston in an LS2/LS3 block. The math makes sense, the only thing I can't find is aftermarket piston schematics to ensure there's proper pin placement. I'd also like to keep compression in the 11-11.5:1 range.
So on to the math
Crank 4" Stroke
Rods 6.064
Bore ~4.070 neighborhood
Deck height 9.240
Now assuming I cut a modest .010 the deck off any used block I buy, that leaves me with a piston that requires a compression height of ~1.165, which a quick search shows JE has, but I did not see any in a -5cc configuration, only domed.
So assuming the "shelf" pistons have the same pin placement as the stock LS7 piston, and if there's not, what is an acceptable deviation that would still allow for a reliable piston to rod configuration? And what other brands would have something in a valve relieved -4cc to -6cc configuration?
Thread Starter
Melting Slicks
Joined: Jul 2016
Posts: 2,521
Likes: 219
From: Los Angeles CA
OP do you already have the LS3 block, LS7 crank and rods? How serious is the car going to be on the road course? In my experience if you aren't under more than 1.2 lateral G's you are ok with the two piece C5Z oil pan. I'd pickup a LS3 and throw a cam in it and swap the oil pan and go down the road if you want to do it fast and cheap.
My old track car (88 Mustang) would peak around 1.34g with R6's and I would like to best that with this car. It won't be every weekend, but when I do drive my cars, I push them to their engineering limit, if something is going to break, I will find it. This is basically a way to get a win/win with both setups, torque curve of the 4" stroke and dry sump.
This isn't really a "should I" inquiry, as a "can I" I need to know if wrist pin location on the LS3 piston is the same/similar as the LS7, or if there exists a piston with an acceptable wrist pin location for my proposed idea before going with a completely custom piston.
