390 stroker LS2 vs 376 LS3?

[jwvand02]

A class ruleset I'm working within for my car allows up to 6.4L (to include 392 hemis). I came across parts that would allow stroking an LS2 to 390ci - with the same set of square port heads, any guesses as to whether the extra cubes outweigh the disadvantages of the smaller bore versus a standard 376 LS3?

[shainiac]

If you're already going to spend money on crank, rods, pistons, check out the OEM GenV L8T crank. It's from the 6.6L gas engine for the newer HD trucks.
With a 3.860" stroke and a 4.0" bore, it works out to 388CID. It's an oddball stroke, but IIRC, there are off the shelf pistons for 4" stroke that can work with a 6.200" rod.
It's supposed to be a badass crank, though. It's center-counterweighted, which is usually only found on $$$ stuff, and forged steel from the factory. It also uses 8 bolt flywheel, so you may have to replace yours. The Gen2 CTS-V stuff is 8 bolt also, so there are some Gen4 options. They're $820 on BTR and Scoggins' sites, so not cheap cheap, but a nicer piece than most aftermarket budget cranks.

[MPbdy]

The absolute best running engine would be a 4.125" bore and a stock 3.622" crank for a 388" cubic inch combo.  You could run LS7 style heads and make a ton of power.  With a sleeved block a 4.15" bore would get you 392".

An oldschool way to do what you're looking for would be to offset grind a factory crank to increase the stroke to ~3.75" and run a 4.065" bore LS3 block for a 389.3" combo.  You would grind down the journals to a honda journal size and run a SBC 6.125" rod and the appropriate piston.

https://www.ebay.com/itm/285000397682?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1w06uFkDeS9S7MsxPcTkDhA40&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=285000397682&targetid=2321310837104&device=c&mktype=pla&googleloc=9031601&poi=&campaignid=21214302385&mkgroupid=161029887581&rlsatarget=aud-1297930287258:pla-2321310837104&abcId=9407524&merchantid=101685941&gad_source=1&gclid=CjwKCAiA5eC9BhAuEiwA3CKwQopEY5UNExOZ_MVHHfSDM7YOOlAPzjms212e1Ta3iY_ljpJIDbAVmBoCPPYQAvD_BwE


An LS2 block, 4" bore and a 3.900" stroke crank would make a 392.07" combo.

Is 390" the limit, or is 392"?  6.4 liter is 390.5".

Are there any limitations what you can do to the engine beyond displacement? Are you trying to stick to any kind of a budget?  To answer your specific question, 390" LS2 vs SBE LS3 - going to need to know about your build limitations and budget.  In general, the larger bore is advantageous.  20 cubic inches will be approximately 32 horsepower at 1.6 hp/cube which is a fair amount to make up for if sticking with the LS3 combo.

Shaniac's suggestion is also good - if you went 4.020" on the LS2 block with the L8T crank you'd be right at 392".

[shainiac]

I would shoot for a couple cubes under the max so you have room to go up 0.005-0.010" bore if you run it long enough to need a refresh.

[jwvand02]

The absolute best running engine would be a 4.125" bore and a stock 3.622" crank for a 388" cubic inch combo.  You could run LS7 style heads and make a ton of power.  With a sleeved block a 4.15" bore would get you 392".

An oldschool way to do what you're looking for would be to offset grind a factory crank to increase the stroke to ~3.75" and run a 4.065" bore LS3 block for a 389.3" combo.  You would grind down the journals to a honda journal size and run a SBC 6.125" rod and the appropriate piston.

https://www.ebay.com/itm/285000397682?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1w06uFkDeS9S7MsxPcTkDhA40&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=285000397682&targetid=2321310837104&device=c&mktype=pla&googleloc=9031601&poi=&campaignid=21214302385&mkgroupid=161029887581&rlsatarget=aud-1297930287258:pla-2321310837104&abcId=9407524&merchantid=101685941&gad_source=1&gclid=CjwKCAiA5eC9BhAuEiwA3CKwQopEY5UNExOZ_MVHHfSDM7YOOlAPzjms212e1Ta3iY_ljpJIDbAVmBoCPPYQAvD_BwE


An LS2 block, 4" bore and a 3.900" stroke crank would make a 392.07" combo.

Is 390" the limit, or is 392"?  6.4 liter is 390.5".

Are there any limitations what you can do to the engine beyond displacement? Are you trying to stick to any kind of a budget?  To answer your specific question, 390" LS2 vs SBE LS3 - going to need to know about your build limitations and budget.  In general, the larger bore is advantageous.  20 cubic inches will be approximately 32 horsepower at 1.6 hp/cube which is a fair amount to make up for if sticking with the LS3 combo.

Shaniac's suggestion is also good - if you went 4.020" on the LS2 block with the L8T crank you'd be right at 392".

The rules I'm referring to are SCCA Time Attack Max 2, for what it's worth. They reference a 6.4L OE measurement limit, which is in and of itself a little goofy wording. I take that to mean up to 392 personally since it's pretty clear they wanna give the hemis space to play in that class. It's not serious business at all so it's mostly honor system with this sort of stuff but I'd like to be able to be honest about what's in there. The rules just changed this year to allow "engine modifications" at that displacement, I am currently running an untouched crate LS3 right now, so the next step is probably an actually good cam (thinking cam motion track weapon), restricted/thicker wall pushrods, maybe shaft rockers, and some as-cast heads to bump compression and flow (open to recs there too). This question really comes out of a back burner desire to have an extra short block eventually ready if this one ever chews up a bearing or something, I figure it's only a matter of time since I can induce some oil pressure drops in a couple corners around this region.

This is purely for plastic trophies on the weekend so I'm not trying to go max effort, but I'm willing to spend money where it's efficient for power or is prudent for durability.

[gnx7]

If you need any parts I'm a BTR dealer.  I also have an L8T crank on the shelf brand new and some Molnar rods would go very well with them.

LS7 style heads hands down flow the most air.... but since you already have the LS3 just send those out for porting to be cost effective.  BTR makes a shaft mount setup for the rocker arms and it sounds like you are probably ready for a real dry sump system hahaha.  Save the $ on just getting your heads done and splurge on a real dry sump.  This is for literally a plastic trophy after all.  Invest in maybe some more aero bits also.

e85 supports around 13:5:1 compression or a touch more...

[cholmes]

gnx7, what's your preference regarding dry sump systems? Not just for the track, but for a car that's 95% street use, 5% track day use.

The accusump idea works "ok", but I'm thinking if GM can put a reliable dry sump in the 'Vettes which almost never see track use, surely something similar can be done for our little old LS powered RX7s.

[jwvand02]

If you need any parts I'm a BTR dealer.  I also have an L8T crank on the shelf brand new and some Molnar rods would go very well with them.

LS7 style heads hands down flow the most air.... but since you already have the LS3 just send those out for porting to be cost effective.  BTR makes a shaft mount setup for the rocker arms and it sounds like you are probably ready for a real dry sump system hahaha.  Save the $ on just getting your heads done and splurge on a real dry sump.  This is for literally a plastic trophy after all.  Invest in maybe some more aero bits also.

e85 supports around 13:5:1 compression or a touch more...

My office is actually about 15 miles from BTR headquarters

I have been looking at doing a dry sump for a while too. The car already has a splitter with tunnels and a nine lives wing. This mostly came from some goofing around when I saw the new season's rules come out re: engine modifications for my class, the actual priorities on the car right now are brakes (in process) and a much better diff (likely OSG 8.8 with the ronin kit).

[Exidous]

Have you looked at a Wavetrack? It's a torsen but won't go open on an unloaded inside wheel. Less heat in the diff but they're spendy.

[paul_3rdgen]

Drysump is doable.  But the tank location is the issue.  Good luck.  I like the engine idea. 


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[gnx7]

The factory LS7/Grand Sport is kind of a POS and was more for marketing.  I had one and you need to get the Katech pump which is $950, the LS7 pan and front cover (around $500 used), a specific long snout crank for that pump, and then you are supposed to run an external pump if you really want it to work.  Aviad/Dailey etc or similar are what you should do if you have the $ and I put the tank in my FD behind the passenger seat.  In reality since this is 95% street car just do the 4th gen fbody oil pan, IR baffle, overfill by 1 quart and Accusump. 

I have the Wavetrac in my Chevelle 9" and it drives awesome.  Lifetime warranty also!

[cholmes]

Good info gnx7, thanks. I didn't know the 'vette setup was so lame, I'm surprised at that.

I've got the right pan and IR baffle. What size Accusump do you recommend? Electric valve with pressure switch or manual valve?

[Exidous]

The biggest issue the pan stage was undersized and couldn't pull enough oil/air to match the pressure side doing just oil.

The katech pump does a pretty good job but you need an LS7 pan(that won't fit) or a custom setup. I've been tinkering with the idea on making my own pan since I run a CNC now.

[jwvand02]

The biggest issue the pan stage was undersized and couldn't pull enough oil/air to match the pressure side doing just oil.

The katech pump does a pretty good job but you need an LS7 pan(that won't fit) or a custom setup. I've been tinkering with the idea on making my own pan since I run a CNC now.

I think I'm going to just end up welding return bungs into an f-body pan and run an aviaid system, most of the off-the-shelf dry sump pans don't clear the steering rack from what I can tell.

[cholmes]

Good info on possible dry sump setups, thanks.