FUH Q

I searched alot and couldnt find any good comparisons. My question is simply which of the two (427 ls3/l92 or 427 ls7) would be better for performance/reliability/fuel economy? I know alot think big cubes and reliabilty/fuel economy don't go together, but if im paying top dollar for a build, i want it done right. I think the only differences between the two blocks are that the ls7 uses a bigger bore and shorter stroke while a 427 ls3/l92 would use a longer stroke and smaller bore (than the ls7). All opinions are welcome.

See5

iTrader: (53)

Don't think the economy will vary much. The output put will be pretty close but the durability is another issue. Boring these sleeved LSs is a compromise. Stroking is good to a point, considering the shorter cyl sleeves of the LS2 and LS3. 4" stoke is ok, more is debatable.

FUH Q

The 427 from tsp uses a 4.065'' bore with a 4.100'' stroke. Would the ls7 have a much longer life?

kidreno_21

I am doing the same thing. I was looking at SDPC's LS2 402 short block, then I saw the LS7 short block. To me, since I will be doing a road course a couple times a year, I decided on the bigger bore of the LS7 over the LS2. Granted, it is not by much (.122"), but the LS7 block was designed for the 4" stroke.

I am no expert, but I would think the 427 LS7 would get better mpg over the 427 LS2. The 427 LS2 is also operating at a much higher than stock stroke nearing its limits.

novaflash2002

iTrader: (51)

an old racers thought is small bore and longer stroke get about 3% more power. about 3 years back engine masters did a artical on this to prove that it is so.

FUH Q

I could imagine the longer stroke having more torque. The ls7 may be more reliable and I'll already know what mpg it gets. I dont see a reason why the ls3/l92 would have a huge difference in mpg though.

sdbrown84

iTrader: (22)

LS7 is made for a 4" bore as stated before. I would just go that route or not even mess with a LS3 and call it a day at 6.3L. For reliability it is ALWAYS best to stick with an engines' designed bore and stroke. Otherwise GM would have made 1 block and just stroked it differently for each application.

FUH Q

Thats a good point, but the ls7 costs quite a bit more, so im really trying to figure out if the cost difference is justified. It seems power output would be about the same perhaps a taaaad bit less. Fuel economy would be a little better (i think) because of the shorter stroke. It would likely be a little more reliable. But everything is "a little" and "a taaaad bit" different. Is there any major differences? If not i dont see a reason to go with the ls7 for that much more money if there is no great advantage.

OneQuickCoupe

iTrader: (1)

The stock LS-7's stock 4.125" bore should serve you well. They do cost more as you state however. I have one in my 07' Z and drive it every day. I average at least 25 MPG if that's what you are looking for. Oh yea it's fast too when you want it to be and a great all around engine. Nothing bad to say about this combo.

LSX

AU N EGL

ist it the other way around? Larger bore and shorter stroke provied mote TQ?

Covette examples:

The LS7 has a 4.125 bore and 4" stroke
the Ls7.r has 4.180" bore and 3.875" stroke

2006 Corvette Engine Specifications
2008 Corvette Z06 -- 2008 Corvette C6.R
Displacement (L / ci) 7.0 / 427 -- 7.0 / 427
Horsepower 505 @ 6300 rpm -- 590 @ 5400 rpm
Torque (lb-ft) 470 @ 4800 rpm -- 640 @ 4600 rpm
Bore diameter (mm / in) 104.8 / 4.125 -- 106.2 / 4.180
Crankshaft stroke (mm / in) 101.6 / 4 -- 98.42 / 3.875

LILS

There is a lot more different between a stock LS7 and an LS7.r than just the bore and stroke.

OneQuickCoupe

iTrader: (1)

Larger bores unshroud the intake valves which are located close to the cylinder walls. This in turn increases intake flow all the way around the valve. A porter will lay down the intake valve side of the combustion chamber to take advantage of this increased clearance which unshrouds the valve.

LSX

1lejohn

iTrader: (9)

Large bore short stroke is where it's at for a drag race engine. The piston manufactorers don't recommend a longer then 4.0" stroke in a L-92 or 3 block for power adders. The top ring land gets close to the top of the piston. The short cyl. bore of these blocks with longer storkes will have piston rock which effects cyl sealing and relibility. Its like the old Ford 5.0 debate between 347 and 331 engines. Hell build one with a long stroke and see what happens. I'm going to stick with a 4.0" stroke. Scat recommends this as the max stroke for these blocks.

05JUDGE

iTrader: (26)

The LS3/L92 427 has a 4.08 bore and 4.1 stroke. I have one from Texas Speed and love it. I can't say the economy is good though. I'm averaging about 10mpg in town and 15mpg on the highway. But, I've got all the power I need. I'm sure with a smaller cam I would have a lot better economy.

BA.

iTrader: (3)

another somewhat significant difference between the LS7 and the LS3/L92 is the valve angle.

I believe the LS7 is at 12 degrees and the LS3/L93 is more like 14-15.
Feel free to correct me on that or chime in on it's significance.

sdbrown84

iTrader: (22)

The LS7 was simply made for a 427 displacement. You can make most anything anysize you want, but you will be sacrificing something in the long run. It's just a matter of how much you are willing to let sacrifice on the cost to performace scale.

Heck you could make your LS1 a 427, but you are so far stroked and bored that any little slip will cost you a block if you haven't darton sleeved it, which is half the cost of a short block of any of your other options listed above.

For cost wise, why not just use an LS3 and just work on the other potentials of the engine, port match everything, put your leftover money into suspension and weight reduction, then get a great tune. You will come within your HP range and not be sacrificing your reliablility, which is what was stated as a concern at the beginning of the thread.

Don't forget an LSX which can be anything you want as well, just about 100 lbs heavier, but you'll never break it.

OneQuickCoupe

iTrader: (1)

BA, Good point.

LSX

formula17

iTrader: (4)

I've heard this debate a few different times. Most of the comments on it are from people who have no experience with the set up what so ever, but have read other opinions. I have this set up, but it has yet to be finished. All the engine builders I've talked to have no concerns with the set up if done correctly and the correct pistons are used. Power adders are another debate and concern. I don't see the difference between this set up and lets say a 440 set up that uses the same size stroke but with a larger bore. If companies like scoggin dickey, mast motorsports and texas speed sell these set ups everyday I wouldnt be worried about it. As far as one being better then the other I would deff lean towards the Ls7 being better as far as performance, generally its better to run a smaller stroke and larger bore, this is what nascar does. The idea behind this set up is that its more of a budget 427.

Nick

Busted Knuckles

Use the LS7 block and stroke it to a 438. If you're on a limited budget, start with some of the less expensive L92 heads, you can always upgrade later to LS7 stuff. The longer cylinders of the LS7 block will work better with the long stroke than the 6.2L block, IMHO.