LS7 - 7100rpm

[Terry D.]

Full page article in the new driveline about the new LS7 engine being able to turn 7100 rpm. I'm not trying to burst anybody's bubble, but the original Z-28 motor could do that and that was back in the late 60's. Seems to me it should not have taken over thirty years to do this again. Am I missing something here?
Is it because of the multi-valve arrangement?

Just an old man trying to keep up with the times
Terry

[Duke W.]

Re: LS7 - 7100rpm

The 302 Z-28 engine is actually redlined at 6500, but with its short three-inch stroke and 30-30 cam it will pull useable power to 7000 and beyond even in OE trim, and the soft action of the 30-30 cam with the standard small block "068" springs allows this without valve float.

LS-7 has a titanium 2.2" inlet valve and titantium pushrods along with unique higher stiffness rocker arms, and, of course, roller lifters. All this combines to allow the valvetrain to run safely to 7100 while meeting GM durability requirements even with a very aggressive lobe that lifts the valve to nearly .600" on only 211 degrees duration at .050" lifter rise. The exhaust lobe is 230 degrees at .050" lifter rise, which equals L-72 on duration with more lift. BTW, emission controlled engines can't handle much overlap, so the exhaust cam is likely phased very early, which is going to produce a very sharp exhaust note.

Bottom end inertia forces increase linearly with stroke, but the use of titanium rods allows 7100 without overstressing the bottom end because the rods are as strong as steel, but 30 percent lighter.

The last consideration is the oiling system. As revs increase it is tougher for oil to return to the sump and most production wet sump oiling systems get "iffy" beyond 7000. The LS-7s dry sump system ensures that oil is scavenged from the crankcase and returned to the supply tank. A properly designed dry sump cannot be run out of oil due to high revs.

The following link is s good article on LS7 and includes several photos of the internal parts including the fully machining ports and combustion chambers, titanium rods, and the dry sump oil pan, which includes cast in scavenge pump inlet passage and cast in pressure pump passage. It's quite a "trick" setup.

GM pulled out all the stops to engineer this engine. I'm still amazed! All that remains is to see how much it will cost.

Duke

[Duke W.]

Oops - forgot the link!

http://popularhotrodding.com/tech/0504phr_ls7

[Mike Cobine]

Re: LS7 - 7100rpm

It is probably based on the ADVERTISED redline rather than the real one. After all, the L88 was 430 hp @ 4600 rpm in '68, the '66 427 450 hp @ 6400 rpm (425 hp @ 5600), and the '68 435 hp at 5800 rpm. The 302 was 290 @ 5800 in some sources, and we know 5800 wasn't close to the limit.

I had a friend in '71 running a crate 302 in a '64 Chevelle ran regularly shifted at 8000 rpm and never broke. (He busted, not the engine, and eventually had to sell it.) My 302 was beyond stock, so its 9500 rpm doesn't count, but is just an indication of what it would do, even with Chevy rods.

Of coruse, the downfall in almost all of these previous engines were the iron rods and heavy pistons, restricting piston speed and RPM. Drag racers have gone to steel rods and aluminum rods to achieve much higher RPM limits. The LS2 is using titanium, very strong and very light, so they can up the limit.

Add lightweight pistons and pins, something the stock '60s and '70s engines didn't have, and you can increase piston speed and RPM greatly.

The 104.8 mm x 101.6 mm LS7 is equivalent to a 4.126 in x 4.000 in engine, such as a stroked 396 (a 454 crank in a 396 block) and so the amount of lightness that had to be made is impressive, as most know a 396 stroked with a 454 crank would not rev well at all.

[Duke W.]

Re: LS7 - 7100rpm

The redline and advertised power peak revs are two different numbers. The LS7 tach will be redlined at 7000, and the electronic rev limiter will engage at 7100.

Few, if any, auto engines designed after WWII have "iron" rods. All vintage Chevrolet V8s have forged steel rods, and the modern generation has "powdered metal" rods, which have proved to be quite durable. This technology was pioneered by Porsche on the 928 V8 in the late seventies.

Duke

[Justin B.]

Re: LS7 - 7100rpm

500 H.P., good gas mileage, better durability and driveability, pump gas, light weight, with all the EPA requirments met.

[Harold #43147]

LS-7

That Number should have been retired.

[Terry D.]

What Number is that? *NM*

[Harold #43147]

Re: What Number is that?

LS-7 # was 454 Cu In. it was going to be optioned for 1970 Corvette was canceled they could be bought through Dealers.

[Chuck S.]

Re: What Number is that?

I don't think it makes any difference...many would say that Z06 and LT1 are the numbers that should have been retired. Some would say LS7 is at least unused, where the other two numbers were "used" once before. The LS7 was never really sold to the public. It's the General's call anyway; they own the copyrights...who are we but mere mortals.

[Warren F.]

Re: What Number is that?

You might as well add ZR1 and LS6 to that list as well.

[Mark #28455]

c'mon guys!

What's in a name, a rose by any.... you know the quote! The only thing I hate to admit is that the new cars are likely BETTER performers that the old namesakes ever were. Case in point the ZR1 - I bet the new ZR1 vs. the old ZR1 would be a joke. How about the LS6 - seen any old ones that stock have A/C, CD player etc and can still easily run 12 sec. quarter miles and be driven to work every day?

Don't get me wrong, I have several big block cars and enjoy them all but I wouldn't claim they are better performers than the new ones. I also own an original L88 and I bet the new ZO6 would be able to kick it's butt! On the other hand, I hate the styling of the new cars!

Let GM use whatever name they want, at least we've gotten out of the performance doldrums of the late 1970's.

Mark