Got this idea from another member on my more broad post about my motor swap. Wanted some more input on it. Goals with the motor are reliable, high reving, around 500hp. Keep in mind car is for road racing mated to a 8hp trans. Any info helps! Thanks in advanced!

Currently it�s a LM7 with 682 heads. Btr stage 2 cam, better push rods and dual valve springs.

Suggested LM7 bore it to LS1 size and install a 4.8 crank. Install Summit ProLS domed pistons and H-beam rods, then mill a set of 706 heads to 58CC and have them CNC ported with lightweight valves. 312 cubic inches, about 11.7:1 compression, and 8K RPM ability. Should also make over 500 crank horsepower with ease.

Original thread : Here
Credit to : @LS1Formulation

 

Pretty sure you'll get it to 3.905" without a problem, but no 4.8l/5.3l Ironblock is going to a 4.000" bore without sleeves.

If it could everyone would be doing it.

 

You mean 5.3l....

 

LS1 bore (5.7L), but that's 3.898, whereas a 6.0L is 4.00". The max recommended overbore for an iron block 5.3L is 3.910. So you can match a 5.7L bore, but not a 6.0L.

Looks like @Summitracing has an .005" overbore 5.7L pistons with longer 6.125 rods. That'd get you to 3.903 bore (313cid) and the longer rods should help the higher rpm.breathing and reduce piston side loading.

For the heads, you'll need a very stable valvetrain for sustained rpm use, so you'll need a shaft rocker system. As for the camshaft and valve springs... there's many camshafts with valve event timing that theoretically could make power in a 312/313cid engine up to 8k, but again it has to be stable and be capable of enduring very high rpms for extended periods. To that end, you'll want a custom camshaft with lobe profiles specifically designed for that use. And the valve springs should be specific for that purpose and that camshaft as well.

Don't forget the manifold design will also be critical to meeting your rpm target too.

 

You have a keyboard error or doing it on purpose?

 

Thanks, definitely not on purpose. Hitting the wrong character Fixed it.

 

My apologies. I�m still new to this ls thing. Always thought ls1s where 6.0s till now lol.

 

That'd be the LS2..

 

Thanks for tagging us in this @68Formula.

@BlooBmw,

We understand you're aiming for a reliable, high-revving build, but there are a few things to consider based on your parts choices.

If you're set on using the 4.8 short-stroke crank (3.267"), the forged pistons and 6.125" rods mentioned won�t be compatible. However, we do have forged 4.8 rods (6.275") with the .945" pin and -3cc dome pistons that will work with either the 3.898" or 3.903" bore, giving you the high-RPM capability you�re after. This setup would scream at high RPMs, but keep in mind that you'll lose some low-end torque, and building compression can be more challenging with the shorter stroke.

For dual-purpose use, we�d recommend sticking with the stock 3.622" stroke. With the larger bore, you'll maintain better overall torque, making it easier to hit 500hp without needing to push the engine to 8,000 RPM. You could still rev to 7,500 with the right cam, intake, and exhaust, but with more manageable power delivery. This setup would also be less "peaky" than the short-stroke combo, giving you a more balanced powerband for both the track and the street, without sacrificing too much on either end.

Here are combos we could put together for whichever route you're leaning.

Big Bore Short 3.267" Stroke Combos:
Pistons: These options have a -3cc dome and two valve reliefs. This option with 58cc heads, a .040" head gasket would net 11:1 compression with the factory 9.240" deck height. Our pistons sit .005" in the hole.
- SUM-3269453898-3 (3.898" bore)
- SUM-3269453903-3 (3.903" bore)

Rods
- SUM-LS6275945 (4340 forged H-beam 6.275" rods with ARP-2000 rod bolts)

Piston Ring Options
Non-Gas Ported
- SUM-136SN9035STD (3.898" bore)
- SUM-136SN9035007 (3.903" bore)

Gas-Ported Rings
- SUM-GP389812 (3.898" bore)
- SUM-GP390312 (3.903" bore)



Big Bore Standard 3.622" Stroke Combos
Pistons: These options have a -3cc dome and two valve reliefs. This option with 58cc heads, and a .040" head gasket would net 12:1 compression with the factory 9.240" deck height. Our pistons sit .005" in the hole.
- SUM-2999273898-3 (3.898" bore)
- SUM-2999273903-3(3.903" bore)

Rods
- SUM-LS6125927 (6.125" with .927" pin) - These are out of stock and not expected in for approximately 1-2 months.
Suitable in-stock substitutes:
- BTC-S0368 (4340 forged H-beam with ARP-2000 rod bolts)
- ESP-6125O3D2000 (4340 forged H-beam with ARP-2000 rod bolts)

Rings
- The same ring options as above will work


Summary
Don�t get us wrong, OP�we�re not against the big bore short-stroke combo. In fact, the writer runs a 358 SBC big bore short stroke engine from Mullins Race Engines, the best in the circle track game. If this is a dedicated track car, we�d go that route too.

But if it�s a dual-purpose build, we�d suggest sticking with the standard stroke for better overall performance on both street and track. Either way, we�ve got a Pro LS camshaft and MAX EFI intake to suit your needs.

Let us know which way you�re leaning�we�re happy to help!

 

Thanks summit, this helps a lot. For reving the motor up to 7.5 rpm what valvetrain work do you guys recommend?

 

I don't think there is anything to gain from a 4.8 rod compared to the 5.3 rod. Lack of revving ability isn't an issue. The only reason someone would do this is if they needed to be under a certain amount of cubic inches for a class rule.

 

that�s essentially what I landed on after talking to people. Makes no sence with the goals I have for the car. Gonna run just an ls1 bore like summit suggests. I just gotta figure out valve train stuff

 

No problem. Sticking with the standard 3.622" stroke is a solid choice�we�re fans of that too.

Now, when it comes to keeping your LS stable at 7,500 RPM, the valvetrain setup is critical. The camshaft is a big factor, but assuming you�ve got smooth lobes that can handle those RPMs, let�s start from the top down.

Rocker Arms
- You�ll want to upgrade the trunions on the stock rockers or go with rockers that come with upgraded trunions. We recommend sticking with stock rockers�they're lighter, which helps at the valve where keeping things light is key at high RPMs.

Valve Springs
- Given that your cam will likely be in the .600"+ lift range, a quality dual spring with titanium retainers is a must. This setup will prevent valve float and keep things stable. Make sure your springs match the requirements specified by the cam manufacturer for optimal performance.

Pushrods
Valvetrain stability heavily depends on the pushrods. We�d recommend our 11/32" HDR pushrods with a .120" wall. These provide the rigidity needed to handle high-RPM stress without deflecting.

Lifters
For lifters, Delphi LS7 or Morel 7717 are excellent choices. These are proven and come as a kit with trays, so you�ve got everything needed for a clean install.

Head Refresh
Finally, don�t overlook the heads. A good refresh with porting, upgraded seats, guides, and lightweight valves will help the engine breathe better and maintain durability under high RPM conditions.


By combining these components, you'll have a valvetrain that's not only stable at 7,500 RPM but also built for longevity and performance.