Yes, but all 3 still use a SBC crankcase. Size difference is next to none really.

 

I'd imagine an LSx FC/FD to outhandle a 20B FC/FD. You'd likely have the 20B boosted, yet you can keep the LSx FC/FD NA and make the same power. A 20B with all the turbo hardware (snail, IC, piping, etc etc) should be a fair bit heavier than an aluminum SBC, let alone more top heavy, too.

I can see absolutely no downside to an LSx FC/FD, and that's exactly why it's my #1 choice.

 

I must say, I seen an LS1 powered First Gen in the states. It had to be the fastest Rx-7 I've ever seen. It was a street car and it ran sub-9's if I remember correctly.

On the V8 note, I'll also say I drove a new Porsche Cayenne yesterday. I had forgotten how harmonious a V8 can sound at high RPM.

The thought of an LS7 FD grows on me night and day.

 

I'm pretty sure the LS7 is a fair bit taller than the LS1, and LS2s. When i heard of the new LS7 and Z06, i thought about an LS/RX 7 combo, but i'm too poor. I think it would have the same mounts and everything but you'd need a taller hood, 4" cowl:P ahaha i'm a fan of the LSx idea

 

As turb0wnd pointed out out, all three share an engine block that is basically identical externally, and for the most part, internally as well. In fact, assuming adequate clearance for the rotating assembly, it is possible to get 454 CID or more out of a re-sleeved OEM, GM LSX, or aftermarket LS block of the same overall size.

To get more displacement from a rotary engine, you typically have to add more rotor housings, which increases the size (especially length) and weight of the engine. With piston engines, stroking (increasing crankshaft rod journal offset) and boring (increasing cylinder bore diameter) are commonly used to increase displacement without requiring an increase in the overall size of the engine. There's really no significant weight penalty for that additional displacement either.

Don't feel bad, you aren't the first to assume that piston engine displacement and size are directly proportionate.

The LS7 intake is marginally (~1/4") taller than the LS1/2 because of the raised intake ports, but that's not really an issue, at least in an FD. The throttle body is where you run into hood clearance issues. There's very little difference between an LS7 intake and the FAST LSX intake for the LS1/6. Both use 90mm throttle bodies, which will require cutting out a small section of hood support, unless you use a spacer and move the TB down away from the intake.

LS7 mock-up in an FD...



LS7 intake (left) vs. L76 intake, which is comparable to an LS2 intake in dimensions...

 

I don't feel bad. I am learning here. But my question is if there is no real change in the size of the engine although the displacement is much larger why would a manufacturer leave so much room for enlargement. I mean the thickness between cylinders is so large that it permits this?

 

Leaving more material between bores improves stability and therefore promotes longevity, but it also promotes reusability, allowing a worn block to be rebored without compromising the internal cooling passages.

Keep in mind that increasing stroke results in a larger increase in displacement than increasing bore diameter, so it's the more popular method for obtaining more displacement. This is one reason why many people refer to a larger displacement version of a standard engine configuration as being a "stroker" engine (e.g. a 383 "stroker" vs. a standard 350).

Bore * Bore * Stroke * # Cylinders * 0.7854 = CID, SBC 350 = 4.0" Bore, 3.48" Stroke

Example 1 - Effect of an increase in stroke on displacement

4.00 * 4.00 * 3.48 * 8 * 0.7854 = 350 CID

4.00 * 4.00 * 3.75 * 8 * 0.7854 = 377 CID (+27 cu.in.)

Example 2 - Effect of an increase in bore diameter on displacement

4.00 * 4.00 * 3.48 * 8 * 0.7854 = 350 CID

4.03 * 4.03 * 3.48 * 8 * 0.7854 = 355 CID (+5 cu.in.)

Example 3 - Effect of both on displacement

4.00 * 4.00 * 3.48 * 8 * 0.7854 = 350 CID

4.03 * 4.03 * 3.75 * 8 * 0.7854 = 383 CID (+33 cu.in.)

Yes. Almost any steel production block will have enough material for at least a 0.030-0.040" overbore, which will clean up a worn cylinder, and some can take a larger overbore (0.060-0.090") depending on design. Sleeved aluminum blocks (like the LS1) can have the sleeves removed, the block rebored, and new larger sleeves installed. This is the process GM uses for the LS7, long after the same thing was done with the LS1 block by Katech to create the 427 CID C5R racing block. Darton is another aftermarket sleeve manufacturer with a hand in the big cube LSx arena.

An aftermarket or performance block, by comparison, will typically have much more material between bores to allow a very large overbore without compromising the cooling jacket or bore stability. The cast iron GM LSX block, for example, will allow a maximum bore of 4.25" with a minimum of 0.2" wall thickness remaining, and the World Products aluminum "Warhawk" can accept a 4.125" bore with 0.10" of dry sleeve and 0.3" of support. Add a 4.25" crankshaft and you've got 454 CID in a small block-sized package and weight without safety issues or breaking much more than your budget.

 

This really depends on the engine. With the change from LS1 to LS7, GM increased the bore by 5.9% and the stroke by 10.4%. But the bore's contribution to volume must be squared, so the bore increase was more effective, adding 12% in this particular case.

I thought the C5R block was a unique casting. If they're just sleeving standard LS1 blocks, the results and price are surprising.

I must be up too late. Simply don't see how this can work with 4.400" bore spacing.

 

I think you mean it depends on whether you're comparing two completely different engines...

An LS7 is not an LS1 with an overbore. It's a completely different engine with much larger bore sleeves.

I was talking about what an average engine can accomodate without major structural changes. In the case of the LS1, that's about an 0.010" overbore for '99-up engines and only 0.005" for '97-'98 engines. An increase in stroke is far more productive and cheaper in this case, as it is in most examples.

It is a unique casting... based off the LS1 block. There are very few differences.

Take it up with GM and World Products, I merely quoted their specs.

Maximum 4.250" bore @.200" minimum wall thickness

Even with a bore of 4.125” you’ll have .100” worth of dry sleeve and .300” support.

The ball is in your court, have fun.