LT1RX7

I'm working on stroking out my LT1 and just want to find the best route before jumping in. I also just gave myself permission to spend an extra couple grand on the bottom end. The LT1 computer would just be temporary until I can afford/find a stand alone engine management.

I was thinking of getting 4.125" pistons, 4" stroke, 6" rods (not sure what displacement that would give me yet). On top of that, I'll probably end up getting a pair of Brodix heads that flow 325cfm out of the box. Probably have to have a custom efi intake manifold made for my low hood clearance.

The biggest problem I think would be to modify the timing cover to work with the Optispark. Again, this is just until I can dish out $2000 for a stand alone. Seeing as how I used an SBC gear drive on my LT1, I know it'll work, just don't know how much time it would take.

Anyways, what do you guys think? Is there anything I've overlooked?

Spinner

Why not use a normal LT1 block? They can be stroked to 396 reliably, 408 with a little extra work. Get some SB 2.2 heads converted to reverse flow cooling, or RR AFR heads, and they'll both flow more then those brodix heads. Saves timing cover issues, for sure, cost would probably be similiar either route you went, but a 396 LT1 with AFRs would be the cheapest high end combo for sure.

LT1RX7

With a Motown I could go up to 427ci reliably. I could even go as far as 454ci. That's alot of cubes we're talking about here. Those brodix flow #'s are strait out of the box. I'm sure alot more can be had with some porting. I know it's more work and alittle more $ but I'm sure I'll be alot happier down the road with the extra displacement and from what I hear a much stronger block.

Josh-'04 GTO

Not to mention larger bore diameter that will unshroud the valves. And a near infinite amount of standard SBC intake manifolds and heads that could be used. Definitely has some serious potential.

LT1RX7

Yeah, that too

I really wouldn't mind keeping the LT1 computer if it can keep up with what I'm doing. The opti is obviously going to be my weakest link. Next would probably the MAF. Stock computers run so much better than stand alones (from my experience). I've been around lots of cars with stand alones and they put out awesome numbers at WOT. As far as everyday driving, stock computers when tuned right rarely have issues with not starting, bucking, warm ups, everyday things. So it really depends on how well the PCM holds up. I'll probably go as far as getting the coil per cylinder setup and ditch the opti

Injuneer

Properly tuned, aftermarket ECU's can peform as well as the stocker, and have the added benefit of carrying N/A and nitrous tunes simultaneously, etc. Don't write them off. Mine starts at the first turn of the key, idles smooth as butter at stock RPM with a decent solid roller cam, can provide 20+ MPG under cruise conditions, and will pass NJ rolling emissions (obviously will not pass "visual" ).

I can't conceive of managing to bolt an OptiSpark distributor to the front of a Motown Gen 1 SBC block.

You might want to look for one of the few Electromotive Super Direct Igniton/Opti-Eliminator (SDI/O-E) setups that were built back in the late 1990's. They use a crank wheel, feeding a signal to a "chip" that synthesizes the high and low res pulse patterns from the Opti, and allows the stock LT1 PCM to funtion "normally". The only downside to this setup is that, because it uses only a crank signal, it can't always correctly synch the sequential fuel injectors. Not a big deal, but can lead to extended starting cranking, and a slight stumble off idle until the valves get warm enough to vaporize the fuel that gets sprayed on the closed vales (actually, no different a situation than you get with a batch-fire setup like the 93's). I ran my 94 LT1 without an Opti for about 2 years using the Electromotive system.

You might want to contact Delteq. Appears that one of the guys behind Delteq (JC Hyde) is the same guy that designed the Electromotive SDI/O-E system.

FASTFATBOY

Can't you use FAST E dist setup for this? Or a crank trigger and a magnetic cam sync to work with a stock pcm? Or a distributor, crank trigger and magnetic cam sync?

What Brodix heads you looking at to flow 325 CFM? And at what lift do they flow that, keep in mind I have NEVER seen a head on a flow bench that actually made the advertised flow number. Just so you know that 325 CFM would be good for the 396, be marginal on a 427 aint gonna be even close to feeding a 454. Have you researched which intakes will fit under a 4th gen cowl to make a high HP number you gonna need a big intake.

I would consider a stroked LT1 and a FAST system, carb style intake, and a set of 23* heads converted to reverse flow cooling, but that's just me.



David


David

Speedfreak19

I think with a little bit of work an lt1 timing cover could be bolted to an old style block.. if you ever compared the old and new the only difference is the top 4 bolts that cover the water pump drive.. would need to cut off the top part and weld up a new face to seal the block but then you could run the stock pcm and opti.. now you might need to run the long waterpump to clear the opti.. surely someone has done this before?

slimdawson

Maybe you could convert to a conventional dist. location(back of intake) like some have done that went to carb. I don't know what kind of induction setup you are going to use.

Spinner

That sounds like the most practical idea.

Injuneer

You can't use the stock LT1 PCM without the Opti, or simulated Opti low res pulse signal. It shuts the fuel down when it can't find the low res pulse.

I think it would be easier to mount the Opti optical wheel and sensor module in a conventional distributor housing, than it would be to mount it on the front of the engine. I have seen the module put in a housing this way, and I have seen the module mounted by itself on the front of an LT1 block. You might have better luck mounting just the module on the front of a Gen 1 SBC block. Then you could use the LTCC or Delteq for computer controlled spark timing, while keeping the PCM happy with the low res pulse signal.

Houdini

I asked damn near the same question as LT1RX7 about a month ago, and I was told it could not be done. Now your saying it can be done, as long as you keep the low res pulse from the optical sensor and use something like the Delteq? I sugested the same and was told NO