Large bore lt1 block

Guys I have a question, is it possible to bore a gen 2 block more than 60 thouands over. What about sleeving the block to 4.120. I have heard that this has been done but I would like to hear from some that have actual engine building experience. This engine by the way will be used on the street not a full on race motor. Thanks joe:D

Not worth it. Put the $$$ in the heads/cam/valvetrain, etc.

Rich

It's my understanding that the cylinder walls would be close to being too thin if it is bored over .060, esp for street duty with the constant heat cycles. Running sleeves is an options but like Rich said above, that's a lot of money that could be used elsewhere. Why not just buy an aftermarket block?

Why not just buy an aftermarket block?

Who makes an aftermarket LT1 block???

An aftermarket LT1 doesn't exist.

I remember long ago there was a guy here that did a 421ci LT1 (VIPRETR?) and there was even an article in GMHTP on it but it was just a fad and wasn't a good idea for longevity.

He claimed to have built two versions of the 421..... 4.030 x 4.125" stroke and 4.090 x 4.000" stroke... described the difficulties with doing a complete sonic thickness check on the cylinder walls, then recentering each individual bore within the block to provide the required wall thickness on the thrust side. Seemed like a lot of work for questionable benefits.

Anyone remember the screen name of the guy that built the sleeved 427? He posted a couple times when the issue of sleeving the LT1 block came up.

Who makes an aftermarket LT1 block???

When I typed that I was thinking of a SBC in general that could be used for a large bore project. Something like a Motown or Dart block. Staying with a factory block and trying to make it live on the street will be tough and costly.

i agree, a 400+ inch factory block isnt going to last more then 20,000 miles before starting to go sour...

the way to go is call up dart, motown and order your self a big inch smallblock...there makin 472 motors now...its insane..

"nah man its just a 383 with a big cam"

Thanks for the responses guys I was wondering if it would be able to be done. but you all are right it isn't worth it. Thanks again

When I typed that I was thinking of a SBC in general that could be used for a large bore project. Something like a Motown or Dart block. Staying with a factory block and trying to make it live on the street will be tough and costly.

Now my curiosity is aroused.

Would it be possible to use a regular sbc and a set of regular sbc heads (ya know I’m thinking 15 degrees or so) and set the thing up with sensors so it would pass an emission test or is the Optispark the main obstacle??

Sweated bricks on that I'd have issues with sheetmetal intake and it was so simple it was pathetic. A bunch to do about nothing.

What’s the deal on the blocks that makes it so hard??

Hey Denny, as far as using an aftermarket block, I have heard that using a GM Bowtie block is an easier way to go. I understand that the Bowties use a cam retainer plate, like the production block, and that opens up the possibility of using the Opti. All you would need to do from there is mount up an electric waterpump, and bolt up your accessories. I believe OneFlynZ28 is/was using a set up like this, maybe he can chime into this and share some info.



Nick

Hey Denny, as far as using an aftermarket block, I have heard that using a GM Bowtie block is an easier way to go. I understand that the Bowties use a cam retainer plate, like the production block, and that opens up the possibility of using the Opti. All you would need to do from there is mount up an electric waterpump, and bolt up your accessories. I believe OneFlynZ28 is/was using a set up like this, maybe he can chime into this and share some info.



Nick

Thanks! If there is a will there is a way and boy I'd really like a 450 ci motor.

A 450ci small block needs over $5,000 in heads and valvetrain parts to support it.

Rich

I've also been looking into an aftermarket block for more cubes. I'd like to stay with the opti cam position part of the opti and use my LTCC for the high tension side. I have no problems runing the GM PCM. As long as I don't go over 7000 the thing works great and the LTCC doesn't miss a beat. Can an electric water pump be spaced out far enough on a Bowtie to fit a cam driven opti? I would like a 421 for my Formula, It has a nice nostalgic Pontiac sound to it. :D

Steve

If you wanted to keep the opti a SBC would be some trouble, but if you wanted to go with a aftermarket ECU this would all be much much easier. 450cubes and SB2.2 heads with a sheetmetal intake would make it easy.

Bret

A 450ci small block needs over $5,000 in heads and valvetrain parts to support it.

Rich

Probably have that much now in heads and valvetrain, mostly because the heads were ported twice with larger valves each time. Not counting about four different sets of springs to find the ones the car liked and seem to last.

Planning on my next engine to be a real duzie and no great rush. Maybe I shouldn't have said that.....The weather is finally turning to better air and have a tendency to drive a little bit harder.

If you wanted to keep the opti a SBC would be some trouble, but if you wanted to go with a aftermarket ECU this would all be much much easier. 450cubes and SB2.2 heads with a sheetmetal intake would make it easy.

How about using the LT1 water pump housing and a SBC to get opti clearance and mounting, Drill & Tap the water pump housing to plumb water to the front of the heads and go reverse cooled on the Bowtie. Will an LT1 Timing cover fit a SBC? An aftermarket ECU, crank trigger, and CNP would work also, but thats about another $1200 or so (which may be cheaper in the end). Am I just token on the crack pipe?

Steve

Probably have that much now in heads and valvetrain, mostly because the heads were ported twice with larger valves each time. Not counting about four different sets of springs to find the ones the car liked and seem to last.

Planning on my next engine to be a real duzie and no great rush. Maybe I shouldn't have said that.....The weather is finally turning to better air and have a tendency to drive a little bit harder.

Well, I did say "over" ;)

Yeah, a big inch small block truly is an expensive proposition. There is no point in building one without also having the needed top end and valve train. Other than bragging rights, if you used "typical" LT1 components it would not be a very good combo.

Rich

. 450cubes and SB2.2 heads with a sheetmetal intake

Bret

No porn allowed on the site Bret.:)

why use an opti ignition when a trigger and a dfi system would be a 1000 times better? as for SB2 HEADS HERES A DEAL FOR YOU!
http://www.need2speed.com/vb_forums/showthread.php?t=19460

Opti optical sensor with a full sequential aftermarket ECU.... best of both worlds :)

Honestly, The only downside of the opti system is the High Tension side and LTCC takes care of that. The 7K limit can be an issue if your spinning higher. Other than that fuel is fuel, 12.8 AFR is 12.8 AFR and 36 degrees of advance is 36 degrees of advance. I don't see how there's any HP gain with $1,200 worth of Big Stuff, DFI, Fast, or anything else.

Steve

There's something to be said for adjusting injector timing relative to inlet air flow, at least MoTeC thinks there is.
Injection Timing - With a synced engine which uses 1 injector in each intake manifold runner, it is possible to phase the firing of the injector so that it only sprays during the intake stroke. This allows you to introduce fuel into the intake stream precisely at the time when the airflow into the cylinder is the greatest providing the best possible atomization and the highest efficiency. MoTeC offers a user definable 2 or 3 dimensional Injection Timing adjustment table so that you can accurately match any engine's injection timing demands. Tuners can select either beginning or end of injection on which to base the timing table. This allows the tuner the ultimate in adjustability to suit any engine combination.
Is it important to the average builder? Probably not, but its something that can be used to optimze performance, emissions and fuel efficiency.

There's something to be said for adjusting injector timing relative to inlet air flow, at least MoTeC thinks there is.

Is it important to the average builder? Probably not, but its something that can be used to optimze performance, emissions and fuel efficiency.

Yeah that would be nice to have. Not sure if I want to spend $3500+ on the computer in my "street" car though. I'm having a hard enough time coughing up the money for a FAST system.

There's alot to be said for that kind of tuning potential though:)

Fred,

I'll conceed to your point that in some max effort combinations individual injector timing and individual cylinder timing can help. In fact a friend of mine that runs NMRA EFI Renegade retards timing and adds fuel to one cylinder to keep it alive. That being said, most typical street/strip combos, and most tuners wouldn't normally have to delve into this stuff on a NA application.I suppose my point is that a big SBC could be managed perfectly fine with a properly tuned GM SEFI system, and that could be more cost effective and produce results on par with the aftermarket guys. Using stock PCM would also clean up the underhood wiring. The only hurdle is mounting to optical portion of the opti, then the rest is cake.

Steve

Steve,
I think there is a guy a couple of clicks up the road (in Y-springs) that can make that 421 a reality in a stock block :D I swear he has aliens working for him...

Give me a call sometime, My tuning schedule is booked and could use some help.

Dennis

After giving much debate... why do it with a gen 2???? why not do a gen 3/4? it already solves many of the problems we face and 427 is just readily available. Factory programming is at its greatest and its really a lot cheaper and neater than any fast/motec system....

In the end .. aftermarket blocks and heads will be more expensive.. when you get to see a really good system for how much money.. a crate ls7 is really really tempting and good, specially when you can still use a gen 2 computer with a simple 58x to 24x crank sensor signal converter...

My thoughts, if they mean anything

sprintcars used "batch" type njectionwith fuel sitting on the vlave waiting for it to open, seems like they make GOOD power with Hilborns.


Is a 4.040 bore with a 4 inch stroke and a 6 inch rod to safe to street drive? Seems to me that would be the limit to a street Lt1, 410 inches.


David

Gen 2 computer on an LS1/LS2 ?? Sounds interesting. Is the cam position signal compatible? What's involved?

Steve

Cubic inches are the nuts, IF you have the heads/intake/valve train to support them. Otherwise, you end up with a truck motor.

Rich

Yeah.. truck motors are great.. but a set of ls7 heads work like a charm.

So really.. my "local" machine shop told me they could sleeve it to 427 w/o problems... I have a block laying around there that needs to be finished... maybe i'll go ahead and do it with a 3.75" stroke and some 15º heads with a supercharger.

Call me a jabronie, but I'll never get sick of hearing about LT1s over 400 cubes.

ARE YOU LISTENING, BRET?!:D

My thoughts, if they mean anything

sprintcars used "batch" type njectionwith fuel sitting on the vlave waiting for it to open, seems like they make GOOD power with Hilborns.


Is a 4.040 bore with a 4 inch stroke and a 6 inch rod to safe to street drive? Seems to me that would be the limit to a street Lt1, 410 inches.


David

Dave, I think a sprint car/street car comparison is invalid, not that there's any problem with batch firing injectors.

I dont see why you would want to use a LTx block. I would just go with a 400 SBC block bored to 4.185 and a nice 4.125 sroke for a 454. Its entirely possible.

I would then use SBC standard cooling. If you are good with electronics, you could set up a crank trigger off of the pulley to replicate the opti signal and then use a Delteq or LTCC system for spark. Its not that hard, you would just need to copy the internals of the opti and use LEDs and light-diode recievers. We use them all the time in our research and the wiring isnt that tough... they just send voltage signals when light hits them. Getting the voltages right shoudnt be hard either.

The hardest part is getting past the double speed of the crank vs the cam, but Im sure there would be a way around that.

If you are good with electronics, you could set up a crank trigger off of the pulley to replicate the opti signal and then use a Delteq or LTCC system for spark.
You can't use a crank signal off the pulley to replicate the Opti signals. You need true cam position to run sequential injection and direct-fire ignition.

I just though of a major problem running a Large cube motor off of a Gen III PCM. The Gen III has no provisions for Acceleration Enrichment (AE) All of the AE stuff seems to be hard coded for the intake characteristics of the LT1. My guess is a big cube SBC would stumble on tip in and thats something that may be hard to get around. Perhaps a strategy of early onset PE or a couple whacky cells in the VE table could help but that's a poor work-around in my book. Will DFI or Big Stuff drive LS1 coils?

Steve

You guys worry too much.

I did a conversion on a 400 sbc to use LT1 management. It's actually very cheap and easy and when I get back from the sandbox I plan on putting up a 'how-to' thread with some pics :D

You need some 1" water pump spacers, and electric low profile pump, internally balanced rotating assembly, a custom timing cover and adapter, and heads. Ignition and valvetrain depends on how much you want to spend and what you want to do. The conversion could work a dozen different ways. For example, I have an LT1 running TPI components in my '86 iroc-z right now. No butchery.

My plan was at first a 420 ci. sbc. I was going to just put on some good heads, single plane, and tune the PCM for the combo. I was going to make it roughly the same as my current 383 LT1 but proportionately bigger and compare the power and mileage differences.

Since I'm deployed, the project has stalled. But I have gotten it together to know that the engine bolts together fine as a package, so I dont see why it wouldnt work. The whole point is to do this, then duplicate it on a 454 sbc with some nasty heads. And say it's a 350 :D This has been together with the accessories, opti, and water pump. I added a mount to the lifter valley for the factory oil pump driveshaft adapter, but you could use a distributor if you wanted to.

Food for thought.

Oh yes, and the water pump clears the radiator, but barely. Only some types of pumps will work depending on how long they are. The conversion is easier than it looks...anyone with enough knowledge to build an engine could easily do it. It looks more intimidating than it really is.

I just though of a major problem running a Large cube motor off of a Gen III PCM. The Gen III has no provisions for Acceleration Enrichment (AE) All of the AE stuff seems to be hard coded for the intake characteristics of the LT1. My guess is a big cube SBC would stumble on tip in and thats something that may be hard to get around. Perhaps a strategy of early onset PE or a couple whacky cells in the VE table could help but that's a poor work-around in my book. Will DFI or Big Stuff drive LS1 coils?

Steve

Grrr. . . this is one of my pet peave's. I've been living with a lean bog on tip-in for a few years now. It's better in open loop, so I disabled closed loop. I sure wish someone would figure out how to fix this. If I ever switch to a standalone, it will be for this reason.

Mike

Open loops should take care of that and i think that can be taken care of with the obd2 pcm.. i will check out which tables are there for that...

Acceleration enrichment is used a lot with the V6 crowd.

Another possible solution to the AE dilemma on the PCM is to step back to a 93 SD PCM. All of the AE tables are mapped out for those. Then you've got the speedo inputs to deal with (unless you own a 93 obviously)

Steve

You need some 1" water pump spacers, and electric low profile pump, internally balanced rotating assembly, a custom timing cover and adapter, and heads. Ignition and valvetrain depends on how much you want to spend and what you want to do. The conversion could work a dozen different ways. For example, I have an LT1 running TPI components in my '86 iroc-z right now. No butchery.

Can you specify which pump is short enough to clear stuff? Also did you start with an LT1 timing cover for your modifications or something else?

Thanks

Steve