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You'd have to get the LS2 resleeved, and you might as well build a 427 at that point.

The great thing about the LS3 is the heads, the bore size just helps with flow around the larger intake valve.
I'm actually considering that. I may reach out to a local engine builder this week and get an estimate on what the machine work and bottom end labor cost would be, and then I guess I'll go from there.

I suppose I'll make the decision on what is best once I get a better handle on the cost of everything.
Be careful with local builders if they don’t have experience with LS based engines. There really are benefits to using someone like TSP that builds LS stuff every day. They will know exactly what you need to make everything play nice together in your car.
 

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I got a L92 shortblock off Craigslist for $500 that needed rebuilt. I only used the block and crank. I put JE/SRP 4.070" pistons in it with stock LS2 rods and the stock crank, new cam, crank and rod bearings. I also bought a new GM 24x reluctor wheel and replaced in myself in the garage. It's not that hard. The big difference is I put LSX-LS7 heads on it with the LSX454 cam and a LS7 intake.

I also tuned it myself with HP Tuners, no issues.

The only thing I would change is the cam. I've gotten used to it, but it has 21 degrees of overlap and under 1800 RPM it has some bucking (stick car).
 

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Discussion Starter #23
You'd have to get the LS2 resleeved, and you might as well build a 427 at that point.

The great thing about the LS3 is the heads, the bore size just helps with flow around the larger intake valve.
I'm actually considering that. I may reach out to a local engine builder this week and get an estimate on what the machine work and bottom end labor cost would be, and then I guess I'll go from there.

I suppose I'll make the decision on what is best once I get a better handle on the cost of everything.
Be careful with local builders if they don’t have experience with LS based engines. There really are benefits to using someone like TSP that builds LS stuff every day. They will know exactly what you need to make everything play nice together in your car.
Good advice. The shop I reached out to is a performance builder and fabricator, but they've been doing a ton of work on Mustangs recently, so I don't know their track record with LS platforms.

I have also been pricing out TSP and other shortblocks. Right now, I'm just trying to put together a couple of possible build sheets, and then I guess I will go from there.
 

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Discussion Starter #24
I got a L92 shortblock off Craigslist for $500 that needed rebuilt. I only used the block and crank. I put JE/SRP 4.070" pistons in it with stock LS2 rods and the stock crank, new cam, crank and rod bearings. I also bought a new GM 24x reluctor wheel and replaced in myself in the garage. It's not that hard. The big difference is I put LSX-LS7 heads on it with the LSX454 cam and a LS7 intake.

I also tuned it myself with HP Tuners, no issues.

The only thing I would change is the cam. I've gotten used to it, but it has 21 degrees of overlap and under 1800 RPM it has some bucking (stick car).
The L92 was in good mechanical shape at that price? I worry about used blocks since they're aluminum...
 

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Good advice. The shop I reached out to is a performance builder and fabricator, but they've been doing a ton of work on Mustangs recently, so I don't know their track record with LS platforms.

I have also been pricing out TSP and other shortblocks. Right now, I'm just trying to put together a couple of possible build sheets, and then I guess I will go from there.
It's unlikely you can build a forged short block cheaper than you can buy one from someone like TSP or Thompson. Even then you are going to have to put your trust into a local machine shop that may not do a lot of LS stuff and also may take way longer.

I saw a guy on facebook had the best engine builder and best tuner in the country or so he thought. The engine builder wasn't an LS guy. He gets the engine in the car and now it will not run. Engine builder can't even remember what reluctor he put in it...LOL. Go with someone that builds LS stuff every day and make sure you ask plenty of questions being specific about your vehicle, ecu, and goals.
 

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I'm not a tuner, so I'm not sure what the problem is exactly. I was reading some threads on here that had a handful of professional tuners that were trying to figure out why they wouldn't idle right in the GTO. Something to do with the existing computers and the airflow values needed.

I think it was finally resolved, and it involved replacing the intake(?) and associated sensors to the LS2 versions before it would run right.

I'm not sure 100%, and I don't know if there is a reliable tuner that can figure all that out near me.

its not the intake thats the issue. Its the LS# Maf that reads different frequencies than the ls2 maf. Thats the issue. You use the reluctor wheel off your Ls2, (you pull it off the ls2 crank and press on the ls3 crank, requires special tool) Use your Ls2 MAF and all of your ls2 sensors. The computer does not know what engine you have, It reads the sensors and responds with your programmed data. Getting it to idle is no problem and I've never heard of a hard wired 800 rpm idle in 05-06 cars. My buddy Has an 06 and it idles at whatever is comaanded. I think its set at 1000 rpm right now. If you dont set idle airflow correctly, it wont idle at your commanded rpm.
 

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Original poster I am in the middle of a engine build also. I would look at Texas speed for a short block. I got a re sleeved 5.3 gen 4 block and run a 4.125 bore with a 4.00 stroke for 427 cubic inches. I got a little crazy and put billet crank and rods. But you could just go with forged rotating assembly and save some money. The darton sleeves are way stronger and longer then factory sleeves.
 

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Discussion Starter #30 (Edited)
Original poster I am in the middle of a engine build also. I would look at Texas speed for a short block. I got a re sleeved 5.3 gen 4 block and run a 4.125 bore with a 4.00 stroke for 427 cubic inches. I got a little crazy and put billet crank and rods. But you could just go with forged rotating assembly and save some money. The darton sleeves are way stronger and longer then factory sleeves.
That's what I'm leaning towards spec-wise. I sent TSP an e-mail today, but I suspect I won't hear anything until Monday. Any ideas on how much of my stock LS2 stuff can be used on a 427? I'm thinking things like alt., water pump, sensors, etc.

This will be my first time putting a non-stock replacement engine in a car, so I'm trying to do as much learning as I can about what all parts will need to be replaced before I pull the trigger.
 

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Discussion Starter #32
its not the intake thats the issue. Its the LS# Maf that reads different frequencies than the ls2 maf. Thats the issue.
So use a different MAF cal. Lots of guys run an LS3 maf.
Is there any value in using the LS3 MAF instead of just using my LS2 MAF?

I'll probably have to put a "wanted" ad on the forum for a tuner in Houston anyway. Maybe I can get someone with HPTuner to come set the CPU up from here lol.
 

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The LS3 maf is a little better for flow since the housing is 100mm. Other than that, not really. Unless you have a pretty extreme setup, the LS2 maf is fine.

If you do use an LS3 maf, you have to remap the IAT as well as the MAF cal, unless you use an IAT breakout. Just an fyi.
 

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Is there any value in using the LS3 MAF instead of just using my LS2 MAF?

I'll probably have to put a "wanted" ad on the forum for a tuner in Houston anyway. Maybe I can get someone with HPTuner to come set the CPU up from here lol.
Some of the best LS people in the country are in your state so you shouldn't have trouble finding a tuner. Go with the best tuner you can find. Not just someone popular on the internet, but actually the BEST tuner you can find. Don't let them just tune it on the dyno either you want street tuned and time spent on all the details...cold starts, hot starts, drive ability in traffic, response, shift points...every thing.
 

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Texas, you have several great options!

21st Century Muscle Cars
LG Motorsports
AMP
Houston House of Power
Serious HP

Just to name a few. If you want local House of Power and Serious HP for sure, but if willing to travel 21st Century does amazing work.
 
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