Has anyone actually tried to put LS3 heads on a 5.3? I know they are listed as not fitting, but just wondering if anyone has tried and knows 100% that they won't work.

 

Gm has a set in their performance book made for small bore engines. I was thinking about going that route but did 6.0.
A high revving 5.3 would be fun.

 

Just mock it up, mark where the valves hit the bore then take a hammer and chisel and clearance the bores.

Before you get all upset about the smartass answer............

Add the valve sizes together and then consider the size of the 5.3l bore, then consider the valves need room all the way around them, they don't touch in the middle, they aren't perfectly in the center of the bore, they don't move in line with the piston but are set at an angle.

Those heads need a 4.00" bore to CLEAR and more to be properly deshrouded and you are proposing a 3.78 bore.

 

I understand and fully agree with you on the numbers. Seeing that the valves are at an angle and do not drop straight into the bore, I was just wondering if they might work. I have completely thought the senerios through, but Not having some in hand to check for sure, I had to ask.

 

The exhaust valves hit the top of the cylinder on a 5.7. It might be a stretch to even make the small bore heads work on a 5.3.

 

Yup, GM did that and they came up with the conclusion that on any bore below 4" the valves will smash into the cylinder wall. Then they went out and said these heads stock require a minimum of 4.000" bore.

 

Mast also makes a set of small bore LS3 style heads, but I dont know if they would work on the 5.3. My question is , what would you do with the motor if you did get a 260cc head to work on a 326cid engine. Its hard enough to get a 376cid engine to not be a dog below 3000rpms with those heads. It would be a super high rpm screamer, but it would take a while to get up there.

 

So would putting a set of Mast Small Bore's on an LS6 would be less effective than a set of AI ported 243's? I am planning a total rebuild on my LS6, and am inbetween deciding on ported 243's/FAST Intake/90mm TB, or Mast's SB LS3/LS3 intake.

 

Monte Texas speed and MAST both have small bore ls3 heads. Mast are wicked expensive and i paid $2500 for the Tsp heads. You may wanna look into those.

But let me forewarn you about the ls3 stuff. Minimum of a 4" bore and even then its not ideal. The valves are shrouded badly from the cylinder wall and limit your ability to mill for compression and larger cams because of PTV clearance. Id recommend at least a 4.030 bore to really take advantage of the ls3 heads.

 

Ls1 It sounds like you have tried this. Thanks.

Newschool This project is a twin turbo drag only engine, so the intake will most always have positive pressure in use. I asked because I am at the turning point, where I need to decide on a intake and as to start porting my current heads or buy new.

FoD I can't answer that for sure, but I would like to think that Mast feels there is a use for them. I know if my bore was big enough, I would go LS3. A better flowing head for less money.

 

Well I'm leaning toward a 383 stroked build with the Mast heads/LS3 intake. If upping the cubes from 346 to 383 is still not ideal, I'll go with the 243's. I was looking for first hand experience info as well.

 

Look what AI did with their 706 heads vs. the "ultimate" 11 degree cathedral port head.
https://ls1tech.com/forums/dynamomet...-gm-5-3-a.html

If I understand things right PI that made that compared head was the company Mast bought to put their own name on heads.

Kind of makes you wonder what the 243s would do?

Not saying the Mast stuff is bad, it certainly is good stuff. Just sometimes the real world testing reveals something different than popular opinion.

I am sure had he asked the forums about going from the 11 degree aftermarket head to "just a ported 706" they would have told him it was a huge mistake.

 

Link to the TSP Small bores? All I can find are the 227 Cathedral port small bores, which would not be LS3...

 

FoD It sounds like we may think a little bit alike, I am a "show me prove it to me" type of guy. I can't count the number of times in the past 30 years of building racing engines, that information was found to be inaccurate, or that a part needed very minimal work to be used but was said to not fit or work.

 

They are on their website. PRC aftermarket ls3 heads 250, 255, and 260cc heads.

 

Our LS3 heads still need a 4.0"+ bore.

 

Yeah I don't think those were designed for a bore smaller than 4.00". I think those are just LS3 heads, not smaller bore variations.

EDIT: Too slow.

 

Does anyone have any results of the Mast small bore heads on an ls1?

 

I would think more about how it runs, then IF it can be fit. look into the valve to bore space, and see what that dose, dyno, even on the bench is easy. bigger isnt always better, more junk in the way of the basics.

 

Are you building this for a specific cubic inch class?

You could destroke a 6.0 by using a 4.8L (3.268") crank and custom pistons with a longer rod and end up at the number.

D&A Performance built one for the Engine Masters competition.
https://ls1tech.com/forums/generatio...id-inside.html