It's good to know others will still experiment, trial and error with things that are important. Like going fast in a car.

Pro maxx extreme 240 heads a rec port and for 3.800 bore That would be interesting as well. But yeah a 5.3 with a 300 plus cfm head na will be spun to the moon but will be mean on boost

Wow you Def answered a question I've had on my mind for the past few years since I've been watching you. Thank you sir. More great information sir.

I Wondered about this swap, Now I know. TY for showin us!

They developed back in the 60s i believe the w-series v8 where they cut “valve reliefs” into the block to run larger valves. Cool motors ahead of its time but went away so soon

Nothing a grinder can't handle

Pro max has a rec port head that they have put a smaller valve and moved it over to work on the small bore engines. That should work well

the LS Guru

Now this was a damn good video.

Thanks for your demonstration. Sounds like the same problem that Chevrolet had that similar problem with the 348 and 409. Also the possibility of hot spots in the cylinders at the point of the head gaskets and a little way down the cylinder wall. In other words it would really complicate those arias nearest the valve and the cylinder walls too.

Your my hero Richard

Promaxx makes a small bore rec port head.

Edelbrock makes bolt on LS3 style rectangle port head for small bore LS #61319.

Well HOW COOL WAS THAT! TY

I solved this by trading for a 6.2 block. I used LT pistons, milled to fit chamber, and give slight compression boost. PVC MUST be ck'ed. Very tight !

man, basic ported old catherdral heads flow over 300cfm...

Awesome video. Would really like to see a small bore ls3 head test. I’ve got a 383 stroker in my 4th gen f body. Trying not to run a spacer plate for the LSA and pickup some power too na before hand.

I’m going to go out on a limb and say yeah grinding it out like that doesn’t seem fine. Also you probably will affect the flow with part of the valve in a pocket like that. Cool video was guessing those heads would be fine. Oh, and that chunk you would have to grind out also adds as the the compression chamber volume.

A set of custom pistons could resolve some of your problems, domed pistons to bring back compression, then move the rings a little further down the piston to allow for adequate clearancing for the valve pocket. Bada bing bada boom

I am runnin ls7 heads on my stroked ls3, the exh valve was the main issue and we machined it to give 0.030” valve to cyl wall clearance.

This would make for an interesting build if combined with that big bore 4.8 idea

You so are awesome!

Not being an ls guy EXCELLENT video

@Richard Holdener I'm over here crying laughing listening to you telling people how bad of an idea to put rec port heads on a small bore it is! LMAO

Fly cut the block like a big block chevy and use a copper head gasket so you could notch it for clearance only where it needs it

Just like the 348/409 Blocks and heads swaps.

I seen those heads on LS1 they machined valves smaller so it fitted. Worked on a turbo application like a bomb. So nothing a bit of thinking outside box can't solve

the real whip shit, raised floor 821 heads on a 3.900 bore block with notched bores, might all work out with smaller valve, but the relocated valve centerlines are a bit more challenging to deal with. A 2.050 intake valve, slide the exhaust valve over 60 thou with a offset guide, move the seat weld the chamber and ports up etc but a epoxy filled raised floor 821 style head could be a real screamer on a small bore 3.900 motor

I think it can work. Just a little more

Have you tried the ls3 small bore heads on ls1 or a 5.3? I tried to look. Kinda curious about those heads..

We stuck ls3 head on a bare 5.3 block rolled it look down the bore and started laughing

good vid

More like this! In the shop an not in front of a webcam

You also have an issue with the cylinder shrouding the valves and disturbing the airflow, so you won't be able to take advantage of all the additional flow anyway. The large-valve, small-bore head may actually give you more or equal flow due to undisturbed, smooth airflow.

I stuck a rec port 6.2 823 heads on a 5.3 and I thought is wasn’t going to clear but it cleared, but now I’m looking for a 243 cathedrals just to be on the safe side lol

You would be LOSING so much air flow from a third of the valve being shrouded to the point of being useless

Thank yu , helps the what if magic machine shop voodoo

This is handy if you want to rev to 10k. L86 heads should work somewhat better.

I had to leave the chat to see what you actually did. Your right on with this. If its port volume that is the target. I think it might be better to CNC the SQUARE port pattrrn into a set of cathedral heads. This way youd be usine a maximum size port and valve. Without compromising the block and sleeves. But again this is a massive cost just to see if the SQUARE port is going to give you more horsepower. Hmm. You need someone from the more money than brains to indulge your every whim to test a theory.

Wonder how much closer a 3.9 bore gets to fitting.

Like 396 and the 402 valve placement is critical

Reminds me of a certain quote from Jurassic Park. 😎

You could use lower lift cam with longer duration.

so what we learned is, 6.0 block + 4.8 crank with rec port heads will be the only way to see what a 5.3 engine can do with one of these heads. obviously have to have custom pistons because there will have to be some machine work performed to get that compression ratio back up. would be interesting to see where the difference is the heads and intake manifold compared to a l33 with the fast intake. would still love to see a small bore/long stroke 5.3 vs a big bore/short stroke 5.3 with as much of the same parts are possible.

They make small bore LS3 heads by Pro Maxx. You can get those or maybe bore it to a 3.9 5.7 piston and see if that works better.

Mill the head (or buy a head with a smaller chamber), add a thicker head gasket, clearance the cylinder wall, and use a low(er) lift cam. It'll work, but you'd probably just kill the bottom end power. Neat video

Make it happen Add boost for the loss of tq The next big bang. What will fail first? The block where the cylinders are machined for valve clearance or something else?

I guess I haven't been looking at the basic horsepower per liter of these engines enough to know if the larger bore engines that use the cylinder heads actually make more horsepower per liter.

On a positive note at least you can’t drop a valve… 😂

Might even cause a detonation problem too.

Gee Richard just angle the valve guides like a boss 9 BBC Cleveland Answer is to just turn up the boost on a cathedral port head Max Wedge and others had notched blocks from the factory but not here

Could take some off the valves and bore to 3.900. It's not worth the effort though. Going to have to mill too much off the heads or get dome pistons.

Thick head spacer/gasket (+0.5" lol) and a really tall domed piston?

STOP FING YELLING AT THE BEGAINING GET OVER ! your videos are great to watch no need for the hype any longer. any head improvement is going to make more power if one wants to put in the work

Just for the sake of trying to make it work, why not retrofit 5.3 valves into the rec port head. Install new seats for smaller valves but blend the bowls to the smaller valve size. I think it would work this way with notching bores.

So if the rec port head can be used on a 6.0 with a 4.000 bore then why should you need a 4.100 gasket to make this all work together? I feel like you took a little more than necessary out of the cylinder wall up top. I'd like to see how it performs but on a small displacement engine we would have to expect these to perform similar to the 317 heads with maybe a few more horses up top.

So i guess if you were building 11k rpm motor then it could utilize that extra air flow.

Flycut the deck or top bore for valve clearance. Just like Any 3.0 v6 ford or even a 396 big block chevy.

Thanks, just put smaller valves in the rec port head...

Haha i knew what would happen but they got some big valves in em. Maybe...Off set guides and a smaller exhaust valve would make it work. Lol good looks tho. With the power people can make on other heads would be way more beneficial. With the money you'd spend on getting a good cylinder head guy to do them, not worth it.

I think people are more likely to take a 799 243 and want an LS3 port

Could you run a custom piston to give you a little more room, groove out a metal gasket instead of using an oversized one, run whatever cam fits.....then BOOST it to overcome the compression loss and take advantage of the flow you're now making?

Looking at your display engine... I don't even think they would work on an LS1 5.7L (3.898" bore) Bore that to 3.905", I still think it would be dangerously close to interfering. By what you showed, I see why a 4" bore is the minimum for rec ports.

I read the title and said well Richard holding would be the one to be getting the answers... and I wonder what the numbers would be on a stock 3rd gen early or late 2004 5.7 aluminum engine and the one with the revised 241 head and came with a factory LS6 intake I always wondered what LS3 top would do on that... or an LS3 top on the Gen 3 5.7 LS6 243 head... I was wondering recently what an LS3 top would do to either one of those engines approximately

Question: So if I wanted to put a 383 rotating assembly in a 4.8/5.3 block, with that bore size could I run those heads and have cylinder wall clearance that I need?

Bigger question is can you mill rectangular ports in a cathedral port heads and use Rectangular port intake???? And will it make more power??

If im not mistaken, that fuelie in the background was in the last episode of Engine Masters.

Can we cant the valves a 2-3 degrees without any valvetrain issues and relocate the exhaust so its minimal thickness between the Intake and Exhaust valve??

Old dirt track trick cam. Just enough lift to clear, lots of Duration

Hey Richard. The gasket is 4.1 to suit the head chamber. So the 5.3 is on 3.780. What about the ls1/6 with 3.903 bore size that is a common oversize used? Just unde .200 difference between them over the 5.3 at .320??? Also what if you run a slightly smaller valve in the rec port head to help clearances. Say .040 smaller valves.

Would the valves from the cathedral port head clear on the rect port? Then you could just install new seats and use rect port.

Someone needs to try mast motorsports small bore rec port heads

Now my question is, what size bore would it take to fit and run properly? I know a 4 inch will fit, but what about like a 5.7 or even a slight overbore 5.7? I know you're just making a large bore out of a small bore but if you have a 5.3 that you're changing rods and such in anyways would it be worth the bore

Does this mean you can’t run LSA heads on a 5.3 engine?

How much compression will be lost when clearancing for the valves?

Now ya gotta do the 4.8 heads on a 6.2. Lol, just kidding.

Why not just use a carbide fly cutting tool? This way you can get clean cuts

Im all for R&D but as you eluded to in your intro; just because you can do something.., should you? Cylinder heads are specifically designed for a specific RPM utilizing a block's bore and stroke. Through engine math and complicated algorithms port sizing, pinch point and valve curtain are determined; all for the purpose of maintaing proper airflow velocity throughout the expected RPM range. Your vids are entertaining and most often there is something to learn. In this video you missed a greater opportunity to teach WHY you shouldnt use those heads on a 4.8/5.3. That missed opportunity was how to qualify size. When is big to big. When is small to small? In other words how do you qualify the size of a port or the size of a cylinder in a block as small, medium, or large as it relates to power output being mild, moderate, or maximum? Those commenters thinking these heads are perfect for a 4.8/5.3 dont understand basic engine theory - only because no one is teaching them.

Yeah I wouldnt try something like that....

At one time when ls was new they said u could make a ls sbc hybrid can u do that with an 96 LT1

Offset dowles?

Would these big valve heads fit on the 3.898 bore?

What about doing this with a 5.7l ls? Or say, a lm3 5.3 bored to 3.903?

Would it work better if you selected a smaller valve size and fitted correct size seats so the throt size is 90% of the inlet valve and 88% of the exhaust valve before any porting was done so the bowl area only needed the guide needed cleaning up.

Would a 4.0 bore clear without notching? The head gasket on the display was for a 4.0 bore?

Would be WAY better off to just put a shorter stroke in a bigger bore block

I’m just wondering how many more test there is that you haven’t done

Aren’t there Indy engines where they shorten the stroke of the pistons so they can turn em up to 10k RPM? If you did that in this situation you could lose down low but turn crazy RPM

How can these heads work on a 6.0 with a 4.00 bore when you say they say they hit a 4.01 gasket?

Does anyone know how big a valve could you run in a 706 head on the small bore blocks?

As long as we’re on this subject, what are your thoughts on a 2.30” valve in a 4.250” bore?

You said Rec-Port heads make less power down low. Can you give a ballparkk RPM for where that would be true? I'm currious if there are any use cases where Cathedral is better, or are you talking so low that only internet trools could care?

Also what about the promaxx small bore extreme 240cc heads? They come in a 59 and 63cc chamber.

Well they fit a gen 3 6.0 lq9?

Will they fit on a 3.898 in. bore block?

I have a 4.8 what are some of the Modifications To Do to the engine to give it some more power.its in a type 3 69 vw wagon c4 corvette suspension manual

Ok so what about a 3.9 bore LS

Would the heads fit a 383 ls Stroker

😢

Turbo it problem solved