Deano Lewis

Hey guys i want to put 823 cyl heads on my 6.0 lq9 bottom end.I also have a mild aftermarket camshaft.Do i have to change my pushrods?Also heard guys talking about ptv.Really need some advice thanks.

HappySalesman

iTrader: (3)

Any particular reason for the 823s? The valves are shrouded pretty badly in a 4" bore, and quite frankly the intake ports are a bit big for that displacement, especially with a mild cam. Your low-end torque and driveability are going to suffer with those heads.

To answer your questions though, I'd absolutely recommend changing pushrods, or at the very least measuring to make sure they fall within an acceptable pre-load range for your lifters.

As for PTV, you should always check ptv, even when manufacturers say "it'll be fine". It's just cheap insurance. From what I've read the 823 heads on sbe motors only really have PTV issues when milled though. What are the specs of your cam?

01CamaroSSTx

iTrader: (3)

FYI the 2010 Silverado HD 2500 has an iron 6.0 block which is a 4.00 inch bore with 823 heads from the factory. My daughter's 2008 Silverado has a 5.3 block which is 3.780 bore with 243 heads and those originally went on a 4.000 inch bore.

01CamaroSSTx

iTrader: (3)

Current build is a LQ9 bored .030 over with LS1 crankshaft, 12cc domes and stock 823's. The camshaft is 238/246 .633 int. and exh. and my compression is around 12.4:1 static and 9.06:1 dynamic. No P-V issues here and I think it will respond well to C85 and other high octane fuels.

HappySalesman

iTrader: (3)

This is true, however factory motors built for trucks are entirely different from performance applications. The 265cc intake runner is HUGE compared to the cathedral ports that originally came on the 4" (210 for the 243 heads fyi). Hell even most aftermarket head manufacturers don't get much bigger than 230cc for Cathedral's. So you've got a large intake port that's going to reduce low-rpm air velocity, and a 2.165 intake valve which is shrouded by the bore. I'll admit I misspoke when saying 'badly' shrouded, but shrouded is shrouded.

I'm not saying that 823's won't work on a 4" bore, but I think you can make more torque across a wider range with a good cathedral head.

Ls7colorado

iTrader: (3)

In a heavy truck I’d rather have cathedral heads, they clearly do make more low speed power.
Anyways to the OP what cam do you have?

RichyB33

I haven't seen a lot of graphs posted, but I do know there are more than a few folks making some really decent power across the bad on stock bottom 6.0s with 823 heads and ported intakes. I would be interested in dyno graph comparisons between square and cathedral ports on the low end with a 4.0" bore. I'm considering this myself for my LS2 with a 229/244 ish cam.

https://www.corvetteforum.com/forums...3-top-end.html

This guy over on the Corvette Forum seemed to have a pretty stout low RPM curve with a stock bottom LS2 and LS3 top end.

Ls7colorado

iTrader: (3)

In a car or anything that isnt gonna be towing I would go with rec port heads.
As you can see from this test its not a huge difference either way and if you already have one or the other installed on your engine I dont think it would be worth swapping. But if i was putting an engine together in for a heavy truck/towing application and I can pick up and extra 20 ftlbs down low and sacrifice it up top ill take it. Also what this test doesnt show is the part throttle power at say 2000-3000 rpm witch you can only assume would be in even more favor of the cathedral heads, but once again that only matters if alot of weight is involved.
The other thing (witch is also mentioned in this video) is the factory intakes for the Rec port heads are almost as good as the best aftermarket intake available for the cathedrals.

WE TODD DID

iTrader: (2)

Every bit of that is false

WE TODD DID

iTrader: (2)

Runner cc’s are virtually useless for anything except selling cylinder heads.

You can have two runners with the same cc’s, both with drastically different air speeds and they will run differently.

WE TODD DID

iTrader: (2)

Hypothetically speaking the pushrods should be the same length, but you should always check along with your ptv clearance. Most mild cams get by okay.

01CamaroSSTx

iTrader: (3)

Yeah, my 03 Silverado with 317's does has more down low compared to the 823's.

01CamaroSSTx

iTrader: (3)

They are 317's

low2001gmc

iTrader: (148)

I have had Ported 243s on an LQ4 and Ported 821s on an Lq9.

On my Lq9, my 821s were milled 15 and used Cometic 40 head gaskets with a Lunati 232-238, 599-601 on a 113+4 with a 4l80, FTI 3800 Stall and 4.10s. It had more midrange and top end, but I wanted it that way.

On an Lq9 because it has flat tops, I recommend Rectangle Port Heads all day long. With the right cam just better. Stock Rectangle Ports outflow most Ported Cathedrals.

That 229-244 is a good cam and will be a better all around cam than what I ran at the time.

On build with dome pistons, I am sure they have flycuts to allow for the bigger cam so PTV is not an issue.

On an Lq9 or any motor, the cam duration and LSA are the PTV factors. Just for reference, on an Lq9 with Unmilled Rectangle Port Heads, I have seen as big as a 235-239 Cam on a 113+1 LSA. But every engine can be different especially if you don't know its history and PTV should be checked and Pushrod Length measured.

Original Poster, need more info like your cam specs, vehicle, other mods, etc. If cam is on the smaller side, Milling Heads is possible and would help increase compression thereby increasing torque and power.

Providing as much info about your vehicle and all mods would make it easier to try to help you.