Just piecing together my motor, I got 243 heads for my LQ4 block. there are a couple Cams I'm looking at. all are torque Cams / truck Cams for low end. LSA specs range from like 108 to 114. I've got to match my cam and piston so I end up with a DCT that will be safe on 87 in a heavy truck (2500HD)
​​​​​​To do so I have a few questions

Will bumping up Static compression ratio make up for using a cam with a larger LSA? (like it will still have similar low end torque? will the larger LSA Rev higher even though DCR is the same?)

What's considered a safe DCR for 87 pump?
Guy I bought my heads from had a similar build he said he had 10.6:1 with a 112 LSA on 87.

sorta unrelated but kinda related
I know forged pistons have better detonation resistance which might be a plus. Is there any large draw backs the going with forged pistons over hyper cast? I understand they are louder, I'm more concerned about longevity. will the pistons be slapping after another 100k miles?

Thanks everyone

 

Forged pistons can be fit to ensure a quiet engine, especially the 4032 forgings. Unless you're going FI, Hyper cast pistons would be OK for what you're doing, WITH A SPOT ON TUNE. Realize that they offer no insurance with a marginal tune or marginal gas, which the forged pistons do. But they can last a long time with a real good tune. That is why most LS engines come OEM with hypereutectic cast pistons. What bothers me a little bit is you're looking to raise compression. High DCRs and hypereutectic pistons aren't known for long marriages..

 

There is a difference between safe and efficient. You can pull all kinds of timing out of a high compression engine and run on 87, but is it worth it?

 

Ya, I'm definitely going forged. I think with a heavy truck any bit of towing is going to be a high engine load which could result in detonation. I think I noticed a bit already on the stock motor when romping on it (of course the cam will also be smaller), but GM says very little under high load is normal (i also don't usually romp it when towing, Just drive it where it's smooth). Considering I'm looking for 450 - 500 Crank HP and Torque, best be on the slightly safer side.

Plus If I ever want to turbo the Truck, all that has to be done is slap the old LQ4 heads back on.

 

I'm under the impression it's better to have a motor with a bit more compression than a motor with less and more timing. That said, I'm trying to figure out a safe margin. Shell 87 in Canada is 88 or higher, which also gives a small margin. I don't want to have to pull tons of timing, I'll likely end up with a forged dished style piston

 

500 crank hp, even 450 hp, out of 364 cubes, using dished pistons and a torque cam, while limited to 87 octane is going to be a tough one, imho. The extra weight of a 3/4 ton truck which is used for towing will be a limiting factor on hp, too. I'd forget the hp numbers and aim for torque, as it seems you are stating info on torque cams. But to be realistic, a 364 cube motor that has high torque for towing will probably fall shorter than you're hoping for in the hp dept. My .02

 

I second this - I have a 2006 2500HD I use for towing, and I don't think it's ever seen the high side of 5200 RPM. I'm probably going to cam it for torque, because adding power above 5000 is kind of pointless in a tow vehicle. Torque gets heavy vehicles moving, not horsepower.

 

My peak power is ~5,600 on my SBC 383 that is in my Express I tow with. Peak torque is at about 3,500 rpm. Tows perfectly with a 2,800 rpm converter in the 4L85E, 3.73 gears on the 30.5" tall tires. It has a 218/228 @ 0.050 on a 108 LSA with 0.578 lift. Sounds beefy but builds torque very quickly.

I would not waste my time on 87 octane. 91 or E85 both allow for enough additional timing even on a 9.4:1 engine that I run both more economically than 87.

 

I'll just say this, I know someone with a 6L 1500 who is making about 440hp wheel with similar torque numbers, and they have a very very similar build with even higher static comp on 87. That's why I say that's around what I'm aiming for. I am also doing 243 heads, long tubes (smaller for torque), Nnbs intake, probably 2800 - 3000stall. through my research it's obvious that torque Cams like the truck Norris have a very low LSA to boost DCR which boosts torque, but also seems to sacrifice peak power and how far the motor will Rev out (that is to say peak hp isn't necessarily higher with a cam with a larger LSA but the cam seems to rev out further while the lower LSA Cams appear to just drop off quickly). That is all good for a stock motor with the stock 9.4:1 comp ratio but since I'm raising my comp to around 10:2 I don't need the low LSA to boost DCR for low end, as my static already boosts it enough. From what I've seen online stock 5.3 with a torque cam low LSA will have around 10 - 15ft lbs less torque than a truck cam with a larger LSA but that's also what I should be expecting from the SCR difference from swapping 706 to 243 heads. in theory I'm pretty sure this will allow me to have a motor with similar torque figures to a "torque oriented" cam but also allow me to rev a little further should I choose, all while producing more engine vacuum and possibly having a less aggressive sound. Of course cam choice is still up in the air, and I'll probably stick with dished pistons for the safer margin on 87.

also, it's more of a winter daily truck, might haul a heavy car, wood, or scrap metal on a trailer once in a while. (I'd guess like 8k lbs max) in the summer I mostly ride my motorcycle, using the truck to go to motocross tracks on the weekends. So I'm not supper worried about loosing a slight bit of torque but I doubt with the added static CR that I actually would

​​​​​​Honestly at this point I'll probably have dished pistons similar to the stockers, with a TSP truck stage 3 for some peak HP but also to bleed off some DCR but still get good torque

 

Ya sounds similar to what I'd be doing maybe a little smaller, seeing as I've got a 4.10 rear end and 33s. off course that cam would be great for torque as the LSA is very small and it's got a lot more exhaust duration.

I'm probably going with a 2800 - 3000rpm converter. Do you find yours is tight enough below the stall to drive nicely? how does it affect the trans Temps?

I live in Canada so 91 would have to be a fair bit more efficient to actually make it worth switching too. I calculated a difference of about 5L less per 100km was necessary in order to make to equal out costs. of course if 4 or 3L less would also put me in a better position because I wouldn't mind the extra 5 - 10$ per tank at that point. maybe I will do it know that I say that
anyways, how much more efficient did you find 91?

 

Dang metric system. It really depends on the setup. The L31 in my Van was very knock prone even on the stock timing advance table in it. When I switched to 91, the knock went away and I was able to add 4-6* of timing advance almost everywhere. It made more torque and ran cooler. From memory gained about 1.5-2 mpg average in my normal driving. Been so long since it had the stock 350 in it and I ran it on 87. I built the current engine with an 11:1 static compression ratio to take advantage of the higher octane of the 91+ or E85 that I run anyway.

As for the converter I have driven trips of over 200 miles without getting over 2,500 rpm at any point. It is a little looser than the stock B82 in normal driving, but stalls about 400 rpm higher at WOT. With the way I have the TCC mapped the transmission temps were not changed. When it was 105*F outside and I was pulling 5,000 lbs it held 165*F.