Lq4 compression for towing

[White Stripe]

I appreciate any input on my build for compression ratio goals. Im rebuilding a Lq4 for towing and daily driving. I just want it to last a long time, have more power than a stock Lq4, and be a good multi tool truck. Want to have no problem running cheap pump gas while towing heavy loads up long high elevation mountain passes. I got a btr stage 2 v2 truck cam for it. I'm using forged 4.030wiseco Tru street pistons. With the 317 heads my compression ratio will be about 10:1. The machine shop thinks I should shave the heads for even more compression. I honestly think 10:1 might be a little high and should knock it down closer to 9.5:1. I know the later model 6.0 trucks gm bumped the compression to 9.8:1. I have a feeling gm kept 6.0 truck motor compression ratios lower because they knew people would use them for towing. Should I follow the machine shop advice and shave the heads, leave it at 10:1, or drop it lower than 10:1 for my purposes? I will have it dyno tuned once it's in the truck.

[mt-engines]

Are you doubting what the engineers at GM rated the towing capacity also? You will be fine if you are at 10:1-11. you have knock sensors that will pull timing twin 02 sensors and multiport fuel injection.

just dont be stupid and try going up a 6 percent grade in overdrive, full timing 10,000lbs and 85 octane fuel.

a good tune and a camswap wakes these up, no need to reengineer the engine because of follklore

[White Stripe]

Are you doubting what the engineers at GM rated the towing capacity also? You will be fine if you are at 10:1-11. you have knock sensors that will pull timing twin 02 sensors and multiport fuel injection.

just dont be stupid and try going up a 6 percent grade in overdrive, full timing 10,000lbs and 85 octane fuel.

a good tune and a camswap wakes these up, no need to reengineer the engine because of follklore

Stock compression for this motor which was used in all the bigger GM pickups is 9.5:1 which is lower compared to what the cars got such as the ls3 which is 10.7. I assumed the lower compression was for when towing to keep cylinder temps down. So I was just getting opinions if I should stick with the stock 9.5:1 or if going to 10:1 would hurt towing. I would try not to lug the motor, but would like to not worry about having to run premium. I'm not sure the limits of the stock ecu in pulling timing and if it would pull so much that it would cancel out the extra power from higher compression anyway.

[mt-engines]

Are you doubting what the engineers at GM rated the towing capacity also? You will be fine if you are at 10:1-11. you have knock sensors that will pull timing twin 02 sensors and multiport fuel injection.

just dont be stupid and try going up a 6 percent grade in overdrive, full timing 10,000lbs and 85 octane fuel.

a good tune and a camswap wakes these up, no need to reengineer the engine because of follklore

Stock compression for this motor which was used in all the bigger GM pickups is 9.5:1 which is lower compared to what the cars got such as the ls3 which is 10.7. I assumed the lower compression was for when towing to keep cylinder temps down. So I was just getting opinions if I should stick with the stock 9.5:1 or if going to 10:1 would hurt towing. I would try not to lug the motor, but would like to not worry about having to run premium. I'm not sure the limits of the stock ecu in pulling timing and if it would pull so much that it would cancel out the extra power from higher compression anyway.

Lq9 came in the escaldes and the vortec Max trucks I believe. And the towing capacity is still something like 10,800lbs at 10:1 compression. The newer engines are over 11:1 . You will be fine if it is tuned right.. Even at 9:1 and a bad tune you can have problems.

[mt-engines]

The stock tune pulls out something like 10 degrees of timing almost immediately. And takes for ever to put any back in. This can be adjusted, also power enrichment delay needs to be adjusted. You can find 20whp and about that torqueon a stock enginewith a tune. With a 220@.050 cam and lq4 heads you will normally gain 50-60whp

[White Stripe]

The stock tune pulls out something like 10 degrees of timing almost immediately. And takes for ever to put any back in. This can be adjusted, also power enrichment delay needs to be adjusted. You can find 20whp and about that torqueon a stock enginewith a tune. With a 220@.050 cam and lq4 heads you will normally gain 50-60whp

Thanks for your reply and advice. I was just concerned because the mountain passes here are pretty good climbs. So power is secondary to durability. It can be wide open throttle for 15 minutes or so at a time with a trailer going up to 12000 feet altitude with a 6 or 7 percent grade.

[mt-engines]

In high altitude compression is your friend.

[Racer71]

At that compression you’ll be fine just make sure whoever tunes it or if you do it yourself via HP tuners or the like that you leave the low octane tables alone and tweak on the high octane table solely. When these pcms detect knock they revert to the low octane table. You can change the thresholds for it to make the change and what parameters are met for it to get back into the high octane table. I see many previously tuned vehicles come in and the tuner copied the high octane to the low. There is no safety margin when that’s done as the pcm can’t pull timing if it’s tables are the same. The power enrichment settings leave a lot to be desired in factory form as well on these trucks. Shift points especially when the lockup is engaged also have lots of room for improvement. Biggest gripe from 6.0 guys that tow is how busy the 4l80 is dropping In and out of lockup and downshifting. Spend a little time with those tables and makes things much better for towing.

[Bill Chase]

The lq9 was identical but had flat tops wasn't it? I've seen a few of them still go 225k being used to haul boats, ATVs, etc. As well as in general being driven hard since new. Just an observation.

[ProPower engines]

Shift points especially when the lockup is engaged also have lots of room for improvement. Biggest gripe from 6.0 guys that tow is how busy the 4l80 is dropping In and out of lockup and downshifting. Spend a little time with those tables and makes things much better for towing.
[/quote]

There is some kits available to stop the lock up till trans is in 4th gear which makes it nice for towing up hills.
Just did a 4L80 for a customers truck a while back and he loves it. Even around town it does not cycle the conterter as fast as well making it just a joy to tow stuff

[White Stripe]

Ok I appreciate the replies. Just wanted to check because it's easy to install a thicker head gasket while apart if compression is too high. Hopefully the tuner I got can squeeze some decent fuel mileage out of it too compared to a stock tune. I ordered the btr stage2 v2 truck cam for it hoping that would help towing as well.

[mt-engines]

The BTR cam makes about as much power as the $230 Elgin-1838-P You will be satisfied. I also hope your Tuner knows what they are doing, some guys just load a similar bin file without really modifying the part throttle, tip in, etc. You can also ask him if he has a lean cruise patch, It makes part throttle spongy when active but does provide additional fuel economy.

[White Stripe]

The BTR cam makes about as much power as the $230 Elgin-1838-P You will be satisfied. I also hope your Tuner knows what they are doing, some guys just load a similar bin file without really modifying the part throttle, tip in, etc. You can also ask him if he has a lean cruise patch, It makes part throttle spongy when active but does provide additional fuel economy.

Lean cruise patch? Is that similar to highway mode in the earlier obd1 gm ecu's? This is the first time I've gotten a custom tune on a engine but I've done some reading on tuning and understand a little. Is that normal for tuners to be able to program a type of lean cruise? The tuner here has good reviews. I'm in Denver and we have a lot of tuners around here, so it's tough to figure out who to pick. If a tuner sets up a lean cruise in a tune doesn't it have to be in open loop? Would that mess with the emissions monitors not setting? Would changing elevation significantly make it more difficult to have a consistent lean cruise afr?

[White Stripe]

So I thought I would see what the factory gasket looks like in regards to intake port match. The Mahler gasket mates up with the truck intake fine I think. I bolted the intake, gasket, and head together on the bench. Traced the gasket od on the head, pulled it apart, put the gasket itself to the head on the tracing lines, and this is what I got...

20210106_182816.jpg

It's a good 1/8 step to the head. Should I open up the floor of the intake port on the head to match the gasket?

[mt-engines]

So I thought I would see what the factory gasket looks like in regards to intake port match. The Mahler gasket mates up with the truck intake fine I think. I bolted the intake, gasket, and head together on the bench. Traced the gasket od on the head, pulled it apart, put the gasket itself to the head on the tracing lines, and this is what I got...20210106_182816.jpg
It's a good 1/8 step to the head. Should I open up the floor of the intake port on the head to match the gasket?

leave it. you will only be wasting time by gasket matching.

viewtopic.php?f=1&t=53120

Here is a 317 head thread i posted with some minimal work. Notice how the port entry wasnt made larger. Unless you are trying to get some serious power or rpm there is no need to touch the gasket area. and if this is a max effort deal, cathedral ports are the wrong head.

Just do a quick bowl blend and thats all you will need.