Speed-Talk is running on www.Speed-Talk.com

IMPORTANT: Update your bookmarks to https://www.speed-talk.com/forum/
(Right-click the URL and select "Bookmark this link")

Modifying an LS 5.3 Head for Towing

General engine tech -- Drag Racing to Circle Track

Moderator: Team

1980RS
Member
Member
Posts: 149
Joined: Thu Oct 13, 2016 10:03 am
Location:

Modifying an LS 5.3 Head for Towing

Post by 1980RS »

So recently I was looking at how to get some more low end torque out of my 5.3 for towing. I looked at cams and most either have a lope at idle or are so expensive it's not worth the swap. So I decided to look at the LS head closer and was surprised by what I was seeing. A 5.3 head is almost 205cc runner and max flow stock is around 226 cfm @ .550 and up lift on a 205cc runner and the Vortec head is 225 cfm @.450 lift on a Vortec head. Now I think this is fine for racing but in my mind I think for towing that's wrong. A 170cc runner Vortec head flows almost the same numbers and I know the Vortec engines were 5.7 vs 5.3 but I think if one were to maybe try and epoxy the port floor on the 5.3 head then make the runner closer to lets say 180cc might help out the low end of the 5.3 as these engines are just dogs when using the original 5.3's for towing. So would making the port smaller help low end power as I don't need an extra 50hp at 6K I need it at 2500 to 3800 rpm. Let's hear your ideas on this.
turbo camino
Pro
Pro
Posts: 331
Joined: Sun Aug 10, 2008 11:51 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by turbo camino »

The 5.3L is a Vortec. Says it right on the intake tube.

EDIT: Also, as if there's only one 5.3L and one "LS head".
DON'T PANIC
mt-engines
Member
Member
Posts: 151
Joined: Fri Sep 27, 2019 12:35 pm
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by mt-engines »

1980RS wrote: Sun Sep 13, 2020 11:54 am So recently I was looking at how to get some more low end torque out of my 5.3 for towing. I looked at cams and most either have a lope at idle or are so expensive it's not worth the swap. So I decided to look at the LS head closer and was surprised by what I was seeing. A 5.3 head is almost 205cc runner and max flow stock is around 226 cfm @ .550 and up lift on a 205cc runner and the Vortec head is 225 cfm @.450 lift on a Vortec head. Now I think this is fine for racing but in my mind I think for towing that's wrong. A 170cc runner Vortec head flows almost the same numbers and I know the Vortec engines were 5.7 vs 5.3 but I think if one were to maybe try and epoxy the port floor on the 5.3 head then make the runner closer to lets say 180cc might help out the low end of the 5.3 as these engines are just dogs when using the original 5.3's for towing. So would making the port smaller help low end power as I don't need an extra 50hp at 6K I need it at 2500 to 3800 rpm. Let's hear your ideas on this.

the 4.8/5.3/6.0 pick up huge with a good tune, they will drive like a different truck, especially with a TCM tune.

seems like you have a lot of time to waste if you want to epoxy some heads. i would not touch the heads, a simple cam swap regardless of duration is still going to make peak torque in the 4000rpm range and pick it up a bunch of power everywhere.
a higher stall converter and TCM tune will wake up the stock engine a bunch.

both engines make about the same torque yet the 5.3 ls has more passing power. stick a cam in the 5.3 and a tune. you will make more power everywhere period. and not reinvent the wheel.

if you want to epoxy the ports, then you'll want to separate the intake manifold and epoxy the runners and bell the entries. I can tell you from experience its a waste of time unless you are building a superstocker.

a cam in the 208-210@.050 will pick you up 50-60 hp and about the same torque. it will only pick up 10-15tq below 3800, but will accelerate harder everywhere.

if you really need 50 more hp at 2500, build cubes or a diesel
peejay
Guru
Guru
Posts: 1925
Joined: Tue Aug 10, 2010 9:16 pm
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by peejay »

You can't really compare intake ports by CC across different engine families because the ports are going to be a lot different. A port with half the CSA but twice the length in the head is going to have the same CC.

That said, I've never run out of power towing with a 4.8 in an extended cab 4x4, or for that matter with a 3 liter V6 in a smaller truck. Seems to me that trying to modify for more power to make towing easier is just spending money so you can hold the accelerator pedal a little higher off the floor. As long as you still have a 4L60 you're going to want to be towing in 3rd gear anyway, right?

Unless you literally meant you are towing with a 5.3 LS in which case, I didn't think Impala SS/Grand Prixs had a very high towing capacity :D
turbo camino
Pro
Pro
Posts: 331
Joined: Sun Aug 10, 2008 11:51 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by turbo camino »

I picked up 70 (seventy!) ft/lb in my absolutely mechanically stock 5.3L truck just in spark timing. Still no knock. It was around 12* total in the ~.70g/s parts of the map. 2006 LH6.
DON'T PANIC
jeff swisher
Guru
Guru
Posts: 1090
Joined: Wed May 23, 2007 11:13 am
Location: yukon ok.
Contact:

Re: Modifying an LS 5.3 Head for Towing

Post by jeff swisher »

I know where you are coming from with needing more pulling power in a truck.
I pull loads all the time in my vehicles Gen 1 SBC and they out pull and out MPG my friends and relatives with the LS engines.

I run 305HO heads on 350" and 268H NO overdrive either just TH350.
My Ford Van would get even better MPG and pulled like the 5.3 trucks I know of.

Now I have looked at the LS head and the runner is very long and this adds to the CC.
Velocity and ability to atomize fuel will be your friend when porting the LS head.

That rocker stud boss is a big brick in the intake port I do not know how clean your heads are but the ones I got to play with had a lot of sticky goo on the upstream side of that rocker stud boss.

Dead air there and reversion polluted that area.
Remove it.
Rough up the runner as much as you possibly can to atomize that fuel.

You can look at many dyno tests on the LS and cam changes I have seen do not benefit the below 3000 rpm area where pulling is happening.

I had to come up with a grind for a friend that has a stock LQ9 6.0 and converted to carb . Long bed 1977 truck 4000 lbs using it for pulling and racing me and other buddies.

The cam I decided would work well was the old LT4 Hot cam the 218-228 @ .050 with .492" lift at 1.5 rocker ratio.
Took his stock 6.0 cam and reground it and advanced the intake lobe while grinding it and set it at 109LSA.
Had to use .050" longer pushrod on intake side and stock length on exhaust side with Morel Rollers.

That truck made way more low end power before it would spin about 20 feet out of the hole 3.45 gear and after head work and cam it could not hook at all at any speed in first.
He stuck a Posi into it and that did not help either.
15 PSI more cranking pressure after the cam swap.

That is a positive right there.

He still could not beat me but it was darn close from a roll.
That is the only LS I can say i actually have respect for naturally aspirated.

Of course you will not have the 218-228@ .050 with 1.7 rockers and the lift will be in the .557" area.
About 222-232 @ .050

There may be other old school roller grinds you could use that would bump the cranking pressure.
You could also grind the cam intake side advancing the lobe and then manipulate the exhaust to make a 112 or wider for more MPG.
Basically running a wide lSA advanced.

It hurts top end a bit but you are not looking for top end.
That above 6.0 would rev smooth to 7000 rpm.
He did destroy the cam over revving to 7500 and floating the valves. Not enough spring pressure . Running 130 seat and 313 rate spring.
Need 145 or more and possibly 425 rate to live at those RPM's

Should not float valves.
turbo camino
Pro
Pro
Posts: 331
Joined: Sun Aug 10, 2008 11:51 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by turbo camino »

Looking at my previous logs I noticed a couple of spots where my tune-only 5.3 would do 300 torqz at 1750 RPM, less than 60% throttle opening. This tune increased MPG by around 1.5 in 'city' driving, too.
DON'T PANIC
motormonkey
Member
Member
Posts: 149
Joined: Fri Nov 11, 2005 1:52 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by motormonkey »

If you are running the factory 3:73 than you need to go to 4:11 rear gear for towing. It was a option. Your Trans will thank you also.
Or swap in a 6.0, probably cost you the same sans labor. Your trany will than need help.
gmrocket
HotPass
HotPass
Posts: 7601
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Modifying an LS 5.3 Head for Towing

Post by gmrocket »

mt-engines wrote: Sun Sep 13, 2020 3:44 pm
1980RS wrote: Sun Sep 13, 2020 11:54 am So recently I was looking at how to get some more low end torque out of my 5.3 for towing. I looked at cams and most either have a lope at idle or are so expensive it's not worth the swap. So I decided to look at the LS head closer and was surprised by what I was seeing. A 5.3 head is almost 205cc runner and max flow stock is around 226 cfm @ .550 and up lift on a 205cc runner and the Vortec head is 225 cfm @.450 lift on a Vortec head. Now I think this is fine for racing but in my mind I think for towing that's wrong. A 170cc runner Vortec head flows almost the same numbers and I know the Vortec engines were 5.7 vs 5.3 but I think if one were to maybe try and epoxy the port floor on the 5.3 head then make the runner closer to lets say 180cc might help out the low end of the 5.3 as these engines are just dogs when using the original 5.3's for towing. So would making the port smaller help low end power as I don't need an extra 50hp at 6K I need it at 2500 to 3800 rpm. Let's hear your ideas on this.

the 4.8/5.3/6.0 pick up huge with a good tune, they will drive like a different truck, especially with a TCM tune.

seems like you have a lot of time to waste if you want to epoxy some heads. i would not touch the heads, a simple cam swap regardless of duration is still going to make peak torque in the 4000rpm range and pick it up a bunch of power everywhere.
a higher stall converter and TCM tune will wake up the stock engine a bunch.

both engines make about the same torque yet the 5.3 ls has more passing power. stick a cam in the 5.3 and a tune. you will make more power everywhere period. and not reinvent the wheel.

if you want to epoxy the ports, then you'll want to separate the intake manifold and epoxy the runners and bell the entries. I can tell you from experience its a waste of time unless you are building a superstocker.

a cam in the 208-210@.050 will pick you up 50-60 hp and about the same torque. it will only pick up 10-15tq below 3800, but will accelerate harder everywhere.

if you really need 50 more hp at 2500, build cubes or a diesel
I drive an 07 Silverado with the 4.8 and a 3:42

It’s awful for towing any kind of weight, car trailer with a 3300 lb car is fine on the flats but any kind of slight hill, my foot is to the floor. Even with my small trailer and the ATV which is maybe 2000 max, it struggles on small long hills.

What’s the best tune chip, or whatever, I can put on this thing to help it on the highway? I’m ok with off the line pulling big weights..it’s the highway sluggishness that I hate,, the TQ between about 1800 and 2500 is horrible for even keeping up to speed
1980RS
Member
Member
Posts: 149
Joined: Thu Oct 13, 2016 10:03 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by 1980RS »

gmrocket wrote: Wed Sep 16, 2020 3:54 pm
mt-engines wrote: Sun Sep 13, 2020 3:44 pm
1980RS wrote: Sun Sep 13, 2020 11:54 am So recently I was looking at how to get some more low end torque out of my 5.3 for towing. I looked at cams and most either have a lope at idle or are so expensive it's not worth the swap. So I decided to look at the LS head closer and was surprised by what I was seeing. A 5.3 head is almost 205cc runner and max flow stock is around 226 cfm @ .550 and up lift on a 205cc runner and the Vortec head is 225 cfm @.450 lift on a Vortec head. Now I think this is fine for racing but in my mind I think for towing that's wrong. A 170cc runner Vortec head flows almost the same numbers and I know the Vortec engines were 5.7 vs 5.3 but I think if one were to maybe try and epoxy the port floor on the 5.3 head then make the runner closer to lets say 180cc might help out the low end of the 5.3 as these engines are just dogs when using the original 5.3's for towing. So would making the port smaller help low end power as I don't need an extra 50hp at 6K I need it at 2500 to 3800 rpm. Let's hear your ideas on this.

the 4.8/5.3/6.0 pick up huge with a good tune, they will drive like a different truck, especially with a TCM tune.

seems like you have a lot of time to waste if you want to epoxy some heads. i would not touch the heads, a simple cam swap regardless of duration is still going to make peak torque in the 4000rpm range and pick it up a bunch of power everywhere.
a higher stall converter and TCM tune will wake up the stock engine a bunch.

both engines make about the same torque yet the 5.3 ls has more passing power. stick a cam in the 5.3 and a tune. you will make more power everywhere period. and not reinvent the wheel.

if you want to epoxy the ports, then you'll want to separate the intake manifold and epoxy the runners and bell the entries. I can tell you from experience its a waste of time unless you are building a superstocker.

a cam in the 208-210@.050 will pick you up 50-60 hp and about the same torque. it will only pick up 10-15tq below 3800, but will accelerate harder everywhere.

if you really need 50 more hp at 2500, build cubes or a diesel
I drive an 07 Silverado with the 4.8 and a 3:42

It’s awful for towing any kind of weight, car trailer with a 3300 lb car is fine on the flats but any kind of slight hill, my foot is to the floor. Even with my small trailer and the ATV which is maybe 2000 max, it struggles on small long hills.

What’s the best tune chip, or whatever, I can put on this thing to help it on the highway? I’m ok with off the line pulling big weights..it’s the highway sluggishness that I hate,, the TQ between about 1800 and 2500 is horrible for even keeping up to speed
Exactly how I feel except mine as the 3.73 gears so it's not quite as bad.
gmrocket
HotPass
HotPass
Posts: 7601
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Modifying an LS 5.3 Head for Towing

Post by gmrocket »

1980RS wrote: Wed Sep 16, 2020 4:24 pm
gmrocket wrote: Wed Sep 16, 2020 3:54 pm
mt-engines wrote: Sun Sep 13, 2020 3:44 pm


the 4.8/5.3/6.0 pick up huge with a good tune, they will drive like a different truck, especially with a TCM tune.

seems like you have a lot of time to waste if you want to epoxy some heads. i would not touch the heads, a simple cam swap regardless of duration is still going to make peak torque in the 4000rpm range and pick it up a bunch of power everywhere.
a higher stall converter and TCM tune will wake up the stock engine a bunch.

both engines make about the same torque yet the 5.3 ls has more passing power. stick a cam in the 5.3 and a tune. you will make more power everywhere period. and not reinvent the wheel.

if you want to epoxy the ports, then you'll want to separate the intake manifold and epoxy the runners and bell the entries. I can tell you from experience its a waste of time unless you are building a superstocker.

a cam in the 208-210@.050 will pick you up 50-60 hp and about the same torque. it will only pick up 10-15tq below 3800, but will accelerate harder everywhere.

if you really need 50 more hp at 2500, build cubes or a diesel
I drive an 07 Silverado with the 4.8 and a 3:42

It’s awful for towing any kind of weight, car trailer with a 3300 lb car is fine on the flats but any kind of slight hill, my foot is to the floor. Even with my small trailer and the ATV which is maybe 2000 max, it struggles on small long hills.

What’s the best tune chip, or whatever, I can put on this thing to help it on the highway? I’m ok with off the line pulling big weights..it’s the highway sluggishness that I hate,, the TQ between about 1800 and 2500 is horrible for even keeping up to speed
Exactly how I feel except mine as the 3.73 gears so it's not quite as bad.
It shouldn’t be as bad as it is on the highway on slight grades.

I had a Ford Ranger 4x4 with 3:73’s and a tall tire which pulled better than this thing on highway hills.

It didn’t have to downshift at all, just come out of OD or lockup and continue on...this thing has to go into 2nd and 4000 plus rpm to keep up
turbo camino
Pro
Pro
Posts: 331
Joined: Sun Aug 10, 2008 11:51 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by turbo camino »

gmrocket wrote: Wed Sep 16, 2020 3:54 pm I drive an 07 Silverado with the 4.8 and a 3:42

It’s awful for towing any kind of weight, car trailer with a 3300 lb car is fine on the flats but any kind of slight hill, my foot is to the floor. Even with my small trailer and the ATV which is maybe 2000 max, it struggles on small long hills.

What’s the best tune chip, or whatever, I can put on this thing to help it on the highway? I’m ok with off the line pulling big weights..it’s the highway sluggishness that I hate,, the TQ between about 1800 and 2500 is horrible for even keeping up to speed
This is the high octane spark map from a same year/engine truck. You're probably in the outlined range when towing as you describe. Looks semi-decent, except the main spark table isn't the whole story. There are tons of other tables that affect the final spark at any given moment. Coolant temp above 210 and IAT above 90 both begin pulling spark. There are other things that can reduce it further, the final calcs are very complicated. That means in a particular cell where it says 15* in the main table, after all the calculations it might end up at only 7 or 8 degrees. That is even when it's not picking up any knock. The stock tune is simply too conservative.
2007-Silverado-4.8-HOspark.png
You would really need to datalog it under real operating conditions to know what could be changed where and by how much. The days of 'chips' are long gone.
You do not have the required permissions to view the files attached to this post.
DON'T PANIC
gmrocket
HotPass
HotPass
Posts: 7601
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Modifying an LS 5.3 Head for Towing

Post by gmrocket »

turbo camino wrote: Wed Sep 16, 2020 4:43 pm
gmrocket wrote: Wed Sep 16, 2020 3:54 pm I drive an 07 Silverado with the 4.8 and a 3:42

It’s awful for towing any kind of weight, car trailer with a 3300 lb car is fine on the flats but any kind of slight hill, my foot is to the floor. Even with my small trailer and the ATV which is maybe 2000 max, it struggles on small long hills.

What’s the best tune chip, or whatever, I can put on this thing to help it on the highway? I’m ok with off the line pulling big weights..it’s the highway sluggishness that I hate,, the TQ between about 1800 and 2500 is horrible for even keeping up to speed
This is the high octane spark map from a same year/engine truck. You're probably in the outlined range when towing as you describe. Looks semi-decent, except the main spark table isn't the whole story. There are tons of other tables that affect the final spark at any given moment. Coolant temp above 210 and IAT above 90 both begin pulling spark. There are other things that can reduce it further, the final calcs are very complicated. That means in a particular cell where it says 15* in the main table, after all the calculations it might end up at only 7 or 8 degrees. That is even when it's not picking up any knock. The stock tune is simply too conservative.

2007-Silverado-4.8-HOspark.png

You would really need to datalog it under real operating conditions to know what could be changed where and by how much. The days of 'chips' are long gone.
Ok, so it’s not as simple as you said in the beginning.

It’s a healthy motor and well cared for, unloaded it’s fine...and it’s ok pulling a real heavy 5500 lb trailer from a stop,, it’s highway hills that’s the problem

What are my options?
turbo camino
Pro
Pro
Posts: 331
Joined: Sun Aug 10, 2008 11:51 am
Location:

Re: Modifying an LS 5.3 Head for Towing

Post by turbo camino »

And the stock power enrich settings aren't helping either.
2007-Silverado-4.8-PE.png
You have to be above 87% throttle to get any power enrichment, and when it eventually, sloooowly comes in, at 2000 RPM it's only giving you 13.51:1 (divide stoich (14.68) by EQ to get AFR).

Let the PE operate when it's needed, and at 12.6:1, and 10 degrees more timing, and it'll be a completely different truck.

It is as simple as I said, the stock tune is crap. You weren't aware how complicated an E38 ECM is. Sorry.
You do not have the required permissions to view the files attached to this post.
DON'T PANIC
gmrocket
HotPass
HotPass
Posts: 7601
Joined: Wed Nov 12, 2008 6:40 pm
Location: Grimsby Ontario

Re: Modifying an LS 5.3 Head for Towing

Post by gmrocket »

turbo camino wrote: Wed Sep 16, 2020 5:18 pm And the stock power enrich settings aren't helping either.

2007-Silverado-4.8-PE.png

You have to be above 87% throttle to get any power enrichment, and when it eventually, sloooowly comes in, at 2000 RPM it's only giving you 13.51:1 (divide stoich (14.68) by EQ to get AFR).

Let the PE operate when it's needed, and at 12.6:1, and 10 degrees more timing, and it'll be a completely different truck.

It is as simple as I said, the stock tune is crap. You weren't aware how complicated an E38 ECM is. Sorry.
I’m aware how the truck runs stock, I’m asking you how to improve it.

Not how screwed up the stock set up is...I’m very aware

I’m asking for your help...what would you suggest I do to help it’s pulling problem at highway speeds?
Post Reply