Disappointing numbers
Thread Starter
Staging Lane
Joined: Aug 2014
Posts: 60
Likes: 9
From: Viera, Florida
Disappointing numbers I just finished my Hummer H2 project. I went for a final street tune and using HP Tuners hp calculations, it only pulled 390 hp. Seems absurdly low to me.
I started with a brand new GM LQ9 long block. I pulled the rectangle port heads and installed a set of 243 heads with a fresh 5 angle valve job. Added a BTR stage II low lift truck cam, springs and correct pushrods and topped it off with a TBSS intake with flex fuel injectors and shorty headers running thru a Gibson cat back 3.5 single pipe. I also have a built 4l65E transmission with a TBSS I6 converter which is stalling in the 2600 to 2800 rpm range. It runs really strong but I am still disappointed.
Is the HP tuners number reasonable?
Tim
I started with a brand new GM LQ9 long block. I pulled the rectangle port heads and installed a set of 243 heads with a fresh 5 angle valve job. Added a BTR stage II low lift truck cam, springs and correct pushrods and topped it off with a TBSS intake with flex fuel injectors and shorty headers running thru a Gibson cat back 3.5 single pipe. I also have a built 4l65E transmission with a TBSS I6 converter which is stalling in the 2600 to 2800 rpm range. It runs really strong but I am still disappointed.
Is the HP tuners number reasonable?
Tim
TECH Senior Member
Joined: Jun 2016
Posts: 22,301
Likes: 3,625
From: Central Cal.
First off, LQ9 engines all came with cathedrals, and were rated at 345HP.
You put in a cam good for about 45-50 HP.
The TBSS intake flows better than the OEM manifold, but not a lot.
Shorty headers usually gain little if any power.
So the calculations are a little low, but not absurdly so.
If you like the way it runs, enjoy it. Numbers are just that, and could be inaccurate.
Not from a dyno, but an estimate?
You put in a cam good for about 45-50 HP.
The TBSS intake flows better than the OEM manifold, but not a lot.
Shorty headers usually gain little if any power.
So the calculations are a little low, but not absurdly so.
If you like the way it runs, enjoy it. Numbers are just that, and could be inaccurate.
Not from a dyno, but an estimate?
Thread Starter
Staging Lane
Joined: Aug 2014
Posts: 60
Likes: 9
From: Viera, Florida
First off, LQ9 engines all came with cathedrals, and were rated at 345HP.
You put in a cam good for about 45-50 HP.
The TBSS intake flows better than the OEM manifold, but not a lot.
Shorty headers usually gain little if any power.
So the calculations are a little low, but not absurdly so.
If you like the way it runs, enjoy it. Numbers are just that, and could be inaccurate.
Not from a dyno, but an estimate?
You put in a cam good for about 45-50 HP.
The TBSS intake flows better than the OEM manifold, but not a lot.
Shorty headers usually gain little if any power.
So the calculations are a little low, but not absurdly so.
If you like the way it runs, enjoy it. Numbers are just that, and could be inaccurate.
Not from a dyno, but an estimate?
The long block I purchased had rectangle ports, its was GM#19370163 Ls 364/450 so would have been 10.3 to 1. I had hoped with 11 to 1 via the 243 heads that I could move the power down lower for the truck and then the cam would not loose but gain down low. I'm not running this thing at 6800 to 7000 rpm either so there might be more in it. I was hoping for 450 or better I guess. I have some left on the table. There is an issue with knock sensor #1 so we disabled it so we can throw more timing at it.
Tim
TECH Senior Member
Joined: Jun 2016
Posts: 22,301
Likes: 3,625
From: Central Cal.
LQ9's never came with rectangular ports. If it really is a GM engine it may be a Gen IV 6.0? Many of them did come with rectangular heads. LQ9 is a Gen III engine, and rectangular heads started showing up when Gen IV came out, not before.
Edit-- Just looked up the number. It is a GM Performance build using a combo of a lot of different parts. It was rated at 450HP, but that all changed with you swapping out the cam and heads for smaller port heads.
The BTR cam mentioned is (I believe) 212/218 which is a little bigger than the 204/218 LS6 cam it replaced, but it has less LSA which really helps.
For what you want, the 243 heads will do a better job making low end torque than the LS3 heads they replaced.
I bet you are now putting out more low end torque but less total HP than before.
It will feel better pushing around that H2 especially at part throttle and below 5k RPM
Edit-- Just looked up the number. It is a GM Performance build using a combo of a lot of different parts. It was rated at 450HP, but that all changed with you swapping out the cam and heads for smaller port heads.
The BTR cam mentioned is (I believe) 212/218 which is a little bigger than the 204/218 LS6 cam it replaced, but it has less LSA which really helps.
For what you want, the 243 heads will do a better job making low end torque than the LS3 heads they replaced.
I bet you are now putting out more low end torque but less total HP than before.
It will feel better pushing around that H2 especially at part throttle and below 5k RPM
Last edited by G Atsma; Apr 7, 2021 at 12:00 PM.
Thread Starter
Staging Lane
Joined: Aug 2014
Posts: 60
Likes: 9
From: Viera, Florida
LQ9's never came with rectangular ports. If it really is a GM engine it may be a Gen IV 6.0? Many of them did come with rectangular heads. LQ9 is a Gen III engine, and rectangular heads started showing up when Gen IV came out, not before.
Edit-- Just looked up the number. It is a GM Performance build using a combo of a lot of different parts. It was rated at 450HP, but that all changed with you swapping out the cam and heads for smaller port heads.
The BTR cam mentioned is (I believe) 212/218 which is a little bigger than the 204/218 LS6 cam it replaced, but it has less LSA which really helps.
For what you want, the 243 heads will do a better job making low end torque than the LS3 heads they replaced.
I bet you are now putting out more low end torque but less total HP than before.
It will feel better pushing around that H2 especially at part throttle and below 5k RPM
Edit-- Just looked up the number. It is a GM Performance build using a combo of a lot of different parts. It was rated at 450HP, but that all changed with you swapping out the cam and heads for smaller port heads.
The BTR cam mentioned is (I believe) 212/218 which is a little bigger than the 204/218 LS6 cam it replaced, but it has less LSA which really helps.
For what you want, the 243 heads will do a better job making low end torque than the LS3 heads they replaced.
I bet you are now putting out more low end torque but less total HP than before.
It will feel better pushing around that H2 especially at part throttle and below 5k RPM
thanks!
Tim
How is HP tuners calculating its figure? Could it be modeling it similar to a wheel Dyno?
You need to keep in mind that the Factory engine is rated at the Flywheel. 450HP - 20% Drivetrain Loss = 360 at the wheels. This gives a rough Idea on what to expect at the wheels. So if Hp tuners is generating an approximate wheel Hp figure then 390 is no slouch.
Get the tuned dialed in and take it to a real Dyno and see what it puts down.
You need to keep in mind that the Factory engine is rated at the Flywheel. 450HP - 20% Drivetrain Loss = 360 at the wheels. This gives a rough Idea on what to expect at the wheels. So if Hp tuners is generating an approximate wheel Hp figure then 390 is no slouch.
Get the tuned dialed in and take it to a real Dyno and see what it puts down.
It appears you are disappointed because you confused flywheel/crank HP with RWHP. Figure at least 18% drivetrain loss , maybe as high as 20%, going from crank to the wheels. Using a 19% loss estimate, you have ~480 at the crank...not too shabby. Keep in mind, these are estimates based on estimates, but since you said it feels great, I bet it's right where it should be.
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You will definitely pick up TQ/HP going to long tubes (go 1 7/8 primaries) with no downside once you retune. Shorties are better than factory manifolds, but only by a little. Bet you pick up 20-30 across the band with long tubes.
Thread Starter
Staging Lane
Joined: Aug 2014
Posts: 60
Likes: 9
From: Viera, Florida
I know it seems silly but as I was swapping engines I got to the point where I didn't want anymore work, so I stuck with a new pair of shorty's I had sitting on the shelf. Hummers might appear to have all the room in the world to work on but laying on your back cutting out exhaust was not on my wish list considering I had also recently just added a s/s cat back. Maybe the next iteration of the beast but not this time. If the HP guestimate is indeed rear wheel, I'm tickled to death.
Thanks to all the advice, I appreciate this forum and all the answers along the way.
Tim
Thanks to all the advice, I appreciate this forum and all the answers along the way.
Tim
I know it seems silly but as I was swapping engines I got to the point where I didn't want anymore work, so I stuck with a new pair of shorty's I had sitting on the shelf. Hummers might appear to have all the room in the world to work on but laying on your back cutting out exhaust was not on my wish list considering I had also recently just added a s/s cat back. Maybe the next iteration of the beast but not this time. If the HP guestimate is indeed rear wheel, I'm tickled to death.
Thanks to all the advice, I appreciate this forum and all the answers along the way.
Tim
Thanks to all the advice, I appreciate this forum and all the answers along the way.
Tim
TECH Regular
Joined: Dec 2011
Posts: 420
Likes: 115
It appears you are disappointed because you confused flywheel/crank HP with RWHP. Figure at least 18% drivetrain loss , maybe as high as 20%, going from crank to the wheels. Using a 19% loss estimate, you have ~480 at the crank...not too shabby. Keep in mind, these are estimates based on estimates, but since you said it feels great, I bet it's right where it should be.
That's probably not a bad number, given the drivetrain inertia. That's a small cam, so peaks won't be high, but area under the curve is decent.
Launching!
Joined: Aug 2020
Posts: 205
Likes: 70
From: Phoenix AZ
Dyno # are just that a # - 10 more and 400!!! Man if I could just make 400HP, I'd be happy!!
Just rev it up another 1000rpm see what happens!!!
You mentioned you made 390 WHP at what RPM??
You also mention it drive great. Enjoy it!! Take it to the track run a 1/4 mile see what those numbers are.
H2 is a heavy vehicle see no mention of amount torque you put out but that is more important for Drivability.
Just rev it up another 1000rpm see what happens!!!
You mentioned you made 390 WHP at what RPM??
You also mention it drive great. Enjoy it!! Take it to the track run a 1/4 mile see what those numbers are.
H2 is a heavy vehicle see no mention of amount torque you put out but that is more important for Drivability.
IMO it makes sense with no headers (shorty headers is same as not having any). that cam is tiny tiny with low lift. Cant expect much more tbh.
Last edited by Johnnystock; Apr 20, 2021 at 04:42 PM.
I think my F150 had something like 25% difference between factory engine rating vs. chassis dyno.
Thread Starter
Staging Lane
Joined: Aug 2014
Posts: 60
Likes: 9
From: Viera, Florida
I'll get it tuned again once I change my knock sensors. I might not have mentioned it earlier but the tuner had to back out some timing because I had the front knock sensor going from zero knock to 10. He adjusted the sensitivity but finally cut the timing and turned them both off. There was zero audible knock so he thinks I just got a dud sensor.
Tim