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Outside-the-Box Power Options

zebra

Well-Known Member
Messages
115
Location
cold & windy
again: we really can't get too crazy on the power anyway because these dinky car transmissions were only rated for 260lbft of torque & have 5000lb of truck to lug around.
i'm guessing the clutch is still the weakest link in the chain (would hope so anyway) & would be a decent buffer before breaking internals with a v8 turning it, but that's why it's tough to justify a $5k-6k engine swap for a measly 60hp/80tq advantage.

i realize "ratings" are typically garbage undersells because my last truck's nv3500 is only rated for 300ish lbft but i've seen a dude beat on one with a 454 BBC swap before blowing the engine & dropping in a Vortec 8100... and then adding a turbo before the trans finally called uncle. and that was in a 4500lb 1/2 ton Silverado.

that said, i figured the power of a little-more-than-stock LH8 would be a good stopping point. it was just learning what all else was involved electrically, mechanically, and the ridiculous costs associated with those bits that started to deter me & cause me to start searching for more economical alternatives that most other engine platforms do.

maybe i should check out 355 forums for head porting results, intake manifold mods, etc. that could likely get us halfway to the v8 power at <1/4 the cost. that's why i started this conversation.
 

cbetts

NERD!!!
Messages
3,182
Location
Rancho Palos Verdes, CA
The AR5 is actually quite a brute. Do a little reading in the Solstice/Sky forums. Some people are pushing over 500HP through those things. You also find owners of the later year models yanking the 6 speed to replace it with the AR5 for reliability. To be honest, I was surprised my H3 tranny lasted with how I drove it. I had the front diff out for a while and discovered I could get second gear rubber . . . with my 35" KM2s! (Yeah, I know, I am immature)
 

zebra

Well-Known Member
Messages
115
Location
cold & windy
i get that part... but the difference is the weight: 2900lb vs 4900lb
that means all the world regarding transmission longevity, especially with extra power running through it. case in point is the truck i mentioned above; he was putting more than twice the rated torque through that thing but it was just on a little hot-rod 2wd, 2door, short bed truck that never pulled anything or was loaded down. i burnt up my truck's exact same transmission with half that power by towing this Hummer home from the dealership in 5th @ 70-75mph (like a retard... because i had to drive 800mi home & couldn't miss my flight for work the next morning).

same with fullsize trucks doing t56 manual swaps... it works if you never try to tow with it. i've seen a Suburban swap burn it up after a couple years under the vehicle weight alone, yet my C5 vette's putting almost 700whp through it just fine.

still encouraging to hear yours held up fine, especially given yours looks to've been an 06 (before the factory synchro & clutch upgrades in 08). thanks.
 

cbetts

NERD!!!
Messages
3,182
Location
Rancho Palos Verdes, CA
I had plans to use the 07 flywheel and clutch but I could never get all the specs to see if it would fit. I put the 35" KM2s on around 40K miles and did my first clutch at 86K. Also combine this with all the all the weight I had after my mods (7800 lbs normal, 8100 with gear). Overall, it was great to drive. I had to really wind out the engine to climb grades on the highway but the 4:1 transfer case was perfect for wheeling. I never needed more power to get through obstacles.
 

Gpcalero

Well-Known Member
Messages
234
Location
SW Florida
should on an 06... probably 07s, too.
ours is an 09 - which matters because starting in 08, the engine control module in automatics required communication with a separate transmission control module for everything to work the right way.


GenIII+ LS exhaust manifolds already flow about the same as a shorty.
i wasn't sure about the one on an Atlas engine.


If I wasn't doing a swap, I'd keep the stock shorties. But most likely I'll be selling the LH8 as a complete motor with headers to a hummer member for a swap, which you'll need the headers for.

Plus the new ones will be coated and hopefully help keep things a bit cooler.
 

amrg

Well-Known Member
Messages
2,317
Location
Qatar
again: we really can't get too crazy on the power anyway because these dinky car transmissions were only rated for 260lbft of torque & have 5000lb of truck to lug around.
i'm guessing the clutch is still the weakest link in the chain (would hope so anyway) & would be a decent buffer before breaking internals with a v8 turning it, but that's why it's tough to justify a $5k-6k engine swap for a measly 60hp/80tq advantage.

i realize "ratings" are typically garbage undersells because my last truck's nv3500 is only rated for 300ish lbft but i've seen a dude beat on one with a 454 BBC swap before blowing the engine & dropping in a Vortec 8100... and then adding a turbo before the trans finally called uncle. and that was in a 4500lb 1/2 ton Silverado.

that said, i figured the power of a little-more-than-stock LH8 would be a good stopping point. it was just learning what all else was involved electrically, mechanically, and the ridiculous costs associated with those bits that started to deter me & cause me to start searching for more economical alternatives that most other engine platforms do.

maybe i should check out 355 forums for head porting results, intake manifold mods, etc. that could likely get us halfway to the v8 power at <1/4 the cost. that's why i started this conversation.
Realistically speaking, nothing will get you considerable power under the curve other than an engine swap or boost. This is a modern efi engine with low-ish compression so 240 hp from a 3.7L is good to start. Regearing is out of the question due to being maxed to 4.56 at the front diff, unless you're willing to lose 4WD by disconnecting the front drive shaft and regear just the rears to 5.13 then call it a day.
A tune/CAI/free flowing exhaust + headers are your other options, but ive done all on my I5 and with that all my 4.10 geared alpha was still way better on 35s.


Sent from my SM-G960F using Tapatalk
 

zebra

Well-Known Member
Messages
115
Location
cold & windy
Realistically speaking, nothing will get you considerable power under the curve other than an engine swap or boost. This is a modern efi engine with low-ish compression so 240 hp from a 3.7L is good to start. Regearing is out of the question due to being maxed to 4.56 at the front diff, unless you're willing to lose 4WD by disconnecting the front drive shaft and regear just the rears to 5.13 then call it a day.
A tune/CAI/free flowing exhaust + headers are your other options, but ive done all on my I5 and with that all my 4.10 geared alpha was still way better on 35s.

i wouldn't necessarily call 10:1 static compression 'low' at all... but then again, i don't know the cam specs to see how much the variable exhaust timing drops the dynamic ratio to supposedly not knock on 87 gas. it's certainly not the 9:1 of most GenIII truck engines (or 8.5:1 of that twin turbo 4.2 science project).

4.56 is already more gear than we'd like or need because nobody enjoys highway cruising at 2500rpm... except maybe rice burners. i actually would've swapped over the 4.30s from my GMC before I sold it if the front would've worked because you can always shift later - until you run out of gears.

and we specifically bought the H3 because it's a stick-shift 4WD SUV that ain't a Jeep, so chopping the driveline certainly won't work because that castrates its capability to have fun on the trails & keep my wife safer driving in the snow.

PS: you ain't in Doha, by chance? i feel like i saw one or two light-colored H3s a trip or two ago (granted that's been a few years now), and there can't be THAT many of them rolling around there.


as for further developments, i thought i'd stumbled upon an easy one the other night that i hadn't seen here (using a trailblazer throttle body) until i dug further & found that only the 2.8/2.9 had a smaller unit (ours is the same)... and porting ours won't do much without rebuilding with a bigger blade - throwing cost:benefit out the window. :(
 
Last edited:

amrg

Well-Known Member
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2,317
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I think i read you were running 34" coopers, that alone wouldve thrown the truck off gearing wise, thats why i said 5.13s. But yet, losing 4WD is a big deal but some people dont care about ir. My point was that the H3 is pretty much well designed. Unlike certain vehicles that respond greatly to mods, the H3 improvements ate marginal, which is why I recommended going with an Alpha.
Just to put it into perspective, i swapped my alphas 5.3 with a cammed 6.2, my friend swapped in my 5.3 inplace of his 3.7. We had a rolling race 10 mph to 40 mph and he kept up, only difference was he had 4.56 gearing while I had the stock alpha 4.10s.
Yes im in Qatar, there are actually alot of H3s here. I see daily about 10 ish but sadly they are decreasing year by yeaf due to expensive maintenance costs esp compared to the value of the vehicle (im seeing more and mpre H3s being parted out simply due to a transmission failure)

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zebra

Well-Known Member
Messages
115
Location
cold & windy
computer's in the mail to NC. got a tune sheet filled out & paid for last night - which was surprisingly more detailed than i expected for a mail order, so fingers crossed. after talking to him & hearing how many stick H3s he's done (and seeing how everybody does the same few mods), i feel like it should come out good.
called this morning, and he said they'd start working on it so it hopefully goes out before they leave Wednesday. nice folks so far.

I think i read you were running 34" coopers, that alone wouldve thrown the truck off gearing wise, thats why i said 5.13s. But yet, losing 4WD is a big deal but some people dont care about ir. My point was that the H3 is pretty much well designed. Unlike certain vehicles that respond greatly to mods, the H3 improvements ate marginal, which is why I recommended going with an Alpha.
Just to put it into perspective, i swapped my alphas 5.3 with a cammed 6.2, my friend swapped in my 5.3 inplace of his 3.7. We had a rolling race 10 mph to 40 mph and he kept up, only difference was he had 4.56 gearing while I had the stock alpha 4.10s.
Yes im in Qatar, there are actually alot of H3s here. I see daily about 10 ish but sadly they are decreasing year by yeaf due to expensive maintenance costs esp compared to the value of the vehicle (im seeing more and mpre H3s being parted out simply due to a transmission failure)

yeah we're running 34s, but it ain't a huge difference from the way the stock size felt... this altitude has made more of a difference than anything (gets up around 7000' in some parts).

again, losing the stick shift is right-out, so trading for an Alpha ain't happening because it's easier to put a v8 in a manual base model than a stick into a v8. i actually remember reading your posts about those heart transplants... seemed like quite the saga of parts shipments.

and i get how big a difference gears can make. i went from 3.73s to 4.30s in my cammed 5.3 GMC on 33s & could effortlessly pull from 70-100 in 5th. ain't looking to build the H3 into a race truck (got a blown corvette for them shenanigans); we were just looking for a few more ponies & figured there'd be more cost-effective 3.7 mods than intake tube/muffler/tune. the trans & clutch can only take so much torque anyway, and a bolt-on 5.3 can quickly exceed that.
 

zebra

Well-Known Member
Messages
115
Location
cold & windy
Good people at PCM of NC

that they are!
they started writing our tune upon payment then received/flashed/shipped the computer back on the day before Thanksgiving.

initial impressions were expectedly underwhelming: my wife'd just spent a week driving the Cummins around town while i drove my car... so she got used to simply letting the clutch out on its own & almost never having to downshift - leading her to instantly reassess the LS swap.

after a month of driving, though: overall, it does feel a bit smoother & pulls a little better up top with a noticeable improvement going uphill at speed. being a stick-shift, i didn't really expect a huge difference because torque management's what means the world to the slushbox 4L60 - a muzzle we ain't had to try & bark through.

and for anybody who actually cares about or uses it: there was no more shift light after the tune (based on RPM & engine load for 'optimized economy'), same as with my Sierra... but then it actually came back after a couple weeks in the H3 & works the same as it did before.
 

zebra

Well-Known Member
Messages
115
Location
cold & windy
i did some digging around and am a little stuck:
after rolling around under the 09 again, it doesn't look like the 2nd cat has any sensors or anything to monitor it... is that true? is it literally just there in the middle of a pancake pipe doing whatever it wants?

if so, does anybody make a bolt-in 'off-road' mid pipe that gets rid of that restriction & is actually circular the whole way between the 1st cat's lower flange & where everybody's cat-back kits start?

that'd be so much easier than cutting out both sections of flat pipe just to weld in round sections on each end of a cat... especially if the truck wouldn't even notice the cat 'running away'.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
Doesn't take much work for a good independent shop to cut and weld in the necessary tubing to replace the runaway cat.
 

zebra

Well-Known Member
Messages
115
Location
cold & windy
i didn't figure so... it's just that half the time, a shop's either unwilling to remove cats or they cost the same as buying a bolt-in piece that i could do myself & have look better.
not afraid to have it cut, though... just wanted to verify that second cat's actually unmonitored (because we ain't in a spot to turn around & retune the computer again right now).
 
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