Test Drove a 6.2l Yukon Denali

[jerem0621]

Just like the title said, I just test drove an older 2007 (or 2010). Yukon Denali XL AWD with the 420 HP 6.2l all aluminum V8. I am considering purchasing this vehicle but have not yet.

This vehicle had high miles (200k) but was absolutely immaculate and seemed to be well maintained.

The coolant looked great, there was no apparent blow by on the engine. The transmission shifted great and it drove just like a new one (as far as ride is concerned)

The price was great and the interior was way above average for a vehicle this old.

The only problem was two fold.

1) there seems to be a .5-1 second delay when I depress the gas after I let off the accelerator. Spirited driving was a challenge. After all, this was a test drive.
2) When the engine would go it left me kind of surprised. This does not feel like 420 HP. This feels more like 285 HP. My FIL has a 2007 Navigator with the 5.4 that only had 300ish HP and it was much much quicker.

All that to say, does this sound like a normal 6.2L from GM with 3.42 axle ratio? Could the AWD be stealing power?

There are zero leaks, the frame is clean, the suspension looks and feels great. Just these two nags.

Thanks!

Jeremiah

[TurnThePage]

Nevermind... 🙂

[BenK]

Hey Jeremiah

Know you like half ton's over higher class...but...since you were looking at a hot rod 6.2L half ton (assume for the kick in the pants while running empty)...consider an 8.1L Suburban

Be sure to look in the glove box RPO code label for 'F60', that get gets 1 ton front torsion bars. Why I tongue n cheek refer to mine as a K3500. As ordered mine with that F60 and knew the rear axle assembly is the same as the 1 ton dually of that year. On that, there are two brake assemblies for that era and the why parts counter folks always ask what shoe width...the 'regular' 3/4 Sub has 2.5" wide shoes and the 'big' 3/4 Sub has 3.5" wide shoes (same as the 1 ton dually). The diff is that the 1 ton dually has a bigger bored MC and Cylinders, of which I've switched out on my Sub

I also ordered 4.1's and they used to smoke the rear tires at will in 1st gear. Now that it is older and bigger tires, can only chirp the tires from a stop

Am almost done re-engineering and finalizing the details. My rebuild will be stages.

First stage will be:

• Will leave the stock 7.4L and 4L80E in there for now. Know that they are in need of a rebuild soon. Drive and tow HARD, but always change fluids with synthetic and on my own aggressive schedule
• Both differentials will get 5.3's or even higher numeric if can find them, but only Randy's for now. GM diff ratios are about 10% from one ratio to another...so am going about 30% MORE gear, therefore about 30% more torque
• GearVendors 0.7 ratio and that replaces the tranny tail housing, so no cutting/changing the drive shaft. Will use their gear splitter to turn the 4L80E into an 8 speed with a double OD
• This will pro ide an approx 2.5 final diff ratio to the axles and with the almost full torque at about 1,800-2,100 RPMs, should give some good MPG's running in the flats as a car

Second stage will be, ICE:

• Rebuild the 7.4L. Engine builder has passed on and will need to search for another 'good' one.
• Of course a cam. Most likely a 280* and has to pass Calif SMOG. Don't know if there are any performance roller tappets out there and a ditto for the push-rod/rockers/springs.
• Definitely SS valves with a 3 angle grind and hardened seats
• When rebuilding my performance ICE's have always had the block and heads shot-peened after magnafluxed
• Last engine rebuilder said GM left little meat on the stock heads, so flowing/shaping/etc is out of the question, as it will leave them to thin and cracking will be an issue...just polish the runners is about all
• Trying to increase red line is going to cost too much on this 'truck' engine...my L88 big block Vette could spin higher, but a 'car' engine, not a 'truck engine's duty cycle
• Of course will break it in with either Molybdenum Disulfide or Tungsten Disulfide and have both powders in my stock (they are both 1 micron) and will flow through the Wicks filters (NAPA Gold) or PureOne filter I use
• undecided whether to explore a tuner or not...just a maybe

Second stage will be, tranny:

• There are several 1,000 HP and some have options for 1,500HP and 2,000 HP applications.
• The 1K HP has a 3 year warranty and since am expecting about ~350HP out of the 7.4L rebuild, it should last a long time
• no moly or tungsten, as that is too slippery for the clutches. Just synthetic
• Will increase the AFT Aux cooler size by 2x or more. Designed a mid ship setup for a buddy who had a 1995 7.4L Suburban. We could see the dash engine temp gauge drop when those electric fans kicked in

Check out this thread, as it might give you some ideas

3.73->4.56 Regear Results

BenK wrote:
Congrats on your updated Suburban !!!

Many time...going to a higher numeric diff ratio will gain MPG when towing heavy. A lot depends on the drivers style, terrain and resistance (wind, weight, etc)

If you have the budget (OP and others noodling) consider a GearVendors OD. It has a 'gear spliter' function that will insert itself between each tranny gear. Turning your 4 speed auto into an 8 speed with 8th gear a double OD




Mine is a big block, 7.4L, with 4.1's with 31.6 dia tires. Similar RPM at 65MPH as your new gearset

Click For Full-Size Image.



Am noodling going to 5.1's for the rebuild/update of my 1996 GMC K3500, 7.4L, 4.1 Suburban for those who have similar and considering keeping these towing beasts and rebuilding/updating

rv.net Gear Vendor/Gear splitter, page 3

Gear Vendor 0.5 OD is on my list of stuff going to do when time to rebuild the 7.4L...and IMHO...germain to this discussion

Either the 4.88's or 5.13's will have lots more torque multiplication than my current 4.11's...torque multiplication works both ways...

Chart in below quote is for a GearVendors 0.7, thinking of going to 0.5 so that the final double OD to the axles will be a higher gear (lower numeric) than stock

Should I keep my old truck? This is that thread quote below is from

BenK wrote:


With the cost of new vehicles today...going to save some coin rebuilding my 1996 GMT400 K3500, 7.4L Suburban with all new interior (seats, dash stuff, etc)

8 speed tranny with double OD vs stock of 4 speed and single OD....1,000 HP rated rebuilt 4L80E that has a 3 year warranty...diff ratio either 4.88's (will be 0.7 GearVenders) or 5.13's (will be 0.5 GearVenders)....etc, etc, etc


Posted on another members thread where he is noodling stuff for his rebuild or not. Hopefully he found this of interest and helpful in making up his list of stuff to do

gear ratios, page2

BenK wrote:

Similar to my nooddling plans for my 1996 7.4L K3500 Suburban. Stock is 4.1's and noodling going to something north of 4.56's. Currently think 4.88's will be it, but can't find enough info on that config's strength. IIRC, the pinion might be too small (both face sq/in and tooth root section...cantilever strength)

First, gear boxes are for a change in direction and/or torque multiplication (some times just a change in RPMs)

Here are the listed ratios for my 4L80E:

Gear Ratio
First 2.48
Second 1.48
Third 1.00
Fourth 0.75

Here is just one link to a +1,000 HP 4L80E and cost is similar to a plain Jane rebuild locally vs the 750HP version. The +1,500HP version just a couple thousand more...all warranted


Stage 2 – Warranted 750 HP...Stage 5 - Warranted +1,500HP


The Gear Venders OD noodling and is whether an 0.7 or 0.5 ratio that will split (insert itself) between each 4L80E gear. That would turn my 4L80E into an EIGHT forward gearbox and if you count the XfrCase...16 forward gear ratios...and...a lower 1st gear ratio than the 4L60E...AND...a similar to potentially higher OD final...

Here are the resultant gear ratios




Then switch from LT265/75R16E's to LT255/85R16E's for a LOWER rev's per mile and still not lose much in width...just 10mm, or 5mm each side of rim center.

Toughest part is finding a HO crate 7.4L that will pass SMOG. Most found to date are offroad and/or carberator. No Vortec to be found.

The guy who built the L88 for my Vette has passed on and no one even understands what an L88 was/is... Sure an L88 was a hot rod engine, but most of it can be for a TV...all in the cam...

[jerem0621]

falconbrother wrote:
I'm a shade tree mechanic, brakes, water pumps, various things like that I can do. For the symptoms you describe I would totally take it to a professional shop and let them look at it before I dropped real money on it. I like my 5.3 Suburban, mostly because I know it. Don't end up with regrets, let a local shop do a compression test, etc..

Thanks, I ultimately passed on this truck. After doing a little digging/research I can find similar trucks for much less money. I am pretty convinced that I want a Suburban/Yukon XL. Hopefully, I'll have enough saved to pay cash for one a little later this year.

Gotta get the Ole 57 Chevy running and driving first.

Thanks!

Jeremiah

[falconbrother]

I'm a shade tree mechanic, brakes, water pumps, various things like that I can do. For the symptoms you describe I would totally take it to a professional shop and let them look at it before I dropped real money on it. I like my 5.3 Suburban, mostly because I know it. Don't end up with regrets, let a local shop do a compression test, etc..

[VernDiesel]

Buy it then get the black bear tuner to change the throttle response. Magically you will realize you did buy a 400 HP truck. Then go put another 100k on it.

[colliehauler]

If it was a slug solo what will it be like towing?

[jerem0621]

mooky stinks wrote:
Not sure what you mean by 2007 (or 2010) but they don't feel like 420hp because they aren't. 2007 was 380 and 2010 was 402.

I couldn’t remember the model year. It was a 2010 and you were right I was off by 17 whole HP.

You didn’t get the point of my question....regardless of those few HP I was off the truck WAS A SLUG compared to the higher HP ratings.

Everyone, Thank you for your responses. I’d like to buy it but still considering and your responses help play into my decision.

Thanks!

Jeremiah

[APT]

If you get a GM, budget for a Black Blear Tuner to change the throttle response and shift behavior so that it feels like 420hp.

[mooky_stinks]

Not sure what you mean by 2007 (or 2010) but they don't feel like 420hp because they aren't. 2007 was 380 and 2010 was 402.

[Durb]

I remember looking at a truck comparison test before purchasing my 2008 Titan. One part of the test was zero to sixty times. Theoretically the 400+ Hp chevy should have smoked the 318 HP Nissan, as their curb weights were almost the same. The Titan beat the Chevy by over 2 seconds to sixty MPH. Turns out, for fuel economy, Chevy programmed the truck not to make full power unless the accelerator had been fully depressed for two seconds. Not so good for passing maneuvers. Maybe give the motor some time and see if comes on at full boil.

[carringb]

I'd get an oil analysis done, before buying a 6.2L with that many miles. Keep in mind it's a light-duty motor with a light-duty design life (150,000). It's designed for power over longevity, and feeling sluggish could be low compression .

The lag is probably just the electronic throttle body. The earlier GM ones were slow to move, relative to a mechanical throttle body, and combined with somewhat invasive torque-management, can make it feel how you describe. And a high-mile one might need a good cleaning.

The AWD in that rig won't "steal" power, since it's still a mechanical coupling (clutch based engagement), and the clutches won't engage anyways unless it detects an difference between output shaft speeds.

[Bionic_Man]

I have an 11 Yukon Denali. Pretty similar to what you are talking about.

While I don't feel like the rig is under powered, I don't think it feels like 400 + HP.

My complaints on mine is it runs hotter than I think it should as a tow vehicle (swapping to a bigger tranny cooler next week). It has more rattles than any vehicle that I have owned (other than a 2500 Burb I bought with 120k on the clock). Interior does not compare to the top trim levels of similar year Ford or RAM. And I have had ongoing issues with the Stabilitrack - have had wheel sensors go out twice where it shuts the stability control off, and am experiencing similar problems again.

When I was looking for this vehicle 3 - 4 years ago, I found TONS of Burbs/Yukons for sale with 200,000 plus miles. So they do seem to stay on the road forever - and they hold their value well.

[jrhanbar98]

I have a 6.2 in a Silverado. On the ruck boards they report GM ‘detuning’ HP and torque off the line to save the tranny. So far I love the engine, like the 5.3 need to let it sing to get max power . . . But it sounds great when singling!