CNC Heads, Shorty Headers and other engine mods..

[EnigmaMan]

So ive been doing a little bit of reading from Truck Trend on the 5.3L motor and what potential it actually has form its stock form. Ive done other motor rebuilds in the past so pulling things apart and putting them back together is not a problem.

http://www.trucktrend.com/how-to/engine/1208tr-5-3l-bow-tie-builds-mild-to-wild/

I was looking at starting to do the Stage 2
CNC the heads ($1400)
78mm Throttle body ($300)
Short Tube headers ($200) - due to idle / midrange throttle 90% of the time

They were able to achieve:

Peak Power: 363 hp at 5,300 rpm
Peak Torque: 385 lb-ft at 4,400 rpm

(stock is 320hp / 335tq - which is pretty weak for 6,000lbs!!!)

This is by far cheaper than the bolt on edelbrock super charger @ $4500+ for the package plus ECU upgrades. I figure these upgrades along with the 3.73 gear swap (front / rear for 4wd) and 33" tires should be a pretty good combo out on the street.

Later on I may attempt Cam upgradewhich would push it up a little more..
COMP XR281HR .571/.573 lift, 228/230 duration split, 112 LSA

Peak Power: 436 hp at 6,200 rpm
Peak Torque: 410 lb-ft at 5,100 rpm

I would be interested if anybody done additional motor work to their Yukon like this?

Thanks!

 

[Jason_S]

A couple of things first:
-That electric water pump added to the HP number for the stock engine. There were also no paralytics from the alternator, power steering pump, ac compressor or tensioner/idler pulleys.
-The shorty headers vs the long tube headers will affect your numbers.
-Those numbers are from and engine dyno, not a car or truck on a dyno.
-Before you start to modify your engine, you should make sure that it is running right.

If you start pushing that power through your stock transmission, you will need a rebuild. Usually at the most inconvenient time. I would budget that expense in with your engine upgrades. I would also do the cam at the same time as the rest of the work. Then you can just spend the time and money getting it tuned once. Keep in mind that you should change your valve springs with that cam, so you should budget for springs and followers to support your cam.

I would recommend doing the re-gear to 3.73 or maybe even 4.10 (especially with 33's or bigger) first. You will be very surprised with how a more appropriate set of gears will wake a vehicle up. Ever tried 4.1 to 4.88 on a 2.5L Jeep with 33's? Night and day difference.

 

[EnigmaMan]

Thanks for the input! I appreciate it!
I have re-geared other vehicles in the past and it makes a huge difference as well..
One thing also to consider when upgrading your cam is to 1. have the matching springs and lifter ratio for your cam, and 2 have correct stall converter / gears that matches your cam as well. I cant seem to find the specs for a stock stall converter on either transmission.
What are some of the weak points in these transmission? Clutches slipping? gears? Input Shaft?

I did a tranny build a few years back and took an Buick Grand National Th200-r4 (4 speed) and bolted it up to an olds 455 that's pumping out 475hp / 550tq at the crank. Everybody said it wouldn't hold up but with the work i did, i have not had an issue with it and many passes down the track!


According to the specs I found the following info on the 2 transmissions that *could* be in your Yukon.

=====================================
GM 6-Speed 6L80 MYC Hydra-Matic Automatic Transmission

Type: Six speed RWD / AWD, electronically controlled automatic overdrive transmission with torque converter clutch. Clutch-to-clutch architecture, with integral Electro / Hydraulic Controls Module
Maximum engine power: 469 bhp (349 kw)
Maximum engine torque: 439 lb-ft (595 Nm)
Maximum gearbox torque: 664 lb-ft (900 Nm)

Gear Ratios
First: 4.03
Second: 2.36
Third: 1.53
Fourth: 1.15
Fifth: 0.85
Sixth: 0.67
Reverse: 3.06


=====================================
GM 6-Speed 6L90 MYD Hydra-Matic Automatic Transmission
Type: Six speed RWD / AWD, electronically controlled automatic overdrive transmission with torque converter clutch. Clutch-to-clutch architecture, with integral Electro / Hydraulic Controls Module
Maximum engine power (gasoline, truck): 452 hp (337 kw)
Maximum engine power (diesel, truck): 300 hp (223 kw)
Maximum engine power (passenger car): 555 hp (414 kw)
Maximum engine torque (gasoline, truck): 531 lb-ft (720 Nm)
Maximum engine torque (diesel, truck): 520 lb-ft (705 Nm)
Maximum engine torque (passenger car): 550 lb-ft (746 Nm)
Maximum gearbox torque: 885 lb-ft (1200 Nm)
Gear Ratios
First: 4.03
Second: 2.36
Third: 1.53
Fourth: 1.15
Fifth: 0.85
Sixth: 0.67
Reverse: 3.06
Maximum shift speed: 6200 rpm

 

[EnigmaMan]

I think I found my answer. Good to know which gears are most prone to failure with the clutches! The input shaft is always been an issue on gm vehicles as this is what I did to my TH200-R4 (Hardened input shaft, 10 vein pump, 2200 stall lockup converter and a B&M Stage II Shift kit).

The mechanical workings of these transmissions are pretty stout, but the weakest links are the 3-5-Reverse clutches and the 4-5-6 clutches. The next component most prone to failure is the spline area of the 4-5-6 hub where it engages into the output carrier," says Kyle. "To address these needs, our standard rebuild includes heavy-duty 3-5-Reverse, 4-5-6, and 2-6 clutch packs. They feature custom nitrided steels to prevent warping, and more durable clutch linings that are more resistant to heat. With these modifications, a 6L80E can handle 500 to 600 rear-wheel horsepower in the typical street/strip application, although we have had customers push them all to the way to 1,000 hp."

 

[Jason_S]

I believe the reason that you cannot find the stall rating of these torque converters is because they are electronic lockup and controlled by the TCM. Which I interpret to mean that it is programable. However, automatic transmissions are not a strength of mine, so I could be way off.

 

[EnigmaMan]

Ha! I wish the stall converter was electronically controlled! That would make it nice and easy! Usually a stock stall is around 1000-1500rpm. Typically stall lock up is defined by the impeller speed in the torque converter and the lockup is a solenoid that engages the impellers to "lock" together creating a 1:1 connection (which is used at cruising speed on the highway). Think of it as 2 fans facing each other the fan that is turned on is on the engine side while the engine that is turned off receiving the wind is the transmission side.

A Higher stall allows for a higher RPM launch with out spinning off the line and also needs to be matched to the cam mfg recommendations. The downside of a higher stall is worse gas mpg around town and higher heat but yields higher performance getting out of the hole quicker :-D

This is why when installing a new Torque Converter to always fill it up with fluid first before installing it on the transmission and also to spin the torque converter once attached as it takes a series of "clicks" to lock in correctly and be pushed back to the transmission housing. Otherwise the torque converter can become destroyed if not installed correctly.

Here is a great demo on how Torque converters work and the fluid mechanics behind the process.

 

[JennaBear]

I wouldn't bother with the throttle body either. The stock one flows just fine, you wouldn't need one til you went over the 600HP marker, and even then, you should be looking at a much larger one.

long tubes over shorties any day of the week

If one is looking for a cheaper route for extra ponies: LTs, cam, stall and one would be really happy!

 

[EnigmaMan]

long tubes over shorties any day of the week

Do you have a recommendation which Long Tubes would be the best?
There are some that are <$200 on AutoAnything.com
Thanks!

 

[JennaBear]

You get what you pay for. If you are wanting good quality LTs they would be well over $500.