7427 install, first impressions

[JeepsAndGuns]

That should be a real good higway cruiser!

Around town, and whatnot, yes. But actual highway, NO. I'm running about 3100 RPM at 70 MPH. Kinda screaming! I need a overdrive to get me around 2500 rpm. That seems to be its sweet spot crusing rpm. My engine as its built is not a high RPM engine. Its built more twards low rpm torque, rv style cam (comp cams 256H XE)
It pull great, but there is a still a pretty good diffrence spread in gear ratios, as you dont use 1st for normal driving.

[EagleMark]

33 inch tires!

[JeepsAndGuns]

Going bigger. My future build for this jeep is as follows, (and I already have the listed parts)

High pinion driver side drop, kingpin dana 60 front axle (need to buy locker and finish rebuilding)
Smooth bottom, factory disc brake dana 60 rear (need to buy gears and lockers)
Early chevy NV4500 trans, with the lower 6.34 first gear (I have completely rebuilt it)
NP-205 transfer case, driver side drop ford version (completely rebuilt)
SOA on the front, shackle inversion on the rear (for about 7 inches of lift on stock springs)
35x12.50-16.5's BFG MT's (bought used, but nearly 95% thread)
Re centered hummer 12 bolt beadlock wheels, pvc beadlock rings. (need to cut out old centers and weld in new ones)
I will be running 5.13 gears, and lockers front and rear.

[woody80z28]

Going bigger. My future build for this jeep is as follows, (and I already have the listed parts)

High pinion driver side drop, kingpin dana 60 front axle (need to buy locker and finish rebuilding)
Smooth bottom, factory disc brake dana 60 rear (need to buy gears and lockers)
Early chevy NV4500 trans, with the lower 6.34 first gear (I have completely rebuilt it)
NP-205 transfer case, driver side drop ford version (completely rebuilt)
SOA on the front, shackle inversion on the rear (for about 7 inches of lift on stock springs)
35x12.50-16.5's BFG MT's (bought used, but nearly 95% thread)
Re centered hummer 12 bolt beadlock wheels, pvc beadlock rings. (need to cut out old centers and weld in new ones)
I will be running 5.13 gears, and lockers front and rear.

Do you really think you'll need the deep NV4500 granny gear and 5.13 gears? My truck is probably a similar weight to your Jeep and with the 5.61 1st and 3.73 with 33s I rarely ever use it. And with the 3.73 and 33s the cruising RPM isn't bad on the highway.

[EagleMark]

Having lower first gear really helps when doing rock crawls or other obstacles and gives tremendous control. My sons Toyota has the Trail gear 4:70 to 1 ratio gears and it is incredible, can just about idle over all obstacles, but he is now adding a second transfer case with stock gears as well.

[PJG1173]

IDK 5.13 with 35's is still a bit much with a v8 and that transmission. I use this site to compare crawl ratios and final drive ratios www.grimmjeeper.com/gears.html It is very useful since it allows you to compare two different ratios side by side.

[EagleMark]

You can go ridiculously low as what my son is doing! I had wide ratio T19 trans 6.xx first gear, and a Dana 20 transfer case 2 to 1 low range and 4:11 axle gears and 36 inch tires which was fine for me, crusied nice on highway, crawled great off road.

[PJG1173]

what engine does your son's toyota have? It probably needs the extra gearing to multiply torque.

[EagleMark]

22re, .060 over, head shaved, port match, crawler cam balanced bottom... 5:13 gears, lockers, 36 inch tires. He's really fine where he's at, never has a power issue as is, but a friend was selling the dual case adapter and skid plate cheap so he got it and already had another transfer case...

I guess he want's to win the slow race? I can already walk faster then his first gear in low range at 2000 RPM...

[JeepsAndGuns]

IDK 5.13 with 35's is still a bit much with a v8 and that transmission. I use this site to compare crawl ratios and final drive ratios www.grimmjeeper.com/gears.html It is very useful since it allows you to compare two different ratios side by side.

IDK, I think 5.13's will be about perfect for what I want. With those gears I will still have plenty of pulling power, awesome low range/crawling ability, and can take advantage of the overdrive 5th.
I too use that caculator, it puts me at about 2500 rpm at 70 mph in 5th with this setup. Thats about perfect.

[EagleMark]

Couple more points you may alreay know... 5:13 gears will spin the driveshaft about 25% faster then 4:11, at 70 that is fast! CV joints and perfect driveline angles with lift at ride height will be critical!

Choose of tire will also be a factor. Tiller tires put majority of weight further from center point and further from rim where balence weights go. Goodyear Wranglers are an excellent 70 MPH tire but just OK off road. Super Swampers are excellent off road but poor choice for 70 MPH! Not only are they lope sided heavy most are not round. Many come with 4 to 8 once patches in tire to begin with. One guy went to an old school truck stop that still spun tires to true round and lost 1/4 inch tread on one side of each tire to make it round. My Super Swamper Iroks were incredible off road in all conditions, but had 16 onces of Dyna Beads in each tire and still shook at 65, tires were 1/4 to 1/2 inch out of round...

[sfara002]

Gentlemen,

I feel I am in the presence of EFI legends. I have read countless threads about the 7747 to 7427 swap taking meticulous notes. I assembled a wire harness to make moving back and forth a 15 minute job and double checked the harness twice with a multimeter. I followed Dave's instructions from the CK5 website and Fast's from TGO to apply this to my 91 Full Size 5.7 Jimmy. I installed the 3.9K knock sensor and bypassed the ESC. I got the truck to turn over and start but barely ran, I am talking 300-400 RPM bad. I managed to capture a few seconds of data logging with tuner pro. Looks like it flagged the Knock Sensor but I have no idea why. Any experts willing to take a look at the data? I am stumped on this one. I have good resistance with a multimeter from the old ESC back to the battery ground. I pinned B7 to B15 with zero resistance. I will check the resistance from the wire harness at the pcm to ground in the morning but it should be ok since it runs just fine with the 7747 and 100k knock sensor just fine with no fault codes. It is just frustrating thinking everything is right and things still don't turn out the way you expected.

[sfara002]

Alright I found the problem! My harness I build with the 7747 pigtail and ecm connector made a poor connection. I cleaned this up now have a functioning truck and pcm. If anyone is going to to make this pigtail just make sure the pins seat in deep enough in the pigtail on the 7747 side. If I were going to do this again I would just unpin the wires from the wire harness and repin on the 7427 plug, the harness has been more of a headache than what it has been worth.

Steve