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Discussion Starter #1
Tips?

I'm clueless as to how it works.

I assume T-case in high gear then floor it and row through the gears (SM 465 - doh!) like a man posessed?

Wonder if I can do it with the 42" TSLs on or if I should temp mount the tow-rigs tires?

Local place is an import tuner joint - the looks on their faces should be prieless!
 

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tcase in 1:1

trans in 1:1

start at about 1000 RPM and go WOT until the valves float. They will most likely only want you to go from 2000 RPM on up, but make sure you tell them you want data from almost an idle speed.

I would strap down your suspension though!

EDIT- i should make this more clear... don't start from a stop with your trans in 1:1. drive through first, second, etc until you are in your 1:1 gear. Then take your RPM to 1000, wait for them to start recoding and hammer it

get roller tires, something in a stock size that wont bounce all over and something they can input into their computer
 

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You shouldn't have any trouble dynoing it so long as you have a good way to strap it down ( axles should suffice in this case). You won't have to row through the gears like a madman, take it easy on the way through them. You will likely dyno it in fourth since that is the 1:1 gear and that is where you normally dyno a rig.

You run it up to fourth and mat the pedal at low rpm and record the run all the way through.

I would take off the 42's as big bias tires (swampers) have a tendancy to balloon like a drag slick at the wheels speeds you will be seeing, it will effect the wheel hp numbers some by going with a smaller tire but I don't wouldn't want to be standing next to a 42 thats spinning 80 mph :D

Have fun :smokin:
 

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I did it when I was dialing in the supercharger I used to have. I put little roller tires on the jeep and strapped the susp down to the axle to minimize the twisting action. If you have a detroit or welded rear, make damn sure your tires are exactly equal in diameter:eek:

It's a great way to dial in your fuel/timing curve but don't expect to see a ton of power. These drivetrains we run eat a lot of power. Most dynos start recording around 2k rpm and go to redline. Make sure they use a wideband O2 in the tail pipe, it really helps flatten out any rich/lean spots in the curve.

and yes, t-case in 2hi and the pull is in direct gear (drive with auto, 4th with manual)
 

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I have run my XJ on a dyno several times when trying to dial in my stroker motor. I know its no buggy but same rules apply.

Tell them you want a real low starting RPM like what was mentioned before. They should be able to set up the dyno to start anywhere on the RPM band.

You will want a set of rollers. I ran lots of passes on a set of 35x12.50r15 BFG M/Ts and it wasnt that scary but the employees sure did have some big eyes when the rev limiter kicked in at the top of 4th :D Also with a locker or spool in the rear, make sure both tires are the same size and have the same pressure cause if not, its not going to be a happy time.

When strapping it down, go to the axle tubes with the tie downs not on the body/frame. I wouldnt worry too much about the body unless you have a crap ton of torque and a super soft suspension at which point straps could be put on both the axle and body. The shop should know how to properly strap it down.

AARON
 

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Discussion Starter #7
OK, thanks for the help guys.

I'll flip the rear ARB to open, smash the brakes and engage the front cutting brakes, tie down the rear axle and strap the rear suspension down a bit.

I'll also be running a matched pair of brand new LT245/75R16E Bridgestone V-steel Black Wall All Season Steel Belted Radials on the rear (the never-used spares from mine and a buddies 07 Silverados.)

That is - if the go-fast boys let me anywhere near their gear :eek::laughing:
 

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CrazyRC had my tow rig on his truck for the dyno/engine tuning as they refuse to run his big tires.
 

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When you are done, then stick it in the lowest available gearing and have them take readings from idle up just to see what kind of torque you are producing at crawl...
 

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Medusa(Jack Rice) dynoed his truggy at Wong's Performance in Portland OR and he did it with his 42 tsl's on. he was limited to the top speed and rpm. by the italian joint cv in the rear driveline. He said it was funnier then hell seeing the prolong grease slinging out of the joint hitting the z06 vetter that was in the bay next to it. I am really interested to know what the loss is from drivetrain to the rear tires. Real world numbers with doublers vrs. atlas. manual vrs. auto. The klune looking deal on the fornt of the 4 speed atlas vrs. a 2 speed atlas. Best case senario would be a engine dyno then a chassis dyno, but who's going to pull their motor for that. I did drill a 02 bung in my exhaust to hook up the wideband. Nice to, cause if you buy one you can have a passenger look at the air/fuel mixture while your testing. What ar eyou running for injection and is it programmable via laptop or do you have the ability to have them flash the stock computer?
 

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I had my old CJ chassis dynoed. I was amazed at how well it did. I did put some old 31" Buckshot Gumbo Mudders on it for the test instead of the 37's.

They had no issues with it. I was amazed it made 201 ish hp at the tires with a 304 AMC (EFI), np 435 and d300.

I have had my TJ dynoed on 35 and 37" mtr's a few times. The dyno operators said nothing about the tires.
 

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When my buggy was still toy drivetrain on 38" SX's, I had to smog it to keep the plates legal. They put it on the rollers and chained it down while I sat in the booth. It was wild watching the SX's wobble. When the dude would shift, the truck would almost raise up off the rollers. It was borderline scary to see it out of the truck. I heard a story of someone else in town who had to do the same thing in a commando and it hopped the rollers and shot out of the place and smashed into a brick wall in front.
 

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when I put my EFI on I was having some tuning issues, I took it to a dyno. when I did the baseline run in 4th @ 5000 rpms it was mad fawkin loud in thier garage they had the dyno in.

After that pull the owner requested we used 3rd gear as he was afraid of the tires going too fast. they were 39.5 iroks. :D
 

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Discussion Starter #15
What are you running for injection and is it programmable via laptop or do you have the ability to have them flash the stock computer?
It's a 79ish 350 that's been worked over at some point, but when and what I have no idea. Cam sounds lumpy.

I just swapped in 80's GM TBI from a 5.7 Blazer.

It runs OK, but not great. Idle is fairly poor, seems rich, backfires sometimes, and throws MAP codes.

Not sure if I'll bother with any tuning on the dyno- seems to me the ECU will always be battling the cam.

I really wanna do this to get a basdeline feel - so when I'm shopping for a new engine or planning a rebuild I know what I'm working with. What I mean is, I know this buggy pretty well - so if it dyno's at 250, then I know I want at least 250 in a new motor.

Thaks for the great stories.

So - what % loss do you think we're dealing with here through the drivetrain? 10%? 20% Just so I can calculate what specs to look for in a new motor
 

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tons. I'd say the second number you threw out is low still, just guessing though. Real world experience?
here's an idea, have ian pull an engine, dyno it, then put it in a buggy with a doubler/4speed case, etc and chassis dyno it. seems like a good show
 

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Discussion Starter #17
tons. I'd say the second number you threw out is low still, just guessing though. Real world experience?
here's an idea, have ian pull an engine, dyno it, then put it in a buggy with a doubler/4speed case, etc and chassis dyno it. seems like a good show

I'm telling my wife what you just said means I need 500 hp :D
 

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I just swapped in 80's GM TBI from a 5.7 Blazer.

It runs OK, but not great. Idle is fairly poor, seems rich, backfires sometimes, and throws MAP codes.

Not sure if I'll bother with any tuning on the dyno- seems to me the ECU will always be battling the cam.
Hey, contact DynamicEFI. They'll help you get that dialed in for your engine.

www.dynamicefi.com

I installed their EBL setup on my TBI. I'm far from done tuning and I just got a wideband (haven't had the chance to install it yet). Guaranteed you can get your engine running 100% better.

Since you have the chance to do some dyno tuning, I'd definitely suggest you get the setup and hook up your laptop while you're on the dyno! You stand to benefit significantly from being able to run your engine in a controlled environment.
 

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So - what % loss do you think we're dealing with here through the drivetrain? 10%? 20% Just so I can calculate what specs to look for in a new motor
typical trans is going to 18%-22%.

Small gear driver tcase in 2wd (D300, D20, etc) will be smaller 3-6% ish. the NP boat anchors will be more.

Plus figure you probably have a heavy ass driveshaft... ~1%

The heavier the ring and pinion and axleshafts in the axle, the more power there too.

I would guess you're losing close to 30% total... perhaps more.

most of the loss is simply due to the rotating mass of the heavy ass gears, flywheel, driveshaft and heavy fawking rims/tires
 

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typical trans is going to 18%-22%.

Small gear driver tcase in 2wd (D300, D20, etc) will be smaller 3-6% ish. the NP boat anchors will be more.

Plus figure you probably have a heavy ass driveshaft... ~1%

The heavier the ring and pinion and axleshafts in the axle, the more power there too.

I would guess you're losing close to 30% total... perhaps more.

most of the loss is simply due to the rotating mass of the heavy ass gears, flywheel, driveshaft and heavy fawking rims/tires
on a side note then, doesn't all the extra moving weight give an increase of torque (all that extra rotating mass)????


not saying that they *increase* torque, simply that the dyno will measure more torque...
 
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