Thumper 401?

[shimniok]

I have a pretty good challenge that I think most people seem to have no answer for... Maybe you can help? This is long.

I have an FSJ (86 GW). It weighs 5500#. It has a 3 speed auto with low stall converter. It has tall gears (33" tires, 3.73:1) and a 4" lift. I take it four wheeling. It has a 3" exhaust with Magnaflow muffler.

The 360 in it now was rebuilt about 10k miles ago. It has a Comp Cams 260H, AFB, Edelbrock dual-plane Performer, and 8.5:1. It STRUGGLES to get me up the rocky mountain passes west of Denver. The only way to get up most passes without my foot to the floor is to run 2nd at 55-60. I want more power. Do NOT tell me I haven't tuned it right after 2 years of trail and error-- and improvements-- unless you plan to drop by this Saturday and fix it for me. :D

I run 2000-2800 rpm in the 40-75 mph range. About 2600 @ 65. I have virtually no power in this rpm range as evidenced by lots of throttle to get up even slight hills and slowdown on big hills at altitude. The auto trans never lets the motor see more than 4000rpm by the way so the Chevy answer of building all the power from 3500-5500rpm isn't going to work. :D

I now have a 401 in the garage waiting to be built. Your challenge is-- can you build a motor that will solve my power woes -- without changing anything else about the vehicle? You are allowed to change exhaust. :) How would you build it?

What I really want to know is what kind of torque curve would you shoot for??? What power band would you select? Would you rather have more hp at 4000 or more torque at 2000? Or a balance?

Does any of this make sense? Am I insane? Wrong? Stupid? :D

Many thanks!!

Michael

[jeepsr4ever]

Welcome aboard Mike!!


First I would use a aluminum intake or possibly MPEFI (if in the budget) just cam/pistons/intake/carb alone would do the trick on a 401. I woudl warm it up a little with 9.6-1 speed pro's. Its a real basic build to get ample power for your rig out of a 401. Fuzz or tufcj will probly come around and go into more detial. Let meknow if I can help in any way


-MC

[tufcj]

Mountains suck.... The best way I've found to get up to the tunnel is "turbo diesel". My EFI 360 CJ struggles up too. I'm running 37" tires and 4.27 gears. I'm going to 4.88s as soon as I can get the jeep in the garage.

You really need more gear with 33" tires and that kind of weight. I'd say at least 4.11s, and maybe 4.56s. (I'll give you a great deal on my 4.27s if both of your axles are Dana 44s). The only way to keep up speed in the mountains is to have the engine spinning near the top of it's power band. You also have a problem with a carbed vehicle. Even if it's jetted properly for the 5000 ft. elevation of Denver, you need to go DOWN a jet size for every 2000 ft of elevation gain. At the tunnel, 11,000+ elevation, you're rich by at least 3 jet sizes, your engine just can't get enough oxygen to burn the fuel it's being fed. Without enough air, the timing needs to bump up too. Things you can't control automatically without a computer.

Where are you from. I'm in Aurora, CO.

Bob
tufcj

[shimniok]

Thanks for the responses so far! The advice is VERY valuable.

The reason I didn't want to change anything but motor is I just spent $1800 on rebuilt, locked and regeared axles. Now I'm married and spending $ is... limited. :)

I wanted to keep hwy rpms to stock level. A mistake? Maybe. But get this...

A friend has an 87 GW, 33" tires, 4" lift, roof rack, very similar to me, but runs 3.31 gears and a 401 with 10:1 CR and mild/stock cam plus a Quadrajet which he just got dialed in a few weeks ago. He is now running 3/4 throttle in 3rd up that first big hill on 285 to keep up with traffic running 60-65. He runs most passes in 3rd. I've personally seen this truck PULL AWAY RAPIDLY from me on hills where I am foot to the floor to hold 55-60 in 3rd with only modest accel in 2nd. On Monarch Pass I was in 2nd where I could accelerate ok but he STILL pulled away quickly (I think he was in 2nd too). I've also seen him accelerate from 65 to 100 on nearly flat ground where I could barely make it to 80 in the same timeframe. Frankly it is jaw-dropping to see.

So, that is what is possible. Btw, Spitfire built his motor.

I've been playing with Desktop Dyno a lot (just ordered the 2000 vers). I modeled my motor and his as best I could. What I've found is my Comp Cams 260H is a horrible choice with stock CR and exhaust, weak on torque in just the rpm band I most use. He has like 100 lbs-ft on me with his combo.

In a 401 with 9.5:1 CR, small tube headers, the Edelbrock Performer cam puts out 430+ lbs-ft in 2000-3500 range, and with 320 hp @ 4000 (best of 260-ish cams). Factory Pontiac grind specs I found on the web puts out 440+ lbs-ft from 2000-3000 (447 @ 2500, 'only' 435 @ 3500 and 408 @ 4000) with slightly less hp @ 4000 (311 vs. 320). No other cam comes close to these two in torque. The next best are down 10-20 lbs-ft 2000-3000.

Seems the Pontiac grind puts peak torque @ my cruise rpm, most torque in the power band, and peaks hp @ 4000 suggesting good off-idle torque. I doubt 9 hp matters since it'll be 30 more than I have now. I think it's the best choice I've got. That's what I am leaning towards.

But this is all cloud pushing based on a lot of assumptions, book learning, and junk. What are your thoughts?

Also, EFI is planned too.

Michael

[cobra5laddict]

your cherokee is not a red white and blue 2 door with 33's is it? i see that truck here local running around. i am in arvada and went to school in gunnison... i know that 285 drive all to well not to mention monarch. i had a 79 cj5 with a new stock 304 and a 3spd t-150 with 31's the gears were 3.54. throughout most of the large hills and monarch i had my foot burried into the floor board. i could never muster 50 mph in 3rd. 2nd sounded like i was winding it too tight. although i had a 2 bbl.. on the 360 i am building (different jeep) i am going to run tbi.. i bet that will make a bit of difference.

[fuzz401]

might want to go to 9:1 or 9.5:1 cr and might want to look at the comp 268 cam

[shimniok]

Mine's a white GW with woodgrain, 33's, roof rack. I live in Centennial.

http://www.cfsja.org/rigs/michaels/tc/index.html

Thanks for additional replies!

What D.D. sez is higher CR (9 or 9.5) and small tube headers is the only way to make good power at low r's with stockish cam.

Pontiac specs looks best to me so far; ideal match to my rpm...

I am going to call a couple cam shops and engine builders for advice too.

Desktop Dyno 2000 is on the way to help too.

Michael

[jeepsr4ever]

That really looks like a jeep I saw in FSJ magazine

[cobra5laddict]

SHIMINOK,


what are you going to do with the 360 in your rig if you go to 401? i might be interested if you would like to sell.


Byron@waringoffice.com

[Goose]

I am originally from Central City Co (moved here 5 years ago) and I have 5800# J-10 with a 360 I ran around up there all the time, While I wont say I had "ample" power at the tunnel I could easily have run 80 or better climbing either side.. I would suspect there is something out of whack in your set up, unless that cam is really hurting you. My 360 was essientially stock with a Edelbrock torker and 1406 carb with a mallory hyfire ignition box and headers. Bob is right in that at the tunnel it's gonna be a dog to a certain extent but it should still run pretty fair unless it's tired. So I guess this is a long way to say.. If I were doing it I would build the bottom end essentially stock, Maybe bump the C/R If you can swing the dough. But the money I would spend would be on the cam/headers and Fuel injection, With the best ignition system you can afford. I have always believed the ignition system is one of the best places to improve performance, since most other mods are aimed at getting more fuel/air into the engine..It seems the greatest gains would be made by making sure you can burn all you do get in there.

(Jeez I'm getting to be a wordy bugger)