Thumper 401?

[KJMac]

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

Is there AMC engines on the Desk top dyno 2000?

[Mudrat]

Is there AMC engines on the Desk top dyno 2000?[/quote]
In my version - only if you build it ...

Pat
Still in the UK

[Holeshot]

I have to ask, why take a great breathing engine & choke it down with lil cams, carbs, & exhaust?

The 401 will easily put out 550 HP & 550+ ft/lbs below 6500 RPM with std hotrodding techniques. I think the tq peak is around 3000 or 3500. PLEASE don't choke it down!!! It's not like a Chevy or Ford or whatever. Those heads flow GREAT and 10-1 compression should be fine with pump gas as long as you have it tuned correctly. Take a look at the 292H for a much better Comp cam, although they grind their cams too similar to their SBCs cams, and offer little in dual-pattern cams.

You actually have to build your 401 choked down to get less than around 430 ft/lbs of torque. And then you are wasting those great ports when they need to breathe.

I am assuming that you want power, of course. If a guy wants to put around on trails, he could use an inline six.

As far as I'm concerned, all that naysaying advice about using little cams carbs & exhaust is strictly for rock crawlers or trail riders. The 70 and up AMC heads turn out to be some of the best passenger car heads and make the AM V8s some of the most responsive engines to build, if you don't starve them. A stout 360 can use every bit of 850CFM, for instance. AMC even sold HiPo Holley 3bbl carbs up to 900CFM to go on top of the Edelbrock R4Bs they were also selling at their dealerships.

If you want to peak your HP at 4000 RPM, you are not even getting into the powerband that the heads were designed for. Like shifting a 125 motocrosser at 4000 RPM - ICK!!!! I think the STOCK cam HP peaked at 4600 or so, you are going the wrong way!!! Less RPM = less power!!!

Those Performer numbers you quoted are no better than a stock 70s 401.

The 401 can go to 6500 safely with ease, and is completely safe there so long as it is a sound engine. I would definately suggest spending the extra few bucks for forged pistons, and get them with 1/16" compression rings, TotalSeal gapless rings being worth 30~50 cheap HP, especially over time. Set your piston to head clearance at .045" to eliminate ping and have the heads "open-chambered" and you should end up with ten to eleven to one CR.

I have TONS of AMC cam, head, & "*.dyn" files for Dyno2000. (1800HP twin turbo anyone???)

OH YEAH: Another COOL thing about Dyno2000 is that the "*.dyn" files that it generates can be directly imported into other programs, such as "DeskTopDragStrip" and "DragStripPlus" so you can actually sim the 1/4 mile. PLUS you can import the dyn files into Bethesda Software's "HotRod Magazine's Championship Drag Racing - Burnout: Player's Choice Edition" and "NIRA Drag Racing". "PCE" (as it is called) came with a hunter green '69 AMX, so I have mine painted up just like my BigBadOrange with black stripes. If I put a stock 390 in it, it runs low 14s. When I simmed my 518HP 390, it ran low 11s in the low 120s in street trim, just like my car!!! With traction it goes hi 9s/lo 10s, just as you would expect. Extremely cool. Back when the sim was current, we would race all night on line & sanctioning bodies were popping up everywhere. Really came up with some QUICK setups!!!

The sim went the way of 3DFX, but I did keep my old Pentium 200MMX w/VooDoo3 just to run that sim. Of course, I couldn't resist painting an SS/AMX!!![/b]