Thumper 401?

[Dallas Lemon]

Check out this link. It has an excellent write up on heads, and results of the modifications performed.

http://www.amcforums.com/cgi-bin/yab...num=1116866495

[Dallas Lemon]

I'm honored that I have gone from a NEWBIE to a Cook. That's a good thing..............Right?

[Mudrat]

I'm honored that I have gone from a NEWBIE to a Cook. That's a good thing..............Right?

Yup .... a GOOD thing

Pat

[MoPedal]

Thanks much Dallas, alot of info about heads there. Sounds like the 502's with different valves is the way to go if staying close to stock. Even if you go with Edelbrock they may be some changes to make. Good info! You've given me something to think about!
I have been known to float the valves a time or two...you recommend the roller rockers for woods use? How often will they need adjusting (assuming they are still solid lifter only)?
Many thanks for the info!

[Dallas Lemon]

"I have been known to float the valves a time or two...you recommend the roller rockers for woods use? How often will they need adjusting (assuming they are still solid lifter only)?
Many thanks for the info."

Actually, I am still using a hydraulic setup, just with the roller rockers. No adjusting required. Just set them up initially how the instructions say and forget about 'em.

[Holeshot]

hey, guys!!!

A STOCK '71 401 put out 430 ft/lbs of torque!!!

The heads are extremely RPM friendly & can flow well past 7000RPM, which the crank & rods are fine with.

An old-school build will net 500+HP & over 500 ft/lbs of torque.

Choking down a 401 with little cams, intakes, carbs, & headers may be OK for rock crawlers who want a 401, but for those who want to go fast, an old-school, musclecar build with 500+ HP at 6000~6500RPM STILL gives over 500 ft/lbs of torque from around 4000 to around 5500, that's with a "little" hydraulic .550" lift 292 DUR cam. This build STARTS with almost 400 ft/lbs of tq at 2k RPM!!! Another 30HP is available with 2.08/1.74 valves, maybe 50+ with a rad roller cam, & 30 with TotalSeal gapless rings. The bigger valves hurt the bottom end perf little due to the big, great flowing ports we started with, but choose your cam by what your REAL RPM range and other mods will be.

A good rbld with 10.2~1CR, 600CFM carb, 2 plane intake, small-tube headers, & a Comp 252H (LESS lift than stock!!!) should be around 580 ft/lbs @ 2000RPM & 340HP @ 4000RPM (SHIFT before your head hits the windshield!!!!!!).

A stock '70 360 with free-flowing exhaust puts out around 290 ft/lbs at 4k & 287hp at 6k, the 401 is almost double, as someone remarked. The 401 can really make use of those great heads.

I would like to see the dyno charts of someone building a rock-crawling 401 who tries the early '69 style heads. I have to believe that the little ports would give more tq at the low revs, as the '70 heads have very large ports that scream for revs.

Note that I DO use the Dyno 2000 program and have built most stock AM V8s in it & the number are close but for the head flow you choose should be "Canted Oval Port" as they are close to what the '70 heads flow. I have made flow files from flow charts and the numbers come out real close.

[zero cool]

hey, guys!!!

A STOCK '71 401 put out 430 ft/lbs of torque!!!

They changed the way they measured HP and Torque starting in 1972.

Before then, they used gross ratings. They would hook up the engine to a dyno, run the oil pump and water pump remotely, have no AC or power steering pump, attach open headers, put a velocity stack on the carb, etc. and then run the dyno.

Starting in 1972, the rules changed and they started using net horsepower ratings. You had to run the engine as it was installed in the vehicle. It had to have all the accessories hooked up (i.e. water pump, AC compressor, power steering pump, etc) as well as full factory exhaust and air filter.

That caused an across the board drop in horsepower/torque ratings of 20-40%. But it more accurately measured the true horsepower and torque being generated by the engine as it sat in your car.

[tarior]

Weren't the '70 and '71 360's rated at 395lb/ft torque and 290 hp? With the 401 having 430 lb/ft and 330 hp. Both were fairly conservative.

[Holeshot]

Those spex sound right.

As far as the way of measuring changing in '72 (SAE), correct. Joan Claybrook and the tree huggers had also gotten the CRs dropped a bunch along with retarded cam & ignition timing & smog controls plastered here, there & everywhere!!!

NOW we can start talking about 300HP 426 HEMIs & 427 Chevies!!!

Either way that makes you feel comfy.

My 390 AMX pushed out 518HP to the rear wheels, thru full exhaust, with all the accys running. That's with std hotrodding techniques & 9~1 CR.

[KJMac]

On the 360, planning to get a cheap FSJ without motor and swap in and sell the whole shebang to try and recoup cost.

I think the cam is hurting me. I am usu foot planted to hold 50-55 up to the tunnel. Motor is new. I've played with mix/timing for some time and improved power, but not lots. Ignition is already about as hot as it gets.

May install O2 sensor and tune carb more. Headers too. And may even try another cam. Hate to build a 401 without knowing what went wrong with the 360.

Higher CR is a must have as far as I can discern.

On the 80mph J-truck, what gearing, tire size, and cam? Thx.

Michael

What kind of timing curve are you running? I would look in to an HEI distibutor from mallory. Headers and dual 3" exhaust. If you don't do TBI than I would contact Sean Murphy ans have him build you a Quadrajet. A friend of my brother built a 401 for his Grand Wag. to pull his sleds up to the mountains. The build consisted of 9.5:1, stock heads,home ported. 270 Comp cam, Edel. performer intake poerted exhaust manifolds, single three inch with flowmaster. 3.08 gears, automatic. 32-11.50 tires. 272hp 368 torque at the rear wheels with edel. 750 carb and Mallry ignition.