Help on 401 Compression Ratio??

[radjeeper]

I put a set of 50.60cc 390X heads on a 401 with stock dished pistons in a 1978 Jeep Wagoneer (57.92cc heads). Spent one night on a on-line engine calculator trying to figure out what the new compression ratio is. I came up with somewhere in the range of 9.5 to 9.8. Any body out there know for sure what it would be.

[fuzz401]

I would say that should be close

[tufcj]

I was told the 50cc heads raise the compression by .5 to .75, with everything else unchanged. Factory compression on the 401 was 8.25, so my guess would be 8.75 to 9:1.

Bob
tufcj

[radjeeper]

Thanks for the help. Sounds like I will be fine running pump gas.

I've got another question that you may be able to help me with. What could I expect in the way of horsepower and torque with these heads, performer cam, roller rockers, performer manifold, Holley #4010 750 cfm carb, K&N filter and top, Doug Thorley Tri-Y headers into a single 3" exhaust, MSD Pro-billet dist. and Jacobs Omni Pac coil?

I know that I should have more cam but I am not going to do that until I pony up for Edelbrock Pro-Flow MPFI.

[jeepsr4ever]

a change of 4 cc's changes 1 point of compression according to numbers posted by Edebrock

[radjeeper]

So, that would be a change of 7.32 cc's which would mean I have gone from 8.25:1 to 10.08:1. Is that right? If it is 10.08:1 then will pump gas be ok. I have read that AMC aren't as sensitive to higher compression ratios as are Chevys. That they won't ping. Is this correct?

[Dusty]

But speed pro claims thier forged pistons are 9.8:1 with 58cc heads and 10.5:1 on 51cc heads


my 401 .030 over with speed pro forged 9.8:1 w 58cc head pistons checked by a machine shop penciled out to 10.17:1 when combined with the 54cc edelbrock heads.

if i remember correctly it been almost a year since i had that all measured out. :wink:


Id re-think the performer cam.


Disclaimer i cannot verify these numbers i did not see the prinout just got the email from him and have yet to hear back, not uncommons we email and then talk to each others once or twice a year.

Got an email from a friend, stuck his fresh 401 onto a dyno. FYI i have no idea on the build besides what he told me but here are his numbers. I do believe he has a HEI dist.

The idle is smooth he says 750 rpm very mild tone (lope) indicating a performance cam but nothing annoying for what that is worth.
forged pistons .030

800 edelbrock 4 Bbl
Air Gap intake
9.76:1 Compression
58cc Stock heads (i imagine he ported and polished, including combustion chambers but i dont know)
Long big tube headers (old fenderwell headers i believe)
.479 lift 222 Duration @.50 292 dur 114 center


Herb Ferguson's 401 4/21/05
RPM HP TQ
2000 164 431
2500 213 453
3000 258 456
3500 323 474
4000 372 487
4500 391 463
5000 373 391
5500 369 357
6000 338 291

I can not verify these since i havent seen his print out or anything but i thought i might post em up

[radjeeper]

Very impressive dyno numbers, what cam was that, a Howards? I guess that would be at the rear wheels? Mine is very similar all but for the cam. I'll have to check the compression and have it dynoed. I'm sure interested in what your engine will do?

[Dusty]

Engine Dyno in Great falls montana. I think they are impressive but i havent heard much more from him. i know another guy up there says they still havent gottne the motor into the heep yet.

Howards and Crower has the identical grind too. MC has a point though that a split duration cam is more efficient with the 401 but i think we are getting close to spliting hairs over 15-20 ft/lbs and a a few hp's.

[radjeeper]

If I was to build a 401 from the ground up, for a Jeep to be wheeled very fast and slow, what would you do? This would be for a future "Jumpin Jeep" project, and my third 401. Nothing exotic. Pistions, heads, rockers, valves, springs, pushrods, cam, induction, ignition, oiling, headers, water pump, etc.?