401 deck clearance

donwag

Thinking about using the early 390 rods (5.79" vs 5.858" late 390 and 401 rods) in a 401 block. Reason is to lower compression with Speed Pro forged pistons. Would make the piston to deck clearance about .050. Target CR is about 9:1. Got the pistons worth the money, but I do not want 10.5:1 compression. Want it to run without problems on pump gas. Any engine builder pro's out there with comments? Seems a little deep in the hole for me, but I am new to AMC engines. Thanks.

donwag

Come on, anybody got an opinion? This was recommended to me but I think the quench height will be too extreme and cause severe detonation even at the lower compression. The .050 deck clearance and a .045 compressed gasket thickness would be a .095 quench height. I was under the impression a zero or even some negative piston to deck clearance would get the best quench. How does the piston dish figure into this? Anyone done anything like this?

Mudrat

donwag wrote
Come on, anybody got an opinion? This was recommended to me but I think the quench height will be too extreme and cause severe detonation even at the lower compression.

The .050 deck clearance and a .045 compressed gasket thickness would be a .095 quench height. I was under the impression a zero or even some negative piston to deck clearance would get the best quench.

How does the piston dish figure into this?

Anyone done anything like this?

Well donwag, I really don't have an answer to O/A compression other than the dished pistons will open the combustion area and lower compression. I'm not good with the math in this area. We have a thread that discusses quench and this one http://www.bulltear.com/forum/viewtopic.php?t=1473&highlight=quench talks about stroking a 401.
Your situation may a bit opposite J20 is trying to do.

Check into a search for "quench" and read the threads there.

Pat

donwag

Thanks for the reply Mudrat. Actually my situation has a lot of similarities. Although I am planning to use the stock stroke. The thread you referrred to was helpful. Lots of info there. I think I will give the Edelbrock techs a call. I have decided to go the custom piston route as well. When we get it built in a few months we will run it in on the dyno. I will keep you posted. Thanks again.

Mudrat

donwag wrote
I have decided to go the custom piston route as well. When we get it built in a few months we will run it in on the dyno. I will keep you posted.

Thanks again.

No sweat - would like to see the dyno numbers and see how well you meet your goal :t:

Mudrat