Late Dart Big M exhaust ports

[Jim]

I am currently working on some late Big M heads. I first noticed that the short turns in the exports as cast are laid back more compaired to some earlier Big M's and a lot more than the pro one's. The short turn as cast feel's like a lump at the crest. The problem I am having is the airflow numbers in the mid lifts are off considerably. These heads are going on a 700in. marine blower with cam lift under .700. The port is unstable and sounds like hell. It settles down about .800 lift. 1.880 valve 28" no cheater pipe

Lift Big M Iron Eagle

.2....143...................143
.3....187...................199
.4....225...................249
.5....248...................275
.6....283...................292
.7....308...................302
.8....325...................308

I missing something? Should I be conserned with the hole in the mid lift? Can someone post some numbers for the Big M head?. The 325 number shows high because of the orifice change (different question). Any info is appreciated

[Jim]

Well I think I found the problem. With a little seat work the port stabilized but the mid lift numbers left with the short turn. I have 330 cfm exhaust port @ .850 lift.

[cboggs]

Jim,

I haven't worked the new Big M, .. but I may have some tricks to help
your mid lift number, ..

too hard for be to describe on here, so call my shop if you like, .. after 10 am, .. 703-541-0565, cell 703-626-1610

Do you have a radous under the exhaust seat?

Curtis

[Guest]

Jim,

I haven't worked the new Big M, .. but I may have some tricks to help
your mid lift number, ..

too hard for be to describe on here, so call my shop if you like, .. after 10 am, .. 703-541-0565, cell 703-626-1610

Do you have a radous under the exhaust seat?

Curtis

Curtis, thanks for the info. The mid lift numbers increased some and helped on the top too. Thanks for your help! Doing mostly marine stuff I don't normally check flow past .700 lift.


.2......135
.3......184
.4......227
.5......268
.6......299
.7......320
.8......330
.85....332

[cboggs]

Curtis, thanks for the info. The mid lift numbers increased some and helped on the top too. Thanks for your help! Doing mostly marine stuff I don't normally check flow past .700 lift.

Jim,

I'm glad it worked out, .. did it help with turb. too??

Anytime I can help, .. glad too, ..

Curtis

[Jim]

Oh yes, settled down nicely

[cboggs]

Oh yes, settled down nicely

Ahh, that's good, glad it worked out.

Cheers,

Curtis