350/255HP Help please

[Alan Roehrich]

Originally Posted by Adger Smith

He said "Cold" Leak. That never has told me anything. I don't race Cold Engines... Could have bad ex seats and when it gets hot they go away..... Just Saying...

Agreed. Cold leak down is useless. Honestly, on these engines, you need to be using a Dwyer gauge, or something, to test blow by on the dyno. Leakdown, even hot, can be misleading. Measuring blow by eliminates all of that.

[Jim Hanig]

If its a junkyard block 384 is not that bad,if its leaking more than 6% you got problems, Call Greg at race rings get his ringpack give him the grove dept,and he will fix you up get it honed with a plate . Cam should be in at 103-104 with a three speed.spring pressure around 145 -385 with reg lifters. Bowtie should pick you up 20. good luck.Not all dynos are the same.

[Chipper Chapman]

I'll get it up to temperature and do another leakdown. Don't have access to a Dwyer guage. Cam is in at 103. What you guys are saying about 35-40 and 600rpm down is exactly what I have been figuring but can't find why. Engine is a factory block but fresh at .065 with plate. Pistons are a couple years old, Manley rods, (light piston heavy Rod)

[Alan Roehrich]

Originally Posted by Chipper Chapman

I'll get it up to temperature and do another leakdown. Don't have access to a Dwyer guage. Cam is in at 103. What you guys are saying about 35-40 and 600rpm down is exactly what I have been figuring but can't find why. Engine is a factory block but fresh at .065 with plate. Pistons are a couple years old, Manley rods, (light piston heavy Rod)

Is the block poured?

To the water pump holes?

Piston to wall clearance?

Hone finish?

Oil clearances?

Oil weight?

Oil pump type?


A Dwyer gauge is pretty cheap, find one online, probably for less than $100. They're easy to hook up. And they tell the tale about real ring seal with the engine running.

[Chipper Chapman]

-Block is not poured,
-.005" piston to wall as per CP
-Plateau Honed with torque plate, cannot remember exact grit but we spoke to total seal and did what they said
-Bearing clearances .0025 rods, .0037 mains
-Broke in and dynoed with amsoil break in 30 weight
-now running amsoil dominator 5w20
-M55A pump with stock spring,
-Champ CP40 pan

Cam specs
Bullet CHS 307/315-06H duration @.050 262/270

[Alan Roehrich]

Originally Posted by Chipper Chapman

-Block is not poured,
-.005" piston to wall as per CP
-Plateau Honed with torque plate, cannot remember exact grit but we spoke to total seal and did what they said
-Bearing clearances .0025 rods, .0037 mains
-Broke in and dynoed with amsoil break in 30 weight
-now running amsoil dominator 5w20
-M55A pump with stock spring,
-Champ CP40 pan

Cam specs
Bullet CHS 307/315-06H duration @.050 262/270

Okay, in my opinion, for whatever it is worth, what I have highlighted above is problem one. There is no production block that I know of that will stay round under stress at 0.065" over. I've never seen an 010 or other block thick enough to do that.

If you want to run that big a bore size, you need to pour the block with Hard Blok or Embeco 885. At a minimum. You really need a BowTie or Dart to make it work well.

Ring seal is the most critical and fundamental part of restricted engine performance. You simply do not have one single solitary cfm to waste, the engine is suffering pumping losses just to breath, you cannot waste what it breathes. The bores have to stay round and straight, period.

I do not know if you can salvage what you have by pouring that block. You could try it, and maybe open the clearance up to 0.006-0.0065. If you pour a block one side at a time with either cylinder heads or torque plates, it will sometimes get a little smaller. Not every time. And if you cannot get it back round and straight by 0.0065" clearance, you'll have to change blocks.

I run tighter oil clearances, and use a lighter oil ring with a Napier cut second ring. No more than 0.001" per 1.0" of journal size. Of course, the bearing bores have to be dead round and stay that way. But it allows around 10-12# oil ring tension with no oil consumption.

Next, with a cam ground on 106 and in at 103, you're going to have an early HP peak, especially considering low lift and relatively low compression. You might consider a cam ground on 108 and in at 104-105. You can try moving the cam you have around.

That's about all I can offer you on the forum. Take it for whatever you think it is worth. Good luck.

[Chipper Chapman]

Cam is in at 103 as per bullet's instruction. Really can't see the block being the issue, none of the other engines around here out powering me are aftermarket or filled blocks. I can understand where you are coming from there and if there was an extra 3k in the budget it would have got a dart or bowtie.

[Mark Ugrich]

Originally Posted by Alan Roehrich

Agreed. Cold leak down is useless. Honestly, on these engines, you need to be using a Dwyer gauge, or something, to test blow by on the dyno. Leakdown, even hot, can be misleading. Measuring blow by eliminates all of that.

Alan, could you describe how the Dwyer gauge works?Is it basically installed like a vacuum gauge? I've never heard of one.Looks like there are several different calibrations.Which is correct to use to measure ring seal as you described? Thanks,Mark

[Alan Roehrich]

Originally Posted by Mark Ugrich

Alan, could you describe how the Dwyer gauge works?Is it basically installed like a vacuum gauge? I've never heard of one.Looks like there are several different calibrations.Which is correct to use to measure ring seal as you described? Thanks,Mark

Mark, if memory serves correct, you want one that reads 0-10 scfm. The 12" tall model is probably the best.

What you do is connect the gauge to the only outlet where any crankcase pressure can escape from the engine, everything else must be completely sealed. The easiest way is to connect the gauge to a breather with a tube outlet, such as the one used in a crank case evac kit. The gauge must be mounted perfectly vertical.

You then make dyno pulls as you normally would. We normally use our vacuum and or evac system for a while to seal the engine up, then after we've got it where we want it and tuned, we make a couple of pulls with the Dwyer gauge on it to make sure it is sealed up.

[V M Kauffman]

The one I used was a Fisher-Porter same one Chryser Race Group used was about $300.00 30 years ago. I could hook it up as Alan described and if it was bad enough the weight in tube would bounce just spinning on starter. We would check engine every time we loaded car to come home by hooking up meter and just free rev engine to 6500 rpm if Blowby was over 2 cfm engine would come apart we we got home. Difference on a 740 hp engine on dyno at 6 cfm down was down 60 hp to 1 1/2 cfm. Ted Flack showed us how to use it.