Increased Comp ratio 1 point--dyno results

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RAMM

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Like the title implies I had the chance to test a 440 RB @ 9.4 static compression ratio and then again (due to an oil leak) @ 10.4 static compression.

This is a 446 I recently built for a customer using '915 heads and flat top Wiseco forged pistons. It ran all right during the initial dyno session but the rear main was leaking a little and that was not acceptable so I took it off the dyno and couldn't leave it alone.

When I was assembling the engine the pistons measured .055" in the hole. Also understand the customer really wanted to save these pistons so I cleaned them up and CNC machined them with a slight conical dish netting a little more volume. Basically I knew there was plenty of room to play with here so I decked the block exactly .045" per side which put it @ 10.4 comp. I had the chance to re-dyno with NO other changes. The power increase is somewhat expected but the timing requirements changed dramatically. Previous timing for max power was 35-36 total--Now 30-31 total is all that it likes. Interesting to say the least. So +30 HP +38 ft/lbs at the peaks was observed--the graph tells a much better story. J.Rob
 

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Nice increase but that timing change is really curious. I have always ended up
around 36-38 degrees total on B motors....even before we had low compression.

Of course, in the old days I was reading the compression ratio in a brochure or
on a box. I'm not a machinest so maybe I didn't have what I thought I had.

38 degrees total used to be the "majic number" on a stone stock 383 or 440
Magnum. Worked every time.
 
I like how the shape of the curves improve to a smoother line. This shows that the engines cam was a bit more aggressive for the engines ratio. Basically what we have here is a better balanced engine with the ratio increase.

Thanks Ramm. It's posts like this that help peoe see what a good combo will do and how it can & will do better.
 
Good info and a smooth difference in the power curves. Thanks.
 
This is VERY interesting, thanks for going to the trouble. I was absolutely astounded when I first read what the 3G hemis like, about 22 degrees I think?

(This by the way, shows you how full of crap eff bee oh is about timing, he wrote a book According to that, timing can be mathematically calculated by ?? the angle of the stars 'er somthin)
 
at .055" down and a closed chamber it was prime for a change to get some quench, how thick head gasket? 1 up on the comp. ratio at 500hp would be good for +20hp , u got +30hp and less timing needed is a good thing showing quench improvement good for +10hp , and at 10.4 comp with quench it will not need any more octane than 9.4 without quench
 
Old Man Mopar said:
Nice increase but that timing change is really curious. I have always ended up
around 36-38 degrees total on B motors....even before we had low compression.

Of course, in the old days I was reading the compression ratio in a brochure or
on a box. I'm not a machinest so maybe I didn't have what I thought I had.

38 degrees total used to be the "majic number" on a stone stock 383 or 440
Magnum. Worked every time.
Click to expand...
The total timing was the first thing that had me curious. I'm with you, most every big block I've drag race seemed to like a total of 36-38.
 
Cool test RAMM. I think more than the power numbers, your result show the increase in efficiency of the combustion - which is a direct reuslt of controlling the chamber size and shape, and the "pre-ignition" treatment of the mixture. I've found that total timing any engine likes is generally betwen 28-32° when the quench is tight and the burn can be controlled.
You really can't beat the return on investment for great machining and building to take advantage of quench. Easier on parts, less octane required, and more power.
 
I wonder how much duration could be added to the cam and still have it act the same with the added point of compression? Now what would that dyno test show?

I know going from 88cc to 84cc heads (albeit ported) the corresponding cam was 10 degrees more at .050. The projected power difference is astounding.
 
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