Compression changes and Dyno tuning

Williboy

Well-known member
Supporter 2018
I was wondering what changes on Dyno Tuning would happen if you increase the compression??? And add headers??

Here's the story, I'm running a H/W 5200 on a '70 head that was only milled .010 or so and a block that was zero decked.
I was not aware of the gasket issue at the time of the rebuild. :oops:

It's running good but I was thinking about getting it Dyno'd to get the jets dialed in.

Some day in the near future I plan on pulling the head, cc-ing it, shaving off a bit more, go with adj. rockers and adding a port divider and then maybe headers. (But need to spend my money on the susp. and steering first)

How would that effect the Dyno?? or the jets??
Should I wait to do the head work first???

Thanks,,,Glen
 
Hi Williboy,

The changes you have in mind will require re-jetting. Unless you feel the need to Dyno the car now and later, I would hold off until your head and header work is done. As for the CR, a zero deck 200 with a .010 mill and a .045 gasket would have a CR in the 8.2 to 8.4 range. As a side note, if you're going to add adjustable rocker you should consider a 1.6 ratio set.

Steve
 
You didn't mention this above, if you did I must have missed it. If your going to switch to adj rockers you might as well go with solid lifters. You will have to get new push rods as well. The adj rockers have ball ends instead of cup ends. Can you say chromoly?
 
What exactly is 1.6 Ratio Adj. Rockers???

Is that different than the 144/170 adj.??

What's the prices difference between the two??
 
Howdy Glen:

I believe that it is important for you to rejet to get the most out of your current combo, but Dyno time is expensive and your engines fuel requirements will change when you add headers and get a good head rebuild. You might be just as well off to tune your carb with plug readings and stop watch dyno testing.

Given your combo, well tuned, you can expect an additional 5 to 8 HP with the addition of a port divider & headers.

Your stock rocker ratio is 1.5:1, which means that the rocker multiplys cam lift by 1.5. ei stock lift at the cam of .232" times 1.5 equals .348" fo lift at the valve face. Changing to a 1.6:1 rocker is .232" times 1.6 equals .371" or an increase of .023". I haven't priced them in awhile, but they are pricey. Other options are to install a higher lift cam at rebuild time and/or back cut the intake valves when you're redoing your head. Back cutting is my preference, because it is cheaper and lightens the intake valve.

Adios, David
 
I guess I didn't tell the whole story...
I'm already running a 252 cam and the head was rebuilt with new valves, guides, hardend seats etc...
About the only thing it seems is that the head wasn't milled to comp for the gasket.
My mech. who mostly deals with V8s so he, nor I, wasn't aware of the gasket issue at the time.

After I get the front end done, I guess I'll start shoping for a set of adj. rockers and headers and do it all at once.

Thanks for all the info,
Glen
 
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