This is a little blurp from a Tech Talk Article #41 that David Reher wrote in National Dragster

"The downside of this situation is that overly generous valve reliefs cost horsepower. For example, a 2.50-inch diameter valve pocket that is .100-inch deeper than it really needs to be has a volume of 8 cc’s. That much volume at TDC can significantly lower the compression ratio, reducing efficiency and power. It’s much better to have the proper piston-to-valve clearance and a shorter dome that doesn’t intrude as far into the combustion chamber.

Imagine two engines with the identical compression ratio. One has pistons with valve reliefs that are too deep and domes that resemble Mt. Everest; the second has pistons with optimized valve reliefs and shorter, rounded domes. Both engines have the same volume above the piston at TDC, but the engine with the proper valve reliefs and shorter domes will have a substantial horsepower advantage."

Just something that caught my eye as i was reading some of his articles.

My thinking is that some of you guys that are making plans for engine builds might read this and find a new inspiration to try something besides large chambers and tall domes.


Those of you who are waiting patiently for me to put some track times on my new combo i have an update.
I have some minor problems to take care of, and i want to be very sure that the car is safe to drive before blasting down the 1/4, but expect to see some ET's within the coming few weeks.

All of his articles that have appeared in ND and elsewhere are very informitive and should be read by anyone getting ready to build a performance engine.

Here is a link to all of his ND articles
http://www.rehermorrison.com/techTalk/indexStart.htm

That is just the thing behind using small chambers and true flat-top pistons...

pdq67

Now if someone would make a BB head that you could get decient compression with a flat top piston and less than 540 inches. Plus be streetable.

Tall piston domes hinder proper flame travel, therefore make less HP and torque.
The lower dome is to be preferred, since at least the 1980s.
I have had many instances where the lower dome has actually increased HP. Even just rounding the edges on a high dome piston will improve flame travel.

UDHarold

Mike,someone does make a head with a small chamber. GMPP Aluminum @ 110 cc. Cut another .022" to take it to 104 cc. With the SRP's that are profiled to these heads, I ended up at 11.53:1. That's with a 498". :D

I like Reher's articles. One of the recent ones warned about the ticking time bomb in your engine - flat tappet lifters. His advice, get them out of there and put rollers in.

Originally posted by Pat Kelley:
I like Reher's articles. One of the recent ones warned about the ticking time bomb in your engine - flat tappet lifters. His advice, get them out of there and put rollers in. I read that one today, it was in the back of ND. I run a hydraulic cam and big "Mt. Everest" domes. So there is 2 strikes against me. But then again, I have always been a rebel :D

I have a hyd cam with flat tops that have huge valve pockets. 2 strikes for me too. smile.gif

I have tiny domes and tiny chambers :D

Originally posted by mr 4 speed:
I have tiny domes and tiny chambers :D You da' man, now just drop a solid roller in there and you will be all set :D

So I guess this would be "bad"....
http://www.chevelles.com/showroom/Epistuff/Mvc_479f.jpg

Performance/ET wise,I think its a sweet combo graemlins/thumbsup.gif

Originally posted by Epistuff:
So I guess this would be "bad"....
http://www.chevelles.com/showroom/Epistuff/Mvc_479f.jpg I'm in the same boat, Jim. My Wiseco pistons have a .455" dome rise. Although from the pictures your pistons appear to have even more rise :eek: Those valve reliefs look mighty big, too. Regardless, your car still hauls arse smile.gif

It is still kind of messed up though. That piston is at TDC, but look how far down the hole it is. graemlins/sad.gif

Yeah, all my stuff has 5/8" domes too.
But in my own defense, I've had some of it for
over 15 years now! I do radius the ridges for
flame travel and notch the block to unshroud the
valves.While my engines aren't the latest
technology, what made horsepower in 1968 still
makes horsepower today.I just wish I didn't have
to buy fuel in drums!Man, I must be dating myself something awful! :D
By the way, congrats Brian on nearing completion
on your project.Nice work!

thanks! hopefully i can get a good video on here.