Thank you for your ovservational input.

The two pictures that just posted, and looking at the original web postings= By looking at the milling and the carbon tracking they are obviously two different pistons.

In the upper picture I see the "lower" groove as being poorly milled, like the piston or mill slipped and made the groove wider and deeper toward the convergence. See the milling overlap?

In the second picture I see between that corresponding groove and the dome what appears to be a dimple that looks like someone with a hand held ball mill made an uh-oh. There also appears to be an irregularity in the edge of the high dome that might have been made by a "chuck" hitting the edge of the dome.

Knowing that many flat pistons have been milled reducing their head thickness to alter compression height, others have had their domes lowered, many have had gross amounts taken out for hand cut valve reliefs... I feel that a minor spot of that nature would not necessarily jepordize the integrity of the piston head. I speculate that the EMC builder concurred.

Based on these pictures, without personally examining the pistons, I cannot state that "clearly eating itself up" is a term that could be used to describe this situation.

I also will comment that the recommended grooving is with a .063 ball mill with a depth of .080, then filed to .120 max surface width. It looks to me that the pistons in question have been milled with a ball mill of three times that diameter, and inconsistently done, one to the other.

JMO thanks,
x

And what would a piston "eating itself up" have to do with how grooves can't work?

C'mon, its like we're in a character debate and two candidates are mudslinging. I don't care if my candidate used to bang hookers, if he does well in the office, I vote for him.

I don't care if a 12.5:1 engine ate pistons on pump gas, if the grooves work, they work.

A few years ago a company called Hi-Tech (Nusource) developed a piston for the SBC that supposedly promoted swirl, increasing horsepower, etc. It didn't catch on.

I wonder if a groove in the piston as opposed to a groove in the head may have the same effect, similar to those in the pictures posted.

I rember when some Nascar teams were dimpling the intake side of the combustion chamber. I wonder if any are doing that now.

I am not "for" or "against" the head grooving process. I just haven't seen any evidence proving that it makes a big difference. For something that has been around as long as it has, it hasn't set the world on fire. I think there may be something to it, but there are many variables that may mitigate the effect, such as deck clearance, piston dishing, basic combustion chamber design, etc.

Hi kdrolt,
i haven't heard from you in a while. I'd like to hear your opinion on this now that some time has passed.

I should be finishing two set of heads this week, I'll post pictures later.

Dart 345 BBC heads for a high compression bracket car

and Edelbrock SBF heads for a street strip pickup truck with a Eaton blower

True, but in that context, EFI was around for about 15 years before it "caught on". Caddy, BMW, Jag, and some Japanese companies had EFI examples as early as 1974 and it was dismissed as complicated and that it wouldn't ever catch on.

And that 2 speed rear planetary of the 40s-50s,
and that overdrive transmission thingy of the 50s-60s that died out... called worthless because they "lugged" the engine.

Not to mention that 8-6-4 Caddy idea that resurfaced last year....... oh I did mention it.

what peaked my interest in this subject was the claim that .50-070 quench was ideal for use with the grooves. this meant i could (i thought) use my heads without having to mill my block to get 040. which is ideal for non grooved engines. i.e. it was a fix: it would make me run better without spending money and use pump gas. i think that in the racing world, rather than try these grooves, people would be more inclined to do the machine work, match parts better, or just use higher octane race gas, change timing, and forget about detonation issues. i'm not saying grooves wouldnt work on a racetrack, because i believe autobreaths accounts of his work on racecars. but i do believe they work better at lower rpms (also illustrated by a-b's race results in a harder launching car), and will work to make less-than-ideal parts or specs for detonation better: as per EMC when he felt like his c.r. was too high for pump gas.

anybody think the same way on this?

(as for EMC using pistons out of the box, i would think the reasoning there is that the engine isnt going to be running long enough to get any carbon deposits just doing a few dyno pulls. and correct me if i'm wrong, but the guy in EMC who used the grooves placed second just a few points behind first. too bad he cant run w/o them and see if he wins or places third, we'd be done here)--hey wait! maybe he did? where's his number? right here:

BES Racing Engines
78 Harrison Brookville Road, Dept. PHR
West Harrison, IN 47060
(812) 637-5933 i called and LM. they are moving their shop. i asked if they dyno'd before and what improvement the grooves made. they may call back ... might not! they also are changing their number after the new year

This is true but EFI had to wait for the computer technology to advance to the point that is was feasible to control it in a manner that was mass-producable. The head-grooving thing, on the other hand, is a simple process that can easily be accomplished and tested.

tom

The head grooving thing as a modification to existing engines should work... for some engines. It promotes turbulence which promotes better burning. I think we can all agree on the second statement anyway. On more efficient combustion chamber/head designs, there's already enough turbulence and the grooves will have less, and in a few cases no, effect. That's the plain and simple truth! It's not a mod that will increase efficiency enough on all designs to be worth the effort. That's why manufacturers haven't jumped on the band wagon -- they can improve chamber designs without grooves from the drawing board. Should be a great mod though. Just need to figure out which heads benefit the most from increased turbulence.

Obviously "older" heads will reap the most benefit, in most cases. But what's "older? Depends on the manufacturer for one thing. Pre LS-1 heads should benefit as far as GM, and maybe even LS-1. I doubt anything newer would benefit much, if any. Computer control makes a big difference too, as the computer fire the plug at just the right time compared to a distributor, which is more limited.

Dome contouring is not about "preventing" carbon buildup.

The carbon buildup is "caused" by incomplete or irregular burning....... which is what the grooving and contouring is trying to improve.

Radiusing domes/ contouring a similar purpose. Improving the flame propagation.

I would almost bet that if an EXACT repull could be done with contoured domes there would be a noticable power increase across the board. Maybe even a significant increase despite lowering of compression due to smaller domes.

If you look at the pistons shown, you will see that there is a significant and irregular carbon buildup for the short amount of hours on this experimental engine.

Older engines that actually had some chamber quench area (closed chamber heads) usually had full dished pistons. Open chamber heads are moot.

Maximzing the quench between piston and head is the key. Any engine that has "some quench" should benefit. Those with reverse dome pistons should see benefits from grooving even though their maximized quenching is trying to acheive the same purpose = flame front turbulence to reduce detonation so higher compressions can be used.

If you study David Vizard about combustion chambers and turbulence, grooves absolutely have to help..... anytime.

Looking more at these pictures and those available elsewhere, I see that the marks are there, but an optical illusion occurs and rather than that being a dome with the mark on the edge, that is actually the valve relief that has the irregularity. The valve relief is ajacent to the dimple, and a slip of the tool could have easily produced both.

I still can see no evidence that the piston was disintegrating.

Quench It If You Can

.....the squish effect, wherein as the piston closes the gap in the quench portion of the head as it approaches TDC, the combustible mix in this portion of the chamber is rapidly displaced, creating combustion-promoting turbulence, speeding the burn.

.....as the propagating flame front expands, the pressure can get high enough to auto-ignite the end gas at the far side of the chamber. Since with a tight quench clearance,....the chances of auto-ignition (detonation) are greatly reduced.

.......An engine with effective quench will be more detonation resistant, and it is typical for surprisingly substantial improvements in torque to result from the more efficient combustion. Most builders consider .040 inch ...... to be an effectibve target for piston-to-quench-area clearance.......

Steve Dulcich
Winter 2006 (sic- Dec. 2006) Engine Masters Magazine p.23

The cold of winter has limited my tinkering but I was able
to groove a couple of sets of BBC heads on the warm days.
The local track is open so hopefully I'll get some first
impressions from these soon.






[

" If quench is so good at supressing detonation and allowing the use of higher CRs for more power and better mileage, why doesn't the factory make it tight to start with? In a nutshell the answer is emissions.

Tight quench..... causes unburned hydrocarbon emissions to go up.....
the trend has been to use a more open chamber with less quench area, but to make the quench action more active by tightening it up as necessary...

...optimizing quench clearance and quench area is something of a tight wire act done at the OE level and you may ask if we should worry about this (emissions) for our street machines? The answer is "no".

David Vizard, PHR magazine, June 2006, "Compression Comprehension", p. 85

spelling