fire slots in piston domes

[toddcalo]

Is there any advantage putting a fire slot in the dome in front of the spark plug, ( the plug is real close to the chamber roof,however heads have been angle milled .200 ) dart iron eagle head with .400 dome ht?

[RT]

If your talking about the Seing(?) groove it's supposed to be in the squish areas not in the chamber on top a dome and the benefits seem small

If the piston dome squashes the area near the plug, the piston will need a little pocket to help the flame start ,look at piston catalogs for ideas

[toddcalo]

No Im talking about the dome where its closest to the plug.

[automotive breath]

Here's some ideas Larry Widmer used long time ago

[FordManVT]

The problem with some domed pistons is that they effectively split the chamber in two. Cutting the dome to allow the flame front to propagate is beneficial.

[toddcalo]

Anybody else have any other coments, thanks

[SStrokerAce]

Yeah put the dome in on the intake valve side and take it out of the exhaust valve side.

[seattle smitty]

Recently looked at an old Smokey Yunick book on building a fast Chevy. FWIW, he said don't bother with fire slots. Smokey didn't know everything, but he got to test a lot more ideas than most of us.

My own guess would be that the effects, if any, of fire slots and Somender Singh's famous grooves would vary greatly depending upon combustion chamber shape and piston crown shape and spark plug orientation, and how they fit each other. Since these shapes and fits have enormous variations, I find it hard to accept the claims of anyone that they work, period, or they don't work, period. Results would surely be highly conditional.

[Hendrens Racing Engines]

We don't build many engines anymore with 23 deg heads but when we did we cut a fire slot in all the ones with a max dome.the only apparent difference with or without was the amount of total timing required.without the fire slot would require 3 more degrees timing to make the same power,if there was any gain it was small enough that the difference would be in the range you would expect dynoing on two different days.Bill

[#84Dave]

StrokerAce has the answer that benefited us considerably with mechanical experiments we ran over a two week period. Particularly with a dome .250" - .500" in height. 'Slope mill' the dome along the pin axis. The outside of the dome exhaust side even with the piston crown. The outside of the dome intake side at near maximum height. Yes, you'd obviously lose some geometric compression ratio. Then take 2°-4° of total ignition lead out of the engine, depending on bore size. You might be pleasantly surprised with the new torque numbers and BSFC. Dave

[automotive breath]

Something like this? I think it came from Larry Widmer.

[jimivice]

At one time the idea of putting fire slots in domed pistons was all the rage.We all clamoured to our local machine shop to have fire slots machined in our pistons "To promote flame travel". Who knows how that theory started but we all bought into it,valid or not. After a time fire slots were no more relevent. Did fire slots actually help? Who knows? At that time I followed suit. Ididn't want to be at a disadvantage in case there was some hidden horsepower. Periodically these old theories pop up and they are given as much credence now as they were "back in the day". Some "old school" guy said this what we did back then,and what was old becomes new. I mean no disrespect because I fit in the category of "old school". Generally, if a piston has to be machined in the area of the spark, it is to clear the electrode. That operation is dictated by a large dome and excessive milling,if there is any gain, it is a mere by-product. I have a tendency to agree with Hendrens Racing. The gain they saw could be contributed to the difference in days. This explanation is in reference to a fire slot. Some other posts expressed severe working of the dome and there is probably a gain. In theory the spark is fired at some time before TDC depending on application. Do fire slots aid in flame propagation? It all depends where the piston is located during firing. Is the dome(during ignition) located to where it is apparent to where a slot is required? It is accepted the less dome the better. Heads are being manufactured with various chambers,and the need for large domes are no longer required. Granted there are applications ,what you have is what you got, and you have to work with it. In itself, will fire slots increase power? Maybe,but so minor, considering it would have to be a neccessity.

[machine shop tom]

Jimivice certainly brings up a good point. How much effect can a slot, groove, or trench have on a combustion burn that starts at 34 degrees before TDC? Enging speed, dome configuration, chamber shape, groove size, etc., will all have differing effects on burn efficiency. What works well in one combination or set of circumstances may actually be a detriment in another. This is an area where one change at-a-time, back-to-back dyno testing is probably the best way to evaluate any possible benefits to changes like piston or head modifications.

Some of the supposed benefits of Sommender Singh's grooves may actually be attributes of other, unrecognized modifications. That's why I believe the jury is still out on Singh's modifications. The same thing probably applies to piston grooving.

I remember seeing the old Crane Fireball SBC heads with BIG, ROUND exhaust ports. Didn't see them any more after flow benches made their way into regular use. I imagine that many of the old, now NEW modifictions will be finally properly tested in proper manners and conditons.

tom

[Troy Patterson]

Seems to me in the race car is about as good as it gets for real world testing.

If a modification allows / requires you to pull nearly 10% of your total timing, I'd figure - that in real world terms, that was a big deal.

Very very few developments results in "big" gains.

I've asked this before, but has anyone ever heard of John Flinchbaugh? He was patenting a piston treatment which reduced timing a full 30% as a result of accelerating the combusrion process - in chamber. John passed away before he finished testing, and I've yet to evaluate it for myself.

P.S., you can do something right with one thing, and scr*w it all up unknowlingly with something you've done wrong with something else. Qualified testing isn't everyone's best characteristic.

Troy Patterson TMPCarbs.net TMP Carbs

[tommurphy73]

Is this the work you were talking about?

http://www.patentstorm.us/patents/6609490-fulltext.html

Regards
Tom