quench effect on blower motor
 

I am trying to find the truth on the quench effect on blower engine and is still confuse me.

Someone say the perfect quench for n/a motor is at .040'' to crate turbulance (flame front) and also they are say this is the perfect # for blower engine also.

On the other hand someone say on a blower engine it is not so important to maintain a .040'' of quench and i notice that they have some engine run with as much as .100'' and more of quench on boost engine and someone say that is ok because the a/f mixture are in turbulance in the combustion chamber on boost condition that turbulance are need to help to burn all a/f mixture.

We need to consider that the detonation is an effect at ATDC and pre ignition a effect at BTDC and they are cause by detonation because detonation make hot spot in the combustion chamber.

So if i understand right a smal quench # are use to make turbulance and make a more efficient mixture burn to get to a no a/f mixture for the rest of the stroke (ATDC firing) Thats help for detonation occur.

Pre ignition occur BTDC and before spark firing due to hot spot in combustion chamber (due to detonation event) at inlet stroke,
In blower engine they have more hot inlet air and more cylinder pressure, as wee know all is there to promote pre ignition.

I am not an expert so if i am not right corect me, I just trying to understand the squich effect on boost engine vs n/a engine.

So which quench is promote to make the burn faster .040 or
.100'' ?

Don't know the answer to your question but I'm running .040 quench my blower engines.

Quench (a tight squish) is an excellent thing to have on any motor that has to run on marginal octane.

Quench doesn't necessarily MAKE extra power, but it "snuffs" detonation from the outer edges of the combustion chamber, and creates turbulence that makes it less likely for detonation to occur in the center of the chamber. This "stretches" your octane and lets you run closer to the detonation line.

A 8:1 N/A motor will run fine on pump gas, with full expected timing advance (36*) with no quench (squish clearance more than .070" is essentially "no quench").

Push that motor up to 10:1 (still no quench) and you are gonna start fighting to keep the dreaded knocks away. Same 10:1 motor with .038" quench will have no problems - even on up closer to 11:1 with the right cam.

Blower motor same thing. Many people lower their compression for blowers, and that's fine but you STILL want to match the deck heights and such to keep a tight squish with the piston and heads you've selected. Sometimes if there's not the right piston available, you may have to get a custom. BBC and SBC are pretty much available in every sort of combination you can think of, but if you are running a 360 Mopar, you can find it difficult to match a target CR with your preferred squish.

Squish/Quench is good for any motor - especially blowers.

How about this? If, on a NA motor, .040 is good quench; Then on forced induction, when you pack twice the A/F into the cylinder, why wouldn't .080 be the same?????

Can we can get the same effect of quench on a open chamber head style?

I am ok with you for a tight quench on n/a engine to make that turbulance need to help to avoid detonation, I have make some recherch on the net on that question on boost engine and they have 50% of peapole still run .040'' quench and the other 50% peapole say that is not so importan in boost engine
that in n/a engine and they run at more quench like .100''.

So i am still confuse on that for my built and even more with open chamber head style.

mcollinstn has it right

The actual clearance when running is much less than the static clearance. After the piston grows from heat, rocks in the bore a little, and the rod stretches a bit at RPM the piston is close to kissing the head at .040 - which is actually a good thing.

We used to run a reverse dome (dish) if needed to lower compression that mirrors the combustion chamber to leave the quench area intact as opposed to just increasing the deck clearance.

Here is a good article

http://www.chevyhiperformance.com/te...e/viewall.html

From the article: "According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch. He has built engines with far tighter clearances than this, but much of this depends on the piston-to-wall clearance. All pistons tend to rock slightly as they transition through TDC and this rocking motion reduces the piston-to-head clearance. Smaller-diameter pistons with tight piston-to-wall clearances don’t rock nearly as much in the cylinder bore compared to larger-bore pistons with wider piston-to-wall clearances."

My normally aspirated 489 has the piston .008 in the hole, and I was planning to run a set of Cometic head gaskets with .030 compressed height for a quench of .038. I was running a set of Fel Pro's that were .039 previously, but I thought the tighter quench would be beneficial. This article makes me wonder if I should go back to the .039 gaskets for a quench of .047. Pistons are Mahle flat tops with a 3 cm single valve relief.

Thoughts? Oh, sorry for the :hijack: :)

You know what opinions are like .. .040 is what most builders will shoot for .You want the quench area almost kissing........
Maybe Ken was talking about tightest quench for those that aren't real good with math, measurements and machine work

Kind of what I thought. When I measure deck height (how far down in the bore), do you take the measurement closer to the intake side of the bore, close to the exhaust side, or more in the middle? Logic says in the middle, to address piston rock, but want to be sure. I don't have a depth gauge, just a Mitutoyo dial caliper with a machinists rule on it that can check depth to some degree. Thought about zeroing a dial indicator on the deck and then swinging it over across the bore, but not sure if I could maintain accuracy.

From what I've read on drag racing web sites, you want to run a tight quench on n/a and supercharged motors up to about 15lbs of boost. Over that and on heavy nitrous motors, you want to open up the clearence to slow the combustion process. Quench causes turbulence which speeds up combustion and that is a good thing for detonation control up to a point. Beyond that point it increases detonation. Also, there is a zone of clearence from about .060 to .100 that is supposed to be avoided at all times as this will increase detonation.

I run about .050 on my blown 468's. One block came in around 0 deck, and the other around .008 out of the hole. so engine 1 got a .051 HG, the other a .060 HG.

http://www.competitionproducts.com/P...uctinfo/66798/

Well, considering that mine is a NA engine with only about 8.7:1 compression and a max RPM of about 52-5400 RPM, do I stay with the tighter .038 quench, or go with the greater safety margin of.047? One of the reasons that I wanted to go with the thinner head gasket was to get my compression ratio as high as possible, considering that I am struggling on that front to begin with. But now I am wondering if I am exposing myself to risk of damage.

I'd stick a standard .039 head gasket on a call it a day

agreed

The word quench comes from the idea that the top of the piston is cooled (quenched) as it stalls at the top of its stroke and is in near contact with the head. .038-.040 is where I like to put them even though it is said you can go tighter. I like a little margin in case the engine gets over revved. I don't see how this cooling effect is not good n/a or boosted.

Not trying to completely hijack the thread, but wondering if deck height measurement is always taken along the edges of the piston. I don't have access to a depth micrometer, so I tried measuring it both with the straight edge / feeler gauge method and with a dial indicator. In both cases I noticed that the top of the piston (Mahle flattop) has about .001 crown across the middle. I assume this is normal, and that the high point will be inside the combustion chamber so clearance at this point is not an issue, right? How far in along the edge do you want to take the measurement - half inch or so?

Thanks.

I take one measurement on each side of the piston parrellel with the wrist piin, then I average those two figures. I always use a depth micrometer.

Last year i have run my blower engine at .050, this year i will try to close them to .040 after some research it's look like that is the way to go.

At .050 last year i get some sing of detonation after a wot run, when i shut off the engine the engine still to make some explosion without ignition but i need to say that i haved projected plug when that symptom occur.

So at .050 with non projected plug do you have nitice that symptom?

I am pretty sure the plug was the cause over the quench in my situation.

Nothing like that here. Sounds like it was "dieseling'' on you. I'd definitely look at the plugs.

What plugs are you running??

I run the piston .005 to .007 out of the deck of the block and use a .039 or .040 gasket. That gives you .032 to .034 clearance. If you tell some of the sprint car guys that you need a quench distance of .040 they are gonna look at you like your crazy. They build there motors much tighter and the guys that really know what they are doing can just barely get the pistons to touch the head. The key is to squeeze the air and fuel out of the quench area into the combustion chamber. The theory on the quench area is starting to change though. Pistons are being made with inverted domes and a couple degrees of slope to push fuel away from the quench. Your real big motors have the pistons in the hole up to .200 thoose real big motors are also running 0 degrees of timing to get them to live...

I start with ngk bcpr7es and finish the year with ngk r5671a-10.