Tuner.. could you elaborate on personal examples?
I'm going off what seasoned engine builders have said and these builders have significant experience with big horsepower blower/turbo engines.

I honestly would like to think that these details of quench would separate a killer engine from average. That it would give me an advantage over someone who just slapped their engine together. But, it appears this detail on a blown application does not bare fruit.

 

What did the F1 Turbo era cars runs for quench?

What do modern record setting turbo motorcycles run for quench?

What do OEM's do for quench on newer turbo cars, say, like the SRT-4?

 

I don't dude. that's the question.
If they are multi-valve heads, then they probably don't have hardly and quench pads what so ever.

Might as well ask me what tire pressures they were running on the transport vehicles that brought them to the track.

I believe the srt-4 has a no quench from what I remember reading. If you look above, you will see I'm currently on the side a wide quench.

 

would it make any difference if youu were using a thicker headgasket to git you .50 thousands? my flat top comes out of the hole .010 and i ordered .060 thick head gaskets.
Thanks, Matt

 

The F1 turbo cars ran quite a bit of quench. The engines had some where around 7:1 to 8:1 compression ratio. Boost pressures were between 50-75 psi and I'm not sure what rpm they ran at or up to. The F1 problems were complete burn at higher rpm and toluene as fuel helped with this as well as the high pressures.

I am not familiar with the turbo motorcycles, but am interested. Don't they use a twin swirl style chamber?

The SRT-4 uses a small quench area (.015?), but the forced induction and piston design have a large impact on the combustion process.

I hope I am not too far off on this as I am going from memory or what little I have left.

Sean

 

Good info guys. Tuner on your .005 per inch of bore diameter rule...I come up with .0225 for my 4.5" bore 557 bbc. Is that right? I've found .027" head gaskets, that would put me at .052.

 

You need to be very careful on how you read these dimensions on quench.

1) Say you have a steel rod that will stretch ~ .040" in length at high rpm. You also have a Zero Piston Crown Height to Block Deck Surface dimension. You would need about a .043" crushed thickness head gasket to keep from banging the pistons into the head. Gaskets do not crush EXACTLY to .043" so you will be very close to running into the head assuming the .040" rod stretch.

2) Say you have an Aluminum rod that will stretch ~ .060" in length at high rpm. You also have a Zero Piston Crown Height to Block Deck Surface dimension. You would need about a .065" crushed thickness head gasket to keep from banging the pistons into the head. Gaskets do not crush EXACTLY to .065" so again you will be very close to running into the head assuming the .060" aluminum rod stretch.

3) If the MAXIMUM quench distance, per Taylor is .005" per inch of bore and you have the mentioned 4.5" bore, as was said you could potentially run .015" "down in the hole" with the .043" gasket and be close to Taylor's maximum distance from the head for a good quench dimension: .040" + .0225" = .062"

Again, you must take the rod stretch factor into the quench/ head gasket calculation. (or you will be sorry!)

Tom Vaught

 

None of those examples had any quench by our standards.

The SRT4 is .200" down the hole.

 

SRT4 pistons are also domed...not dished or inverted...

 

The F1 turbo engines; how did they have nearly no quench with such a low static compression ratio?

 

My guess would be the Pent Roof, 4-valve, small bore and superior port design might have had some impact on that capability.

Tom Vaught

 

My apologies Tom. I should learn to be more specific. Although I did not know the head and chamber design for the old F1's, I wondered if it was piston design that lowered the compression ration so low.

 

interesting read on compression and boost.

http://www.zzw30.com/HondaRA168EEngine.pdf

 

I also don't see how any of all those examples have a bore over 4" or 2 valves per cylinder.

 

Appreciate the response and information.
What are the specs on that mustang?

Your explanation is pretty much exactly what I found reading other sites other than the dimpling procedure.

Would love to hear some more first hand accounts of before and after dyno tests.

 

I underlined your last paragraph hoping you can take a minute to expound upon the "no fly zone" specifically.......
When you say between .050-.180 are you referring to static quench, or dynamic quench? My interest is specific to a 4" bore pump gas engine. It is 10.2-1 static as is, piston .020-.028 in the hole with a .015" steel shim gasket, old gm 113/zz4 58cc chambered heads. I would like to lower compression, with chamber polishing, valve un-shrouding and a taller gasket I can get it to just under 9.8-1, but quench would be closer to .050 would I be better off keeping quench tight? Pump gas deal, not chasing a number; just 5-9 psi. Obviously custom pistons would be the best scenario, but not in the budget. Interested in your thoughts on optimizing what I have, some have said keep the quench super tight, even as close as .025-.030 provided the engine will never see over 6000 rpm, and just do the best I can to remove sharp edges, polish the entire combustion including piston crown.

Aside from polished chambers, smoothed valve reliefs, and matching the open part of the chambers to the bore to increase volume my only option is increasing static quench with a thicker gasket, but do not want to do so if the tuning window will get smaller. So do you have any advice? Read an old post where a guy mentioned taper cutting the quench pads on a nitrous engine to slow down the burn. Wonder how that would work with boost? Thoughts, comments, suggestions?

 

Since @tuner hasn't been on in 5 years I will express my opinion:

Quench matters a whole lot less in a boosted application. Stick in the gasket that is going to get you the compression you want and call it good. Softening the chamber, grinding out any hotspots will get you a bit of forgiveness under sustained load.

With aluminum heads and decent fuel just softening the chambers may get you where you need to be, depending on how much material you are taking off. I wouldn't be scared of running 5-9 psi on a ≈10:1 aluminum headed engine. The cam will make a difference as well.

 

I talk to Tuner 4 or 5 times in a month. He is working on an early Jaguar vehicle with a newer V-8 engine and a Vortech Supercharger. A good friend used to own the car. He is busy.

I do not post much here but do read the posts.

The fuel used will make a difference too. A Pontiac friend makes 800+ hp with a 206 cid 1963 Pontiac 4 cylinder engine (1/2 of a V-8) at 42 psi using E-85 and modern engine controls.

For a street car running 5-10 psi, you have a LOT of wiggle room with the engine parameters.

Tom V.

 

Would it be a safe & reasonable presumption to stay on the tight side for maximum detonation suppression and the widest tuning window possible when using inconsistent pump fuels? .032-.041 on a four inch bore with hypereutectic pistons and steel rods? seems like if i cannot get it that close the better option is to open it up a lot.

The more I read, and try to learn the more respect I have for oem combinations. the development time for a typical engine must be 40 hours a week for a year, under every worse case scenario imaginable to get the power, drivability, and reliability they get out of modern efi engines. Also Makes it clearer why some aftermarket crate builders will offer a pump gas efi package with x amount of power for the prices they do. after months of reading, the prices they charge with a guaranteed result and warranty are really good for the typical street enthusiast. on the surface the combos seem overpriced and mediocre performing, yet when you set out to duplicate it it is very easy to spend more and get less performance, less reliability.