Alright I have been reading about this for a little while now. Now I want to make clear that if anyone is going to chime in with "half a CR point doesnt matter" or "its only 3-5hp" this is not a question for you.

I have a 370 iron block with forged internals. Ring gap has been set up for nitrous. Pistons are .008 out of the hole. Heads are 64cc. Im trying to figure out what thickness head gasket to go with. From what I have been reading .035-.040 seems to be optimum quench.

I was originally going to find a head gasket with a compressed thickness about .045 which would give me a quench of .037. Since im running nitrous (100-150shot) should the quench be greater because of the increased fuel and cylinder pressure? The cylinder still needs enough time to ignite the fuel so would shortening that burn time by closing the quench be a good idea with nitrous?

.045 headgasket for .037 or
.051 stock headgasket for .043

 

Halfa point of compression won't really make that big of a difference. Lol no, but seriously I'd go with the tighter quench and run the .045" gasket. With the n2o and increased cylinder pressure the tighter quench will really help you control the burn and reduce the chance of detonation. On most of the builds I do personally I try to get as close to .035" quench as possible. The tighter you go the more power you can make, but you run more of a chance of the piston crashing into head face so .035" keeps good and safe

 

Thank you! Thats exactly what I was looking to hear, except the half a point part lol I thought that most guys go with a bigger quench when running a 300 or larger shot or multiple stages of nitrous, but i wasnt sure if it was still the case on a smaller shot. Thanks again. I guess cometic will be the way to go.

 

I would like to hear more people chime in on this. I am in the middle of a 408 build as well. I have spoken with Wiesco and they actually suggested .045~.050 quench. That was a little dis-hearting, since I had already purchased my cometic gaskets. According to Wiesco the pistons "pop up" .010 out of the block. My heads are 59cc chamber patriot performance. With that said the quench on my set up would be closer to .030~.035. So darn confusing!!!!!!!!!!!

 

Bans are you sure that they didn't recomend .045-.050" gasket thickness?
In my opinion I can't see any advantage at all to running .050" quench.

Just for your info, on my 408 I'm running 57cc chambers with a -4 cc dished piston to get 12.5:1 compression, but running a 255/271 cam that drops dcr down to a very pump gas friendly 8.22:1

 

Wiseco prolly doesn't want someone coming back to them later saying "There are marks on my piston crowns and you said my quench was OK!"

 

Yeah, I can see them wanting to go safe with their recomendation. I will more than likrly proceed with the build with what I already have.

 

0.035" quench for me = 660RWHP on a stock N/A pump gas short block!

 

My God man! What size cam and how fast are you spinning it?

 

Just a tiny 258° @ 0.050" intake solid roller cam at 7400RPM! Read all of the details about it here:

https://ls1tech.com/forums/dynamomet...92-octane.html

 

Couldn't have said it better myself. Good advice man!

 

I have just discovered another issue with quench. What about connecting rod stretch? Im being told now that I cant go that tight on quench until i take the rod stretch .070-.080 into consideration? That totally changes the equation and has me thinking that stock gaskets are going to be the way to go. Im not sure about this now?

 

Unless you have aluminum rods, .035 to .040 quench is perfect.

 

Depends on the amount of nitrous.

If it's under 250-300 keep it tight. I shoot for .040-.045 in most street/strip N/A builds. In engines that have decent compression and will use 250-300hp worth of nitrous I shoot for .045-.060 depending on valve angle and combustion chamber characteristics.

If it's a race build with 12.5:1-13.0:1+ compression and 300+ nitrous I shoot for anywhere from .050-.100 quench.

My 434 LS2 14.2:1 LS3 headed engine that will be sprayed with 300-500hp of nitrous(mainly 300) will have a quench of .062. Mainly because it will be run in a jet limited class that limits jet to .082n.

I see it like this, you want to control flame front speed with variables that you the user can control like air fuel ratio, ignition timing and the amount of nitrous jet used. If you have a mechanical variable like really tight quench that is speeding up the burn rate and flame front speed and you have no control whatsoever of that aside from tearing into the engine, it will make tuning on large shots of nitrous and high boost much harder and a much narrower line has to be followed to not create an ashtray factory out of your engine.

Think of tight quench as a coffee can full of gasoline that you baseball pitch at a camp fire, when it hits that fire, all hell is going to break loose with fire immediately flaring up much faster and more violently. This is from mixing air and fuel much more thoroughly right before combustion takes place. Tight quench "squishes" air/fuel mixture together and mixes it much more efficiently to the point where less timing is needed to achieve the same amount of power because the burn has been sped up that much faster.

Now think of loose quench as that same coffee can full of gas that has been slowly poured on a camp fire. It's going to flame up, but not near as quickly and we can control the burn ourselves by how fast or slow we pour it into the fire. This is how I see tuning on large amounts of nitrous and boost. When you have nitrous which is an oxidizer, speeding up the burn rate inside the combustion chamber you don't want other factors speeding that up even more. Same goes with boost, but to a lesser extent as it isn't an oxidizer that is speeding up the burn rate in the chamber.

Hope this clears up the "tight quench vs. loose quench" eternal argument.

 

Scat H beams so Ill be fine. Ill be ordering the .045 gasket. Thats pretty much in line of what I was researching but trying to put truth to 5 different resources is tough. I really appreciate everyone taking the time out to give your expert opinions. Another reason why this forum is the best!

 

No problem.

 

Martin,

I get what you are saying, I would assume that there are many factors that come in to this though. Fuel used, chamber design, piston design, compression ratio, and so on. No I don't build motors for a living, but in some ways, doesnt high amounts of lead in timing (advance) also reflect on a less efficient combustion design. IE you need to start the burn sooner.

I do get what you are saying though, by being less efficient, it gives you more resolution in tuning timing. IE 2* of timing in a very efficient set up would have more effect than in a less efficient set up. It then gives you more leeway all changes being equal.


Another thought, the old idea of 2* timing for every 50hp of n20, is that for a larger quench or a very tight quench? I would assume that would change quite a bit on a motor that is set say at .035 vs .060 or even .100.

 

Exactly. Couldn't have said it better myself. In a nitrous app, you're better off decreasing the efficiency of the chamber, for tuning purposes. You can always "tune in" that few HP you may be giving up by dropping a tenth in compression, or from decreasing the quench. Anything you can do to make the chamber more "lazy" will benefit you when it comes time to tune it. Decrease the quench. Put a dome piston in it, anything.

 

Very true, I would say its just a guide to what will be close.

 

Thanks ed! Coming from you that means a lot!