355 quench and compression [Archive] - Team Camaro Tech

: 355 quench and compression


FlapsFive737
Oct 9th, 00, 11:04 AM
This will be rather long winded, so please bear with me..

I am currently in the planning and machining stages of a street 355 engine for my '69. 4-bolt, stock rods and crank, cast FM pistons.

I would like to build a motor that has a much compression as is practical with 93 octane pump gas. The research I have done so far indicates that for iron heads, 9.5:1 is tops, with 10:1 acceptable for aluminum. Avoiding detenation is a must.

What my real question concerns is the quench. After mocking up the motor, I found that the piston is .035 down in the hole at TDC. I have read the engine building tips on the Speedomotive sight, and they (along with others..) indicate that .035-.045 is a desireable figure to avoid detenation. Just how important is it to stay within this range? I have several head gaskets to choose from in the market place, but even the the smallest compressed thickness I have found, at .015, gives me a quench of .050. I know that I can have the block decked, which would give much more of a selection for gaskets, but that will raise the compression, maybe to an unaccecpable level. I haven't purchased my heads yet, but I'm leaning toward iron Sportsman II's. I would like to be able to use the 64cc version, but that would mean not being able to deck the block in order to keep compression manageable (9.5:1), and the quench would be all wrong. If I 0-deck the block, I would have to use the 72 cc heads, but all the numbers (CR AND quench) fall into place. Does anyone see any advantage, or disadvantage of the 64cc head vs the 72cc?

This car will be used for cruising, and stoplight to stoplight, if ya know what I mean! Definitly not a daily driver. The rest of the specs as follows:

Holley 750vs, PerformerRPM intake, CC XE268 or XE274, HEI ignition w/ 6AL box, 1 5/8 headers, TH350 /2500 stall, 8.5" 3.73 posi.

I have already searched and found some posts regarding the quench debate, but I thought I would ask for a little more input.

Thanks in advance for the help!

Steve

FlapsFive737
Oct 9th, 00, 11:10 AM
Sorry about mispelling DETONATION! I must have taken my dumb pill, instead of my vitamin this morning....

IgnitionMan
Oct 9th, 00, 12:07 PM
What more do you possibly need? .040 to 045 will give the best detonation tolerance, timing lee-way, best tunablilty and allow you to use pump fuels up to 10.00:1 with iron heads, 10.50:1 with aluminum heads.

Less Quench will push the mixture from the quench areas, allowing hot spots and detonation, loss of tunablilty and performance.

Too large quench has the same effect, only by allowing mixture to migrate out of the quench area.

Deck the block.

Galen W. Rouse
Oct 9th, 00, 12:36 PM
Steve, Ignition Man is right on the quench thing. Definatly in your case, deck the block to 0 and use a 1003 Felpro Gasket. Thickness is .039-.041. The 72cc head is fine. The quench area is the main factor to look at. The .015 Gasket you are looking at is not good for your app. The head/Deck would HAVE to be perfectly level with a good finish. Even then seepage may happen. They are realy for race motors that you have to keep up with more so than a street motor such as yours. The Comp Cams High Energy series is a good cam choice for the street. I use Hyd. roller for the street below 6000 rpm. Good power curve across the band even w/ low duration numbers. My nickels worth Galen

------------------
S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
smog legal
Camaro Lover

FlapsFive737
Oct 9th, 00, 12:39 PM
Thanks for the input, IgnitionMan. I had pretty much resigned myself to fact that I'll have to deck the block. In your opinion, then, 10:1 for iron, and 10:1 for aluminum, is not too high for the CR? And what about the differences, as expressed in my post, between the 64 and 72cc heads? Any thoughts on that matter? Does the smaller chamber effect anything besides CR. I know about runner size, and how it affects the HP and torque curves, but I've never seen anything about the actual chamber size and how it effects, or even if it does, the curves. Maybe I'm just putting too much thought into this (as some of my friends are saying, JUST BUILD IT!!) I haven't assembled an engine in over 25 years, and I just want to do it right, with no surprises. Hence my request for additional advise. Thanks again.

Steve

FlapsFive737
Oct 9th, 00, 12:46 PM
Thank you too, Galen, for the response. I have a friend who runs Sportsman II heads, and he builds alot of motors. He seemed rather upset that I would even consider the 72cc heads, but was at a loss as to how the smaller head could be any better, or worse, than the 64. My thought is that the chamber size only affects the CR, and not the power curves. But hey, I'm not a proffessional engine builder, and probably only know enough theory to get myself into trouble!

Steve

Steve

Galen W. Rouse
Oct 9th, 00, 01:29 PM
Your welcome Steve, You are right about the larger chamber. I have not seen where there is a power loss with the larger chamber. The compresion ratio and quench are the concern to you in a street engine. Also polish off any burs or sharp edges on the pistons/combustion chamber.as this will help eliminate hot spots. And also, as Ignition Man said, The curve in the distributer is very important to both power/torque and detination resistance. Make sure it is good mechanical shape and run as much intitial as you can (about 14 to 16 on the crank). and have it come in about 1100 and all in by 2600. Have the curve rise quicker from the bottom of the scale so that most of the timing is in by about 2000. You could send it to him at his place in Whitier and have him set it up. He also converts the point distributers to the Ford mag pickup set up to run w/your 6 series MSD. Same thing MSD uses, only less money spent, f/the same performance. Depending on your tire size, with that gear you will be around 2100 to 2300 around town (30 to 45 MPH). Freeway is about 3000 to 3300 at 65 to 70MPH. (that is where my 79 cruises at w/ the 265/60/15 @27" tall) Galen

------------------
S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
smog legal
Camaro Lover

pdq67
Oct 9th, 00, 04:23 PM
FlapsFive737, Galen and Iman,

This falls right into what I tried to get a discussion on a while back --- namely the Pop Hot Rodding articles that say that it's possible to build high compression engines like from days of yore, but do it the modern way to beat detonation and stuff. This also gets into the fueling head thing, right Iman,??

The Pop Hot Rod article says to take a 58cc small block head and plane it .100" to raise its CR. Use it with a true flat top piston with needed valve reliefs to come up with 11-11.5 to 1 CR or more. Minimize the deck height for minimum quench dimension and run up to a 230 degree cam on 87 octane fuel and get away with it.

What does everybody think???

PHR went on to say to do the same thing with a big block but use a 98cc closed chambered head planed .100" and flat top pistons to come up with 11-11.5CR. They said that it works for Fords as well.

Come back please and discuss further. pdq67

tom3
Oct 9th, 00, 04:55 PM
I haven't seen all that many engines, but I've never seen a .035 deck height. Are you sure the mock assembly was correct? Not so sure I'd cut to zero deck height either. Leave some for later machining/line boring. The open chamber heads will often breathe a little better and make the same power as the smaller chambers.

IgnitionMan
Oct 9th, 00, 05:26 PM
Quench distance being right will make an engine, off will kill it.

Years ago, engineers foound the proper distances for steel rod engines were the aforestated .040/.045. If yiou look at most performance engines fromk the musclecar era, you will find the pistons down in the hole about .022/.025, not a bad thing or wrong, considering the head gaskets were .020 compressed steel, giving the proper .042/.045 quench neded.

Only problem with quench arose from later pack type head gaskets. They seal well, are nicer to use, don't require a dead straight deck/ head surface, as Galen pointed out, but wrecked havoc on proper quench distance. In the beginniing of the quench/pack gasket times, gas was much better, and power loss from incorrect quench wasn't as noticable as is today.

Only time quench rules are altered is for aluminum rods/very high rpm engines, 12,000 rpms and above (steel rod Indy and Formula 1 engines). And, even then, the quench comes back to the same level as a .040/.045 engine after the added stretch is developed.

In motorcyle engines, both 2 and 4 stroke design, quench distance is called squish clearance, and is as vitally important as it is in our engines.

Even today, companies like Silvolite have pistons for regular replacement they call "de-stroked". These pistons are not altered in the stroke, which is determined solely by the rod throw distance on the crank, but have altered compression heights. Compression height is the distance from the flat deck of the piston to the center of the wrist pin. Normally, the average 265 thru 350 small block Chevrolet engine will have a 1.560 comp hgt, "destroked" will have 1.540 distance, for a .020 lower deck as measured in the same block.

If we look at the average 1.560 piston, down .025 and with a pack type .040 compressed thickness head gasket, we get .065 quench distance. With a "destroked" piston of 1.540 c/h and the same .040 pack gasket, the qusench goes to .085.

It is easy to see that quench can make or break performance in an engine, even in a stocker too.

[This message has been edited by IgnitionMan (edited 10-09-2000).]

Galen W. Rouse
Oct 10th, 00, 12:56 PM
To get the quench into the .035 range the block needs to go below 9" if using the pistons made by TRW/KB/and the like. They do run .015 to .025in the hole. They do this for the installion by someone that does not intend to check clearences/blueprint specs. The Silvolite claimer pistons do run at 0 ( the full 1.560 on a 350) as do JE/Wysco/Ross forgings. To get piston need to run .005 out of the hole. It's fine to do that as long as you use the .041 gaskets out there. That actually is o good way to go, I have seen torque increases this way. Like Ignition Man said too, the aluminum rod is a different ball game with numbers. They come .010 shorter as is (5.690 is a 5.7/5.990 is 6.000) The strech is a factor to consider, although todays rods are much better, and as long as they arn't twisted to the limit all the time they do retain length better. As far as that PHR deal on the 11.0:1 pump gas motors, That is debatable. These were very controlled circumstances in all aspects. They went fot the proper quench which in it's self is more forgiving to a point. Then you have to consider the various grades of bear **** at the pumps, given variable temps. and depending on location,humidity,elevation,variations in an ignition sytems,changing cam timing as the chain and parts wear, carbon buildup and on. So, unless you have full control over every one of these factors, leave those things to the editors and the companys that want there name in the lights. I don't see it in the real world. There will always be exceptions to the rules though. Anyway, my nickels worth and I'm back to the Salt Mines. Galen

------------------
S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
smog legal
Camaro Lover

pdq67
Oct 10th, 00, 01:54 PM
Galen,

Thanks for coming back and saying something.

The only thing I have to say about the PHR story is that Fueling is selling his high compression heads to go on trucks that will take more of a beating (although at lower rpm's) then most built street engines and apparently he's not worried about the things you mentioned.

I wish I could afford to build one of the engines PHR said can be built and successfully ran on 87 octane gas just to see if it works or not. If it works, on a 8.5 to 1CR big block built to 11.5 to 1 CR spec's I would gain something like 10 -14 percent more power alone due to the jump in compression which is good to me. Lets see, 400hp x 1.14 = 456hp (56hp more).

If it doesn't work, I would stop and change heads before detonation tore it up, and still have a pretty good engine. pdq67