Quench

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Brambles

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My engine is suppose to have a .040 quench with magnum heads and KB362 pistons, can I run a thinner headgasket to get my compression up a little more? MP makes a .024-.028 headgasket.
 
I wouldn't Brambles. .040 quench is ideal for those heads. If you run a thinner head gasket you will risk having the pistons hit the heads due to rod stretch at high rpm's.

Jack
 
You usually want at least .030" clearance so any closer you will risk contact.
 
I'll just get the head milled once I pull the engine, only looking for half a point in compression to take it up to 10:1.

Plus you guys are saying a .040 quench with magnum heads are really resistant to detonation, unless I run 93 octane it pings at 9.4 - 9.5:1 mind you I"m running a small Comp Xe in a heavy pickup with tall gears so once I stick it in a light car with good gears, higher stall and a bigger cam it should smarten up.

Plus I might be robbing my intake charge with my Exhaust and running a lean condition. I ported the exhaust more than the intake and with these heads that might have been a mistake, especially since the Exhaust duration on this cam is 6 degrees @ .050 longer than the intake. I might actually need a cam with a shorter Exhaust duration than intake.
 
Milling down the head will be the same as running a thinner gasket and youll run the same risk of not enough clearance.
 
Dare Devil, the head didn't get any closer to the piston, but more so the valve when opening.

Brambles, it's the combo you have and in a heavy truck. Thats why it pings. Where and how is the distributor set up?

Whats a small Comp Cam?

On the head, unless you went overboard of the exhaust port, you'll be OK. It's not as much of a problem as you may thik since the exhaust port is the biggest resticktion and is the port that needs the most improvment to reasch a better balance in the heads.
 
rumblefish360 said:
Dare Devil, the head didn't get any closer to the piston, but more so the valve when opening.

Brambles, it's the combo you have and in a heavy truck. Thats why it pings. Where and how is the distributor set up?

Whats a small Comp Cam?

On the head, unless you went overboard of the exhaust port, you'll be OK. It's not as much of a problem as you may thik since the exhaust port is the biggest resticktion and is the port that needs the most improvment to reasch a better balance in the heads.
Click to expand...

The cam is a XE250H 206/212 @.050
As far as timing, its been a few years since I've toyed with the timing, I parked the truck and start it regularly but I've forgotten those details. IIRC the total timing is backed down to about 30 or 32 degrees but the advance might still be coming in a little quick for the heavy truck.

I'm not going to fool with it in the truck, the engine is coming out and going in my Dart after a few modifications.

The heads are magnum heads and the exhaust flows at a good percentage out of the box, opening them up even more and running a cam with more duration on the exhaust than intake isn't going to help matters much.

I think with my new cam I"m going to try a single pattern cam.
 
daredevil said:
Milling down the head will be the same as running a thinner gasket and youll run the same risk of not enough clearance.
Click to expand...

No milling the head will not change the quench area. It will reduce the volume of the head's chamber so the piston to head clearance will stay the same assuming he uses the same thickness head gasket.
 
anyone know the milling specs on magnum heads. ie how many thou per cc to give to the machinest. I have the specs for non-magnum heads but I think the closed chamber heads would be different.
 
When you built the engine, did you check piston/deck clearance? if your pistons are .020 in the hole, with a .040 head gasket your piston to head clearance may be in .060 range, explaining your detonation problem. You want .035 to .045 for the quench effect to quell detonation.

That's a pretty short duration cam to be running that high of a compression ratio in combination with tall gears, high weight and large tires.

i wouldn't worry about over scavenging either with the longer exhaust duration. It just allows you to run a quieter muffler. Magnum head exhaust flow isn't that great to start with either.

If you plan on increasing the comp ratio, you really need to add a bigger cam, whether you drop this in the Dart or not.

It's all about the combo.
 
rumblefish360 said:
Dare Devil, the head didn't get any closer to the piston, but more so the valve when opening.

Brambles, it's the combo you have and in a heavy truck. Thats why it pings. Where and how is the distributor set up?

Whats a small Comp Cam?

On the head, unless you went overboard of the exhaust port, you'll be OK. It's not as much of a problem as you may thik since the exhaust port is the biggest resticktion and is the port that needs the most improvment to reasch a better balance in the heads.
Click to expand...

Magnum flow balance out of the box is 75%. The intake is the worse of the 2,having a lump in the roof for the rocker bolt and a narrow pushrod pinch. The exhaust is pretty good. Valve guide boss is the worst part and it's an easy fix.
 
Done all the calculations works out to be 9.46 or something like that. I am trying to figure out how much to mill the head to bring it to 10:1.


The engine is 0 deck
 
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