Low Miles Headwork Questions

[Williboy]

Would like to run this by the experts before I pull the trigger;

I had a couple leaky freeze plugs on the head so I decided to pull it to repair and while at it check the compression The head is a C9DE-6090-M with 1.39/1.75 valves, hardened seats, 3 way valve grind , new guides, etc.... We also 0.0" decked the block. That being said, we only resurfaced the head. ( The guy who rebuilt my motor was very knowledgeable with motors just not an expert on these straight sixes) So I tested the chamber CC and came up with 58cc. Doing the math on a couple compression calculators (bored 0.060, .045 gasket, 0.0 deck, dished pistons, ) I have 8.7:1. A little to low, from my understanding.

So my questions are: After doing the reading, I'm thinking I should be around 9.4:1. ?? Which would mean I would want to have a 52cc chamber and need to mill off .030 ?? Is this all correct?? Also why does all the online compression calculators come out about the same ( 8.74 +/-)) except for the CI chart??? (8.53) Since I only have 20,000 miles on the motor since it was rebuilt, Is there anything else I should do to the head while it is off and at the shop??

PS. I noticed my muffler is starting to rust, so while the exhaust manifold is off, I REALLY would like to get some headers Any final word on those Speed Daddy headers???

Thanks!!!!!!

 

[CZLN6]

Howdy Back Williboy:

First, a couple of questions; What cam are your using? I don't recall your entire package for this engine. Carb, trans, rear gear, intended use?

Your figures sound about right to reach your goal. A little more compression would help. I'd be a little concerned at your low elevation though. If you have a stock cam I'd shoot for 8.75:1 to 8.9:1. If you have a cam with more than stock duration then a goal of mid 9 is reasonable. Of course what transmission and rear gear at also factors.

You mentioned a three angle valve seat. I'd add a 30 degree back cut on the top of the intake valve faces to help with lower level valve lift flow. Inexpensive and effective.

In in the same boat as you on the Speed Daddy header. Hopefully someone will come along soon with some first-hand experience with them.

I hope that is what you needed. Keep us posted on your progress.

adios, David

 

[bubba22349]

you might measure the carb opening of the head checking that it's at least 1 3/4 inch or more. Did you do any porting to your head and blending of the valve pockets? Good luck

 

[Williboy]

I think the cam he put in was 264?? I don't recall, it was a long time ago ( Unfortunately the car sits in the garage more than it should, but at least I still have it after marriage and a kid!!) I have a C4 tranny with a a Maverick 8" with 3:00 gears. The carb opening is the 1.75" flat log. I'm running a Holley Weber 5200. and just installed a recurved DSII from wsa11. I don't think any porting was done, just the standard head rebuild. Both the mech and machine shop do quality work, they just didn't know the particulars about these motors/heads.
.
One part of me "wants to mill, port, grind the carb opening, headers, adjustable rockers, etc.." and the other part is saying " just fix the freeze plugs and bolt it back up and be done with it" I just don't want the compression so low that it's a waste of what I already have. ( carb, cam, DSII, etc...)

 

[CZLN6]

Howdy Back :

An additional mill of .030" is a go, and while the head is apart for the milling, ask the machinist to back cut the intake valves. It shouldn't add more that a few bucks per valve and worth the extra flow. With a C4 and a 3:1 rear gear, low rpm flow will be needed along with the extra CR.

Let us know how it comes out.

Adios, David

 

[bmbm40]

That is a tough decision to make. If it was my vehicle it would be based upon if I was somewhat satisfied or very satisfied with the current performance. And that most likely the motor would not have to come apart again for repairs until time to rebuild we hope. If somewhat satisfied the reasonable amount of money for the items suggested by Dave would add some hp/torque that would enhance the fun factor over ten years or so. That is a lot of cheap entertainment.

 

[Williboy]

So .030 with a 30 degree intake valve cutback sounds like the plan.

Will the increase in compression cause any more engine heat/temperature??? This motor always seems to run hot 200-225* and that's on a cool 70-80* day. ( I remember reading somewhere the .060 will make it run hotter. ??) I'm running a 195* stat. I tried a 160,180 and w/o and it always seemed it would run around 200*, so at least the the 195* keeps it around the ballpark.

 

[CZLN6]

Howdy Back:

Hmmmm. Milling .030" more and back cutting the intake valves will not make it run any hotter. But 200 degrees is a little hot, 225 is too hot, so your engine is in need of a good cooing assessment. A cooler thermostat will not cool the engine. It only maintains the temp at which the radiator starts to cool the engine. It may be time for a good flush of the block, clean and core the radiator, check the hoses for cavitation, fan shroud, or ????? Also check the accuracy of you temp gauge.

Just some thoughts.

Adios, David

 

[Williboy]

It's always ran hot from the start, I'm now running an alum radiator, with an aux elect fan up front for those really hot days, plus I have a analog gauge under the dash. Normal driving will usually keep it at 195* but stop and go traffic or after a freeway run the temps will creep up. ( I usually try not to drive around when it's too hot due to no A/C and a windshield shaped liked a magnifying glass!! ) I might dig out my old fan shroud and give that a try with the alum rad. I've even thought about an aux oil cooler...

But this is whole other post and subject matter, Thanks for the advice and I'll keep you posted!!

 

[bubba22349]

A good fan shroud would help quite a bit. Do you run water or a coolant mix? If you run water you can mix in some water wetter to help with cooling it down. Do you have a coolant recovery tank and or is the radiator cap holding the correct pressure. The .060 over bore maybe also part of the problem if there is any core shift were the bores are considerably thiner on one side. Good luck