slant 6 head shave

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cudajim

cudajim

cudajim
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Ok so I am new to this slant 6 forum. I have a new (to me) 67 Barracuda with a stock 225 6-banger. I have heard you can shave the head as much as .060 to give more compression, horsepower and better mileage.

How true is this and is it worth my while? What's the downside to doing this?
 
You can shave a heck of a lot more than that. I routinely shave .100 to .150 off a slant head/block combo. YOU NEED TO MEASURE so you know where your at.
What are your goals? Budget?
Frank
 
I've seen where both the block and head can be machined quite a bit. On my /6 rebuild, planning to equal remove amounts from head and block. I'm thinking that .060 total will produce desired results without having to use higher octane fuel.

Upsides: More compression, better fuel mileage, more power (Mo par', to the cornbread and grits crowd. Self included.)
Downsides: May require higher octane. This point is open to debate, but many say that taking .090 or more out of the head/block combo and you'll need new (shorter) pushrods to have room to adjust valves.

Recommend you check out Slantsix.org . Lots of good knowledge there about warming up the leaning tower of power.
 
2 Darts said:
I've seen where both the block and head can be machined quite a bit. On my /6 rebuild, planning to equal remove amounts from head and block. I'm thinking that .060 total will produce desired results without having to use higher octane fuel.

Upsides: More compression, better fuel mileage, more power (Mo par', to the cornbread and grits crowd. Self included.)
Downsides: May require higher octane. This point is open to debate, but many say that taking .090 or more out of the head/block combo and you'll need new (shorter) pushrods to have room to adjust valves.

Recommend you check out Slantsix.org . Lots of good knowledge there about warming up the leaning tower of power.
Click to expand...

Just to set the record straight the stock steel head gasket is .020 the new composite is .038 to .042 so you loose some just by taking the head off. As for push rods most slants will go .140 or more before you lose adjustment. Big thing is to measure. I have taken .100 off and run pump gas.
Dot Org is the place to learn.
Frank
 
I have read that .090 is the max and by cutting .090 off you raise the static CR 1 point. THis would bring the CR to 9.5:1 or 10.0:1 depending on the year slant 6 you have.

I would like to know the max cut you can take on these engines as well. What is the limiting factor?
 
roccodart440 said:
I have read that .090 is the max and by cutting .090 off you raise the static CR 1 point. THis would bring the CR to 9.5:1 or 10.0:1 depending on the year slant 6 you have.

I would like to know the max cut you can take on these engines as well. What is the limiting factor?
Click to expand...

I dont know where your info came from or how it was determined but in my opinion it is faulty.
Most slant 6 198/225 engines have the piston .185 in the hole. add a .020 steel shim gasket and 60cc heads and plug that into a calculator. Most slants have 7.5-8 to 1 actual compression. Advertised was about 8.4 to 1. Throw your .038 Composite gasket of your choice ( I use the Permaseal Brand that I sell) and the compression is even worse. I think about .007 is 1 cc so do your math.
Frank
 
66aCUDA said:
Just to set the record straight the stock steel head gasket is .020 the new composite is .038 to .042 so you loose some just by taking the head off. As for push rods most slants will go .140 or more before you lose adjustment. Big thing is to measure. I have taken .100 off and run pump gas.
Dot Org is the place to learn.
Frank
Click to expand...

Thanks for the heads up on the gasket thickness difference. It would seem you need to cut the head ~ .040 just to maintain stock compression, let alone improve on it.
 
2 Darts said:
Thanks for the heads up on the gasket thickness difference. It would seem you need to cut the head ~ .040 just to maintain stock compression, let alone improve on it.
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Actually you need to cut about .020 to maintain stock CR, when using an "aftermarket" head gasket. If you don't want to do any machining, use the OEM steel shim gasket. If you are going to mill the head, any way, just allow the extra .020 for the thicker gasket. I am running a head on my 66 Valiant 225, that is cut about .125 and the chambers are 39 cc's, and the shim gasket. This is a strip only car.

PS: Frank (66aCUDA) and I both have OEM stock steel head gaskets available.
 
66aCUDA said:
I think about .007 is 1 cc so do your math.
Frank
Click to expand...

Charrlie_S said:
Actually you need to cut about .020 to maintain stock CR, when using an "aftermarket" head gasket. If you don't want to do any machining, use the OEM steel shim gasket. If you are going to mill the head, any way, just allow the extra .020 for the thicker gasket. I am running a head on my 66 Valiant 225, that is cut about .125 and the chambers are 39 cc's, and the shim gasket. This is a strip only car.
Click to expand...


Frank, using your math Charlie would have had to cut .147 off his head to get 39cc's. I believe you that advertised compression is less than what the factory states. WOuld be nice to know an exact formula though. As far as where I got my info, can't remember, some slant 6 forum? NOt this one.

WHat is the mechanical limiting factor as to how much you can cut off the head?

ALso how much would you have to cut off to get 10:1?
 
Rocco
Actually you are close. Charrlie runs 170 CI slants so the motor is a little different that a 198/225. The 170 is a Zero deck motor unlike the others.
Limiting factor on cutting the head. HUM not quite a fair question. You need to figure on both the head AND the deck. I may cut .150 off the combination of the 2. I know people who cut it all off the head and some cut it all off the deck. I like a combination of the 2. Do you have any idea of whether your motor has ever been rebuilt? Is this hypothetical or do you need real numbers? The Actual number is .0067 = 1cc. Other factors are what head gasket will you use, what bore size, etc.
Might be better to PM me if you need build help.
Frank
 
I just bought a 68 two door dart with a slant 6. My other dart is a 440 swinger which was originally a 340 car. I have no prior experience with the 6.

Here is my plan. I do not want to pull the engine. I want to cut just the head. So I need to know how much to cut off of itto get me to at least 9.5:1 but no higher than 10:5:1.
 
Not to hijack the thread but I plan to do an MSD, intake, carb, headers, cam and NO2.
 
I also have thicker and thinner head gaskets than a stock FelPro. So it you want/need to move the compression we can do it.
Frank
 
roccodart440 said:
Frank, using your math Charlie would have had to cut .147 off his head to get 39cc's. I believe you that advertised compression is less than what the factory states. WOuld be nice to know an exact formula though. As far as where I got my info, can't remember, some slant 6 forum? NOt this one.

WHat is the mechanical limiting factor as to how much you can cut off the head?

ALso how much would you have to cut off to get 10:1?
Click to expand...

How did you determine that I would have had to cut the head .147 to get 39 cc's? I never stated my original CC's. You need to know that before anything.

The factory head cc's is "spec'd" at 53.8 cc's, but most are actually larger. The head I used was an old "blue printed" stock eliminator head, which had been milled previously, to get 54 cc's. I had forgotten about the prior milling, and told the machinist to cut .100. This got the 39 cc's. If you do the math 54 cc's minus 39 cc's = 15 cc's, times .0066 = 99 thousanths. Close enough to .100 for me. I do not remember how much was removed in 1974 to get to 54 cc's.
 
Just went to the build thread for my engine, and got some numbers. My 225 engine started with the pistons at .170-.173 down in the hole. Head cc's varied from 53 - 56 cc's. gasket was .021 thick. using this calculator http://www.wallaceracing.com/cr_test2.php the CR comes out to 7.66.
Changing the head cc's to 39 brings the compression to 10.07

Here is a link to my engine/car build, if anyone is interested.
http://www.slantsix.org/forum/viewtopic.php?t=11218
 
Chalie, I set up a proportion using the info I found in the artile I posted and the info you gave.
 
Its just an engine...like any other.
push rod checking tool and a cc meassuring kit will get you there.

or you could just assume and take everyones word for it over at experts.org
since thats where 'you learn' LOL
 
The Mopar performance book says that every .0068" cut equals 1cc. But remember that the combustion chamber is itself like a dome shape, so the further you cut the less cc's you remove. Supposedly a .090" cut (depends on what you read, some books say .100") gives 9.4:1 compression, but I suspect that needs verification.

I've also read that the rocker adjusters can handle a .100" cut or less.
 
I have cut .080 off both the block and head with a .465 lift cam. Trying to get the longer ball stud nuts and lockers. Havent chosen a head gasket yet. Just my 2c:book:
 
1wild&crazyguy said:
or you could just assume and take everyones word for it over at experts.org since thats where 'you learn' LOL
Click to expand...

... or listen to the boys at swapyourslantforaV8.com or whywasteyourtimeonaslant.com. V8 guys are FULL of great slant advice... LOL

Thinkin' about making some posts on turbohonda.com. I mean, I've only changed a starter on a Honda, but hey, they're just engines. I doubt those guys have learned much more than me about those little 4-pots over the years.
 
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