Building a high performance slant engine

[1930]

I plan to learn how to make all the measurements that I should of done on the slant that is in my truck ( my good truck ) before I sent it in for re-build.

When I pull the head back off that good engine/truck at least I will be familiar with what I am doing cause I have already done it here.

Lets say I wanted to build this engine ( see this thread http://www.forabodiesonly.com/mopar/showthread.php?t=278292) for more performance/torque I guess I would need to find its compression ratio ( first ? ) which I can do by measuring its deck height and chamber volume, does that sound correct?

This way I can know how much to shave off the head.

I have printed and saved Dusters ( From slant.org site ) instructions on finding chamber volume but I do not remember seeing anything that went into any detail on measuring deck height.

Is it just a matter of laying a straight edge across the top of the block and measuring how far down the top of each piston is at TDC. '

Do I need to measure all of the pistons this way?

What other measurements will I need to come up with assuming I am building this engine for performance/torque?

Thanks for any help guys.

 

[2 Darts]

I plan to learn how to make all the measurements that I should of done on the slant that is in my truck ( my good truck ) before I sent it in for re-build.

When I pull the head back off that good engine/truck at least I will be familiar with what I am doing cause I have already done it here.

Lets say I wanted to build this engine ( see this thread http://www.forabodiesonly.com/mopar/showthread.php?t=278292) for more performance/torque I guess I would need to find its compression ratio ( first ? ) which I can do by measuring its deck height and chamber volume, does that sound correct?

Not quite. You'll want the volume of the heads for later. The critical volumes you'll need are the volumes of the cylinder with the piston at TDC and at BDC. [Volume of a cylinder= π r²h. vol=((½ of bore*½ of bore) *3.14159) *Distance from top of piston to top of block. CR=BDC volume/TDC volume. The heads don't figure in because they would cancel out in the reduction of the formula. Also, cc'ing a head is an inexact science. Take a head to three different shops and you're likely to get three different measurements. (3.14159=numerical value of π. ) Suggestion: Do measurements after block comes back from machine shop (with a finished bore). Even a bore hone may increase bore size. It goes without saying that boring the block out does.

This way I can know how much to shave off the head.

I have printed and saved Dusters ( From slant.org site ) instructions on finding chamber volume but I do not remember seeing anything that went into any detail on measuring deck height.

Is it just a matter of laying a straight edge across the top of the block and measuring how far down the top of each piston is at TDC. '

Pretty much.

Do I need to measure all of the pistons this way?

I don't think so unless you have good reason to suspect a mismatched set of pistons. Measure after block deck has been machined flat.

What other measurements will I need to come up with assuming I am building this engine for performance/torque?

Assuming you are taking metal off the head and the block deck, keep track of how much is removed. You will either need to shorten the pushrods or shim the rocker arm shaft by a similar amount.

Also, while assembling the motor, keep track of bearing-to-cap clearances (both rod and main). (Too loose, have trouble with oil pressure; too tight, excessive oil heat, engine does not spin freely.) Don't assume it's like replacing a gasket. Also, keep track of the crankshaft end play. (Can affect ignition timing if excessive.)

 

[1930]

Not quite. You'll want the volume of the heads for later. The critical volumes you'll need are the volumes of the cylinder with the piston at TDC and at BDC. [Volume of a cylinder= π r²h. vol=((½ of bore*½ of bore) *3.14159) *Distance from top of piston to top of block. CR=BDC volume/TDC volume. The heads don't figure in because they would cancel out in the reduction of the formula. Also, cc'ing a head is an inexact science. Take a head to three different shops and you're likely to get three different measurements. (3.14159=numerical value of π. ) Suggestion: Do measurements after block comes back from machine shop (with a finished bore). Even a bore hone may increase bore size. It goes without saying that boring the block out does.


Pretty much.

I don't think so unless you have good reason to suspect a mismatched set of pistons. Measure after block deck has been machined flat.

Assuming you are taking metal off the head and the block deck, keep track of how much is removed. You will either need to shorten the pushrods or shim the rocker arm shaft by a similar amount.

Also, while assembling the motor, keep track of bearing-to-cap clearances (both rod and main). (Too loose, have trouble with oil pressure; too tight, excessive oil heat, engine does not spin freely.) Don't assume it's like replacing a gasket. Also, keep track of the crankshaft end play. (Can affect ignition timing if excessive.)

I had no idea, I though the combustion chamber played a role cause the compressed air/fuel was forced into this area. I guess I will need to continue asking questions. Thanks

 

[2 Darts]

You're welcome. I'm going to correct myself and say that the combustion chamber volume should be included in figuring the BDC volume as well as the TDC volume of the cylinder. Also, don't forget to add in the volume of the compressed head gasket material. It won't be much difference, but it will yield a more inclusive result. You are right.

If a smaller combustion chamber volume cylinder head is utilized (not happening on a /6), the compression ratio increases. Although there isn't much to choose from in the way of /6 heads, combustion chamber volume (in the greatest sense) is reduced by milling the deck of the block and planing the cylinder head.

There are some /6 racers on FABO and SlantSixDan occasionally puts in an appearance. They all know a lot more than I do about /6 builds.

 

[my68barracuda]

I have printed and saved Dusters ( From slant.org site ) instructions on finding chamber volume but I do not remember seeing anything that went into any detail on measuring deck height.

DI has good info on determining chamber volume, I use a stringe from Tractor Supply,, intended for farm animal injections,, I can get the same value + / - a cc time and time again,, it aint hard to do...

Is it just a matter of laying a straight edge across the top of the block and measuring how far down the top of each piston is at TDC. '

You got it,, although you want something better than a tape to measure the depth,, a depth micrometer is best.

Do I need to measure all of the pistons this way?

You can measure them all,, for a slant,, however, measuring #1 and #6 and getting the run from front to rear should tell you what you want to know. Understand that the variation mesured from 1 to 6 is due to: the block deck maching front to rear, the crankshaft bore machining front to rear, how parallel they are as well as for the rods: length from bore to bore and piston compression height.
I would expect that on a stock engine 1 & 6 would easily be within .010,, for a block reprocessed be a compentent machine shop, resized rods, good pistons, easily within .005

What other measurements will I need to come up with assuming I am building this engine for performance/torque?

I recommend getting familiar with the definitions and differences between static and dynamic compression. As well as the inputs for each. There are several good on line ( free) compression calculators,, RB is a good one,,
https://www.rbracing-rsr.com/compstaticcalc.html
There are also interesting and accurate computer simulation programs,, for not much money,,
Dyno Sim,, is really cool.
http://www.proracingsim.com/dynosimmainpage.htm
In your engine development planning: camshaft timing, duration and lift will also be important to match up with the compression values chosen.. For that I recommend googling "David Vizard and Camshafts" and be prepared to open your mind.
http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/

 

[1930]

I have printed and saved Dusters ( From slant.org site ) instructions on finding chamber volume but I do not remember seeing anything that went into any detail on measuring deck height.

DI has good info on determining chamber volume, I use a stringe from Tractor Supply,, intended for farm animal injections,, I can get the same value + / - a cc time and time again,, it aint hard to do...

Yes it makes sense to me that there might be some small variations when checking the chamber, evidently vaseline or grease is used ( backyard method ) between the head and whatever is being placed over the combustion chamber ( CD case ) and depending on build-up that alone would cause a different amount of fluid to fill the chamber area if that makes sense.

Is it just a matter of laying a straight edge across the top of the block and measuring how far down the top of each piston is at TDC. '

You got it,, although you want something better than a tape to measure the depth,, a depth micrometer is best.

I may have a set of these, if I do not than I will get a set. Good tools are nice to have and chances are I will use them again.

Do I need to measure all of the pistons this way?

You can measure them all,, for a slant,, however, measuring #1 and #6 and getting the run from front to rear should tell you what you want to know. Understand that the variation mesured from 1 to 6 is due to: the block deck maching front to rear, the crankshaft bore machining front to rear, how parallel they are as well as for the rods: length from bore to bore and piston compression height.
I would expect that on a stock engine 1 & 6 would easily be within .010,, for a block reprocessed be a compentent machine shop, resized rods, good pistons, easily within .005

This makes perfect sense, I will check the variation and go from there.

What other measurements will I need to come up with assuming I am building this engine for performance/torque?

I recommend getting familiar with the definitions and differences between static and dynamic compression. As well as the inputs for each. There are several good on line ( free) compression calculators,, RB is a good one,,
https://www.rbracing-rsr.com/compstaticcalc.html
There are also interesting and accurate computer simulation programs,, for not much money,,
Dyno Sim,, is really cool.
http://www.proracingsim.com/dynosimmainpage.htm
In your engine development planning: camshaft timing, duration and lift will also be important to match up with the compression values chosen.. For that I recommend googling "David Vizard and Camshafts" and be prepared to open your mind.
http://www.popularhotrodding.com/tech/0607phr_camshaft_basics/

Will check this out again but still a bit too technical for me still at this point

 

[jbc426]

Do yourself a favor. Get a hold of Doc, aka, Doug Dutra over on Slant 6 dot org. No need to reinvent the wheel here. He pretty much Knows how to built some amazing Slant 6's and is one of the nicest, smartest, shade mechanics there is, especially when it comes to tuning slants that you will ever meet.

 

[1930]

Yes, Doc does chime in from time to time on .org.

I know he has better things to do than devote every waking hour to my project however and so I am here on these forums asking for other peoples opinion/ experiences with this stuff as well.

It took a village to raise a child so to speak

 

[nm9stheham]

:drinkers::drinkers::drinkers::drinkers::drinkers:This isn't a village....it's a tavern... beside a garage!