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Which is a better year to rebuild?
https://slantsix.org/forum/viewtopic.php?t=56052		 Page 1 of 1
Author:  moparfreak77 [ Sun Aug 24, 2014 8:09 pm ]
Post subject:  Which is a better year to rebuild?
I have the original 68 slant six 1 bbl in my Valiant that was running a couple years ago. i also have a 77 2 bbl. I want to rebuild 1 of them and do it up a little. Here are my plans and questions...feel free to give opinions on any of this...

I also want to bump up compression...

-Stock Block, rods, pistons? decked? if so, how much?
-Which head? planed? if so, how much? (both head and block planed?) I have the bigger valves and valve guides from engnbldr. I think I also have 340 valvesprings which I heard was better, is that correct? If so, does anyone know the part number for 340 valvesprings?
-port and polish/gasket match, not crazy here, just clean up what is there.
-2 bbl, what carb is best? Is there REALLY that much difference between the original 2 bbl intake and aftermarket? If so, which one is best?
-Dutra duals, what size exhaust?
-Pertronix? I think I MAY have the mopar electronic ignition from the 77 Slant but the simplicity of the Pertronix sways me.
-Cam, which one? I dont know much about specs of cams but I like the "lump lump" sound :)

I want maximum efficiency with this (for the mods obviously) and brag about mpg :)
Anything I should be considering?
Is there any "while its apart i would do this"?
Who makes a good rebuild kit for these?

This will go in my 68 Valiant and be driven everyday when there is no snow.

Thanks a lot guys.
Author:  bcschief [ Mon Aug 25, 2014 4:08 am ]
Post subject: 
68 has a forged crank and the 77 has a cast crank

Brian
Author:  DKD [ Mon Aug 25, 2014 5:55 am ]
Post subject: 
Whatever block you can get for free. In street trim or mild race you aren't going to hurt any of them. Sometimes we forget our main bearings are the same dia as a big block mopar which is larger and more robust then anything wearing bowtie.
don
Author:  moparfreak77 [ Thu Aug 28, 2014 8:04 am ]
Post subject: 
Sure wanting some more insight please! :)
Author:  sandy in BC [ Thu Aug 28, 2014 9:00 am ]
Post subject: 
For what you want to do it doesnt really matter.

I prefer the look of the earlier head....

The cam selection and the decking/planing math are very important and need to be done at the same time. First you need to do a little data collection and make some choices.

The stock 2 barrel is sufficient to propel a stout slant ....it pairs nicely with a 2 1/4" exhaust.
Author:  moparfreak77 [ Mon Sep 01, 2014 7:19 am ]
Post subject: 
Quote:

The cam selection and the decking/planing math are very important and need to be done at the same time. First you need to do a little data collection and make some choices.
What do you mean by this? What data collection do I need?
Author:  Doctor Dodge [ Mon Sep 01, 2014 9:46 am ]
Post subject: 
Data you need includes the actual cylinder diameter, deck height & cylinder head chamber size. (in cc's)
That info. will allow you to calculate the static compression ratio.

You can now review & select a camshaft to fit you intended use goals.
The decisions here will include the "power band" (RPM Range), idle quality and the type of fuel you want to run.

Here is the Most Important piece of data: you need to know (find-out) the intake valve closing point for the selected cam.

With all the above information (data) you can calculate the engine's Dynamic Compression Ratio (DCR)

Knowing (and then setting) the DCR in the 8.0 to 8.2 range will make a powerful SL6 that will run on today's pump gas.
DD
Author:  72polara [ Mon Sep 01, 2014 7:54 pm ]
Post subject: 
I defer to Doc and the other experienced builders and their advice.

But, since you mentioned that you have a forged crank and a cast crank to choose from, and I've built a couple (literally two, one cast, one forged) slant engines... They're almost the same, except the cast crank one revs a little faster. Like if you swapped on a lightweight flywheel. The cast crank is considerably lighter than the forged crank, so pick that if you like the way a lightweight flywheel feels.

I understand that at reasonable power numbers (I defer to the real experts here, but something around double stock power output), there is almost no difference in strength.

Also, if you want to bore it way out, you want the forged crank, because the older forged blocks typically have thicker cylinder walls, and the crank, rods, and the block must be matched with each other (unless your name is Doug Dutra).

However, the above considerations are minutia compared the to the advice already offered about picking a good cam that matches the rest of the build you select - remember that engine building is about engineering a system, not picking a whiz-bang part or two.

The advice about measuring (cc the head, measure the deck height, measure the cylinder diameter) is 100% right. I've only had a half dozen or so slants apart, but they've all been wildly different, not what the books say. The only way to know is to measure, don't guess. The factory tolerances were huge!
Author:  moparfreak77 [ Sat Sep 06, 2014 6:07 am ]
Post subject: 
Thanks a lot guys, apprieciate everything. questions...
- Can the cast crank go in the 68 block?

- "you need to know (find-out) the intake valve closing point for the selected cam.
With all the above information (data) you can calculate the engine's Dynamic Compression Ratio (DCR)"....where can I find how to do this?

- "Knowing (and then setting) the DCR in the 8.0 to 8.2 range will make a powerful SL6 that will run on today's pump gas."....Is the "DCR" a lot different then the "normal" CR? I thought we would want CR around 9?

Also, would someone be so kind as to go down my original post and answer my question? thanks
Author:  Sam Powell [ Sat Sep 06, 2014 5:18 pm ]
Post subject: 
Static compression is figured mathmatically as the ratio between the volume of the cylinder at the bottom and the volume at the top of the stroke. Dynamic compression takes into account the fact that one or both valves are open for a portion of the compression stroke, and the intake stroke, thus reducing the total volume of the mixture being compressed.

You can find calculators on line that figure this out for you. Just plug in the numbers they ask for, and you will need to make decisions about cam choice in order to do this. You will also need to take accurate, careful measurements of YOUR engine.

There are too many unanswered questions about your goals here to give you good advice. All decision result in give and take, and compromise, and only you can decide which way you want to go. There are slants that turn 12 second quarter mile times, but you likely would not drive most of them on the street. Well, most folks would not.

Read Dad Truck's recent thread on his engine build and cam choice. If you like his result, then most of your questions will be answered. The search feature here will quickly point you towards his threads.

Sam
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