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79-80 Engine Fireing Position
https://slantsix.org/forum/viewtopic.php?t=32276		 Page 1 of 1
Author:  Dago Red [ Sun Nov 16, 2008 12:09 pm ]
Post subject:  79-80 Engine Fireing Position
:?: Gang, I've got what numbers out as a 79/80 slant six engine I'm building for racing. Here's what I've got:

Crank p/n 4095246-7

Head p/n 4104362

The pad numbers were machined off during surfacing and I purchased the entire bag 'o nuts when the original owner never returned for the stuff.
I installed a Mopar Performance cam (P4529343) straight up, stock rockers and valves, 340 springs.. I have a modified quick advance distributer. It's not aftermarket, but a OEM slanter.

QUESTION: I understand that these two years fired from a different #1 position than every other motor, but the firing order remainded unchanged. Do I plug it in and let it fly or do I need a specific 79-80 distrib?

Thanks, RICK
Author:  Joshie225 [ Sun Nov 16, 2008 12:21 pm ]
Post subject: 
The distributor is fine. You can put #1 just about wherever you want as long as the rotor points to that terminal when #1 is ready to fire and you follow the firing order. Just because the factory went goofy for a year or two doesn't mean you have to follow along.

By straight up I hope you mean degreed the cam and made sure the intake centerline is at 102° ATDC. That's a lot of cam and needs a lot of compression to work well. What's the static compression ratio?
Author:  SlantSixDan [ Sun Nov 16, 2008 2:55 pm ]
Post subject: 
Josh is correct; it doesn't matter which distributor tower is set up as #1 as long as the wires are connected in correct sequence after that. Slant-6 plug wire sets are configured so that the tower at about the 4:30 clock position as viewed from above is #1. And no, there is no difference in firing position in slant-6s from any particular year.
Author:  Dago Red [ Sun Nov 16, 2008 5:05 pm ]
Post subject:  Leading Edge of a Bowling Ball
:oops: Thanks guys! By straight up Josh, I just aligned the two marks on the crank and cam sprockets. My guess is there won't be a lot of compression in this motor, maybe 9.5:1. It's my first Slanter so I didn't want to try and reinvent the wheel. It's still on the stand, so popping off the timing cover and redegreing it would not be too tough. Most of my racing is 1/8th mile and I figured on just taking whatever it threw me in the 1/4. It will have 4.30's with 26" inch tall slicks, weigh less tha 3000# with my carcass in it, no juice, no transbrake and I've held off on a converter until I check in with the experts here.
Author:  Charrlie_S [ Sun Nov 16, 2008 5:25 pm ]
Post subject: 
Those 340 valve springs may not be heavy enough for that cam. I would have to check the specs (out in the shop). Also make sure you shortened the valve guides, to prevent the retainers from hitting the top of the guide.
Author:  DusterIdiot [ Sun Nov 16, 2008 7:36 pm ]
Post subject:  You're gonna need to pull the head...
Quote:
My guess is there won't be a lot of compression in this motor, maybe 9.5:1.
The LSA that that cam has will want something in the 10:1+ realm, as it'll bleed off a fair amount of compression.... 9.5:1 will want something milder like the MP 268 cam aka P4529342...

2 cents...

-D.idiot
Author:  Joshie225 [ Sun Nov 16, 2008 8:14 pm ]
Post subject: 
I was thinking something in the neighborhood of 10.5:1 with that cam and 3400 RPM stall or more. The 340 valve springs will be at about their limit. The MOpar Performance ones are advertised for use up to .500" lift which should just do since the lash on that .528" lift cam is .028 and .032". Mopar Performance actually recommends P3412068 springs for that cam which are dual springs with damper.

By all means check the compression ratio and the cam's installed centerline. Running that cam with too low a compression ratio and late valve timing will make the car an absolute dog. If you cant get the compression ratio up use a shorter duration cam. Check the Oregon Cam grinding profiles thread if you need a different cam. http://slantsix.org/forum/viewtopic.php?p=191616
Author:  Dago Red [ Sun Nov 23, 2008 12:25 am ]
Post subject:  Forest For the Trees
:arrow: Thanks everyone! It looks like this sucker is going to get knocked apart and reengineered. I'll be back with some measurments soon. I have another earlier model head that I may put some mods into. Would bigger valves and a port job help with the big camshaft? I have a terrific head porter that wants to tackle a Slant head. Any do's or don'ts ? Would 10 degree keepers be a better choice with the big springs?

OR......I may just leave everything as it is and change the cam. Stay Tuned !! And once again thanks everybody..
Author:  Joshie225 [ Sun Nov 23, 2008 9:34 am ]
Post subject: 
The cam is easier and cheaper to change than to raise the compression enough to make that cam work. If the pistons are stock type you'll have to mill the block and head enough you'll need new pushrods. You don;t need 10° keepers. Those are for big roller cams and huge valve springs.

Bigger valves and port work help with stock cams and are very helpful with big cams.
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