Another Magnum 408 build!

-
gregsdart

gregsdart

Well-Known Member
Joined
Jun 20, 2004
Messages
788
Reaction score
463
Location
mn
If you have spotted posts by me on valve train, compression, etc, it all led up to this build. I started with a boneyard Magnum 5.9, figuring I would put a cam and valve springs in it and a carb and call it good. Well, upon tearing it down I found just enough bore wear at the very top of ring travel to convince me to bore and hone it. Then after looking over the cost of having it all cleaned , inspected, rods rebuilt, balanced, etc I figured, it is close enough, just go stroker kit! So, a Scat kit was ordered on May 12th and should be here soon. The block is in the machine shop, along with a pair of EQ heads which are getting liners, and 2.02 intake valves plus a bowl port. Brian at IMM is assembling a care package of cam, valvetrain, carb, intake, and a number of other items to finish this deal up. After getting brain freeze trying to figure out what to use for a cam and valvetrain, I opted to go to someone that I know will steer me right, and I am confident the motor will make somewhere near 470 to 490 hp like Brian figures it should.
As long as I do a good job of assembling it and dialing it in, I am sure it will. I plan to have it dynode here in Minnesota, so the numbers may vary, but should be close.
I was warned by Brian that the Muthr Thumpr cam with 235/249/107 timing specs, along with an RPM air gap, 1 5/8 headers might produce more low end torque than I would like, but I am going to accept the challenge of figuring how to make it work in my 65 Dart street car with 3.55 gears and a custom converter. My other 65 started life as a street car with a 535 inch wedge in it, so it won't be the first time I have had a challenge like this. It has been a while since I started a whole new engine project, so this is a bit exciting to me. I will update once in a while with photos. When done, this motor and the rack and pinion setup I built, (thread is in Early A section) will go in the Dart together.
The two darts! Best so far for the orange car, 8.76 at 153 mph, 3055 race weight. (ok, I like donuts!)

Dart pics + others 106.jpg


Dart pics + others 132.jpg


IMG_20130824_152322_410.jpg
 
"I like donuts"
LMAO!!! Yea, I hear ya pal! But ya look good and I see there aren't to many donuts downed!

Can you slip in a link to the rack & pinion please?
 
I bumped the rack thread up to page one of the early A forum.
On the crank, I went with the cast steel. If there is an extra charge for heavy metal to balance it, that might turn out to be false econemy though. $500 more for a forged crank. Since this is a street car, and a Scat product, I figured cast would be way more than strong enough.
That top photo was taken in my yard in 2001, the day Randy Bolig shot photos for Mopar Muscle Magazine. I made it into the June 2002 issue, titled Northland Flyer .
Geez, I'm getten old, that was fifteen years ago
 
Last edited:
gregsdart said:
I bumped the rack thread up to page one of the early A forum.
On the crank, I went with the cast steel. If there is an extra charge for heavy metal to balance it, that might turn out to be false econemy though. $500 more for a forged crank. Since this is a street car, and a Scat product, I figured cast would be way more than strong enough.
That top photo was taken in my yard in 2001, the day Randy Bolig shot photos for Mopar Muscle Magazine. I made it into the June 2002 issue, titled Northland Flyer .
Geez, I'm getten old, that was fifteen years ago
Click to expand...

I'm starting to kick the idea around in my head but I don't want to wish I went with a forged later on down the road. It's a street car that might make 6 trips to the track a year.
 
doogievlg said:
I'm starting to kick the idea around in my head but I don't want to wish I went with a forged later on down the road. It's a street car that might make 6 trips to the track a year.
Click to expand...
If you want to keep upgrading the power, better off with a forged crank. I figured since i would never exceed about 500 hp or 6500 rpmthe cast one was good enough. Hopefully I will have an answer on balancing cost shortly, which might help you out.
 
gregsdart said:
If you want to keep upgrading the power, better off with a forged crank. I figured since i would never exceed about 500 hp or 6500 rpmthe cast one was good enough. Hopefully I will have an answer on balancing cost shortly, which might help you out.
Click to expand...

I'll be keeping an eye on this thread.
 
$60 extra for mallory metal. It took only one slug to balance internally. If a forged crank would not need mallory metal, it would only cost $340 to upgrade to a forged crank $400 extra minus the $60 extra That it cost to balance the cast crank internally.
 
Last edited:
I have a forged Scat crank and it took NO mallory to balance it. The machine shop actually removed metal to get it into balance. Your results may vary.
 
Brian, it was my cast crank that needed heavy metal. My guess is, like yours most forgings will not as long as reasonably light parts are chosen. Here is another case of where if I had known the cost between the two, a forging would probably been worth it just for resale value alone. (I edited my previous post to make it clear what I meant)
 
DNasty777 said:
Did you buy the internal balance cast crank kit?
Click to expand...
Yes. Cnc Motorsports, 1501+ 60 for the heavy metal. Scat 9000 crank, I beam rods with 7/16 bolts, forged Icon pistons with 20.5 cc dish. Molly file fit rings, main and rod bearings.
 
gregsdart said:
Yes. Cnc Motorsports, 1501+ 60 for the heavy metal. Scat 9000 crank, I beam rods with 7/16 bolts, forged Icon pistons with 20.5 cc dish. Molly file fit rings, main and rod bearings.
Click to expand...

I have the same kit with the flat top pistons. My machinist said it needed no extra weight to balance. I bought the flat top kit with the intentions to use it in a LA block but I ended up having to use a magnum block and now I'm worried I'll have to have the pistons milled and the crank rebalanced. Oh well such is life.
 
D, have you computed compression with a thicker gasket? On milling pistons, my machinist said he wants .200 thickness left after machining piston tops.
 
I have not. I don't have the block in my possession to find out where the final deck height landed, I'll be putting it together with the help of a local builder and I'm waiting on him to free up some shop time.
 
Lots of parts showed up today!
My combination is a Quick fuel 850 on top of an rpm air gap intake, EQ heads with 2.02 Free a intake valves bowl blended, 10.0 expected compression with a final deck height of 9.577, .045 Victor head gaskets.
The cam is a Comp 20-601-9, with .348 intake lobes, .339 ex lobes, 235/245/107 duration numbers, and 1.6 ratio steel sbc rockers. I ordered all these parts from Brian at IMM.

0616171429a.jpg


View attachment 1715057821
 
Last edited:
gregsdart said:
I was warned by Brian that the Muthr Thumpr cam with 235/249/107 timing specs, along with an RPM air gap, 1 5/8 headers might produce more low end torque than I would like, but I am going to accept the challenge of figuring how to make it work in my 65 Dart street car with 3.55 gears and a custom converter.
Click to expand...
Too much low RPM torque as in hard to hook up at the strip? Or what?
 
nm9stheham said:
Too much low RPM torque as in hard to hook up at the strip? Or what?
Click to expand...
Street traction is the issue. Especially if front end weight percentage is close to stock. Darts of. 63/66 vintage have a long wheelbase, like 112 inch. That doesn't help any.
 
Got a phone call from my machine shop today! EQ heads, 2.02 intakes, 1.62 exhausts, flowed 270 @ .600 intake, 208 @ .600 exhaust! I am happy with that. This was aa bowl port only, will post pics as soon as I get the heads home. The block piston above deck height came in at .011, so the quench side of the pistons get a .005 cut for a final clearance of .039 using a Victor 3536SG gasket which is .045 compressed, and a final compression of 10.1. Head chamber cc is 63.4 uncut. The pistons original dome (negative) volume is 20.5 cc, so it all works out. It is finally coming together.
 
While it ain't where I head for engines (for various reasons), I am liking the idea of how you look to be making the torque curve match to the traction..... assuming I am putting this together in my haid right.... the 'leaping Dart' picture was the clue LOL
 
nm9stheham said:
While it ain't where I head for engines (for various reasons), I am liking the idea of how you look to be making the torque curve match to the traction..... assuming I am putting this together in my haid right.... the 'leaping Dart' picture was the clue LOL
Click to expand...
Not quite sure what you mean?
I figure build all the torque and low (relatively) hp you can, and work from there.
 
I managed to get the crank into the block today, and the rings file fit. Test fitting the rod bushing to piston pin clearance tells me they will need to be honed. Too tight. I don, have anything to measure pin clearance, but they are so tight I doubt there is a half a thou of clearance at best. At least I can dial in the cam and measure rod clearance, since I can,t get the rods honed till at least Monday.☺
 
You must log in or register to reply here.
-

Back
Top