Budget AMC 360 stroker build - 383 Cubes!

[Greg Taylor]

Hey guys,
Just another news anouncement ... Rick Jones, who helped build my 304 stroker is now underway on building a budget AMC 360 stroker, which should turn out to be awesome.

I'll post up pics and details soon ...

STAY TUNED!

[billyrb]

sounds fun! I just finished building a 383 myself

[Greg Taylor]

Rick's Initial thoughts and ideas for the 360 stroker

AMC 383 Stroker Build - by Rick Jones

The concept is to build a Max Cubic Inch 360 Stroker on a budget, in typical Farm Guys fashion. My original thought is that this would be an ideal engine for the Jeep guys contemplating a chevy swap. The longer stroke should help the low end torque making it ideal for the full size Jeep fans too. Another important factor is that 360’s are everywhere and practically free compared to a 401. So the goal here is to take the old tried and true 360 from a Grand Wagoner and see what kind of ponies and grunt I can get out of it with out spending tons of money. Since I don’t currently have a buyer for such an engine, I will tailor this one for my own use in a street car to prove it all out. This will be the 383 Mode 1. There are all kinds of directions that you could go from this basic concept.

My Goals:
Use as many off the shelf parts as much as possible.
Must be able to run on pump gas – limits the Compression ratio to around 10.5:1 .
Costs- normal rebuild plus, the cost of stroking the crank and aftermarket connecting rods.

Stroke it!: The stock 360 stroke is 3.44” and the rod journal size 2.09”. So… if I off-set grind the crank down to the small common 2” journal, this would increase the stroke by .090” ending up with a 3.53” stroke.

The Math: OK, now we have some math to do to find a off the shelf piston and rod combination to work with our stroker crank in the 360 block… (This is the cool part) To make it simple the block deck height is 9.208”. Subtract half of the stroke (1.765”) and you end up with a dimension of 7.443” to fit a rod and piston in. (It’s looking good now…) Since a 6” connecting rod is the most common connecting rod length we will subtract that, ending up with a 1.443” dimension for our piston compression height. For my application, I want to use flat top pistons at close to zero deck height to get something close to 10.0:1 compression ratio. Speed Pro makes a hypereutectic flat top piston with a 1.425” compression height which will work out well. This leaves 0.018” of deck clearance to play with. If I deck the block 0.010” or so, we are good to go!

Block: ’82 vintage AMC 360. Decked approx 0.010” to obtain approx. 0.008” deck clearance.

Heads: Utilize the stock ’82 heads (63cc) with the bridged rocker arms. I don’t hate the bridged rocker arms…. That is, after I throw away the aluminum pivots and replace them with the powder metal kits. For this application, the 5/16” rocker arm retaining screws will be fine.

Pistons: In the theme of cost effectiveness (cheap), the sbc 400 is close to the same bore as the 360. (4.08” vs 4.125”) This means that there is a plethora of piston choices with a multitude of compression heights to choose from which will be critical for this build. Even if we were to use the 4.125” standard bore chevy piston in the 360 block, it is only 0.045” overbore. So, we could just be way conservative and utilize the 4.125” bore with the 3.53” stroke but, what fun is that? This results in a 377 cu. In. engine. Now if we use a +0.030” oversize 400 chevy piston, the bore would be 4.155”. Do the math and the cubic inch ends up at 382.9. Besides, saying that it is an AMC 383 Stroker sounds much cooler. Yep that is a 0.075” over bore but, many including myself believe that the 360 block will handle that much and more over bore. For a comfort level, I purchased a Sonic Thickness tester and tested my cylinder wall thickness before and after boring the block. The block that I am using is all ready +.030" over bored. I checked all of the cylinders and the thinnest area that I could find was .141" (#2 & #8). If I use my conservative correlation factor of -.010" this leaves me with .131" wall thickness in two areas. Subtract half of the remaining over bore required .131-.023 = .108" wall thickness is the two thinnest spots.

Connecting rods: The stock AMC 360 connecting rod width is .997” and is not machined down narrower at the crank end like the 401 and other makes rods. I was not able to find an off-the-shelf aftermarket 6” connecting rod to fit a 2” journal that is wide enough for the 360 crank. One option is to do what Car Craft did and add material (weld) to the connecting rod and machine it back down. I was guessing to weld, machine the width, and re-size the rods in that manner would be cost prohibitive. My “consultants” and I had a few other Molson inspired ideas but nothing that was simple and easy. So, I called Scat in hopes of getting a set of sbc rods before they machined the big end down. The piston end of the sbc rod is wide enough. I told them what I was trying to do with the wider 360 crank and they recommended using a 6” stroker rod from a GM 250 6 cylinder application. This rod is 1.050” wide, made for a 2” journal and, could be machined down. The bonus is, the piston pin size matches the aftermarket piston that I chose. These rods are expensive but, they were the only ones that I thought might work. I ordered 2 rods and took them with the crankshaft to the crank grinder.

Crankshaft: “And we were strok’n”..… The crank grinder liked my idea of the budget build stroker which was cool because he usually doesn’t like much of anything... (Kidding.. sort of) He has been the business for a long time and machines the billet stroker cranks for our local AMC drag race guys so, I trust his workmanship. As he started to check out the stock 360 crank and the Scat connecting rods he offered a suggestion….. Rather than spend more money grinding down all ready expensive connecting rods, he would machine the rod journals wider to match the rods. I asked him about strength. It is still a cast crank and we are all ready weakening it just by grinding it down to the 2” journal. His response was that he would grind it with a large radius and it may actually end up stronger than stock. The machining cost of turning the crank was the same regardless so I said, “Do it!”

Cam Shaft: I called Isky Cams to get their recommendation on a cam shaft for my application. Great people to talk to and they offered to grind a custom cam for about $140.00 I was amazed at that and was ready to order it until I looked in the Summit Catalogue. Long story short, the specifications on the 8601 Summit cam were close to what Isky recommended. The cost for the Summit cam is $100.00 for the cam and lifters. So price prevails!

Compression Ratio: Using this handy dandy compression ratio calculator ( http://kb-silvolite.com/calc.php?action=comp ) I end up with





Costs conclusions: On a normal rebuild I would have about $175.00 into the crank which includes degreasing, turning, and polishing. This doesn’t include magnafluxing. RO-DY did all of this including the magnafluxing plus, the off-set grind for a total of $300.00 So, I call this a cost up of $125.00 to do the off-set grind. The normal investment into the stock connecting rods would be about $140.00. This would include cleaning, pressing the pistons off and on, as well as reconditioning the rods. The cost of the Scat rods is $560.00 so the cost up for the rods is $420.00. If I was to buy the Scat replacement rods anyway, the cost difference would be even less. Ahh, but did you notice the cost of the pistons? I don’t think that that you can even buy a set of low compression cast 360 pistons for less than $200.00 so, I will take a $25.00 save on that one. Add in $130.00 for having valve reliefs cut in the SBC pistons, for the AMC valve locations and angles. If my math is correct, it looks like you can build the stroker for $650.00 above the cost of a normal stock 360 rebuild.

So, what do we get? We get a 383 cubic inch engine that should be just as reliable as the 360, but with a few more ponies. Is it a race engine? In my opinion it is still a 6000 rpm engine due to the cast crank.

[billyrb]

very cool, would be interested to see what kind of power it puts out when done.

[Greg Taylor]

sounds fun! I just finished building a 383 myself

What combo did you put together for yours?

[Greg Taylor]

very cool, would be interested to see what kind of power it puts out when done.

It might go to the dyno, so we might see those figures.

[Johnbaum13]

Subscribed!

[Greg Taylor]

Crankshaft, Rods ... Assembly

Here are pics of the machined crank, with the rods installed in the block.

[brubakes]

What combo did you put together for yours?

Same here. Should be a very interesting build.

[Greg Taylor]

SBC pistons

Here are pics of the SBC pistons and mock-up for cutting the valve reliefs. Once they were mocked up, Rick had them CNC-machined for all the pistons.

[JeepMods]

Where are the sbc piston pics?...

Gaskets alone will run you roughly $100

[Greg Taylor]

Where are the sbc piston pics?...

Gaskets alone will run you roughly $100

Look up ... it's big, shiny and has 4 valve reliefs in it ... just to the left of the 7032P piston.

Yes, gaskets will cost roughly $100 ... that's not being calculated into the (additional) 383 stroker costs, since you'd have gaskets for either a stock or a 383 build ... the $650 cost is above and beyond normal/typical rebuild costs.

[JeepMods]

I'm currently on the ship so maybe these govt comps are blocking the pics?

[smearig]

Cool idea, but the displacement only goes up about 6% so if you have the parts to build a 300 hp 360 then you're looking at roughly a 320 hp 383 for $650.

[Greg Taylor]

Cool idea, but the displacement only goes up about 6% so if you have the parts to build a 300 hp 360 then you're looking at roughly a 320 hp 383 for $650.

The big difference to consider here is that you have an exhaustive choice of SB Chevy pistons you can use, to build about any compression level and performance level you want, for a lot cheaper than getting custom forged 360 pistons done. and you can use the readily available 58-cc heads, as opposed to finding the more costly 70-71 50-6 cc high compression heads (to use with off-the-shelf 360 pistons).

The 304 stroker pistions were about 900 alone for my build.

When I build another engine down the road, I'd consider building a 16:1 compression 383 stroker, based on the Miller-Cycle design ... 8:1 compression stroke ... 16:1 exhaust stroke ... possibly forced induction ... GOBS or power and MPGs ... but that's for an entirely different thread.