4.3 stroker

[Plechtan]

I need to build an engine less than 262 cid (4.3l) to qualify in a racing class. My though was to start with a 4.0, use standard pistons, chevy 6" rods with a small (2") end. then offset grind the crank .100" to get a 3.64" stroke. I figure that this would put the top of the piston about .030 below the top of the block. Is this correct? The displacement with .030" over pistons should be about 262 ci

[SIXPAK]

How about using a standard 232 crank [3.5 stroke], bore to 3.935 [.030 over] and have 255.4 ci?

[Cheromaniac]

Expanding on Sixpak's suggestion, here's a mini-stroker combination that would work:

4.0 block with cylinders overbored 0.060" to 3.935"
232 crank with 3.50" stroke
4.0 rods (6.125" length)
Silvolite 2229 pistons (1.581" pin height)

This will yield a displacement of 255.4ci (4185cc or 4.2L) and a deck clearance of -0.003". Compression ratio with the Victor-Reinz 0.043" head gasket and no milling of the block/head will be ~10.0:1.
You could offset-grind the 232 crank by 0.045" to a stroke of 3.59" and that would give you the 262ci displacement you're looking for. Unfortunately you'd need custom pistons to go with the 4.0 rods (and also the Chevy 6" rods) making it a much more expensive build.

[Plechtan]

I didn't even think of the 232 crank, I would like to put special rods in anyway, but if i can use stock length Chevy rods vs having special ones made, i would prefer that.
If i used the 232 crank and offset ground it for a 3.6 stroke, used a chevy 6.3" long connecting rods and KB944 pistons (1.353 pin ht). This would give a displacment around 261cid and would support the high RPMs better.

Now, wher the hell do you find a 232 crank?

[Alex22]

Which inline chevy 6 used a 6.3 center to center? The SCAT rods i'm planing on putting in mine are 6.000 center to center. I could always order some with a longer center to center distance but it would probably cost 2 to 3 times as much as their production rods.
Typically a larger bore and shorter stroke is better for high RPM's.

~Alex

[Plechtan]

The 6.3" inch rod is a standard Eagle H beam connecting rod, not a standard chevy production rod. The rods I was looking at were the ESP Featherweight H beam rods. The weigh about 540 grams each, and they come in 5.7, 6.0, 6.125, 6.2, 6.250, and 6.3" lenghts. These are the small Journal (2.0") rods, this give you more room when you want to grind an offset crank. You can also get them sized for a Honda Crank (1.889") if you really want to stroke the crank without welding. Some people like to go to a smaller journal to reduce rotating mass. this is more important in drag racing than rock crawling or land speed racing.

[John]

As far as where doI find one? http://www.rpmmachine.com/crankshaft-ki ... jeep.shtml A lot of places have them. Call Clifford Performance yet? Hesco? Interesting project you have started. Keep us posted.
John

[Alex22]

The 6.3" inch rod is a standard Eagle H beam connecting rod, not a standard chevy production rod. The rods I was looking at were the ESP Featherweight H beam rods. The weigh about 540 grams each, and they come in 5.7, 6.0, 6.125, 6.2, 6.250, and 6.3" lenghts. These are the small Journal (2.0") rods, this give you more room when you want to grind an offset crank. You can also get them sized for a Honda Crank (1.889") if you really want to stroke the crank without welding. Some people like to go to a smaller journal to reduce rotating mass. this is more important in drag racing than rock crawling or land speed racing.

Are going to use a small block chevy rod with a big end width of .940, if so, are you going to be grinding a larger radius in the crankshaft to take up the extra 0.115 side clearance on the big end? Or do you have something in the works with Eagle for a semi-custom connecting rod?
I'm planning on running the SCAT 250 I6 chevy rod that will only have an extra .005 or so side clearance. Of course I'm going to need to run a custom piston.
If you want to go all out on this build and spend a boatload on the pistons and rods you could go with a set of piston guided pistons and rods.

~Alex

[Plechtan]

I would like not to have to by custom pistons and rods, If I am grinding the crank quite a bit, i can make it so the rods work correctly. Pistions and rods will still end up costing about $1,000.00

[Plechtan]

I was trying to figure the compression ratio for this engine, here is the numbers i was using:

Piston dish volume 21.73CC
Head Volume 57 cc
Head Gasket .043 thick
but i seem to have different numbers for the deck height, I think it is 9.450 or 9.445 (crank centerline to top of block) What is the correct value?

Stroke is 3.6
Rod is 6.3
Pin height is 1.353

I assume this would put the top of piston .47 below the top of block, are my assumptions correct?

[John]

Deck height..... Here is a thread from a while back. viewtopic.php?f=15&t=225&p=2804&hilit=deck+height#p2804
John

[Plechtan]

So depending on what block you have the deck height may vary .020 That would make a big difference in the compression ratio. Running the numbers above i end up with the piston .003 out of the block using a 1999 and up block. ( i think). I could probably just shorten the stroke a little to get the CR and Quench height correct.

[seanyb505]

Did you say a while ago that the class youre running in had to keep stock deck height or quench within a certain range?

[Plechtan]

The block you start with has to be the same deck height as stock, you can deck it, they just do not want you using tall blocks.

[Jeep-Power]

I know this may roll a few eyes, as it isn't exactly a stroker...

I've got a 4.3 using the stock 258 crank, rods, pistons and block bored .030 over... the 4.0 head goes right onto the 258.

As far as I know any of the 4.0 cams will fit in the 4.2 block...



Awaiting corrections...