Stroker crank, high comp. pistons, solid roller cams, etc

[Anonymous]

Ok this is long, so I figured I'd let you know in advance. I am looking at boring and stroking to around 390 cubes, going with big valves(big as possible) around 12:1 compression, a BIG roller cam, forged steel crank, rods, and forged pistons. This will be a 300 based engine. It will have to last a decent bit, and I'd prefer to run as little ignition advance as possible, to avoid pre-ignition. My other questions are, is there a header to put this in a car, along with an oil pan to match? Carburetion is planned to be an Offy single plane intake, with a 1000 cfm Holley. I want to compete with the small blocks at Engine Masters, and am looking for all the help I can get. Thanks in advance.

 

[xctasy]

Find a good friend with a drop forge or who specialises in billet steel crankshafts. A 390 cube in-liner isn't possible unless you make your own.

You can't go over 4.06" on the bore unless you use hard fill cement in the block, and there is no way you'll fit anything more than a 4.5" stroker crank in the crankcase.

Your talking custom bits here, and 350 cubic inches is about it.

Cliffords did a 330 cube stroker a long time ago, using a welded steel crank. From the Salnt Six forum, the Chrysler 225 slant sixes got about a 375 thou stroke increase welding the crank, but as soon as you start welding for performance, you runs some risks of grenading the crank. There are some steel cranks around if you want to risk it. I've seen thinwall 265 Chrysler six in-line engines bored 100 to 130 thou over in Australia, but they are risk prone to weeping or blowby from block support issues.

When you consider the stock thin wall castings when new were only 120 to 130 thou, and rust can create less than 90 thou on some engines, then over bores of 100 thou are a worry. A 12:1 compression engine needs 180 thou at the trust face with a 3.5" stroke and 5.7" rods. With 4.5" stroke and even 6.5" rods, it would sure need more iron in the bores than that.

 

[Anonymous]

Thanks. I was figuring a max. bore of .060. It doesn't matter how big it is, I threw that number out for comparisons sake. With cut-down counterweights, and smaller big ends on the rods, would it be possible to get a 4.6 inch stroke? Keep the comments coming, as this is a very interesting subject, and y'all kno more about sixes than I do.

 

[63redtudor]

If you really want to stroke a 300, why not look into using a chev 292 crank? The 4 1/8" stroke would be a decent starting point. From the deck down the 300 & 292 are very simular & the blocks are simular in physical dimensions. I'm pretty sure that a 292 crank could be modified to fit, I have a 300 block that is stripped down & a chev 250 crank (shorter stroke). Out of ciriousity a while back I put the 250 crank in the 300 block. It was a very close fit, lined up almost exactly. It would take a little of modification, but it could (?) work. The thing is though, you're going to end up with a long stroke motor. L6s don't really rev super well & a longer stroke isn't going to help that. One reason that the v-things produce the horsepower they do is that they tend to rev better. Your stroked 300 would out-torque them though. You might actually want to use such a motor in an off-road, or mud drag race instead. Just some thoughts.
Edwin

 

[xctasy]

The GM cranks have the thrust bearing at a different position, so you have to make the rear and front flanges of the steel crank work. It may force yo to use a Chevy auto trans if it doesn't sit in correctly. The Chevy swop sounds great!

I believe the bore spacings are 4.4 for both, but some people have put the bore spacings at 4.48 on the Ford 240-300 Six.

Aussies have been doing Ford swaps into Holden sixes of a similar design, and they have had to weld the Holden flange on the Ford crank. With the GM crank, you could just turn down the crank to fit the rope seal at the end. A lot of work, but perhaps its the way to go. Hope fully, the Chevy front sonout is bigger and can be tuerned down to the Ford size.

I've got some pickies of the Ford 221 crank to Holden L6 swap. It may help you guys get something clearly worked out. The spigoted and welded on Holden crank tail on this 221 Flacon crank is similar to the Chevy one.

WARNING! tHESE ARE BIG PICTURES!

http://www.opensourceguy.com/fordsix/xecute/Ford_221_Forged_Steel_Crank_#101.jpg

http://www.opensourceguy.com/fordsix/xecute/Falcon_221_Forged_Steel_Crank.jpg

 

[6bangerbill]

How about sawing the top of the block down to the lifter bores and make a sleeved cylider case to replace it . Coolant passages could be gun drilled and milled with a bolt on cover. A bore of 4.25 would be easy.Combined with a 4 1/4 stroke gives 362 ci. Adding a Ls-1 hibred head would make an easy 600 hp. Isn't money wonderful!

 

[Anonymous]

OS giken make a 3ltr stroker kit for the RB26DETT engine and with the kit comes a plate (about 50mm thick) that fits between the block and head
the then bore the plate and block and fit sleeves thus giving a taller deck hight

 

[Thad]

OK, so somebody makes a super stroker crank, how far can they go before contact between rods/ crank throws and sides of the block or cam?
The factory is not going to have excessive room in the crank for many reasons. Going from 240 to 300 got close to "filling" the bottom end.

That has always been the ultimate limiting factor.

 

[6bangerbill]

does anyone have experience in sonic testing 300 or 240 cylinder walls? I've read any where from .125 to .160 walls and i've also read that .160 is the required minimum for high horsepower.

 

[Anonymous]

im thinking of trying to increase the stroke of a 300/6.would cuttong down the 300 crank to take chevy 292 rods work .just a thought.
thank you
lrd56 a happy dinosaur

 

[JP]

I recently had my 78' block sonic checked for curiosity. From front to back 1 thru 5 were in the 200 range but 6 was only around 100 ( core shift). So with multiple block testing 200 over all may be possible. Block is bored 30 over.
jp

 

[Anonymous]

OK, so somebody makes a super stroker crank, how far can they go before contact between rods/ crank throws and sides of the block or cam? The factory is not going to have excessive room in the crank for many reasons. Going from 240 to 300 got close to "filling" the bottom end. That has always been the ultimate limiting factor.

This is what I was wondering. Has anyone watched the rod and counterweight clearance in a 300 block while turning over the crank? The amount of clearance available will tell you a lot about how much potential for stroking there is.

 

[xctasy]

Tip 1, measure the width of the internal crank case.

The Chrylser Slant six was very wide, and can be overstroked with the stock rods 2.25" rod journal welded out to 4.50" from the stock 4.175". A few grinds to the sides, and care full checking of the cam clearnace, sweet! With a 100 thou over bore, 260 cubes from a 225 cuber, a 16% improvement in torque with no other mods. Like going from a 302 to a 351!

The 223, what was the longest stroke it ran? It's likely the 300 will take 4.375" stroke.


In Aussie, the little 186 cube holden engines with very tight crank space of less than 9", could take an offset ground Falcon crank, and get a 235 cube monster with Holden stock rods. A 26% boost in capapcity.

Tip 2:
The Holden block was gouged out in the pan area like an ancient glacier path, the cam was ground down for conrod clearnace, and the rods bolts and rod caps were curved with a linisher to create space. A spare block, some time, and allow for reducing a block to scrap when you cut through a water gallery, but a 335 looks possible.

There are some nice long Honda rods, with smaller journals, which would work real nice. Frenctown Flyer noted that the drag racing set had experiemented with them for reducing rubbing speed of the bearings, or destroking. Most of the time you offset grind to upstroke the throw of the crank, you loose strength in the crank. The fillet radii around each of the six big ends can be reworked to a 20 to 30 thou radius, and create a stronger stoker crank than one that doesn't have a prepared fillet radius. The strength is all in the surface, not so much in the overlap and journal size. It's doubtfull you could make a stroker as strong as the stock 3.98".

Last point is that an offset grind on a cast 300 crank with a 1.88" rod journal will only yield about 4.21" tops. 322 cubes with 30 over pistons.

With a steel crank, if you can trace one, you can weld and maintain the stock 2.124" journal size, and still get 4.375". If it doesn't hit the camshaft. 335 cubes with +30's. A 7 to 11% increase.