5 liter MOPAR

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Destroked 318 sounds interesting. Would probably have to use the Viper engine rods though.
 
Well if we want BORE size, go BIG or go home. Destroke a 400.
 
RammerJammer75 said:
A 4.342 bore with a 2.56 stroke would yield 303 inches. That would be interesting.
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You’d be back at a really high R/S ratio or a very tall compression distance or a compromise of both.

I forget the deck height of the B engines but it has to close to 10 inches. Maybe more. I forget.
 
9.98 Deck on a B engine. But if we got a 9.2 inch deck height pro stock hemi block...Hmmm... I'm not even going to bother with the match for a 4-5/8 inch bore size.
 
+.120 291.7 cube 12.5/1 with a solid 300°/.500 lift 1.90/1.60 valves Single plane/750 carb.
514 hp. @7500 and 412 lb/ft @ 5000
Finding a block that could handle +.120 would be the key. Lots of core shift.
 
toolmanmike said:
+.120 291.7 cube 12.5/1 with a solid 300°/.500 lift 1.90/1.60 valves Single plane/750 carb.
514 hp. @7500 and 412 lb/ft @ 5000
Finding a block that could handle +.120 would be the key. Lots of core shift.
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.120 overbore means paper thin cylinder walls, thick bores make more power, every time.
 
yellow rose said:
You’d be back at a really high R/S ratio or a very tall compression distance or a compromise of both.

I forget the deck height of the B engines but it has to close to 10 inches. Maybe more. I forget.
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Yes sir. 9.98"
 
A56 said:
This is for sale on Racing Junk
SS/COMP 300 cu in 340 R-3 block 8.900 deck,4.080 bore, roller bearings,exterior oil pump,vacuum pump,belt drive and front mounted distributor, meziere water pump,crank trigger,MSD 3,Winberg crank 2.90,W-8 heads,T&D rockers 1.65-1.70,Titanium valves,GRP Aluminum rods, 5.84 Gas ported pistons, stainless headers.One run since fresh.Photos on request.
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Wow! I would like a dyno sheet on that motor. W-8 heads could not stay on motor if they are aluminum (rules).
 
RustyRatRod said:
Well if we want BORE size, go BIG or go home. Destroke a 400.
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Rules say either run a 273 block with no weight penalty or a 318 with weight penalty or go home. I spoke to a tech inspector at SVRA who said be able to certify the crank and try using a 340 block. He would not guarantee approval.
 
So sometime in the late 50s, early 60s Chrysler wanted a car that could be run in a 5 liter class, so they built a 301 poly engine and offered it to the general public in the body they wanted to use. This was a short stroke 318 poly. The only change that you have to make to use it in an LA motor was it had an 8 bolt crank like a hemi, so you needed a hemi flex plate or what ever the conversion is for a 4 speed. In the 1980s a machine shop that I used made dirt track stock car motors out of LA motors with these cranks. Since no one builds polys to speak of these days you might find one cheap. I believe they were forged cranks.
 
str12-340 said:
So sometime in the late 50s, early 60s Chrysler wanted a car that could be run in a 5 liter class, so they built a 301 poly engine and offered it to the general public in the body they wanted to use. This was a short stroke 318 poly. The only change that you have to make to use it in an LA motor was it had an 8 bolt crank like a hemi, so you needed a hemi flex plate or what ever the conversion is for a 4 speed. In the 1980s a machine shop that I used made dirt track stock car motors out of LA motors with these cranks. Since no one builds polys to speak of these days you might find one cheap. I believe they were forged cranks.
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Bruce Toth builds Poly engines.
 
I did some research - apparently the 301 poly was built in 1957 strictly in Plymouths. It had a 3.91 bore like a 318 and a 3.12 stroke as opposed to 3.31 for a 318. This is NOT the same as the 301 made in 1955 for Chrysler cars, which was a poly motor, but one generation earlier.
 
2 Darts said:
Will the block take a .040 cut? I thought the max was .030.
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Any and every block needs to be sonic checked for not only how much is there to start with but also how far it can be over bored. Some 318’s have been known to go to a 4.00 and live long happy lives.
So that’s a .090 over bore.
 
2 Darts said:
Will the block take a .040 cut? I thought the max was .030.
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From .030 to .040 is a .010 difference. I know you knew that already but bear with me. Maybe you didn't think of it like this. Another .010 is "only" .005" from half bore. .005 difference in the radius. Got that part? Now, if a .005 difference in the radius of the bore on a block was "too much" and made the block "weak" as you're eluding to, then that block needs to go in the garbage if it ever needs a .030 over bore. Stop and think about what you're saying. You're saying that 5/1000 of ONE INCH is the breaking point.

There's just no way that's true.
 
2 Darts said:
Rules say either run a 273 block with no weight penalty or a 318 with weight penalty or go home. I spoke to a tech inspector at SVRA who said be able to certify the crank and try using a 340 block. He would not guarantee approval.
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I know that. I read that part already. I was merely "what iffing" and being funny.
 
So you either build aa 273 that may not be competitive, stroke a 273 or destroke a 318
 
RustyRatRod said:
From .030 to .040 is a .010 difference. I know you knew that already but bear with me. Maybe you didn't think of it like this. Another .010 is "only" .005" from half bore. .005 difference in the radius. Got that part? Now, if a .005 difference in the radius of the bore on a block was "too much" and made the block "weak" as you're eluding to, then that block needs to go in the garbage if it ever needs a .030 over bore. Stop and think about what you're saying. You're saying that 5/1000 of ONE INCH is the breaking point.

There's just no way that's true.
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100% true but the problem can be thin spots in parts of the bore where that little bit MAY make a difference.

If you are on the edge already with thin bores that extra .005 may be the straw that breaks the camels back.

These castings are wildly inconsistent. I do not like running on the edge (one of the few times I don’t like doing that) if you are trying to make any kind of power or you are going to tow with it...stuff like that.

IMO it’s always better to use the smallest overbore possible to clean and straighten up the bores. Thicker cylinder walls have much better ring seal and ring seal is power.
 
I'd almost run the 318 as is, and accept the weight penalty, or see if you could run a poly 318, which is already heavier than the LA 318.
 
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