340 8 bolt 3.51 crank

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scott hoffman

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Hi Scott here,

I am looking for advice on an upcomming 340 build. I am looking to replace the mild but good running 360 that is presently in my roadrunner. I have been getting parts for build for a long time just have not pulled the trigger. Ok I have this Mopar Crank old school 8 bolt 3.51, matching flex plate and a set of custom diamond pistons a gift from the wife. Has anybody used one of these cranks? I am not looking to race but make a reliable street pounder. I have two 340 blocks one 30 over and one standard. One set of fresh X heads, the camshaft and rockers are from Hughes, Should I be looking for a different crank piston combo or could this work? Thanks Scott for any input.

PS I have a 72 duster to I love them both. Both cars are father and suns projects.
 

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I've never used one, but my thoughts are.....you have it...use it. You've got a flex plate which removes a hurtle; looking for one could be a pain.

Put a good rod between the crank and pistons, have fun.

Good luck!
 
I have a new set of 360 I beam rods from Mopar do you think that will be enough or should i be looking to a H beam?
 
What is your anticipated power level?

I would think a set of Scat "I" beams would do the trick, strong, affordable, lite.
 
I also have a MP stroker crank. 8 bolt, (IIRC) 3.45 stoke, designed to destroke a .030 - 360 to 352. (355 & under rule, NASCAR) All part of a package deal.
These are forged cranks and should take a huge amount of horse power to wreck it.I do not see any problem making use of the crank in your 340. In fact, you'll gain cubic inches.

IMO, use the crank, drill out the oil passages (Oiling mods) to keep it very well fed and have at it. At a .030 overbore, you will have with the stroker crank, 365.32 cubic inches.
This you may allready know, but for those who do not know this tid bit...
The pistons will of course have to be fitted to there own bores. So if the pistons are all ready .030 over, you need to use the standard bore block.
 
Thanks guy, i see your both from New York im originaly from Queens but 21 years in the Navy brought me to VA where im stuck.
 
If you are thinking about the block on the right in the pix, check the lifter bores carefully for excessive rust pitting. Are the '360 Mopar I beams' just production rods or ??? If brand new, then even the stock rods supposedly can handle your power level.

I will say that after buying a set of SCAT I-beams, I like the idea more and more. Saves you $$ on balance work, with them weight matched both overall AND end-to-end. With a new set of good pistons that are also weight mathced (the KB hypers we got were reeeal close in weight, and I would expect other good brands to be that way too), then all you have to do is compute a bobweight and have the shop balance the crank to that number....easy.
 
The rods are brand new mother mopar in the box, but I am thinking of going to look into the Scat rods. The pistons that I have in the pic are forged customs fabricated for this crank from Diamond. The block on the right is a standard and the one on the left is 30 over. I do not think i will be able to use the 30 over block as my pistons are 30 over and I think it will need more then a hone to clean up.
 
The block on the right was originaly machined for this build but it was at a shop that went under here in VA while I was stationed over seas and buy the time i got it back from a shed it was in bad shape, but i did get back a completed set of X heads that somehow ware is grate shape.
 
scott hoffman said:
Thanks guy, i see your both from New York im originaly from Queens but 21 years in the Navy brought me to VA where im stuck.
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Born Jamaica hospital, lived in South Ozone Park for a while, moved to the island later on.
scott hoffman said:
The rods are brand new mother mopar in the box, but I am thinking of going to look into the Scat rods. The pistons that I have in the pic are forged customs fabricated for this crank from Diamond. The block on the right is a standard and the one on the left is 30 over. I do not think i will be able to use the 30 over block as my pistons are 30 over and I think it will need more then a hone to clean up.
Click to expand...

The rods are "MoPar" rods?
Maybe a little heavy by todays standard. But there killer rods.
Even OE production rods are very very good.
 
ok looiking through the boxes in my shed I found a new in the box set of Eagle Sir rods, going to use these over the stock rods.
 
if the eagle rods are made in china, are they better than made in usa stock rods? I prefer made in usa
 
man I did not think of that way or realize thay were china crap. good point thanks, with that said are the Scat rods American made?
 
I have no idea where the SCATS are made.... they seem to have a good reputation. Perhaps go on their website. The Eagles.... I dunno. Seems like their cast cranks had some issues IIRC, so maybe the rods are suspect due to that.
 
I have seen the Egale rods hold up on some reasonably well powered engines. They are advertised at a lower power level than the equal Scat products. I think the biggest problem is people will push the limits of the advertised power level if not just simply ignore it.

I thought the advertised power level of the cast cranks from Eagle were low not only in comparison but in general. 4.00 crank good for only *** HP while the competition has another 200 HP into of there cast crank. Minor price differences, not huge ones.
 
This 367 stroker is going to eventually go back into the Roadrunner pictured and my 18 year old sun on ocasion might be driving it, I was only looking for around 380 HP, when the motor is finnished, but really with the sum of the parts not sure what HP to expect out of it? The crank, Cam, heads and pistons were matched under the advice of Hughs Engines, witch have been sitting in the boxes for 9 years 7 of them I was stationed over in japan. So I need to ask since both the 360s in both my cars run really good, can is it ok to build this motor and have it on the stand in a Bag, or is it better to leave it boxed up till I really need the motor?
 
check with any manufacturer, made in ? any stalling = not good old usa. If U get any cranks or rods not from usa I would have them magnafluxed or x-rayed
 
scott hoffman said:
is it ok to build this motor and have it on the stand in a Bag, or is it better to leave it boxed up till I really need the motor?
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Some people report having built engines, and oil them and turn them regularly but if you are deployed, who is going to turn it over every month? Plus considering the salt air at VA Beach, I'd keep the parts boxed up and wait.
 
Thanks for all the advice guys, and happy to say that I am now retired Navy, I am only missing two parts for this motor, push rods and Harmonic balancer, any thoughts? I was figuring Cooks Brothers pushrods not sure on the blancher as the motor is going to be internally balanced.
 
Does it need to be a certain spec AKA SFI?
 
Balancer, spend the money on a quality SFI one.
Your machinist will need it when he balances the assembly, also some aftermarket ones will need honed to fit the crank correctly.
 
I agree with JBurch you have it use it. You are looking at 365 CID with the .030 over block. Heck balance the rotating assembly, put in a purple shaft .484/ 284 cam maybe buy a small stall convertor and go have fun. Heck it should be fun to run, with good HP and TQ.
 
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