Molnar 4.65 crank or larger crank builds
 

I saw on Molnars website a listing for a 4.65 crank that they say fits the stock 400 block
anyone using this or know of anyone using this or built one?
I see 4.75s listed by other vendors and at one time thought 5" was an option
price is the same as their other cranks too (maybe the 5" is custom and not in the same)
401-4650RC6F is the part #

Anyone have a 5" stroke build? is that only possible with a tall deck aftermarket block?

my thought is if crank prices are the same why not put the bigger arm in now and save bores for later....

email response:
The crank should work fine in your stock block. I checked with Mr. Molnar to be sure and he said that as far as he knows these cranks have all been going into stock blocks and he has not heard of any problems.

Sorry but I can not recommend any particular builder.

That crank is meant to be used with any of the Molnar Technologies big block Chevy rods listed on this page:

https://molnarrods.com/pontiac-400-crankshaft

You need to match the crank stroke and rod length with the piston you want to use. Most of the pistons for this combo have to be made as customs so you have a few different choices in rods.

Generally the 4.5 stroke doesn't work for poop in a performance build using a stock block. I'm thinking any stroke longer than that would be worse. But they can make a crap ton of torque..... JMO

I agree with paul on this.

i agree
i just never saw this stroke before and based off their response i thought it was interesting as i've never heard of anyone using it
but i'd imagine the torque would be so nice to have

even on aftermarket blocks there have been some issues with the 4.75 (hooter) has some street car experience and went with a 4.65 during a rebuild, i think. the .1 difference is a lot of piston left in the bore. I believe there are more than a few RACERS that are in that 4.75 range. Wasn't that tall deck Alaskan gto even larger with a billet crank, many moons ago?

Wrist pin hole will be peeking out of the bottom of the bore.

I believe Hooter went with a 4.375 Molnar . Im debating this as well, I may just go 4.35 Eagle instead of a 4.5 for an IAII.

4.65 isn't uncommon in Pontiac "big power" builds. Usually reserved for heads up class racing where power is the number one priority.

We've built some fast 4.35 stroke combinations. Seems to be a nice compromise.

Sales volume withstanding,
Aftermarket blocks could be cast with extended cylinders in the crankshaft area

Wouldn't have to be the whole circumference
Could be just like the shape of the piston skirt that normally drops out of the bore to keep off the counterweights like .100 at the pin and .300 on thrust areas
Whatever the numbers are basically get the bottom of the bore down as far as possible with emphasis on thrust areas maybe notched for the rod

Stock block?

I believe the Alaskan GTO was 600+ cubic inch. 5 inch stroke. The tall deck blocks were cast with a raised cam tunnel. Not sure what the largest stroke is without running into interference problems between the rods and cam On a standard cam location

After my experience with Molnar (Chinar) and the money i lost and the lies and lack of customer service.
I wouldn’t recommend them for anything.
F em

From experience, a 4.75 arm is not a great choice for a street car that gets driven. I tried that and it scuffed the heck out of the piston skirts. I’m now running a Molnar 4.375 crank. Piston stays in the bore way better.

Thanks for correction Hooter

Both but not sure if the stock block combos would be considered "fast" by definition.

sorry that happened but its helpful info

i was just shocked when i saw that crank size and oddly never heard/saw a build using it

i wish we had some big bore aftermarket blocks like the BBC has

We ran an IA II at 4.425 with a 4.500" stroke. No issues with the combination in general, making around 1500 HP spraying the hell out of it. Drag race only of course. Not much piston life with the long stroke. Skirts would collapse as the run numbers increased. No other issues attributed to the large bore or long stroke. Bearings were fine, no block failures. Usual head gasket issues in the center after 20-25 runs. Hard insert had not been developed when we ran this combination.

I'm building a 4.5 stroke aluminum block engine now. Using a 6.800 rod in it.