308 / 328 stroker crankshafts – An overview

Ferrari Pilot seems to be the most well versed in this topic

 

Heres a 10.5:1 308 custom piston I had made to work with a 360 crank and the 360 Ti rod. Just enough room for a pin under the ring pack. 82mm bore 79mm stroke. I wouldnt bother putting anything less than a 360 crank in, Ti rods are a sweet option to lighten things up but the stock steel rods will do the job.
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I measured the stock pistons with stock pin diameter and believe we have a window of about 79-80mm total stroke we can go for with our rod length. Stock pin is 18.5mm while the 355/360 pins are 20mm. The 360 is definitely pushing the limits with the 20mm pin to where the oil ring lands can be while the stock 308 pin diameter can probably move up another mm for 80mm stroke, but that would of course require a custom crank which is just sort of pointless.


The flywheel bolt pattern have been the same on all Ferrari's since the 246 Dino. I have yet to find out if the 360 crank I am mating my flywheel to while show TDC to be the same as the 308 crank did, but I will know very soon. If it doesn't, I will just mark the correct TDC on the flywheel and go from there. The other difference is the crank from the 348 on were all .049 shorter at the flywheel mating area. Not a big deal at all.


The 308/328 cranks are dimensionally interchangeable. If one has a 308 apart for a rebuild I highly recommend getting a 328 crank as they are pretty available and cheap. Just have to replace the pistons obviously to accommodate for the new stroke length which a person should plan on doing anyway so long as the motor is apart. If you can though, I would get any upgraded later crank you can as it's not much work to make them operate in the 308 block either.



In all, I am finding using the 360 crank to straightforward. The exception is that a .105 thick ring with a keyway and radius cut into the ID it to accommodate for the timing gear offset difference between the 308 and 360 cranks had to be made (thanks Paul). So in other words, the timing gear on the 308 crank sits out .105 further than with the 360 crank which allows the timing gear to sit too deep.

 

Boy, I'd love to do this. Now all I need is the time and money

I'd think that Pizzaman would be all over this.

 

Hi Neman,

I have a question ;

Assuming a 308 on carbs and upgrading to a 360 crank,TI rods and custom pistons
- do you not have to address inlet and exhaust flow to get the full benefit, or would a cam with longer duration get the job done also ?

 

I actually thought quite a bit about the best way to address this without welding and reworking the inlet ports entirely. The port itself is really quite terrible with almost no short side radius and a poor port angle all around. In the end, I went with larger ID and OD valve seats which left about a .040 shoulder around the inside so to enlarge that area in general. I then ported the bowl removing the shoulder and blending through to the throat. The stock type 'tulip' valve shape was tossed and a 11-12 degree back cut 44mm nailhead style valve from Manley was custom made (2mm larger than stock). All around flow is up 11% with the largest gains being over .200. The cams keep flow well over .200 for a substantial amount of time meaning these cams with the new found flow will be more than enough to flow the displacement.

I only replied for Newman because he is doing everything I already did lol. For pics of the ported intakes and nailhead valves, head to the '3.4L project' thread and they are there.

PS. Paul, the other valve seats are supposed to be hear early next week.

 

Got it, so that may be the first thing on the list. Where does one look for 328 crankhafts that are usable?

 

GT car parts in Arizona (ask for Bill), ebay, and Ferrparts are probably the best places to start looking for a good used crank.

 

Has anyone had any experience with the 78mm crank that Tate is making at Carobu?

 

Sorry I didnt see your post until just now. Its a package deal or its a waste of money, its all about the combination of parts as with any engine build so you're altering everything.

One thing that stands out in my mind the most is the weight reduction of the 360 crank, almost 10lbs when running the Ti rods. The 512M also has a light weight crank that is approximately 18lbs lighter than a 512TR crank. I would be curious to hear the weight of the carobu crank vs a stock 308 unit.

I have a 328 crank available if anyone wants one.

 

360 crank vs 308 crank. Narrowed counter weights, hollowed throws and lightened across the center line. Less rotating mass is a good thing and with the longer stroke and longer dwell at TDC it all adds up to an awesome ride. I was out in a 3.4 yesterday and loved it, total transformation sums it up.
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The 78mm crank Carobu sells I believe is made by Scat cranks. It's a good piece, but the 360 crank is better. I still have no idea why if Carobu were having a crankshaft manufactured they didn't go with 80mm stroke. The means piston speed with such a stroke would still be fine and there's plenty of room in there.

 

"I'm curious if "the juice is worth the squeeze".

IMO, not only no but H3ll no! The HP you can gain by doing this vs cost is so low on the cost benefit scale that it won't even show up. That's not to say it isn't an interesting exercise but these are not US v8 motors where pretty impressive gains can be attained at relatively low cost and the parts are cheap due to volume. For someone who wants to do it just to do it, that's great but the cost/benefit for power on these cars clearly points to a supercharger.

Plus, you can return the SC'd engine to completely stock if/when desired for resale. Most buyers are not going to be interested in a modded motor due to the reliability concerns associated with it. I am NOT saying that a modded motor can't be as reliable or more so than a stock motor but the common perception is that mods = problems. Most people's view of modifications is that if they are to be done, THEY want to be the one to do them/have them done. They don't want to wonder about what the previous owner did.

 

Not everyone wants forced induction but I like it (my daily driver truck has an eaton blower on it), in fact I was told very clearly that it was not an option on the 3 other 3.4s and the 512M project because they (the owners) preferred as stock looking as possible. A blower would be like putting a moustache on the Mona Lisa to them. This 3rd 3.4 in no exception even EFI was questioned because of the visual impact but we got past that in the quest for max power and drivability.

 

A 3.4L conversion costs the same amount as a vanilla run-of-the-mill engine rebuild + the cost of the crank. So, if someone is rebuilding their engine anyway a 360 crank is a massive game-changer. And it looks stock, so if someone were wanting to show their car or sell their car as original, they would with zero issues. Last time I checked, judges cannot get inside the engine lol.

And turbos/superchargers look like heck from the outside, and IMO drive like heck.

I knew I guy with a concours winning Maserati Sebring or 3500gt with a Allemano body (can't recall which) but the mechanical fuel pump was actually modified to hold a modern electric fuel pump inside! Concours winning car, looked perfect from the outside which is the point.