89951DREAMER

Hey Boostguy,

Before you deck that block by .020, make sure that the neg deck height won't work for you in compression ratio. The pistons that I saw for the 6" rod SBC were 9+:1. The fact that the piston is lower in the block will decrease the c/r, and you might end up at the magic 8.5:1 ratio for the turbo engine. Also, removing metal from either the block or head changes the cam timing (retards). You want to avoid this unless you have an adjustable cam gear. I'm all for it. Let me know if you do it and how it works out.

Ian

89951DREAMER

I forget to mention that the c/r for the SBC pistons is with the SBC heads, not the Porsche head. You will need to figure out the cc's of the Porsche head and SBC piston and the displacement along with the cc's of the head gasket to get your final c/r. It sounds like your a smart enough guy to figure it out.

Ian

J Chen

Hey BoostGuy,
Go for it man. I spoke to Broadfoot
once about his engines. He tells me
that he uses stroke 951 cranks for
his engines.

BoostGuy951

Yeah its gonna have to be fully blueprinted, everything checked and double checked. I am thinking the 6 inch rod is gonna be a no-go, since with an unsurfaced block, with th 3.47 crank, you'd have to push the pin height down to 1.32 just to get you back even with the deck. And I am betting there aren't going to be alot of dished pistons available for a 350, so we will have to resort to lowering the compression by increasing the deck height, and its already fairly substantial. The 5.7 inch rod is going to have to be the way to go.

I spoke with the owner of the shop today on the phone, and Explained to him exactly what I am trying to do. He said he actually has seen this done several times before on types other cars, due to the huge aftermarket support of the SBC. I asked him about reliability issues and he told me that they have been doing this for 50 years, If anything it will strengthen it. I told him I was going to be swinging some massive pistons around at 7000rpm, and making north of 500-600hp on a 4 cylinder engine. He assured me that there is no question about the strength. Something else I thought of earlier, is that the V8's still only have 4 rod journals, they run two rods per journal, so there is no more stress on a 500hp v8 crank than there is on a 500hp four cylinder crank.

BoostGuy951

And there you have it. I think we may really have something here.

Brian Morris

I'm surprised that one of 928 guys that lurk here haven't responded but I think some of the 928 stroker kits - with custom cranks - are built specifically to use SBC rods. They do exactly what you describe for rods - but they do get a new crank from Skat.

--Brian Morris
89 951

BoostGuy951

I priced some custom cranks from scat back in the day, they ran like 2 grand for a billet custom grind. Thats the only way they said they would do it, not enough market to do a forging run.

mumzer

i run a stroker crank in my 3.0l. offset ground, lightened, re heat treated and re-radiused journals and cheeks.

there is nothing remotely revolutionary about this process...sorry. Or in converting to chevy journals...all the chevy circle track and endurance race guys are going to honda rod journals.

As for rod choice, you get what you pay for. Eagle makes GREAT 400 dollar a set rods...maybe the best in the world....but they are still taiwanese rods from offshore materials, and can not approach the durability of a carillo. My current set of carillos are intact after 3 motor builds (and 2 catastrophic failures) I have broken 2 eagle SBF rods in 7000 rpm motors.

in a motor with 3-400 bucks worth of gaskets a 250 dollar water pump, a 165 dollar throw out bearing etc, saving myself a few hundred bucks on a connecting rod that was not a lifetime investment just doesnt make any sense to me.


finally, the real problem here has never been the crank and rod package, but the availability of reasonably priced pistons WITH THE RIGHT SKIRT COATING. do a search here. Its not clear from your comments how you plan to deal with the dissimilar metals/ Co-Ex problems that are the real headaches in dealing with these blocks.

I would not overbore the block without sleeving. Sleeving, block prep, pistons, pins rings, balancing and heat treating, as well as fitting the custom rod bearing all cost money. By the time you are done, you are approaching the 3 grand that most folks pay for a 3.0l short block in good condition, and you are ignoring the significant benefits of the 968 piston cooling design, and the materially improved water jacket and cylinder configuration of that come along with the stock 968 parts.

I guess what im getting at here is that stroking the crank is a perfectly reasonable approach to displacement from these motors. Your thoughts on SBC or SBF piston and rod combinations are oversimplifications. Im just not sure that you are going to be doing yourself any favors going this way.

Danno

Remember that you do not want to bring the piston up to stock deck-height. Even with a stock piston, you'll end up with too much compression due to the extra stroke. Do the math 1st and figure out the differences. Most likely with stock piston, you'll need to use an even shorter rod than the difference in stroke. So if you increase stroke by 0.25", you need a rod that's shorter by 0.30-0.35" in order to place the piston about 1.5-2.0mm lower than the deck in order to keep the same compression ratio. This is a common mistake people make (putting pistons back to stock deck-height when going to stroker engine).

BoostGuy951

Ok... I have spoken to the crankshaft guy on the phone at length, and as it turns out, the base charge for the stroke increase of up to .375 is $600. There is also a 80 dollar fee per journal to build up and machine the rod journals to 2.1 inches. This is already putting me at 920 dollars, which is right around the cost of a s2 crank, so this method is not a good idea, since cost was the factor in the first place.

The stock journal is around 2.046 inches. I do not have the exact specs. It has come to my attention that there are two sizes of chevy rod journal. The Journals in the earlier 327's were 2.0 inches. If I can have the journal turned down without adding additional metal, this may allow me to avoid incurring the 320 dollar fee for increasing the journal size. I am going to call again and ask about this.

On another note, I recieved an email response from Brian Crower at Crower Rods, and he is of the opinion that their SBC Billet 4340 Steel connecting rods are up to the task of 700hp in a 4 cylinder. 700hp, 28psi and 7200 rpm are the figures I gave him for my expected power level And the 7200rpm figure was WITH the longer stroke of 3.48 range. I wanted to have a little safety room. He says the rods will be fine.

BoostGuy951

Ok, I am pretty fed up with this crankshaft guy. I called to ask about using the 2.0 rod journal, and whether that would incur the 320 dollar fee. The guy is very unhelpful and just rude. I searched around online for another shop and found one in Minnesota where I spoke to a fella named Wayne. Wayne was very very helpful and friendly. I told him the story of what I am trying to do, and he thought it was great, and was familiar with the concept of adapting SBC rods. Apparently this has been done alot in other cars before I thought of it. I nearly dropped the phone when he gave me a quote. Welding, bringing the stroke out to 3.48 inches from 3.11, building up and remachining the journals to 2.1 chevy specs: $250 dollars.

I thought he must not have gotten the whole idea of what I am trying to do. I re explained and double checked the price. He hadn't misunderstood me. Then I thought the quality can't be there for $250. I asked him about the reliability, I said "well this is gonna be run in a very high horsepower engine, it isnt gonna come apart is it?" He said "Oh Hell no. We do this all the time in everything from big cats and other heavy machinery to drag cars. Come down to the shop and I will show you an 8 second car out front that is running one of these cranks." I explained that I was in Alabama, and I had found him over the web, so I couldn't just come down. Wayne was very helpful, and said that I could send him the rods with the crank when I bought them, and he would check the tolerances for me. I'm really happy to have found someone friendly and helpful to work with on this project. I will be getting this underway soon, and I will have plenty of pics and updates for everyone.

westcoastprshe

So what's your displacement and rod length going to end up being? $250 sure is reasonable. Are you still planning on going with larger pistons too?

BoostGuy951

Yeah, If you remember a while back Kevin Vogel of Vogel Manufacturing showed pics of an interlocking Deck sleeve setup which allows much bigger bores. I will be going with his sleeving setup to take the bore up to 4.310" (a standard chevy Big Block size). Pistons will be from arias. It works out to around 109.47 mm. Final displacement should be around 3.3 to 3.4 liters, depending on exactly what stroke I go with. The rod length will most likely be a standard 5.7 inch chevy rod.

Edit: This engine should be called Frankenstein.

westcoastprshe

Wow, 3.4L is a pretty damn aggressive goal, none of the engine builders out there are making anything that large.

With something that huge, you have to be very precise with all your parts. I hope you're able to call it 'frankenstein', and not 'grenade'

Sam Lin

No westcoastprshe, displacement doesn't change the required precision one bit.

Sam