I'll start by saying I did try to look up this information but I didn't have the best luck finding the answer I wanted. I want a solid answer. Anyways...

Ok, currently I have an LT1 with a cast Eagle crank, Scat 5.7" forged rods w/ ARP bolts and factory pistons. That completes the bottom end. This motor has seen 6500rpms consistently during the last few years and never gave me any issues so please refrain from calling cast parts junk. This is not what I'm asking about... I want to build a very budget friendly 383. The current 350 has lots of metals in the oil so it's safe to say something is wrong. (Probably in the clearances as I was quite inexperienced when I built this engine)

I found a cast Scat 383 crank on summit that is pretty inexpensive. The issue I'm concerned about is that I would like to continue using my Lloyd Elliot cam (232/240 .578/.574 110 LSA) without needing a new cam. I discussed this with Lloyd and I got a bit confused. I checked my compression ratio to be 11.82 static and dynamic I got 10.54 using the ABCD calculation following this guide I found.

"The intake valve closing point ABDC is calculated in the following manner. Divide the intake duration by 2, add that to the lobe separation and subtract out any ground-in advance. Lastly, subtract 180 degrees."

Lloyd Elliot replied with this..
"Everything looks good BUT you need to use the adv duration IVC instead of the @ .050".

This will usually be 25-27 degrees higher than the @ .050" IVC."

What does that mean? I was merely copying what I found online for 383LT1 kits. A flat top piston with 5cc reliefs. I want to make sure I can run pump gas with this car so will I need to use a dished piston?

I plan on using Fel-Pro gaskets and as of right now the deck is factory height and the heads are ported aluminum castings. I also plan on re-using my Scat forged rods and clearance the block myself. I figure I can be quite a bit ahead with only needing to buy a crank and pistons. (Obviously I will need to buy more items but those are the 2 big items)

Again, I'm not going to be spending $600 on a forged crank. It's just not going to happen, there are plenty of people who have good luck with cast cranks. I did choose to avoid Eagle cast cranks though as they seem to have the highest rates of failure.

Thanks for the help!

 

Many cams for SBC/LT1s are sold using their duration at .050. To properly calculate things like overlap and static compression, you need to use the cams advertised duration, which is a much bigger number and usually measured at .006.

The cam card should list the advertised duration of that cam, which are the numbers you need to use for that calculation .

 

I think most will tell you that a stock crank is better than aftermarket cast. I know you said you dont care, but maybe you should re-evaluate your plans. Why not find a stock crank or at least find a used forged piece. I bought a used SCAT forged 383 crank for a couple hundred bucks.

 

Hi, First my 3.75" forged crankshaft comes from the Scat "side" in China, on sale NOW for $400.00 though you could get the "ultra" for ONLY a small amount greater, view John's ("ITB" thread below) pictures.
We have a cast crank, same Scat plant, lower price than forged.
I would use King Bearings.

YOUR 2nd question : I would use "Static" C:R for the model.
What is you head cc amount ?
You WILL do a "Valve Job" ?
You could drop the Exhaust Valve to help create a larger volume.

I would fit a RacTec piston at -5.3cc.
These WILL be made to fit your block "HONE ONLY" bore with correct deck.

You ARE using your mind well, engineering first, low cost, top quality items.

I can be of great help if your just ask.
You cauld call John C. as he uses the same mode as you.

Lance

 

I understand but I also don't think there is any real data to back that up. Also if I go with a stock crank then i'm still a 350 and I want a 383 for the extra cubes.

Maybe I'll search for a used forged 383 crank. Then I'm still behind as I will have to have it turned. I'll look around though, not a bad idea.

 

Stock crank, boosted, 648 RWHP = no problems... Thats my data..

 

OP

cast crank failure, especially Eagle, have been reported several times by those who had it happen. Me being one of them. Does every one fail, no. Mine broke just driving down a street at 30 mph. I had about 2k mi on the motor when it happened.

This was a 383 short block built by a reputable builder. Fortunately that shop promptly built another 383 short block for me and replaced the block as the crank took it out and charged nothing other than the difference of the cost of me upgrading to a forged crank. I got a Scat. 10 years and 35k mi later all is good

Given mine broke 10 years ago "maybe" Eagle stuff since has improved.

Understand you are on a budget and yours may be fine, just commentating on you hearing "real data"

 

I have a split in two cast eagle 3.75" stroke crank in my garage, won't make that mistake again.

Back to a stock bottom end motor and luckily nothing else was taken out sans a rod or two IIRC so I was able to swap it to the new shortblock.

 

Like I said I have heard a lot of negative about Eagle stuff but I planned on using a Scat cast crank. The difference in price from $200-250 for a Cast crank to $600 for a forged crank (on Summitracing) is quite the difference in price. I'm looking around for maybe a used forged crank but how much does it cost to turn a crank? $100? I'll post in the parts department looking for one.

Also everyone says that stock cranks are better but aren't stock cranks also cast aka "Nodular iron"? I'm sure there is a difference in quality control but still...

Anyone got a forged 383 crank for sale cheap?

 

If you do buy a used forged 383 crank like a Scat you don't want one that needs "turning"...just a polish. If there are groves on the used crank requiring "turning" aka ground down .010-.020 under I would pass on that crank. You may visually see it have grooves in it and think it can be turned only to find your machinist says "were going to have to cut .030...at least"

Not every cast Eagle crank fails, but sadly mine did.

IDK how good cast Scat cranks are....my issues was with a Eagle

FWIW I have a Scat forged 383 crank

 

Whats wrong with turning a crank down that far? Will it get too weak?

 

Hi, I would state the 1/8" increase @ 90* in leverage makes a great difference in torque.
The change in R/L, the reduction, is also GREAT for a H.C. engine.
This factor allows for "faster" piston movement away for TDC, good for Knock Reduction.

My forged crankshaft my not be the best for a street car, they are used more often in BAJA 1000 race cars.
That mode of operation is "flat-out" WOT engine use for 4,8,16 HOURS.

I am sure that 1/4 mile, ten second operation, a level surface, use would have a different amount of "stress" on an engine crankshaft.

Lance, BTW when a "steel" crank is ground, you face a $175.00 Heat Treat.

 

^^^...and any crank that does need "turning" past .010 likely spun a bearing pretty good (read motor blowed up Dale) and may also have stress cracks (needs to be magnafluxed to check) so of all available used forged cranks for sale I would buy one that just needs a polish vs "turning"

 

Who is huff29zz? They sent me a message regarding my wanted ad and told me to email them. 0 posts and they are banned? Anyone know anything?

 

the thing is casting is merely a manufacturing process, this doesn't set a standard for the mixture poured into the casting, amount of uses the casting mold has, voids in the casting, etc.

if you ever have access to a decent microscope and a handful of miscellaneous castings, check it out. Casting can be a pretty poor method of manufacture if proper care is not taken. You'll be amazed at alot of the things you might see, fine cracks, pitting, voids, etc.

 

I have been doing some digging and it seems lots of people seem to like the SCAT 9000 cast cranks. Lot's of 383's are using them with no issues. I'm kind of torn, I'm not rich so a used forged or a cast Scat is what I'm thinking.

I'm still unsure if I need dish pistons or not. I'm using ported stock casting 54cc heads. I need a bit of help determining that. This static/dynamic compression ratio stuff is a bit confusing. Especially figuring out the dynamic CR.

 

Also a few cranks that are for the "LT1" say they are specifically designed to work with the LT1 balancer and flywheel. Is there really a difference compared to a gen 1 crank? As long as it's internal/external balance it should work shouldn't it?

 

I was looking at using this crank.

https://www.summitracing.com/parts/s...make/chevrolet

Considering it requires a Heavy metal will that jack the cost of balancing up?

 

Some gen 1 cranks are for a 2 piece rear main seal, IIRC any small block made after 1985 up to the gen 2 LT1 requires a 1 piece rear main seal crank.

As far as piston selection if using stock cc heads you will want a flat top piston and aim for a 11-12:1 SCR. As far as SCR vs DCR here is a good read that will explain it much better than I could.

http://www.enginebasics.com/Advanced...20Dynamic.html

 

Lloyd Elliot told me to aim for 11.1 to be able to run pump gas with the cam that I bought from him.

This is very confusing. Plus I don't have the cam card on me and I have no idea where it is. I'm asking lloyd if he has one or at least all the specs on the card.

But I used an online SCR calculator and with the 5cc flat tops I will get an 11.82 SCR and with the 12cc dish pistons i will get 10.87 SCR. Some people say to aim for a certain SCR and some say it doesn't matter that much and to focus on the DCR which I have no idea how to calculate. (adv duration IVC as per lloyd elliot) or ( intake closing time [or angle] in degrees as per the site you just linked)

I'm trying to understand but I don't know what I should be focusing on. I just want to buy the right pistons that will work with my 232/240 cam. Iwould prefer to not change the cam even though I certainly could have lloyd build a very custom one. He said he certainly could. I'm just trying to avoid yet another cost that I can dodge if I buy the right parts.