4.8 crank question
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
4.8 crank question Hi all. Before I start, yes, I did use the search and came up with nothing. I’ve been wanting to do a rowdy 4.8 for a long time. I got my hands on a very nice specimen today and my mind is already spinning with ideas.
The first thing Hong I wanted to look into was forged internals. I can’t seem to find a forged crank for a 4.8. Does anyone know who makes one... or if anyone makes one? If there aren’t any to be had, or if there are but they’re insanely expensive, does anyone know what kind of power the stock 4.8 crank is good for and still maintain reliability? Thanks for your input.
The first thing Hong I wanted to look into was forged internals. I can’t seem to find a forged crank for a 4.8. Does anyone know who makes one... or if anyone makes one? If there aren’t any to be had, or if there are but they’re insanely expensive, does anyone know what kind of power the stock 4.8 crank is good for and still maintain reliability? Thanks for your input.
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
I am thinking much more than that, like around 1000 at the crank. Obviously I’m not going to be driving it WOT at 1000 hp all day, but I want the capability. I also know this is much more easily done with displacement, but I want to use a 4.8 and most likely twins
TECH Enthusiast
Joined: Nov 2016
Posts: 711
Likes: 6
From: PNW
People have put well over 1,000hp through a stock 4.8 crank. It's all revs. I don't even think there is a such thing as an aftermarket 4.8 crank. Eventually I'll be going that route once I blow up my current setup.
American LaMans 3.267" Spares Hi Nick, I have assembled a few LS Racing Engines with a 3 1/4" Marine Crankshaft. (Billet)
The car racing series that used this type of engine is not common today, with "spare" engine parts an easy find.
Would you like my help to find a short stroke crankshaft ?
Lance
The car racing series that used this type of engine is not common today, with "spare" engine parts an easy find.
Would you like my help to find a short stroke crankshaft ?
Lance
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
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Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Hi Nick, I have assembled a few LS Racing Engines with a 3 1/4" Marine Crankshaft. (Billet)
The car racing series that used this type of engine is not common today, with "spare" engine parts an easy find.
Would you like my help to find a short stroke crankshaft ?
Lance
The car racing series that used this type of engine is not common today, with "spare" engine parts an easy find.
Would you like my help to find a short stroke crankshaft ?
Lance
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Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Really I’m not looking for 1000 rwhp, probably closer to 800, but I figured that’s probably close to 1000 at the crank. In a sub 3000 lb street car that should make for a fun ride and not eat as much fuel as my 545
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Totally separate thought, but anyone know how they do with nitrous? That’s power, but it’s a different kind of power
Yes, I plan on making the power with twins and high rpm. It’ll be a little bit different powerband than my 545 build.
I have that article bookmarked on my computer and phone, lol. That’s what spurred this idea years ago. I know it’s been a long time since that came out. I was just curious if anyone made a forged crank for them. Sure the stock crank did it on a dyno, but how many times would it do it in a car before becoming a stain on the road?
engine dynos are harder on the rotating assembly than an auto car
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Yup, they did over 60 pulls at 1000+ hp. I’ve had that article bookmarked for 7 years, lol. I’m not sure if I’d agree that dynos are harder on an engine. I used to have an engine dyno and it was wonderful for tuning, but there’s a lot of stuff that happens in the car that you can’t simulate with a dyno
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Forged LS 3.267 Race Billet Crankshaft Hi Nick, AS STATED the Marine 3 1/4 " cranks are NOS OR 2nd hand from racing engines no longer in spec, POR OR in other words, LOW COST.
Lance
Lance
TECH Enthusiast
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From: PNW
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Just from what I’ve been reading that seems to be the case. It also looks like nobody makes an exact stock length rod, so I’ll either have to go with a 6.250 or 6.300, no biggie. I’m just curious to see how far down in the hole the pistons are stock. If they’re 0.025 or so then that’d be pretty cool. I could get some forged slugs with a small dish or use a different head to keep the compression where it needs to be.
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Well if that’s the case it looks like I’d be needing a custom piston. I’ve used JE/SRP in the past and been very happy with their quality. I just don’t see anything out there for aftermarket, stock length rods. Correct me if I’m wrong, but it looks like you’ve either got to go with a 6.250 or 6.300. I’ve been unable to find a 6.276” con rod.
I guess I could go with a 6.250 rod and have it about 0.020 in the hole and shave the head a bit to bring compression back, but I’m not a huge fan of that idea.
I guess I could go with a 6.250 rod and have it about 0.020 in the hole and shave the head a bit to bring compression back, but I’m not a huge fan of that idea.
Thread Starter
Staging Lane
Joined: Oct 2016
Posts: 84
Likes: 0
From: Lake Charles, LA
Actually I just did the math and sinking the piston in 0.020” (using stock type piston with 6.250” rod) would yield a 9.12:1 CR vs the 9.64:1 stock CR. That’s not bad at all, and even a bit more turbo friendly. Still giving up some quench though.
FYI, that is all based on the assumption I use a head gasket with a 0.051” compressed thickness.
FYI, that is all based on the assumption I use a head gasket with a 0.051” compressed thickness.