Intake swap thought

[JeremyNH]

Yes I know that they make pistons but is it worth the cost versus the availability of the pistons?

I got my pistons from a racer who decided he wanted more compression after he received them so sold them unused for $100. So in my case a 6" rod was definitely worth it. For factory stroker clearanced rods there didn't seem to be much of a price difference based on rod length. I got the crank through a Scat garage sale for $450, one of three available for that price. I didn't go through a full comparison on cost/availability because my combination was accidental. From research there is a general consensus that a 6" rod is vaguely better but not quantifiably so. Basically I would go with what is available at the best cost given quality. Only you are capable of answering as to whether or not it is worth it.

 

[L31MaxExpress]

I didn’t realize that they are making the marine manifold with cats on them. If you do the math for the 3.8 stroke a stock block is too short to put a long enough rod in it to achieve the better rod ratio. The 3.75 stroke w/a 6” rod gets you close to stock ratio of a 5.7 and unless you can find that intake on a deal you’d be better off with a aftermarket one IMO. GM had a lot of trouble with the 400 sbc the bores wore excessively piston pin failures that was because of the rod to stroke ratio wasn’t enough. It’s also why there is a tail deck block because once you calculate the rod ratio you end up with a longer rod and then you don’t have enough room on the piston for the ring set w/o going into the pin bore. The taller deck gives you the room for the correct piston and it also to an extent changes where the engine makes power and it also looses efficiency with a shorter rod. The guys running big cubes don’t worry about a budget or how long the engine will survive. I took the stock L31 intake and ground it more or less flat on the bottom and filled in the low spot opened the ports up to the gasket I got from edelbrock and pinned it so it couldn’t slide all over. Plugged the egr off. I didn’t take any pictures because I don’t know that it’s going to work that well or not and may eventually have to go aftermarket. The biggest issue with an aftermarket intake is the distributor cap plug wire terminals line up with the fuel rails luckily MSD makes a distributor that uses top terminals with a cam position sensor to run the gm ECM. Do you plan on dynoing this when it’s finished?

3.80" with a 5.7 rod is how GM builds 1,000s of them.

I have also put a 3.875" and 6" rods in a 5.7L block at 0.030 its 395 CID from memory. Very common build in the Gen 2 LT1 world. A 395 LT4 I built 10+ years ago has 150,000+ street miles on it at 550+ hp. Still going strong and the only problem it has had was small base circle required failure prone link bar lifters that have had to be changed like twice. I wanted a normal base circle and OE style lifters in my 383 or it would be a 395. The link bar lifters are JUNK compared to the GM setup.

A stock 400 had 5.565" rods. GMs only small block departure from a 5.7" rod except for the 94-96 L99 4.3 with its 5.94" rods.

The 6" rod with a 3.875" stroke still has a better rod ratio than a 5.7" rod 3.75" stroke 383. A 6" rod 383 has only a couple decimals worse rod ratio than a stock 350.

 

[PlayingWithTBI]

The link bar lifters are JUNK compared to the GM setup.

I was wondering about that, I thought about going to link bars on my roller upgrade but, figured I could save $$$ on OE style spider setup.

 

[Pro439]

I know if you want to run up in rpm’s a higher ratio is better. Low ratios push the piston harder into the side of the cylinder an increase in friction and wear. From all the engine builders I’ve read about had said it’s free hp with a higher rod ratio. The 400’s were siamese borers for strength which the 5.7/350’s don’t have. Moving the pin so high into the top of the piston isn’t a good idea either as far as I’m concerned. I guess if it’s just a street beater it doesn’t really matter but if you’re going to run it hard I wouldn’t want to chance it especially for how much it cost to build these. I’ve got $7500 in mine with out a aftermarket intake and fuel injection setup- that’s another $2000

 

[L31MaxExpress]

I know if you want to run up in rpm’s a higher ratio is better. Low ratios push the piston harder into the side of the cylinder an increase in friction and wear. From all the engine builders I’ve read about had said it’s free hp with a higher rod ratio. The 400’s were siamese borers for strength which the 5.7/350’s don’t have. Moving the pin so high into the top of the piston isn’t a good idea either as far as I’m concerned. I guess if it’s just a street beater it doesn’t really matter but if you’re going to run it hard I wouldn’t want to chance it especially for how much it cost to build these. I’ve got $7500 in mine with out a aftermarket intake and fuel injection setup- that’s another $2000

I do not have anything close to that number in my 383.

I have a 350 and a 383 at the shop I am putting together now with spare parts for almost nothing. Only thing I had to buy was some gaskets and head bolts. Going through stuff at the shop, had multiple sets of new STD bearings, multiple sets of stock rings that have just accumulated over the years. I have been known to buy re-ring sets off Rockauto and Amazon and end up just re-gasketing the engine when I get into them because they are so clean. The 383 is getting a GM 6.3L Marine rotating assembly. The 350 is getting used LT1 flat top pistons and LT1 powdered rods and a nodular iron 305 vortec marine crank.

 

[Pro439]

I do not have anything close to that number in my 383.

I have a 350 and a 383 at the shop I am putting together now with spare parts for almost nothing. Only thing I had to buy was some gaskets and head bolts. Going through stuff at the shop, had multiple sets of new STD bearings, multiple sets of stock rings that have just accumulated over the years. I have been known to buy re-ring sets off Rockauto and Amazon and end up just re-gasketing the engine when I get into them because they are so clean. The 383 is getting a GM 6.3L Marine rotating assembly. The 350 is getting used LT1 flat top pistons and LT1 powdered rods and a nodular iron 305 vortec marine crank.

I have been outta this seen for 20 years and am just getting back into it. Bought a set of heads that looked good in the picture but when I got them they were junk and the guy swears they were all set and I didn’t know what I was talking about wastes $900 Had a set of edelbrock heads on order for a year and cancelled them ended up getting small port vortec bowtie heads bare. I’ve been burned and have seen a lot of people get burned so I had more confidence in new stuff versus used. I’m honest but seems less and less people are. That’s the reason for the big price tag and I knew that going into it. Have a 7.4 doing the same thing with only using an aftermarket intake and efi And I absolutely have no interest in the ls engines. These are the last 2 I built in the late 80’s early 90’s and now am getting back into this because I think the newer stuff is junk. And now with the covid excuse it’s hard to get some stuff and some of what you get is junk. You’re lucky to have stayed in it and have stuff. Merry Christmas

 

[PlayingWithTBI]

I seem to remember an episode of Engine Masters where they tested long vs short connecting rods. Bottom line - they didn't do much of anything.