BOTTLE ROCKET

iTrader: (4)

Guys
Ive been trying to pull the trigger on my forged shortblock build for 2 weeks, and just can't get the answers I need. I have found 2 builders that offer a fair priced build for my motor
I am building a stock cube forged short block to handle 12-15lbs of boost and spend 90% of its time crusing (no track car).
Easy, right
The two builders are
Thompson Motorsports
Schwanke enignes

The issue is ring gaps;
One builder recommends a .031 top ring, which I believe would cause crazy blowby
The other builder recommends 17-18, which SEEMS, based on others builds, to be very tight

PLEASE give any feedback you have on the rings or builders. If negative on the builders, please PM me the info instead of posting
Help me get this build going

itsslow98

iTrader: (18)

You have to pick a vendor you trust and let them go with it. In my opinion if they have the reputation and have built some nasty engines they aren't gonna set you up to fail.

BOTTLE ROCKET

iTrader: (4)

I agree; That was one reason I listed the builders, since I haven't used either of them.
Im not a machinist, but have build several engines, and the ring gap is a MAJOR part of the equation, so the huge discrepancy concerns me

pwrtrip75

iTrader: (8)

Keep in mind MACHINIST ARE NOT ENGINE BUILDERS. I have dealt with several "engine" shops that are like this. They are great machinist and can machine stuff perfectly within tolerance.....what that tolerance is varies a lot from shop to shop. How they determine it is based on who knows what. References well above your goal are advised. I mean if the shop has proven cars with 1500-2000hp engines then I would be more prone to trust them. But if they only have stuff proven at the same level stock stuff is doing I would not trust them.

One engine builder in my area has a fail rate thats insane, another refuses to give out any references....lol. I have to drive like 40 miles away for a decent machine shop.

Forcefed86

iTrader: (4)

Talk to these builders and find out what piston is being installed. Depending on bore size and the alloys the forged slug is made of, gaps will be different. There is no set answer. A very common general rule for moderate boost is .005 X bore. So if your a 3.90 bore .0195 is probably going to be fine.

I used .006 on the OEM pistons this time around. I also ran a huge .032 on my last OEM pistons (top) with very little oil consumption. I had no issues at 25lbs on an s475. (5.3 bone stock shortblock right down the the hardware)

That being said for those boost numbers building a forged short block seems silly to me. Guessing at your boost levels, the OEM parts will handle the power you are looking to make and much more. Unless your running twin 88's or something, why are you complicating things with aftermarket parts?

Good luck either way...

BOTTLE ROCKET

iTrader: (4)

Thanks
The builder wanting to run .031 uses Diamond pistons and iron rings
The builder wanting to run .017-.019 uses Wiseco and steel rings
Stock bore LS1

I'm at 700+rwhp at 10.5lbs with my present setup on a stock block and 98 rod bolts. That's WAY over what a stock 98 set up should handle.
I'm swapping cams and upping boost which should get me in the 770-800rwhp range, which I would never trust on stock pistons, rods and rod bolts.
I know guys may have done it, but I don't want to have to flat bed the car home.

Forcefed86

iTrader: (4)

Call up diamond/weisco and tell them the amount of boost and power you want to make and ask them what they suggest gapping the rings at.

I know weisco pistons usually run the 4302 alloy with a ton of silicone in them and don't expand as much as the 2618 alloy (stronger) pistons. Not sure what diamonds are you'd have to ask.

Personally I'd go with the weisco on an LS1 because of it's low expansion rate. I know you can't bore those 98 ls1 blocks much at all. Then gap them at .022 and .024.

Ah gotcha, thats some healthy power for what I'd call low boost Didn't know you were making that much. I'd be lucky to crack 450whp at 10lbs!

FWIW my gen3 stock rods and pistons held 840+whp (going by weight/trap) all season without issue. Timing chain broke or I'm sure it would lasted another season or 2. Motor looked great when I took it down. (what was left of it)

BOTTLE ROCKET

iTrader: (4)

Thanks FF
I called Diamond to get a recommendation, and he said he would have to know the piston and ring part #, which I don't have. The tech did say, however, that for HIS car, he would run something like 21/23 (I forget exactly)

The block will be a aluminum 5.3 bored to 3.9, so maybe it will hold

While I do worry about the brittle stock pistons, my main concern are the 98 rod bolts, which were notoriously weak

BOTTLE ROCKET

iTrader: (4)

The rings being used are total seal steel ring sets
The rep recommnended .0070 x bore, or around .027 (for BOTH)
The interesting part is when I asked him shouldn't the second ring be bigger, he said NEVER!

cory32690

any piston I would do a .024-.026 top and .025-.027 on second

cory32690

the top being bigger or smaller than the second is a engine builder preference I like second ring with more gap that way cylinder pressures will not get stuck between the two rings and bust out a ringl land I would rather it vent into the crank case than anything else

BOTTLE ROCKET

iTrader: (4)

Every post I ever read and even the Wiseco site has lager second ring for no flutter. This is the FIRST time Ive been told to run the same

I wonder if I should just buy a good set of rings, get the recommendation from the manuf. and send everything to the builder.
The problem Im having is not knowing exactly what ring is bong used, so its hard to get a gap recommendation