anyone on here using log manifolds? im debating building a set for my ls1 but have read some issues with cracking but that may have been because of bad welds. should i use sch10 or would i be okay with 14/16 gauge? if logs are a bad idea i guess id have to take some time to build a set of turbo headers. thanks any input appreciated

 

I have the log manifolds from Jon (aka RealQuick). Reportedly, logs can support up to 1,000HP(at the Crank, I'm sure). They offer quite a few benefits (enhanced spark plug access, ability to keep A/C(sometimes anyway. Mine do).

Jon was going to do mine in Stainless but they can be prone to cracking(yes, it's hearsay since I don't have them but I've had friends that did have SS and they cracked repeatedly and they were created by "Stainless Works", not JoeBlow with an $89 110v Harbor Freight welder)

 

The problem is that the log itself expands thermally, quite a bit. I remember calculating it to be more than .100". But, the flange bolted to the head and the head are much cooler. So, the log wants to grow axially, while the flange doesn't. The primary tubes are very short, so they don't flex very well. The result is cracked welds. The solution is to cut the flange between each exhaust port. This allows the flanges to slide across the head independent of each other, and it relieves the stress. You only have to use a solid copper gasket to stop leaks.

The other option is to install flex joints between each primary tube, which I think is usually impractical.

 

ive seen some log kits that crossover from one side through the other log. im talking about merging them in the front so there wouldnt have to be a crossover pipe and i could retain ac. mild doesnt expand as much as ss? would that be better suited for a log app. if not ill trash this idea and attempt a set of tubular manifolds

 

The temperature has way more to do with the amount of thermal expansion than the material.

I don't think you understood my explanation of what's going on. Y-ing them together before the turbo wouldn't change a thing. Cutting the flanges between the ports and running a copper gasket would fix it. Re-read my first post closely.

 

Lots of people use 304/316 stainless sch 10 weld fittings (from McMaster Carr). Stainless steels can elongate over 1/8" per foot at turbo manifold temps (~9 µinch/(in °F)), so make sure you progressively oversize the bolts holes as you move out from the center and use washers on the bolts to allow the flange to slide w/o binding. Thicker material is going to heat up at a more even pace and therefore help alleviate cracking issues. I would only recommend TIG welding using a stainless filler (such as 308).

 

1.75" Unobtainium tubing works the best.

 

hey mike i know what your saying but id only be able to put one cut like in the middle of the flange. i havent heard of any issues with the tti log manifolds shown here . i was going to use some of ace 1.5 sch10 90 elbows since theyre on sale 5$ a piece and a couple foot of 2.5" sche10 piping to fab up something similar without a crossover

hey there Real Quick looked into it a pretty penny