Why would a motor let go on 2 step

[03redzo6]

So I tuned my buddies rx7 the other day and it had been running fine. The other night, he engaged the 2 step, and he said the motor let go. He says it sounds like a rod let go. His mods on the 5.3 are, 228r from tsp, arp head studs with ls9 head gaskets, bw turbo (cant remember the size), e boost 2, msd 2 step, and e85 for fuel on 15psi . Why would a motor let go while on 2step?


trans shift point 3.hpt

2 step pull.hpl

[lukearmstrong1990]

adding to what I messaged you... now ive just viewed the log and file.

at point I see 4300rpm 17# 10psi boost and your wide band shows 17:1 AFR. even the cylinders firing would be copping a beating let alone the ones dieseling

[03redzo6]

I remember he was testing it out, but the last part of the log is where he set it to 3k, cause at 4300rpms, brakes couldn’t hold it.

[Fast4.7]

So I tuned my buddies rx7 the other day and it had been running fine. The other night, he engaged the 2 step, and he said the motor let go. He says it sounds like a rod let go. His mods on the 5.3 are, 228r from tsp, arp head studs with ls9 head gaskets, bw turbo (cant remember the size), e boost 2, msd 2 step, and e85 for fuel on 15psi . Why would a motor let go while on 2step?

My neighbor at my shop plays with turbo LS fox body mustangs. He has had about 6 5.3s let go on the two step so far that I know of. Latest one grenaded a piston in a spectacular fashion. IMO two step seems like it would be very difficult on the engine even if done properly. To me cutting the fuel off for the two step would be a bad idea. Shutting the ignition off to achieve the cylinder deactivation would actually be a better idea than allowing cylinders to lean detonate under boost.

[Ben C]

Wideband will read lean on 2 step due to cylinders missing. You can't look at it.
msd 2 step cuts spark, not fuel.

[kingtal0n]

2-step is significant abuse

flames explode from an engine as ungodly noise erupts

isn't a cocoon of loving embrace

[Jay@HAP]

2-step is significant abuse

flames explode from an engine as ungodly noise erupts

isn't a cocoon of loving embrace

best post of yours so far.

[kingtal0n]

best post of yours so far.

I know what people want, I just don't like giving it to them

because the internet is a popularity contest and I have no desire to become popular

meow sometimes I get in a mood though

[Jay@HAP]

I know what people want, I just don't like giving it to them

because the internet is a popularity contest and I have no desire to become popular

meow sometimes I get in a mood though

you are infamous on LS1tech. we miss you....

[Monzsta]

My thoughts on this are as follows:

On the 2 step you cut ignition, but the cylinder still gets a load of fuel, which gets compressed and then relaxed without ignition. This is now a super homogenized mixture now at a very high temperature, so when the exhaust valve opens to a manifold or header under high drive pressure you have an ignition source, which ignites the mixture as the piston is coming up on the exhaust stroke. It's the same conditions as detonation.

I'll bet if you look at all the engine failures the ones without long tube headers were more likely to sustain damage due to proximity to neighboring cylinders. Shoving a flame first down one 20-30" tube and back up another is less likely than the few inches of space in a log or factory manifold.