legacycentral bbs

This thread is specificaly for Doug and anyone else that is boosting a NA engine. of course anyone with some experiance here feel free to chime in.

I ate the ringlands on 2 and 4 in my first motor before decent intercooling (didn't cut a scoop into the hood). The engine I've got now I assume has done the same as I'm low on compression on 2, but I have a rod knock too from blowing all the oil out when my turbo oil return line cracked. I didn't loost compression until after that happend and the bearing is bad enough that I'm pretty sure I can hear the piston taping the head. So I'm not sure if my compression loss is from killing ringlands due to boost or from smacking the piston up due to the rod knock.

No matter what I need a new engine, I'm wondering though if I should toss in another used NA engine, or if I should throw some forged slugs in the spare block I just stripped down. I'm kinda leaning towards doing another stock NA engine, simply because I want to know how far I can push it since I never got a chance to get a good turbo and a good tune on the engine before I broke it.

so Doug, how many engines have you been though on your rig? You still in the 155whp range? That's identical to what I was making on about 7-8psi ... what did you break and did you tear down and see why?

If I did build an engine, I'd put in forged pistons and keep the compression around the stock NA compression. I have a set of EJ25 SOHC heads and a manifold to throw on it. I want to keep my fuel economy and try to break the 200whp range. There was plans to make this a $2006 challenge car though, so keeping the price down in a must... not sure if I'll still have time to do the challenge, but I'd like to be able to if I could. I can still spend about another $700 on the car and be in the budget.

Damn board losing my post.....anyway.

Timing is what kills the boosted n/a engines. If you can pull/limit timing advance & supply enough fuel, you should be able to boost n/a engines all day long.

Doug should be able to confirm that since the pefect power, albeit having issues does pull timing.

I'm back.......


Both motors that I lost pistons on had NO engine management. And the intercooler sucked, because it was an AWIC that I didnt have a large enough radiator, nor a fan, nor a resevoir.

Both times I lost #4 piston, and the second time I also blew #2. Neither time did I do any damage to the bottom end. I saved that for the last time I ran it without water for 20 minutes.

I did scratch the cylinder walls the second time "just a tad" with a section of ring that got loose and made its way down to the oil pan.

If you are going to stick forged pistons in, just go ahead and get lower compression ones. Or just stock turbo pistons. If you want to go REALLY low budget, simply mill away some of the dish in the NA pistons. Instant low compression.

My current motor is lower compression than the last two (the last "two" was the same motor, just new pistons twice). But I am about 100% sure this motor is lower compression simply because it ran so much better ALL the time with little to no detonation without an intercooler or engine management. Now that I have the FMIC and the SMT6, I doubt it will ever die.

Remember, I also have 370 cc injectors and a minor 1-1 rrfpr.

I ran the Sunday rallycross and other than blowing a charge tube off the damn supercharger once, my other two runs were 100% awesome, with full boost at full throttle about 45-50 seconds out of the 1:08 seconds of running. No detonation.

so you're running forged slugs now? Do you know what your compression is now?


I guess the conclusion is still unclear then. Had you been running your front mount at the time you had the other engine in, it might have survived. Same thing with me. I might be picking up a replacement wagon next week with a good motor. If I do, I'll swap all my stuff onto that wagon and see how long that motor will last with the IC setup right and I'll tune some before I beat the piss out of it. I'd really like to know what this thing could do without eating ringlands.

If I don't get the car, well, I'm still looking for a pair of NA pistons to throw the other motor back together with, at least for now.

No,
I am running stock NA pistons. It is just that this motor must have lower compression than the old one, because there isnt much other explanation to why it never detonated like the old one did.

I suspect that if I had the FMIC AND the SMT6, the old one would have been close to fine, and maybe a bit more power, due to the slightly higher compression.

Oh yeah, I also run 1/2 can of Torco octane booster everytank. I now buy 5 gallons at a time. Adds about $5 per tank, but it keeps the motor happy. I have run without it, but I got nervous.