Blown new motor

[Spool'n Spyder]

Well I took it out to the track Friday and blew the motor on my car. It 750 miles on it and I had performed a leakdown and it showed totally sealed on all 4.

I got about half track and heard a loud exhaust noise come out from under the hood (like an open header or something) then the car shut off. I was revving to about 6800 and running 18 lbs of boost. I logged about 5 3rd gear pulls on the way to the track and I was running a little rich.

Now I got it home and #4 plug has part of the little arm that goes over the electrode missing, #3 the gap is completely closed on it (like something hit it) but #2 and #1 looked pretty good. There is no compression on 4 and 3, 5-10psi on 2, and 110 on 1. I checked the timing just with the cover and it seems to still be in time. I cant really tell what happened or how bad it it is untill I get the head off. Do any of you guys have any guesses. I really hope it didnt get into the bottom end. If it stayed in the head, I can fix that easy. Anyways, any diagnosis?

Thanks

Btw, I ran a 13.1 with a 1.7 60 ft and braoke about half track.

[delta448]

In your profile you list engine mods as "stock with dohc swap". Did you try to run 18lbs on that? -Because with the stock 2.4 bottom end and the 4G63 head, your compression ratio is pretty high... like around 11:1. That's why special pistons are necessary with hybrids, -they move the wrist pin higher in the piston and drop the compression ratio.

Although if you ever get that thing dialed in and can run 18lbs without blowing it up... you're looking at some serious horsepower, evident by the 13.1 sec blown engine timeslip.

[Spool'n Spyder]

No, i'm sorry. I have weisco's and scat rods. Crower 64414 cams and upgraded valve springs. The pistons were ceramic coated on the sides and on the top.

[delta448]

That's a nice setup. Sorry for your misfortune.

My guess would be a problem with the rings, so you did do the leakdown test after the engine blew right? And it held pressure on all 4, correct? But the compression was screwed?

[Spool'n Spyder]

I did the leakdown before it blew to make sure it was good and broken in. I did a compression test after I blew it up. I tried a leakdown but really could not make a conclusion from it.

[dsm-onster]

Your profile says that you're running 450s. 450s cannot flow enough for 18psi on a 2.0L block w/ a set of mild cams and stock intake manifold. . .

Running stock head bolts (even if a 6-bolt), I suspect a blown head gasket. Or worse .

[Spool'n Spyder]

Ok, I guess I missed a couple updates on my profile.

I run weisco's, scat rods, manley valve springs, fic 750's, cometic head gasket, arp everything, bs removal, Crower 64414's, Skunk cam gears, sfp mani w/40mm hks external wastegate, 20g turbo, fmic, hks ssq, gm maft, and keydiver stage 2 chip.

I got the head off today and found that #4 piston is melted I guess maybe I leaned it out a little to far. Yet I always thought #1 ran hotter than an other cylinder. Could it be that something failed or that I leaned it out too far? It looks all the rest are ok though. The cylinder wall has some alluminum on it and a few light scratches but I think it can be honed out. I will probably pull the oil pan, all the rod caps, and pull all the pistons out to check them. I think the head can be salvaged. It has some alluminum in around #4 but I think I can clean it and lap the valves back in.

Should I try to hone #4, check the others and run it like that? Should I hone all cyllinders and get all new rings? Should I junk the whole block and start over? Would I need to replace the rod bearings? I know that I have to remove the oil pump and see if it ate up the oil pump. Keep in mind there is only 750 miles on this motor.

[ZmanIV]

Tear it all down and start again.
Doesnt matter if it had 700 or 70000 miles when it blew the bummer is that those engine/piston pieces can be anywhere in the motor.
If you want to risk a new motor on a half assed job of rebuilding a blown motor go ahead.
Sorry to hear about your bad luck.

[Spool'n Spyder]

I was afraid of that, but hey thats part of the game, right? I guess It'll be down for a little while. Thanks for the help and I may have a few questions.

[Spool'n Spyder]

Well, I got the motor out last night and tore it down today. It looks like #4 and #2 are shot. The good thing is the cylinder walls have very minor scratches that will hone out. I am going to hone the cylinders and put a new piston in 2 and 4, replace every gasket on it and put it back in. I checked the bearings and everything looks to be ok and it didnt hurt the oil pump either. I'll keep yall posted

[delta448]

Good to hear. Hope this time it works out better for you. Did you ever determine exactly what the problem was?

I'm pretty interested in how the 2.4 DOHC works out for you, I'm slowly building up one of my own for a swap into my Talon next year.

[Spool'n Spyder]

I honestly think I leaned it out too much and I blame it all on me. I love the 2.4 dohc. I ran a stock one for about 2 1/2 years and had no trouble. I am only running a 20g on it so you can imagine how fast it spools and how that is