so I am going to check out this car for possible purchase tomorrow morning. The owner sent me this video of it on the dyno. it is supposed to be a heads/cam/intake setup that put down ~450whp on the dyno. the car was built by a previous owner so details are not known but the story is that it was built recently and bottom end may or may not have been redone at that time. car chassis has 80k miles on it.

http://www.youtube.com/watch?v=er3rl...ature=youtu.be

car starts up, drives, idles, etc like normal and put down good power on the dyno but that smoke on deceleration has me concerned but I'm also not super familiar with how stock bottom end cars built to this power level perform? do you guys think this smoke is something I should be worried about? I haven't seen the car yet but on first glance I'd guess worn rings perhaps or valve stems?

what do you guys think? is this smoke something I should worry about or something that is normal for big cam ls1 motors?

thanks for your help!

 

I'd have a leak down test done on it to rule out the rings, but I'd lean towards the valve seals and/or PCV system.

 

looks like my attached video didn't upload?? let me play with it and see

the reason I ask if it's normal is it seems like I see a lot of high horsepower ls motor dyno vids with white smoke when the driver lets off, such as:

 

thanks man, then it sounds like any real noticeable smoke on the dyno IS an issue that needs to be looked at. I don't want to spend much money on diagnosing a car I don't own so if this smoke is anything not normal I may pass, although this is a beautiful car and great great price.

 

If the smoke was blue, I'd be worried. It doesn't really look all that bad to me.

 

Blue smoke on decel can be many things with these LS engines from rings to valve seals to too much valve guide cleance to just having too much oil laying in the pcv system. I would check how much blowby ie crankcase pressure it has on accel. Pull the oil cap off and rev it to 2500 and hold it there.
If its not huffing blue smoke out the hole @ 2500 rpm hot, look at the valves seals, they can let alot of oil past under high vacuum such as deceling after a dyno run.

 

Could be aftermarket heads with bronze guides, stock rockers, and aggressive
cam. This combo can cause excessive valve guide clearance in as few as 10-
15000 miles which as some have stated will let a bunch of oil past the intake
seals on decel. If the piston rings were the culprit (previous overheat) it will
smoke almost all the time when warmed up and crap the sparkplugs out often

 

awesome feedback guys, thanks! I just talked with the owner a bit more and the owner said he was told by the dyno guys they thought it was running rich and that was the reason for the smoke and that he's more than happy to have me bring it by some corvette specialty shops in the area to get their feedback but that he didn't think the smoke was really a big deal so he never dug into it further. I'm not sure a car could smoke that much from just running rich?

off on the 1.5 hour drive to go check it out though so fingers crossed for dry pavement and a healthy vette!

 

Another possibility is oil getting pulled by the rocker arm bolts on deceleration, if thread sealant wasn't used on the bolt threads(easy fix).

Well good luck, and let us know how it turns out.

 

ok guys, thanks for all your help! I had my girlfriend follow me around during the test drive and did my best to try and recreate the smoke under all sorts of painful situations like reving till it hits the rev limiter in 1st gear and then letting it coast in gear all the way back down to 2k rpm, full throttle through 4 gears and then the same, and did this about 10 times (and scared the owner quite badly in the process) and no matter what I did I could not recreate the smoke or really anything. I WILL say that the tune is not spot on, there is some low rpm surging and it seems to be running a bit rich on fuel as well. There is NO catch can setup too.

But other than some low rpm surging and pretty loud sewing machine sound which I hear is normal for big cams, the thing runs PERFECT and is the fastest car I have ever driven by a good amount. Feels faster than my old ls1 m6 camaro did on a 100 shot!


the car appears to be some old Katech build since it has katech stuff all over it (belt tensioner for example), it looks like stock heads (not sure where casting numbers would be?) but they're probably ported since they have clearly been off the car at some point and the front of the heads are chrome polished and the dyno shows a bit more power than I'd expect from a stock head 1999 ls1

it has a relatively mean cam in it, I'm guessing something in the mid/high 230s maybe? has a FAST intake, headers, etc and the owner has dyno sheets showing ~412whp through stock muffler and it now has a borla muffler on there and new mcleod clutch. new electronic shocks, new mcleod clutch, black on black 1999 c5 targa, about 8.5/10 clean all around, chrome z06 wheels and an amazing stereo. has a few little things and needs a better tune but overall it's my DREAM car! can't even describe how hard I was laughing on the way home! haha....

so since it needs a tune I'm going to put a catch can setup on it and take it to the local shop and get it tuned and see what he thinks, the sewing machine is a bit louder than I would expect, so hopefully the guy gives it clean bill of health but I got it for a GREAT price so I can afford to drop some more money into it if necessary but hopefully it is healthy! sure feels and looks like it so far!

 

this was a great idea btw, I had TONS of blowback on my old civic that had ruined rings. when I did this to the vette it had no real crankcase pressure coming out the oil cap that I could feel.

 

heres my car smokes but still runs like a top. <object width="1280" height="720"><param name="allowfullscreen" value="true"></param><param name="movie" value="http://www.facebook.com/v/1015049711...</param><embed src="http://www.facebook.com/v/10150497111994305" type="application/x-shockwave-flash" allowfullscreen="1" width="1280" height="720"></embed></object>

 

mine did the same excat thing and it was cracked ringlands

 

ouch.... really hope that's not what's going on here.... I really REALLY tried to get it to smoke when I was driving it and couldn't get even a slight amount of smoke so hope there isn't anything serious wrong

guess we'll see very shortly when I bring it to the dyno

 

thanks for that post, wow, that's a lot of oil!! did the catch can install fix the oil cloud?

I'll be putting in a big catch can setup immediately and taking this thing to the tuner asap,