I'm not sure y. All I know if u go backwards on gear and engine pretty loaded it pops. Too much pressure going the wrong way. Mike

 

Here i went not from 3rd to 4th but from 3rd to 2nd. Auch.
After this mis shift i consequently shift 'back handed' into 4th. You can see i pulled it too much towards me too much rather then straight down. Luckily the entire engine was 350$ to replace.

ha ha

Here you can hear how it sound if you really mis shift .. Engine completely dead afterwards.

 

Typically, you get bent valves from an overrev because the valve springs cannot keep up with the rpm of the motor. So before the valve is back in the combustion position, It gets whacked by the piston coming up to compress. Or you break a timing chain/ belt and the valves are out of phase with the piston coming up. And I would like to go against the grain here and tell you to enjoy your 4 liter with the 996 cams. Swapping the cams will give more power but you can expect a bunch of problems that you will spend a lot of time and money sorting out. Enjoy the car you have!!

 

As an observation, think you're more likely to make a miss shift changing UP through the box than changing DOWN, therefore folks in left hand drive vehicle's are more susceptible to that mistake than folks in right hand drive as you're pulling the stick towards you for a higher gear but then hitting a lower one. (a right hand drive is always pulling towards a higher gear)

 

Yeah it's abit scary if that happened to the gt3. I grenaded my mk1 vw gti racecar 1st time on track for testing. Went from 4 to 1- engine just died- bent 12 of the 16 valves(16v engine swap). Only costs me $250 to replace engine. Coulda bought 10 16v motors for price of one 3.8 rsr pp when it grenaded. Mike

 

A leak down must be performed at 180 degrees. Does no good at less than operating temps.

 

I undestand the typical test procedure. When you have consistent readings throughout 5 cylinders and the 6th is 10-15% greater, that raises a flag.

In this case, the focus is not so much focused on the leakdown values, but how they relate across the cylinder banks.

Finally, I'm hoping the #3 test result was in error.

 

I was she was fully up and running again but I had a chance to start her up and play around a little more the other night. She would still start up and not make the horrendous pooping noise, but it was "searching" for idle after revving it up and I swear I could hear an air leak somewhere when revving. BUT, that leads me to the whole rubber hoses not fitting properly issue. So I pull the plenum of an really looked at all of the rubber hoses done at the intake manifold. It looks like what happened is that when the main plenum hose blew, there was so much force that it moved the intake "distributors" withing the rubber hoses at the manifolds thereby cocking each site out slightly towards the sides of the car. None of them were completely off but they were definitely close so I think I still have an air leak somewhere. I'm going to try and drop the motor a couple inches, loosen all of the hose clamps at the manifold and at the plenum, re-situate everything and tighten it back up. Hopefully that will solve all of the problems as I'm feeling more and more like nothing internally was damaged (see why below).

No leakdown prior to buying the car unfortunately.

I think what happens is that their is too much air in the intake systems and then the sudden change in RPM sends a quick burst of pressure through the system and blows the hose as it's the point of least resistance. Still thinking about the exact mechanics though and how it would all work.

Sorry to hear the engine was completely dead! But at least it was only $350 to replace...too bad that's not the case with our cars!

Back-handed is definitely the way to shift in to 4th and is the way I do it or at least try to every time (looking through my vids though it seem as if I do).

Completely agree with you on the cause for the bent valves. The good news is that I hooked it up to the Durametric and still had no range 2 ignitions which makes me think the possibility of a bent valve is much less. I did have range 1 ignitions in the same operating hours as I'm currently in though so she hit the rev limiter at some point while out on the track that day.

The 997 GT3 street intake cams really wouldn't cause any problems although I would definitely get it re-tuned. Where you run into more issues / money is when you go to a cam without Variocam as you have to make some other modifications to the cam housings. And of course you have to know exactly what your tolerances are and the exact spec of the cams to avoid any clearance issues which is a path I don't really want to go down. And in reality, I probably won't be doing cams anytime in the near future if I don't have to tear into the motor to get the current issue solved (which I'm feeling like I won't at this point).

I would agree with you, Serge. I think we both know that in a perfect world, a leakdown should be performed warm but unfortunately that just wasn't a possibility in this case. I too hope that the test result in #3 was an error and that once I perform a warm leakdown, we'll see the numbers come down across the board and a more consistent reading from #3. We'll see though.

 

My engine is getting dropped for same reason as we speak. Try spraying carb cleaner on affected hoses when car running preferably when engine is cold(have a fire extinguisher just in case). If it changes idle due to spray its leaking. I'm replacing them with new ones hence the reason for engine drop- its 8 yr old rubber. Mike

 

I was going to do that but didn't have any carb cleaner and was too antsy to pull plenum off and see if any other hoses as blown. Did you spray carb cleaner and notice the idle increase? If so, I'd be curious to hear if any of your hoses were off when you pull it apart? Or if it's such that the system can still pull air in even if a hose isn't completely off? I'm thinking that it can.

 

Sure did. One hose (driver side) was sealed as possibly can when it popped but still car was sputtering like ****. Sprayed carb cleaner on the resealed one no change in idle.Sprayed the other hose(passenger side) which looked sealed to me idle smoothed out. I can see another hose behind the affected one. Not sure how many hoses there are but when engine is dropped I'll definitely replace them. Can u keep a steady idle at 2k when u press gas or it's hunting up/down at this point? Mike

 

The ecu will try to rich up the gas mixture due to the lean condition with the vacuum leak. Talk about smell of unburnt gas. If it fully popped out it wont even start. Ecu can only add so much fuel to get it to combust. It was a chore to get car to tow truck since tow truck can't fit in the narrow alleyway where my garage is. I was keeping revs at 6k to keep it from stalling- nasty sounding ie sounds like engine going to grenade. Mike

 

Car is backing up and running! I dropped the motor a couple inches and found that the top hose directly behind the plenum had also come off slightly which is also the reason it was so difficult to get the hoses on each side of the plenum seated properly. After reaffixing the hose she started right up and settled into a nice idle. Took her for a drive this weekend and everything felt normal. I'm still going to run another compression at leak down at some point here but for now I'm just relieved that I have a living car again! Thanks again guys for all of the help!

 

Woo cheers, she runs again

 

Motor has been dropped. Damn there's lotta hoses involved with intake plenum. One cracked almost in half and the others are old/hard. Need to replace them all(i see 7). If u guys drive them I don't think u need to worry. Mike