V1 Mikes Extended, Full Frame Goblin - 2009 Cobalt LS with 135k donor

[mike_sno]

You only have 5.5 inches under the rear of your Goblin? Your ride height is pretty level then - at least compared to other Goblin builds which typically have 6-7 inches under the rear of the frame. A diffuser can be built to create some downforce, but it all comes down to the design. @Justinreed7 has an effective diffuser under his Goblin, but does mostly track time with his car so the diffuser can extend lower than a strictly street car. @Rttoys (Russel) has a diffuser under his Goblin, but I'm recalling he had moderate success with it for downforce versus ground clearance. I do plan to design up a diffuser for my Goblin, once I get that far. I have another aluminum road sign that has sacrificed it's usefullness (pretty beat up) and I will not lose any sleep over dinging it up if the ground clearance is a little too low.

I bend the sides of the sheet down to give it more stability. That's where I measured the 5.5in. Will check the other designs you mentioned.

 

[Rttoys]

I removed my defuser as I (we) believe it’s holding heat and the cause of me frying shift cables.

 

[mike_sno]

This guy is just amazing! @RobC76 send me the supercharger cover and refused to take any money for it! Not even shipping! I for sure buy you a beer! Thank you very much!

 

[RobC76]

This guy is just amazing! @RobC76 send me the supercharger cover and refused to take any money for it! Not even shipping! I for sure buy you a beer! Thank you very much!

No problem
Glad I could help. This community has so many great and very intelligent people in it. Happy to be part of it!

 

[mike_sno]

I checked my compression on the engine again, and have a cylinder which is at the lower tolerance band. I am not going to worry to much about it at the moment, but I believe I need to do something at some point in the future if the compression will go lower.

After adding some oil in the cylinder compression went up again. I believe it's either the piston rings or the sleeve. If it's the piston ring, would taking off the head and removing the oil pan do the trick to get the rod disconnected and pushing the piston out to the top? That's something I would probably do with the engine in the goblin. And could be done rather quickly. I had the head already off when I purchased the engine in order to get it decked. Would replace the timing chain at the same time.

 

[Rauq]

If it's the piston ring, would taking off the head and removing the oil pan do the trick to get the rod disconnected and pushing the piston out to the top?

I was able to pull my LSJ oil pan with the engine and trans fully installed. It takes some finagling, but is possible. Forgive the blurry photo, but I'm pretty sure all the big ends are accessible without removing the girdle.

 

[mike_sno]

I had to finish up some work and took some pictures of the wing mount.

 

[mike_sno]

My exhaust is made from 2in pipe. I believe the flange adapter is 3in. Now, does it make sense for the 2.0LSJ to convert the exhaust to 3in? I am planning to redo my exhaust anyway.

 

[Rttoys]

I went 3” to make it simple on my experimenal one.

V1 - Rebuilding the DF exhaust system

I have had a rattle for some time now inside my muffler. I figure the baffles have come apart at some point and rattling around now. Also at our last few autocross’s they have been doing db checks and I’m over the limit (104db, can’t be higher than 100db). I figure it’s time to see what’s going...

dfkitcar.com

 

[mike_sno]

Hmm, interesting link. I remembered it. I'll think about 2in vs 3in and will play around with some ideas.

 

[Rttoys]

Still a tough call. The header is 3” and finding the flange in 3” is easier than 2 1/2”. Could start with 3” and neck it down. It’ll definitely be easier to deal with. Not sure how elaborate you are going though.

 

[mike_sno]

Anyone having a good source for unaluminzed exhaust pipe? Local car stores seems to have only aluminzed and I don't think that welds to well.

 

[Joebob]

Anyone having a good source for unaluminzed exhaust pipe? Local car stores seems to have only aluminzed and I don't think that welds to well.

Get a flapper wheel sanding disk for your grinder and buff off the aluminum 1/2" or so back from the edge. Should weld a bit better.

 

[Gtstorey]

Non aluminumized steel is going to look terrible in a very short time. Unless it is ceramic coated. For an exposed exhaust on the Goblin I would only do stainless,

 

[mike_sno]

Non aluminumized steel is going to look terrible in a very short time. Unless it is ceramic coated. For an exposed exhaust on the Goblin I would only do stainless,

Absolutely, my exhaust currently is already looking terrible. That was the only thing the former owner was not happy with.

2 vs 3in. I read a bit on the internet about it... Not scientific proof, but overall I feel like the tendency would be 2in is enough and you need some back pressure and exhaust speed velocity. Seems like there are quite some harmonics and frequencies involved if you really want to make an optimal exhaust.... Well, not going down that route. I just wondered why there is a 3in flange in a 2in pipe.

 

[G Atsma]

You do NOT need backpressure. Ever. You DO need flow velocity, which smaller diameter tubing facilitates.

 

[Desert Sasqwatch]

A 2.0 inch is probably sufficient for a 2.2 NA. A 2.5 inch is preferred for a 2.4 NA and SC. A 3.0 inch is best for a higher HP SC and is almost mandatory for a TC. BTW, a 3 inch exhaust is capable of flowing more than 2.5 times the air a 2 inch exhaust can.

 

[mike_sno]

A 2.0 inch is probably sufficient for a 2.2 NA. A 2.5 inch is preferred for a 2.4 NA and SC. A 3.0 inch is best for a higher HP SC and is almost mandatory for a TC. BTW, a 3 inch exhaust is capable of flowing more than 2.5 times the air a 2 inch exhaust can.

That and @G Atsma makes me now believe I need to go 3in

 

[G Atsma]

That and @G Atsma makes me now believe I need to go 3in

Then you might be disregarding the flow velocity aspect. That is what helps evacuate exhaust from the head at lower speeds

 

[Gtstorey]

Everyone seems to be forgetting that length plays a major role in all of this, except for velocity. Diameter is much more important on a 20' long exhaust 2' (at the extreme) on a Goblin.