Thread: Project Sebring GT Spyder

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I bought this engine as a "practically new" piece that had only been test run. Up until now I had never been able to verify any of that story. I was pleased to find that the lower end did actually look brand new. There was no staining or other signs to indicate that it had many hours of run time. The parts looked like they had just came out of the box. The cam showed no signs of wear. So far, I'm pleased.



While I'm tempted to just hook it up and run it, not having any real history on it makes me cautious. The story that came with this engine makes me suspicious of it's history. Also, the hot rodder in me just won't me let run it as is. You know, the little devil on your shoulder that keeps saying "Hot rod it!!!". The early LS engines had some faults that were corrected in later engines. This is a first year engine and I have a few upgrades planned.

It may sound crazy to some, but my plans are to tear it down and inspect everything. Hopefully I'll wind up with a pile of fairly new parts. Then I can reassemble it with the upgrades and be reasonably confident that it will hold together. So far these are my planned changes:

I picked up a set of older CNC ported heads for a good price. They will accept a higher lift than the stock heads and should really improve the breathing. I need to CC them to verify chamber volume.

The rod bolts on the early engines are known to be weak. I'll swap them out for ARP's and have the big ends checked for roundness. I talked to a reputable machine shop and they told me it could be done without pulling the pistons off the rods (they are press fit). He said they will sometimes have to hone them slightly with the ARP bolts.

The oil pump will most likely be changed to a Melling. The early pumps supposedly have cavitation issues and can lose suction at high RPM's.

The cam will get changed. Right now I'm looking at around 224@.050 with somewhere about .580 - .600 lift and 112* lobe separation. The heads will handle more than that, but that has been identified on several forums as a good daily driver type cam for an LS and manual trans. The cam will most likely be a Howard's, but I'm open to suggestions. You out there Tech?

The trunions on the rocker arms will be upgraded for the extra load the cam will put on them.

The cam swap will require the cam position sensor be moved to the timing cover with an LS2 cover and timing gear.

The valley cover will be swapped to an LS6 part. The PCV was moved from the valve covers to the valley cover on that engine to solve a small oil consumption issue.

The LS1 intake is being swapped out for an LS6 to better support what the heads can flow. I also picked up an 80mm BBK throttle body. It's just a little larger than stock, but is "supposed" to flow 30% more. That's according to BBK. I'll also be using a larger 5 wire mass air flow sensor and plumbing cold air to the intake.

I'm going to go to a full return type fuel system and the injectors will be resized.

I have found a tuner within 60 miles that has a good chassis dyno. His dyno can do road simulation tuning and not just full throttle pulls. That's important to me since I want to drive this car like a stocker on the highway. His reputation is good, so I'm willing to take a chance. That's the reason for the rod bolts and oil pump swap. Hopefully, to keep it together on the dyno. It'll probably get pulled on harder there than I ever will. FWIW - My tuner thinks this combo should put about 400 HP(maybe a little more) to the rollers. That should be fun in a 2500 lb car.

He is going to do an initial "safe" tune so that I can break the engine in before we thrash it. That's real important to me. Dyno's scare the crap out of me. I know they are necessary, but I personally know of more than one person that had mechanical carnage on a dyno. Beating on an new unbroken in engine never really sounded like a good idea to me. Looks like I better make sure the driveshaft is up to it.

I've already started collecting some of the parts for the upgrades. I like engine work and I'm looking forward to it. I still have a lot more work to do before I get there though. Guess I better get back to building.