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Well I finally got around to pulling the engine. Haven't had a chance to dive in yet, but I will say the cylinder bores are in great shape. The engine only has about 110k miles on it. I'm hoping for a quick turn around on getting it back in. I'll try to update as I go. I don't get a lot of time to work on it so this won't be the most exiting (re)build. Biggest thing right now is picking out a new cam. The obvious answer after wiping out a flat tappet cam is roller, but I'm open to recommendations. Is there some contingent of flat tappers out there that have some tried and true method of break in? I'm currently looking at a comp 218/224 (XR270HR). I think I'd like to find something with a greater LSA than 110 for my idle quality. The flat tappet I wiped out was a comp 212/218 (XE256H) on a 110 LSA and it's idle, while it was still living, could've been a little smoother. I'd like to not have to change out the torque converter also. I've also been looking at some howard's grinds. I'm open to idea's and opinions on camshafts. Depending on how the rebuild and install go time wise I planning on doing the turbo set up as well.You must be registered for see images attachYou must be registered for see images attachYou must be registered for see images attach
Thank you, this does make sense. Now that I have the engine out I can spend some time dialing everything in like it's compression ratio. Off the cuff, and with the smaller combustion chambers of the gen 6 heads I figure it's somewhere in the low 9's. I talked to someone at comp a little while back that pushed me to the larger 218/224 from 212/218 I was planning strictly based on a +9cr. The end goal is to keep it pump gas (91). I'm hoping smaller cam, low boost (5-6lbs), intercooler, and conservative timing helps me achieve that.So glad that you have broken radio silence with this status update!
I was really hoping to live vicariously through your towing-oriented
turbo 496ci build...so I was disappointed when it seemed like the project
went silent, as if it had to be shelved for some unknown reason.
(Life happens, been there, done that.)
From over here, I'm thinking that a cam choice for optimized torque
production in your towing RPM band (ie: getting the DCR as close
to the limit that the octane rating of the gas you plan to use will
support) would be the plan.
If you were to do this along with the matching L29 torque-oriented
intake + the 496ci displacement should be a pure pleasure. And then to
seal the deal, you would size the turbo so that A) it didn't push the
motor into detonation in it's NA powerband, but instead B) blows
the powerplant up towards a sparkling finish once the cam/intake
combo starts to fall off. Does this make sense?
The idea is to draw a line where the 87/89/91 octane fuel can
support power production without risking detonation. And
where the cylinder pressures inevitably drop off at the upper
end of the torque curve (3500-4000 rpm?) then the turbo has
spooled up and all that NA nonsense is overcome.
Done correctly, you could definitely dial up many, many ft/lbs
of torque *and* also enjoy a rewarding driving experience
behind the wheel.
I'm all for this, for torque to a GMT400 machine is like deep
bass for a home theater/serious music appreciation. You don't
realize how much it makes everything better until you experience
the real deal.
Great White Buffalo, indeed. This is truly exciting stuff.
I did the initial break in when I put the last cam in. I ran it at 2000-2200 for about 25-30 minutes. I don't think my neighbors appreciated it all that much. I had just finished the exhaust and the buffalo's not what you'd call quiet. There's nothing quite like the rumble of a big block Chevy through dual 3" pipes. I did not however heat cycle it twice. Truthfully, I felt like I got a good break in on it. It ran pretty good after, and though I had other issues that arose, it ran pretty good up until it ate the lifter.If you go with flat tappet the break in is fire the engine up and run it at 1800-2000 for a 1/2 hour. Running it at that speed keeps plenty of oil slung up on it off the crank. Let the engine cool completely then do it again two more times. This also heat cycles the rings. Use high zinc oil on flat tappet cams. Roller cams don't really need a break in period but the rings still need to be heat cycled.