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Old 03-28-2013, 08:09 PM
Northern Chevy Northern Chevy is offline
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It wasn't mentioned if your truck is a heavy duty 3/4 ton or one ton { 8500 GVW or higher rating } as I gather from what I have seen that they used the 191 heads with the lower compression and the standard transmission code MT8 which is the NV 4500 and had a non synchronized low first gear. Your comment about a granny low instantly had me guessing its the heavy duty engine/trans drive line but you can clarify that and if its a two or four wheel drive, what cab and box length it has. The reason I ask is for others to see how much or little weight your already lugging down the road just in truck weight, never mind pulling a load.

I am NOT the engine expert speaking up so keep that in mind but just to relay info on my own truck which is a 1995 half ton extended cab 4x4 with auto trans. It has the 193 heads and has no problem running regular fuel as its been to the coast and so on. What it lacks in a big way is power and lately due to the internals of a lifter failing and leaking down, I swapped in a new cam which happens to be a Comp 12-249-4 and a few other companies make similar spec cams under the so called "TBI compatible" listing. I installed that and right away I knew I had problems with lack of fuel delivery so I ordered a custom chip { actually a MEMCAL } which took care of those issues. The burning question, did I gain any power and the answer is ... precious little. Keep in mind that I am running the stock throttle body, stock cast exhaust manifolds, stock Y pipe, the Cat is removed though and uses a 3" pipe to a low restriction muffler. Would this cam have woken up had I created a better breathing engine from end to end, that I don't have an answer for. I can see from my own experience and in reading a variety of what others have gone through and some real hair pulling experiences if they modified a lot in the way of larger TBI and boosting the fuel pressure, getting the GMPP intake to bolt onto Vortec heads and bored the manifold inlet for the larger TBI, adding EGR to it, headers and so on ... then trying to get it programmed and never getting it right. If you have access to a shop that programs these older computers and has a dyno would be great and pretty much plan on that expense if you change a lot of parts.

Not that I mean to pour cold water on your idea of upgrading the power but there seem to be some pitfalls if not going by a tried and proven match from end to end that has been able to be tuned. I realize I might get razed a little on here by saying that but its just a friendly reminder to get it all planned out on paper before you buy one part or turn a wrench AND price it all out to see if it even makes sense for a budget you may have in mind.

To be honest, with altitude being an issue in your case and planning the vehicle to be used as a tow unit, I personally would be ether looking at a bit more updated truck that would have a larger engine with substantial power in ether a gas or .... I bet you would be smiling power wise sitting behind the wheel of a 2009 or newer Duramax with 6 speed allison that had the factory particulate exhaust thrown and reprogrammed if they allow that down there. You know yourself what a turbo can do and altitude is where a turbo diesel blows the doors off a naturally aspirated gasoline engine. I know, a truck like that may be out of reach price wise but didn't think it would hurt to pose the thought.
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