Date: Thu, 11 Nov 2004 12:27:12 -0700 From: pstraub@gmail.com Reply-To: dtlc@helios.net To: dtlc@helios.net Subject: Re: [DTLC] Turbo Vs Naturally Aspirated On Thu, 11 Nov 2004 03:18:49 -0700, wayne@crushersrule.com wrote: > Sheldon, > the only adjustment I made to the basic 1HZ was to turn the fuel up a bit. I > have not modified the internals at all. the turbo runs the same boost at > highway speeds as the 12HT with the same tires installed. Wayne, I think the point that Sheldon and I are trying to make is that you took the 1HZ from sucking in air at 14PSI (roughly the air pressure at sea level), to 14PSI + 8PSI (or whatever 'boost you are making), for a pressure ratio increase of 1.57. Now, the 12H-T is making say, 14+8PSI, for a total of 22PSI. If you increased this by 1.57, as you did for the 1HZ, that would be 34.5 PSI total, or 20PSI of boost. If you jacked up the 12H-T to 20lbs boost, turned up the fuel, and added propane, I guarantee you it would kick the living arse out of the 1HZ as you have it now. Furthermore, being direct injected, you can actually run 40-50 lbs of boost on the 12H-T is you should so desire before you need to O-ring the head. The tiny hole in the pre-cup of the 1HZ is a significant barrier to how much air you can really push through the 1HZ. The 12H-T incorportes some of the nicest features of all the Toyota diesels. Being an interference type valve train, it is a pushrod engine, wich means you can never break a timing belt and crater the head/pistons. It has a reliable oil lubed in line injection pump. It is direct injected. It is factory turboed. The direct injection motors keep the oil cleaner. The 1HZ, on the other hand, has been described by Rob Mullen has having all the worst features of the all the Toytoa diesels combined into one engine. It is indirect injected. Sure, this mean it runs quieter, but it limits the total air you can put through it. It runs a rotary pump, which relies on fuel for lubrication, instead of using engine oil for lube. It's a non-sleaved engine, so you have to over bore the engine at rebuild time. They still use glow plugs. It has an overhead cam, which reduces valve train power losses and runs quieter, but if the timing belt ever breaks, you have to buy a new head and valve train, pistons, and if you're really unlucky, a rod or two and a crank. Being indirect injected, the o-ring groove needs to be cut into the block instead of the head. They also have a ladder bearing cap, which sure makes for a sturdy bottom end, but lord have mercy on your pocket book if you spin a bearing and need to replace that bearing cap. Not to mention that you have to pull the transmission before you can pull the bearing cap off. The only two things I do like about the 1HZ over the 12H-T are the gear driven power steering and vacuum pumps. Yup, if you ask me, the 12H-T is the ultimate engine for performance AND reliability in a Toyota diesel. There's not a whole lot of them, and no one's done too much to tweak them since they were overshadowed by the overhead cam motors before they really came into thier own. Believe me, if I could have found a donor 12H-T instead of the 1HZ for the Tippy power plant build, I would be doing the 12H-T in a heart beat. Hey, maybe I should SCT (super turbo charge) the 1HZ, swap it into my HJ61, and use the 12H-T for Tippy's power plant. Hmmm..... Peter Straub