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Old 06-24-2010, 05:36 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by Tyler007
Hey all I?m looking to build a 383 and plan on spining it to about 6500 rpm with a rev limit @ 7. I?m on a budget and plan on putting a 100 shot on it and no more than that. It?s going to be a street/strip vehicle. I?m looking to make 400 NA and 500 on the bottle. I?m going to use a forged piston with Gm P rods and a cast crank. I would love to go all forged but its either forged bottom and a cheaper set of heads or good heads and cheaper bottom. What?s some of your advice on this matter??.
The words "budget" and "nitrous" should not be in the same sentence.

Getting power from an engine requires first and foremost keeping it together. As when the the bottom end comes apart all the money, time, effort, blood, sweat, and tears that went into the heads is gone along with the block and bottom end.

With that thought in mind the first priority of a limited budget is to bullet proof the bottom end. Heads, intake, carb, and alternator can always be improved later.

When you're talking 6500-7000 RPM and 400-500 horsepower, you're talking the absolute upper end of what factory production parts will tolerate. This is like playing hose-head on Saturday night, one of those cans is going to blow beer all over you, it's just a question of when, not if. This means a 4 bolt main block, a forged crank, aftermarket 4130/5140 forged crank this would be a minimum acceptable starting place

The need for a forged crank is exacerbated by nitrous. The power application from this stuff is almost instantaneous, this shock loads the crank which can easily break it. It is also easier to balance a forged crank, especially when using heavier than cast forged pistons. A forged crank is denser than a casting which reduces or eliminates the need for expensive Mallory metal installed to the counterweights to achieve balance.

Much the same consideration needs to go into the rods. You'll need something like this for rods

Generally the crank will stand more abuse than the rods or pistons, so when faced with a decision as to where the most expensive parts should be start with the rods, cause when these fail usually the entire engine goes with them. I recommend floating pins in the rods when running nitrous or a blower. These extra fuel burning systems generate a lot of heat. This can expand the piston to where it grabs and locks the pin. With a pressed pin rod this leaves no point of rotation so the piston's pin gudgeon's are forced toward failure because a rotation is going to occur somewhere no matter what. With a rod bushed pin, if this much expansion happens there is a final point of rotation that will save the pistons and pins and maybe the engine.

You need to purchase a high quality damper that would meet the minimum requirement for turning into the 6500-7000 RPM this one would meet the minimum standard:
Damping the oscillations that develop in a crank is most important, insufficient damping can allow destructive harmonics to develop within the crank that will break it or they will cause the nose of the crank to run off center enough that it usually takes out the number one main followed shortly by the number one rod.

Balance is important, the engine needs to be balanced, it doesn't need to be internal, though that is desirable. But even internally balanced engines without counterweights on the center throws run with considerable main to main imbalance while the crank as a whole is in balance but this means that running a little balance outside the oil seals isn't any big deal unless this is a 500 mile NASCAR Cup engine. The real issue with not balancing by each main bearing bay is that other forces called couples and augments come into play, which puts twisting and bending moments on the crank journals and their bearings. This is where 4 bolt mains come in as the center throws see a lot of couples and augments, so 4 bolts on the center three mains helps them cope with these loads.

Oil management is crucial, while everybody immediately reaches for a high volume pump, the real issue is getting oil back into the pan keeping it by the pick up. Let me start by saying that you do not want to restrict top end oiling as is often recommended. Two big problems up under the rocker covers: one is if using ball fulcrums, they get really hot when the revs start getting over 5500 RPM and they need oil for cooling. Two is the valve springs; springs become very hot from their constant action, top end oil is needed to keep them cool, without it they can and do break which at the least will result in a piston to valve collision or at the worst a destroyed engine. Down at the pan you need a good full length windage tray. I prefer a steel tray with more louvers punched in, but for a street engine that only occasionally sees red line RPMS a screen tray will work satisfactorily. To this add a crank scraper, some are profiled for the crank and bolt in at the pan line, these are fine. Others are just a simple angle that's welded to the passenger side of the pan just below the belt line and low enough to clearance the crank, these are also fine. The idea of each is to catch oil being pulled up that side by the crank roation and direct it back to the pan. The pan should be a deep 7 quart if you have street clearance, this design keeps more oil depth above the pick up than kick out pans. But a 7 quart kick out is better than a 5 quart stock pan. The extra capacity in either case gives the oil more rest time in the pan which allows the oil to loose entrapped air. Either type pan needs baffles to keep the oil around the pick up and from creeping up the rear of the pan upon hard acceleration. All this stuff is in the catalogs. I have nothing against high volume pumps, use them all the time, but when your budget limited the first priority needs to be oil pan management The stock pump is plenty adaquate for most situations.

Heads can be changed down the road so if your cash limited these are among the last things you need to worry about, other than having a valve train that will not fail. That of course either means the components of the valve train are up to the revs you intend to turn, or the revs need to be limited to the capability of the valve train. The problem here is dropping a valve. This can be as destructive as tossing a rod, so good attention needs to be paid to the limits of the components. But as I said, the bottom end needs the first attention as the heads and induction are easy to change down the road to get more power from the engine. But an engine with a top end that can make more power than the bottom end can withstand is simply a ticking time bomb. And if you can make that kind of power, rest assured that human nature will cause you to use it at some point.

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