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Discussion Starter #1
Hi All,

What might be the "weakest link" in my engine (a "298" it is bored .065 over)? I have forged pistons and rods. A slightly warmed up cam (Crane), everything has been balanced and smoothed/polished internally. The deck and heads were milled/blocked (slightly higher compression). The cylinders were bored under pressure - so they should be "perfectly" round. The heads have been ported some. I still have the hydraulic lifters (non-roller), but the valve spring rate has been increased. Stock distributor and points. Stock carb, 4100 4V. (I don't know about anything else, it was rebuilt a long time ago and I simply did not know enough about engines at the time.)

If I hold the gas pedal down (say in 2nd gear, 1.93 ratio) the engine will rev up close to 6,000 RPM (70ish mph) before I lose my nerve, and hearing :). (Just did this Saturday) I'm curious what component would likely be the limiting factor for this engine? Valve float, something breaking, etc.

Thanks in advance.

John Harvey
 

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I think it's a combination of things. Valve float would start, which would cause the valve train to start slapping, which would bend a rod, which would crack/blow a valve etc.....

Just my thoughts....Greg.
 

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Valve float is and has been my limiting factor. It starts just over 6k. My engine has probably peaked making power by then so that is okay.

Above a certain point your engine will stop making more power and you will just be screaming your engine for no reason.

289's are pretty tough. Call your redline 6k and you should be fine.
 

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I would run it on a dyno and see where your HP and TQ curves are. That will show you where you stop making power and just make noise!
 

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Sounds like you have done a lot of the right things to make a stronger 289 already. From a theory side, piston speed and valve float are the two main limiting factors. Excessive piston speed cause sealing lose, thus loosing cylinder pressure and power. Valve float starts to also lose cylinder pressure but can lead to damage if the piston crown contacts a valve that is still open. High RPM race motors get around this by using very light parts and stiff springs. But the real factor is when your torque curve falls off. You intake and cam and heads will primarily determine this. A motor that runs good at 1500 to 3500 RPM usually cannot flow enough air to run good at 7000 RPM. A relatively small investment is to get your car dyno'ed. Look for where the torque curve falls off and that should be your max RPM. I would guess it should be around 5500 to 6000 RPM. Good luck and have fun /forums/images/icons/wink.gif
 

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Discussion Starter #6
Thnaks, you've all confirmed what I expected. I think I will look into testing it on a dyno machine.

John
 

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Tell us about your camshaft, heads, intake manifold and exhaust system....

I've had iron headed 289's with similar bottom ends (albeit with nearly 13:1 CR) making power into the 6.5-7K range and spinning to 7.5 in the lights in the race car in past years.....it sounds like your engine, if meticulously built and dynamically balanced, should be good for 7K mechanically.

Getting the engine to actually make power there and not just pump air is another matter, hence the questions about intake, heads, and exhaust...

In your situation, depending on the answers you provide, it's possible your 1.08 4100 many end up being the restriction, but I won't know that without the other info. Also, the rear gear you use will have a real-world effect on the engine's efficiency, depending on state of build...

Lots of things go into making an effective combination and we've just touched upon a few...

I wouldn't worry about 6K in second gear, or high gear for that matter....your engine will do fine...just make sure the rest of the vehicle is up to the stress and speed..
 
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