Valve lifters…solid/hydraulic/roller tappet/flat tappet?

[olddog]

Originally Posted by xb-60

Are you serious olddog, or is this like Brent said, tacho wired for a 6cyl?
What's the story?
Cheers,
Glen

To be fair, the head choice in this program I believe to be expert race ported heads. I expect to actually get heads that good would be in the $5000 range or more.

Now most experts (with far more experience than my reading books and playing with computer simulation software) will tell you that large port heads like that will kill the low end torque. Now, I will tell you that if you use a cam to take advantage of those head's top end power potential, they are absolutely right. It will give you a low end dog. However it is my theory that if you give up the top end power and keep the cam mild, the bottom end does not have to suffer.

I look at it this way. With supper good flowing heads, at low rpm the flow will do exactly what the cam tells it to do. If you have over lap, it will suck exhaust back into the intake like there is no tomorrow. If you close the intake valve late, the piston will shove air back into the intake, leaving the cylinder less than full. On the other hand, if you keep the overlap to a minimum and don't leave the intake valve open too long, these supper good flowing heads are going to completely fill the cylinders, giving excellent low end torque. You will give up top end power, but still have decent power due to the flow capability of the heads. From there you play the rob Peter to pay Paul game with the cam to strike the best balance. The heads allow a much milder cam that give a much flatter torque curve.

Buy going all out on the cam, tunnel ram, 1100 cfm, open stepped headers, I can get 900 hp at 11000 rpm, which drops the low end torque to 200 lb-ft. That is how big these heads are. This would be costly and tough to get your hands on. Not to mention trying to keep control of the valves. These are heads that should be on a longer stroke engine to keep the rpm down.

[xb-60]

Originally Posted by olddog

.... if you keep the overlap to a minimum and don't leave the intake valve open too long, these super good flowing heads are going to completely fill the cylinders, giving excellent low end torque. You will give up top end power, but still have decent power due to the flow capability of the heads. From there you play the rob Peter to pay Paul game with the cam to strike the best balance. The heads allow a much milder cam that give a much flatter torque curve.

The 'rag/mag' article I mentioned earlier obviously doesn't tell the whole story, but what I got out of that article was, I think, in line with what you're saying about decent (but not too big) heads and mild cam. And some compromise on my part on gearing.
Cheers,
Glen

[olddog]

Originally Posted by xb-60

The 'rag/mag' article I mentioned earlier obviously doesn't tell the whole story, but what I got out of that article was, I think, in line with what you're saying about decent (but not too big) heads and mild cam. And some compromise on my part on gearing.
Cheers,
Glen

I gave an extreme example of an engine to show that for enough money it likely can be done, but very likely has not been done. It just isn't the road that is traveled. Few if any builders are practicing in this arena. It is just too easy and too economical to go the direction that Blykins is pointing you, so that is where the crowd has gone. I have thought about these things because I'm an engine geek. People doing it for a living and standing behind their work do not have the luxury that I have. I haven't any skin in the game. It all just academic fun for me.

Yes. I do think you have to compromise in the gearing. If your making 500 hp at 8000 rpm and someone else is making 500 hp at 6000 rpm, to get the same performance your going to have to be geared to turn 8000 rpm at the same mph that the other guy is only turning 6000 rpm. Most guys running big FE are geared 3.5:1, some a little higher some a little lower. Your going to have to have a rear ratio at least 3.5:1 and more likely closer to 4:1 to have decent acceleration, with the low torque of a typical 302. Then the cruising rpm is going to be too high to enjoy the ride (noise). I would go with a 5 speed. The overdrive is very nice. I know that is not what you want.

Or spend a small fortune developing my magic engine. I'd expect it would take a half dozen cams to actually achieve the magic engine. Maybe a couple or three tries on the heads, too.

[zrayr]

Originally Posted by olddog

"....Now most experts (with far more experience than my reading books and playing with computer simulation software) will tell you that large port heads like that will kill the low end torque. Now, I will tell you that if you use a cam to take advantage of those head's top end power potential, they are absolutely right. It will give you a low end dog. However it is my theory that if you give up the top end power and keep the cam mild, the bottom end does not have to suffer........."

I'm no expert, as all that know me will attest to, but the one thing I think you are overlooking is the relationship of small ports to intake charge velocity. If the intake ports are not matched to the rest of the engine, i.e. too big, the velocity will drop and the gas will fall out of suspension. The same thing happens when you try to put a "too big" carb on a relatively small engine. A mild cam will mitigate this somewhat as you suggest, but not enough, and throttle response will suffer and you will end up with a huge bog that can't be tuned away.

Z.

[blykins]

Originally Posted by zrayr

I'm no expert, as all that know me will attest to, but the one thing I think you are overlooking is the relationship of small ports to intake charge velocity. If the intake ports are not matched to the rest of the engine, i.e. too big, the velocity will drop and the gas will fall out of suspension. The same thing happens when you try to put a "too big" carb on a relatively small engine. A mild cam will mitigate this somewhat as you suggest, but not enough, and throttle response will suffer and you will end up with a huge bog that can't be tuned away.

Z.

I would agree with that 100%. Add volume and flow, but take away velocity, and you end up with a port carrying a lot of inertia. A "slow" port is hard to get moving and is considered lazy until the higher rpms. If you don't have enough cam, it doesn't matter how well the heads flow, it won't pull the rpms that you want. It's true that you need less duration as head flow increases, but that doesn't mean that you can have a 600cfm head and a 205° duration and spin to 7000. (Just for example's sake...)

The dyno sims are a great "ballpark" tool. Unfortunately, Desktop Dyno and EA Pro show about 7-8% high compared to the actual dyno that I use. Desktop Dyno seems to be WAY off when it comes to torque numbers as well.

There's NO way that a 302 set to peak at 7000-7500 will have a flat torque curve settling around 400 lb-ft. An't no way. An't gonna happen.

You also have to look at it this way....dynos are cool for breaking in an engine and seeing what kind of power it puts down, but at the end of the day, you can't get on it and drive it. A dyno gives no indication whatsoever as to how the engine will be on the road, in a car, with a transmission and rearend behind it. It gives no indication of how much you'll have to slip the clutch taking off or how fussy it will be cruising at 1500 rpm.

What you would see in reality with this type of combination would be a torque peak at around 6000 rpm, with probably around 100-150 lb-ft available at cruising rpms. The curves would look more like a steep hill instead of having any flatness to them at all.