Compression

[Phreakish]

Then I dare to say that the cam isn’t very large to begin with.
Dyno testing is about maximum and maximizing power where it’s making the power. If you or anyone wants to dyno there grocery getter, well OK then, have at it.

But to say, “it can be nice to know how close the tuneup is” is one very crazy thing I never heard of before. To me that’s literally insane. If you can smell it a rich runner, then pull a plug, read it, adjust the carb etc… for around town driving.

The dyno tune is only good for the dyno and taking it directly to the track expecting it’s a good tune is again, crazy.

You misunderstand my point. Lots of folks drive off-peak and part throttle. Getting a handle on what goes on there isn't insane by any stretch. Race-only efforts are a different animal.

 

[rumblefish360]

You misunderstand my point. Lots of folks drive off-peak and part throttle. Getting a handle on what goes on there isn't insane by any stretch. Race-only efforts are a different animal.

After reading your reply, I think you missed my point.

No worries….

 

[Phreakish]

After reading your reply, I think you missed my point.

No worries….

LOL, I might have.

 

[rumblefish360]

 

[Newbomb Turk]

OK. IDK a whole lot about these machines. A lot of times and even in here once in a blue moon, someone asks the question, and I don’t see much of a reason to be concerned with power output at 1,00-1,500 when your cam is something like 250/260+@050. No one is putting a cam like that in there car with 2/76 gears riding on 28” tires looking for street manors in the city. Unless you’re crazy? Maybe driving your top end machine built for something like a 1/2 mile oval track? But why would anyone want to build that for driving in rush hour in the city?

Yea, I know it happens….

Loading the dyno that low to know how much power it has at 1,000-1,500 with large street cams, small or big race cams seems silly to me.

Is there a reason?
Have you done this?
Why? For what purpose is that t needed to be loaded and tested @ such a low rpm with cams of 250@050 and greater?
What customer needs to know this and for what?

As I said, I only have been told what I said. I’m not arguing with them or you over it. I’d just like to know.

Have you loaded the dyno @ WOT with a 250*@050 cam down to 1,000 rpm?


I’ve been told it’s also related to the cam size and function of the build. If I have an engine with a sizable cam where any meaningful power comes in at 3500/4500, what’s the point of knowing what’s at 1K/1500/2000 rpm.

I’ll just live with what it makes and use the right converter coupled with the gearing and tire size to out out along. After all, the engine means business not at the low rpm’s but where it picks up.

This is what I noted on the shows and what I’d be after.

I have loaded down a [email protected] cam. I’ll be doing my own junker in a few months and I’ll load it down that low. That’s how I figure out how much timing the engine wants, and where it wants it.

I know some guys get weird when you load an engine like that, but it can be what happens in the car, even though I’m very careful to not be rolling along in 3rd or 4th gear at say 20 MPH and then stomping on the throttle.

I’m not sure even with an ignition with individual cylinder timing could produce a curve that would keep the engine out of detonation in that particular case.

One of the things I’ve had to learn (and it wasn’t easy because I’m pretty stuck in my ways until I can prove something I’m doing is wrong) is that these engines are hyper sensitive to timing, especially around peak torque.

It gets even worse when you run a ton of cam and no compression (or not enough compression for the cam timing) in that the engine wants a big load of initial at idle but by peak torque the engine wants less timing than it does at peak power.

So somehow you have to slow the curve down enough to not get more timing than it wants at peak torque and still have enough curve left that at peak power you can get full timing.

The only way I know to actually sort that out is to load the engine down that low and watch power and manifold vacuum and then take notes so you can go to the distributor machine and figure out a way to do it.

I also now have a blow by meter hooked up, and you can bet that will show even trace detonation because that kills ring seal.

 

[273]

Pretty much any cam is streetable, unless it’s a spring eater.
What I mean is, assuming the lobes aren’t real aggressive, anything can be livable. I have went grocery shopping with cams over 270@50

Drivability means different things to different people/projects.

I mean some seem to think that if X cam makes more torque than Y cam at 1500 rpm, that X cam is gonna have more usable power around town. Forgetting eg.. an extra 20 lbs-ft @ 1500 rpms at fully throttle will be like 15 lbs-ft at half throttle and hp is 29% of tq at 1500 rpm making a 4 hp difference.

And all other times your cruising around at X rpm the engine just making what needed not what's possible.

 

[273]

The power production may not matter, but if it gets driven anywhere below that range it can be nice to know how close the tuneup is.

A chassis dyno probably be better for that.

 

[92b]

I can only speak for my dyno as far as accuracy at low rpm. It can measure accurately but if the engine has a " big cam" the engine might not run well at low rpm and if the the engine doesn't run well it might not repeat well. Not having repeatability makes it difficult to evaluate changes.

The dyno tune is only good for the dyno and taking it directly to the track expecting it’s a good tune is again, crazy.

Racers have been using dynos to determine safe starting point tunes for race cars for probably as long as there have been dynos.
If you take two identical motors unfamiliar to the tuner and race them side by side, I think the motor with a well sorted tune off the dyno has a better chance for success than a motor that does not. Not to say that eventually the other motor couldn't be tuned to run as fast.

 

[92b]

Dyno testing is about maximum and maximizing power where it’s making the power.

That might be what is most important to you when dyno testing and much of the time that is what my customer wants . But that isn't always the case for me or my customers at the dyno. As an example sometimes trading a few hp at the maximum in order to increase power somewhere else is beneficial for the customer. There is a lot of other data collected with the power numbers and sometimes that data is more important than the power numbers. Another example is in circle track racing where driveabilty is given precedent over maximum power. In enduro racing the amount of fuel used vs maximum power is a consideration so we might be looking at brake specific fuel consumption and changes to improve that. I have used the dyno to look at oil pressure and changes that affect oil pressure.
Somtimes I swear all my dyno is good for is finding oil leaks. If you have dyno you're chuckling right now.

 

[RustyRatRod]

I know on my car, I could care less what power it makes, except between 5k-6500, because that is where it spends 99% of its time at on the track.
Nothing else matters one iota.

Exactly. That's what most people slap miss. If you're happy with your engine's power where the RPM lives most of the time, what the heck difference does it make?

 

[RustyRatRod]

Pretty much any cam is streetable, unless it’s a spring eater.
What I mean is, assuming the lobes aren’t real aggressive, anything can be livable. I have went grocery shopping with cams over 270@50

You can drive a cheater cam on the street if it's set up right.

 

[rumblefish360]

You can drive a cheater cam on the street if it's set up right.

True and that can be said for any combination. Whatever one is willing to live with is fine by them and OK by me. I’m not driving it.

I can only speak for my dyno as far as accuracy at low rpm. It can measure accurately but if the engine has a " big cam" the engine might not run well at low rpm and if the the engine doesn't run well it might not repeat well. Not having repeatability makes it difficult to evaluate changes.

Exactly

Racers have been using dynos to determine safe starting point tunes for race cars for probably as long as there have been dynos.

No argument there

If you take two identical motors unfamiliar to the tuner and race them side by side, I think the motor with a well sorted tune off the dyno has a better chance for success than a motor that does not. Not to say that eventually the other motor couldn't be tuned to run as fast.

No argument there

That might be what is most important to you when dyno testing and much of the time that is what my customer wants . But that isn't always the case for me or my customers at the dyno. As an example sometimes trading a few hp at the maximum in order to increase power somewhere else is beneficial for the customer. There is a lot of other data collected with the power numbers and sometimes that data is more important than the power numbers. Another example is in circle track racing where driveabilty is given precedent over maximum power. In enduro racing the amount of fuel used vs maximum power is a consideration so we might be looking at brake specific fuel consumption and changes to improve that. I have used the dyno to look at oil pressure and changes that affect oil pressure.
Somtimes I swear all my dyno is good for is finding oil leaks. If you have dyno you're chuckling right now.

You lost a wide verity of variables not previously discussed opening up the rest of the work can!

So, let me ask you, when a customer has a small engine like a 340/350/360 and there camshafts are 255@050, are they worried about the performance of the engine at 1,000-1500 rpm for there street beast?

Are you starting the dyno run at these rpm’s?

 

[92b]

So, let me ask you, when a customer has a small engine like a 340/350/360 and there camshafts are 255@050, are they worried about the performance of the engine at 1,000-1500 rpm for there street beast?

Absolutely. These type of motors can be very challenging. Especially if it is an automatic car. Most customers want a car that will idle on it's own without stalling. They don't want it to stall when they put it in gear. They don't want it to fall on it's face, hesitate or back fire as they accelerate from a stop. They don't want it to foul the plugs or make your eyes water from the exhaust. They don't want it to die every time they stop at a stop sign or run on when you shut off the engine. Etc.
I do my best to minimize those issues. Sometimes successfully sometimes not. Some compromises will probably have to be made. I'll be the first to admit there are tunners that are way better at this than I am. I do the best I can and try learn what I can to improve at this craft. The difference between a well sorted and tuned motor vs the same motor with a bad tune can be night and day.

 

[rumblefish360]

Absolutely. These type of motors can be very challenging. Especially if it is an automatic car. Most customers want a car that will idle on it's own without stalling. They don't want it to stall when they put it in gear. They don't want it to fall on it's face, hesitate or back fire as they accelerate from a stop. They don't want it to foul the plugs or make your eyes water from the exhaust. They don't want it to die every time they stop at a stop sign or run on when you shut off the engine. Etc.
I do my best to minimize those issues. Sometimes successfully sometimes not. Some compromises will probably have to be made. I'll be the first to admit they're tunners that are way better at this than I am. I do the best I can and try learn what I can to improve at this craft. The difference between a well sorted and tuned motor vs the same motor with a bad tune can be night and day.

I am amazed at what I’m reading & what others will pay for but heck, good for you! I do all of that by myself on my own.
Dang!

 

[92b]

Are you starting the dyno run at these rpm’s?

No. That's probably close to the idle speed depending on the rest of the combination. Dyno sweeps are done at full load wide open throttle. I don't think this engine would be used under those conditions at that rpm. I will use the dyno to tune the strongest stable idle I can. I can load the engine to simulate acceleration from a stop sign or load then quickly return to idle too see how stable the engine is when it returns to idle. I can look at o2's, engine vacuum, engine speed, load, timing, egts and etc. To help help sort it out. It can give a good starting point that may require additional tuning when driven on the street or sometimes little or no additional tuning is required.

 

[92b]

I am amazed at what I’m reading & what others will pay for but heck, good for you! I do all of that by myself on my own.
Dang!

If you do your own tuning then you know the challenges and frustration that come with tuning. You also know how rewarding it can be too. Some days i have to ask myself why.

 

[rumblefish360]

If you do your own tuning then you know the challenges and frustration that come with tuning. You also know how rewarding it can be too. Some days i have to ask myself why.

Oh heck yea dude, heck yea. I was never a guy that could just take two or three stands at it and be happy like I nailed it. Never mind the secondary side. Just the primary side is frustrating since it takes time. Getting it to where I’m happy with a crisp response and on the daily drivers, good mileage. It’s also been a long while since I have had to do this chore. It’s coming up soon and look forward to tinkering on my rides again as the garage is getting finished. I expect remembering will be a PIA on the rusty parts of the brain. LOL!

In the end, yes indeed it is very satisfying.

 

[Bewy]

Post#88. Very good post with sensible comments.