Advanced Engine Theory and Design
- Thread starter Alky V6
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A quick note on turbocharger compressors, maps and surge lines.
On big turbo, small engine combinations, you can somewhat adjust how closely you dance with the surge line by adjusting how quickly or how slowly the turbo spools up. Such as playing with turbine housing A/R ratios or progressive boost rise settings with electronic boost controllers. If your running close to the surge line with your particular combination of engine/turbo, you would want to slow the rate of turbo spool up in relation to engine rpm. In a big turbo, small engine combination, quick spool up can be a bad thing.
On big turbo, small engine combinations, you can somewhat adjust how closely you dance with the surge line by adjusting how quickly or how slowly the turbo spools up. Such as playing with turbine housing A/R ratios or progressive boost rise settings with electronic boost controllers. If your running close to the surge line with your particular combination of engine/turbo, you would want to slow the rate of turbo spool up in relation to engine rpm. In a big turbo, small engine combination, quick spool up can be a bad thing.
Thanks for the numbers Don. I cant seem to find any maps for the 47/80. I havent bought the turbo yet and havent totally decided yet but thats about the right size I think. I was told that TI rods were OK but didnt like being pinged at ali, since they dont strech or flex you are hammering the bearings really hard. Also the big boys with the large turbos all say the same thing dont have your turbo spool to fast. But rather spool during the run to max PSI at the end of the run.
Don,
Sorry it took so long but I just got back in town.
The book is "The Chevrolet Racing Engine" by Bill Jenkins with Larry Schreib circa 1976.
Marty
1976. Man, don't that make you feel old. Thanks jjvites.
I would like to stay on the subject of camshafts for now. We have the choice of small duration and large duration, low lift and high lift, amount of overlap if any, cam advance or retard setting, single pattern or dual pattern and dwell time over the nose of the cam. Every single one of the previously mentioned areas is a tuning tool available to the engine builder to take advantage of, or make up for different aspects of an engines breathing ability. Better breathing means more air. More air means more oxygen. More oxygen means more fuel to be burned. More fuel burned means more power.
One aspect of camshaft design is what's called, 'area under the curve'. This is one tuning tool that can effectively make up for a set of heads being too small for the job. Heck, it can even be used on a properly matched set of heads to just plain make more power. Now we're talking! :biggrin: To achieve good area under the curve numbers, what compromises are involved, if any. Remember, high performance engines are packed full of compromises.
One aspect of camshaft design is what's called, 'area under the curve'. This is one tuning tool that can effectively make up for a set of heads being too small for the job. Heck, it can even be used on a properly matched set of heads to just plain make more power. Now we're talking! :biggrin: To achieve good area under the curve numbers, what compromises are involved, if any. Remember, high performance engines are packed full of compromises.
Mike Licht
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- May 23, 2001
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Don,
looking at your can comparision a few posts back did you run the numbers with both cams at 110 l/s and 114 l/s I am curious how that impacted the results. Many computer simulations I have tried run up the HP number as you make the L/S wider with forced induction simulations. What software are you using?
Mike
looking at your can comparision a few posts back did you run the numbers with both cams at 110 l/s and 114 l/s I am curious how that impacted the results. Many computer simulations I have tried run up the HP number as you make the L/S wider with forced induction simulations. What software are you using?
Mike
The comparisons were done at 114 l/c. That seems to be the popular spec everyone prefers, so that's what I used. It does give a very nice compromise between midrange and top end power. I will give it that. In my particular engine setup, the software tells me that the 110 works better at the upper rpm range. Believe me, it does certainly hurt low and midrange, but I am not concerned with that. The juice more than makes up for any tuning shortcomings in the midrange. Since the engine spends the vast majority of its time in the upper rpm range, that is what I concentrated the tuneup on. 6,100 to 7,400 rpm. That is where my engine runs after getting out of the hole and between shifts. The tight T/C causes quite a drop between shifts, but the power band seems to take it in stride quite well. On one run in Vegas where I had mistakingly short shifted 3rd, the rpm really dropped down, but the engine pulled it and I only lost about 2 tenths on that run. I was very happy with the outcome. Actually, that's the run I have posted in the picture and video library on this site.
Performance Trends - Engine Analyzer Pro
Mike Licht
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I was looking at the specs in the post looks like the small one is a 100 and installed at 105 and the big one looks like a 114 installed at 113:
I am also suprised at a 122HP swing from one to the other from 4750 to 5000RPM must come on hard there. I love camshaft stuff. I have a copy of EA Pro as well some very interesting things in there
Mike
I am also suprised at a 122HP swing from one to the other from 4750 to 5000RPM must come on hard there. I love camshaft stuff. I have a copy of EA Pro as well some very interesting things in there
Mike
That's cool. You have the best program for the money. That is a fact.I was looking at the specs in the post looks like the small one is a 100 and installed at 105 and the big one looks like a 114 installed at 113:
I am also suprised at a 122HP swing from one to the other from 4750 to 5000RPM must come on hard there. I love camshaft stuff. I have a copy of EA Pro as well some very interesting things in there
Mike
Yea, I think on the 114 I did have 1 degree advance. I will usually play with a setup with between 1 and 5 degrees advance to find the best advance number. The wide centers seem to need less advance than the tight centers. The more advance seems to help pump up the midrange in a cam that needs better midrange. My 110 l/c, I run at 5 degrees advanced. Doesn't hurt the top end too much.
Maybe at one point we can share some specs to come up with some awesome combinations. You know, like gamers trading gaming secrets.
Mike Licht
I was here first
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I can tell you about my latest one for my 109 stroker with stage 2 iron heads is 228* intake .350 lobe lift 232* exahust (.050) .352 lobe lift 113L/S installed straight up. (solid roller) 4 to 6 degrees extra exhaust duration seems to be the ticket for me right now. 8-10 is too much, 2 does nothing unless I am shooting for a particular event timing and I use it to get there. Do you ever move the intake opening point around to take advantage of the intake tuning?
When you're searching for the elusive max HP number, you move everything around. I spent weeks on the program putting my combination together. Trying this and that. My family must have thought I was crazy.
I went into the project with the notion that I would not be limited by anything but the heads. If I needed a particular manifold configuration to get what I needed, I would build it. The engine was made on the computer first. The head flow numbers were the basis for everything else. It is very important to get good flow numbers.
Believe it or not, the one thing that is holding the combination from doing better than it is now is the turbo, not the heads. My small valve, small CID V6 has taken the T76 to the limit.
I went into the project with the notion that I would not be limited by anything but the heads. If I needed a particular manifold configuration to get what I needed, I would build it. The engine was made on the computer first. The head flow numbers were the basis for everything else. It is very important to get good flow numbers.
Believe it or not, the one thing that is holding the combination from doing better than it is now is the turbo, not the heads. My small valve, small CID V6 has taken the T76 to the limit.
For a drag application, it's nice to have the HP curve somewhat flatten out for a range of about 1500 rpm. That way you don't have a big drop in HP between shifts.
Your second question is a bit tricky. A turbo will raise peak HP and can at the same time narrow it depending a lot on the cam used. Take one particular engine with a large cam (250 @ .050" duration) as an example. Without a turbo, even with a large cam, you can have a very wide power band. Low, but a flat torque curve. Add a turbo to that same engine and the power band peaks much higher, but the curve is not as flat. A small duration cam can give a flatter torque curve even with the turbo, but the peak HP number is not nearly what it could be with a larger cam. The required shape of the torque curve depends greatly on the use of the engine. A small circle track engine would need more midrange torque to get out of the corner. A drag engine is usually an all out effort with the only consideration being maximum HP. Most torque converters that people pick give them a drop of 1000 to 1500 rpm between shifts. As far as I'm concerned that is where I want the engine making the most power. In that 1000 to 1500 rpm range, since that is where the engine is going to spend most of its time when going down the track. A small cam will give you an impressive launch, but will limit your MPH. Torque gets you out of the hole and horsepower gives you the MPH.
Well then I guess it's only going to get worse. I have only just begun.It only got one star because of the long ending
Speaking of max effort turbocharged drag engines, have any of you checked out the Car Craft story on the twin turbocharged BB Chevy? 2800 HP? That is nuts. Or should I say, ya gotta have nuts to drive that monster. Check out the duration cam spec on the engine. I was surprised. A good example of the saying, 'You don't have to choke the engine with a small cam just because you're running a turbocharger. Turbocharged engines will react to cam changes just as N/A engines do.'
There is one truth that needs to be said about large duration turbo cams. If you can't properly tune the intake and exhaust in order to make a large cam properly work, then stay with a small cam. You'd be wasting your time. A large cam is very dependant on gas pressure pulse tuning. You could have yourself a big mess just using any old manifolding system.
Pressure pulse tuning. Now that is music to the ears. :tongue: An engine that is setup to take advantage of pressure pulse tuning will have the advantage every time over the same without.
There is one truth that needs to be said about large duration turbo cams. If you can't properly tune the intake and exhaust in order to make a large cam properly work, then stay with a small cam. You'd be wasting your time. A large cam is very dependant on gas pressure pulse tuning. You could have yourself a big mess just using any old manifolding system.
Pressure pulse tuning. Now that is music to the ears. :tongue: An engine that is setup to take advantage of pressure pulse tuning will have the advantage every time over the same without.
Ok, I'll bite...what is "Pressure Pulse Tuning"? Anything to do with the length of the intake runners and the movement of the peak torque up or down the RPM scale? Corky Bell's book talks about the optimum size of the intake plenum. What is the theory and calculations?
Conrad
Conrad
