Advanced Engine Theory and Design
- Thread starter Alky V6
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Scott. How long have you had to increase the nitrous hose to get the timing right? We're trying to figure out a good starting point. Presently, both hoses are around 8 inches long. My friend wants to go this route. He feels a tenth second delay may be too long.
At your weight and HP, I'd stick with the stock 1st gear. You won't be missing out on much if any. Besides, the low 1st gearsets for the 400 are questionable at that HP level.
The old school thinking you mentioned is still the rule today. Sims are even proving it so.
How big of shot? Also, are you running a relay? What is the max pressure on the fuel pump? The most effective route would be to shorten the supply line from fuel solenoid to the plate or fogger. Get it as close as possible and increase the fuel pressure as much as the pump allows. You can always run 2 regulators for test purposes(one for the carb, the other for the solenoid) Lengthing the N20 side works but will also "soften" the hit as chevyII stated.
Lemme know what you find out.
Scott Wile
The shot is a 250. The present fuel pressure is 8 psi. Not sure what he could take it too. He's running a single Dominator. I'll see if he can move the fuel solenoid closer, first. I'll check to see if he's running the solenoids off a relay. I assume that's the only way they should be run. I think he is running two fuel pumps.
Two regulators. Good info, Scott. Thanks. I'll post the results and changes.He likes his wheel stands, so softening the hit would be a last resort.
Let me try and get something started on my particular engine project and the thought process behind some of my basic configuration decisions.
I want to first say that there are so many ways to skin a cat, and that relates to engine configurations too. I want to be sure that everyone doesn't get the idea that I am portraying my engine setup as superior to anyone elses. It's just the way I decided to go with it. Many are doing as good and better with much simpler and less expensive setups than mine. I just had to build my own special science project, if you will. It also was a very important tool for developing some fabrication skills that I now feel much more comfortable applying to other work projects. Isn't that what R&D projects meant to do?
My first decision was determining the heads to use. I had acquired some 1st gen M&A heads years ago and since my racing budget was and still is limited, I decided to try and take the M&A heads to the limit. I would not perform any fancy mods to the heads besides a max effort port job, lighter valves, and larger valve springs. No larger valves or valve repositioning. If I were to go into that, I would just go to Stage II heads which I couldn't afford to do at the time.
I firmly believe the cylinder heads are at the center of any engine configuration. That the rest of the engine is just systems meant to get the most out of the heads in use or tune them to a particular requirement. The next question being, what HP level will these heads support? To answer that we must first understand the many different efficiencies of the cylinder head.
Port volumes and shape.
Port diameter to valve diameter ratio.
Port flow rates, and at what different valve lifts.
Chamber volume and shape.
Valve shrouding or the lack there of.
Piston top configuration needed to obtain a desired CR (directly related to our cylinder head chamber volume). And the efficiency of that piston top as far as cylinder filling and flame propagation.
Available quench area.
The valve train hardware that the head will support to take the engine to a required rpm power band.
Cylinder head deck strength and available clamp down force.
Available HP head gasket designs.
Anti-detonation characteristics.
Intake charge swirl characteristics.
Heat transference abilities or resistance to (heat barrier coatings).
Believe me, many of these variables I did not measure and don't have the facilities to do so. I just named these to show some of the things that play such an important role in making HP. Notice that I said some of the things. I am positive there is more that I am missing.
Our engines are basically an air pump with the cylinder head being at the heart of its breathing ability.
I want to first say that there are so many ways to skin a cat, and that relates to engine configurations too. I want to be sure that everyone doesn't get the idea that I am portraying my engine setup as superior to anyone elses. It's just the way I decided to go with it. Many are doing as good and better with much simpler and less expensive setups than mine. I just had to build my own special science project, if you will. It also was a very important tool for developing some fabrication skills that I now feel much more comfortable applying to other work projects. Isn't that what R&D projects meant to do?
My first decision was determining the heads to use. I had acquired some 1st gen M&A heads years ago and since my racing budget was and still is limited, I decided to try and take the M&A heads to the limit. I would not perform any fancy mods to the heads besides a max effort port job, lighter valves, and larger valve springs. No larger valves or valve repositioning. If I were to go into that, I would just go to Stage II heads which I couldn't afford to do at the time.
I firmly believe the cylinder heads are at the center of any engine configuration. That the rest of the engine is just systems meant to get the most out of the heads in use or tune them to a particular requirement. The next question being, what HP level will these heads support? To answer that we must first understand the many different efficiencies of the cylinder head.
Port volumes and shape.
Port diameter to valve diameter ratio.
Port flow rates, and at what different valve lifts.
Chamber volume and shape.
Valve shrouding or the lack there of.
Piston top configuration needed to obtain a desired CR (directly related to our cylinder head chamber volume). And the efficiency of that piston top as far as cylinder filling and flame propagation.
Available quench area.
The valve train hardware that the head will support to take the engine to a required rpm power band.
Cylinder head deck strength and available clamp down force.
Available HP head gasket designs.
Anti-detonation characteristics.
Intake charge swirl characteristics.
Heat transference abilities or resistance to (heat barrier coatings).
Believe me, many of these variables I did not measure and don't have the facilities to do so. I just named these to show some of the things that play such an important role in making HP. Notice that I said some of the things. I am positive there is more that I am missing.
Our engines are basically an air pump with the cylinder head being at the heart of its breathing ability.
When you are picking out a cylinder head, it is important to first have an idea of what the engine configuration will be asked to do. This will become more clear as I discuss further. Since I had already picked out the head design, the mission became get the most I possibly can out of this model head. The engine being a race only project, it was clear that any restrictions to make the engine streetable would not interfere with this max effort configuration.
After having the heads ported and flowed, I was ready to pick the rpm band that I would need to get the HP numbers I was targeting. Back then I was running a T70, so the HP target was 800-850 HP. This would be pushing the 70 to the max.
After having the heads ported and flowed, I was ready to pick the rpm band that I would need to get the HP numbers I was targeting. Back then I was running a T70, so the HP target was 800-850 HP. This would be pushing the 70 to the max.
Being that any true blue racing engine is going to be twisted to the max that the pocket book will bare, it was time to pick the max rpm limit for the engine. A few factors had to be taken into consideration first. Just how high could I go with this relatively small head?
A few sources claim that peak power will occur at an intake port velocity of 230-240 feet per second by one and 250-350 fps by another. Peak volumetric efficiency should occur between .3 and .5 mach number. Power to drop off sharply somewhere after .55 mach number.
To quote, "In simple terms Mach number relates the average velocity of the intake charge past the valve to the speed of sound."
More cam duration will affect the mach number. "The higher the intake duration, the lower the Mach number and the higher the RPM for peak volumetric efficiency."
Now, how the heck is someone like myself going to calculate the above stuff?
The answer. We now live in the computer age. There are sims of all kinds available to us now. Sure, someone could calculate each individual formula involved in configuring an engine, or why not use a sim that ties all these formulas into one neat package. Push the enter button and out comes all kinds of information you could spend a week easy trying to digest. Change a variable, push the button and out comes new data that you can use to compare to the previous setup.
I know there are some out there right now that are saying, "Ahh, computers. You can't trust computers. There's no replacement for good old experience."
Well, let me tell you something. It is the people with all that experience that realize the most that a good engine simulation is the most fantastic tool to ever come their way.
I use Performance Trend's 'Engine Analyzer Pro' to setup all my engines and have used it to check customer's engine configs too. And guess who else uses this same program? Mike @ TA Performance and the big K. Yes. Kenny D. uses a sim to test each engine config beforehand. I have talked to others too that use the program and it seems unanimous that they have all seen results within 5 HP of what the sim stated the engine would do. In my case, I was always presently surprised with the results. As you use a sim and have a chance to compare it to real world results, you learn to tweak your input parameters to give you even more accurate results. The old garbage in, garbage out saying. The more accurate your input data becomes, the more accurate the output and the real world results. I firmly believe that I would not have been able to do what I did with this project without the use of a sim. The alternative would have been to rely on the advise of others or years and years of trial and error.
To quote, "In simple terms Mach number relates the average velocity of the intake charge past the valve to the speed of sound."
More cam duration will affect the mach number. "The higher the intake duration, the lower the Mach number and the higher the RPM for peak volumetric efficiency."
Now, how the heck is someone like myself going to calculate the above stuff?
The answer. We now live in the computer age. There are sims of all kinds available to us now. Sure, someone could calculate each individual formula involved in configuring an engine, or why not use a sim that ties all these formulas into one neat package. Push the enter button and out comes all kinds of information you could spend a week easy trying to digest. Change a variable, push the button and out comes new data that you can use to compare to the previous setup.
I know there are some out there right now that are saying, "Ahh, computers. You can't trust computers. There's no replacement for good old experience."
Well, let me tell you something. It is the people with all that experience that realize the most that a good engine simulation is the most fantastic tool to ever come their way.
I use Performance Trend's 'Engine Analyzer Pro' to setup all my engines and have used it to check customer's engine configs too. And guess who else uses this same program? Mike @ TA Performance and the big K. Yes. Kenny D. uses a sim to test each engine config beforehand. I have talked to others too that use the program and it seems unanimous that they have all seen results within 5 HP of what the sim stated the engine would do. In my case, I was always presently surprised with the results. As you use a sim and have a chance to compare it to real world results, you learn to tweak your input parameters to give you even more accurate results. The old garbage in, garbage out saying. The more accurate your input data becomes, the more accurate the output and the real world results. I firmly believe that I would not have been able to do what I did with this project without the use of a sim. The alternative would have been to rely on the advise of others or years and years of trial and error.
Ok. Enough with the commercial. Remember the 4 ways to make HP.
Larger bore.
Longer stroke.
Higher cylinder pressure.
Higher RPM.
The stage II block I was using was already at a bore size of 4.047". Not a good idea to go bigger.
My cylinder pressure would be limited by the range of my engine management system and the efficiency of the turbo. No more than 30 psi with the EMS and 26 psi for the turbo at the anticipated airflow. These limits would be adjusted as the engine development continued.
That leaves crank stroke and RPM.
An important thing to realize is that the crank stroke will affect piston speed at any particular RPM and will in turn affect charge velocity through the intake port. Remember that we have a target velocity for our intake port and changing the crank stroke will change when that optimum velocity occurs in the rpm band.
I have never seen a successful drag engine that did not rev to the mechanical limit, so the decision was made to rev the engine to a max limit of 7,800 rpm, if the heads would allow it. Any higher was just too rich for me. The higher you rev an engine, the higher the load, and wear and tear on the valve train. Massive spring pressures to keep this at bay in a ultra high rpm engine would mean a very strenuous and expensive maintenance schedule. I was looking for something that would give me 100 runs between PMs.
Larger bore.
Longer stroke.
Higher cylinder pressure.
Higher RPM.
The stage II block I was using was already at a bore size of 4.047". Not a good idea to go bigger.
My cylinder pressure would be limited by the range of my engine management system and the efficiency of the turbo. No more than 30 psi with the EMS and 26 psi for the turbo at the anticipated airflow. These limits would be adjusted as the engine development continued.
That leaves crank stroke and RPM.
An important thing to realize is that the crank stroke will affect piston speed at any particular RPM and will in turn affect charge velocity through the intake port. Remember that we have a target velocity for our intake port and changing the crank stroke will change when that optimum velocity occurs in the rpm band.
I have never seen a successful drag engine that did not rev to the mechanical limit, so the decision was made to rev the engine to a max limit of 7,800 rpm, if the heads would allow it. Any higher was just too rich for me. The higher you rev an engine, the higher the load, and wear and tear on the valve train. Massive spring pressures to keep this at bay in a ultra high rpm engine would mean a very strenuous and expensive maintenance schedule. I was looking for something that would give me 100 runs between PMs.
I'm not familiar with the features of that version. Study the features and pick whatever will help you out the best for the money.
My opinion is, anything is better than nothing and some sims will be more accurate than others.
I had a choice of longer stroke and better midrange with better turbo spooling or a shorter stroke and better top end performance sacrificing some low midrange and turbo spool up time. My plan for this project had always included the use of nitrous oxide injection to boost low midrange torque and shorten turbo spool up time, so the negatives that a short stroke would present to me were somewhat mute. The short stroke would also give me less strain on the reciprocating assembly and a slightly stronger split crank pin arrangement. Of course, at the expense of more strain on the valve train. Everything in a high performance engine is a compromise. The rpm power band that I had picked for the engine would ensure me of the HP numbers I was searching for. Little would I realize that the monster I was creating would far exceed what the engine software was feeding back to me. Remember, the sims output is only as good as the input. Since I had very limited real world experience with the Buick V6 at any real HP level my initial inputs were a bit off giving me lower numbers than I would eventually realize. After seeing the performance of the engine in real life, it is only a matter of tweaking some of the variables of the program before you come up with output that is more real world. Then from there you can try different cams, intakes, exhaust, heads, turbos, intercooler efficiencies, fuels, etc. and be confident that the results are closer to real world. Engine software is still only a tool and is not what I would call perfected. Use it with that in mind.
During the development of an engine, always keep in mind the intended use.
In my instance, which was to be drag racing only, I knew that the transmission shift point would be somewhere past the peak HP level. In my case, 450 to 1,000 rpm past the engine's peak HP rpm. This is done to maintain the highest average HP level throughout the track run. This shift point is different in every case depending mainly on how quickly the HP level drops off past peak HP rpm. Since I had picked a maximum redline rpm of 7,800 rpm, I would need to adjust all my engine specifications to obtain a peak HP level at somewhere around 6,700 to 6,900 rpm. The crankshaft stroke and camshaft specifications that I picked for the engine put the upper limit of the target intake air speed (discussed in previous post) at about 6,750 rpm. Notice I said crank stroke and camshaft. Actually, it was a matter of matching stroke, cam specs and rocker specs (ratio), intake runner size and dimensions (degree of taper), intake plenum size (pulse tuning or not), exhaust primary tubing size and style (straight, 2 steps, 3 steps, equal length, staggered lengths), exhaust collector size and style, and turbocharger turbine housing A/R ratio. Every single breathing system of the engine optimized, around the heads abilities or shortcomings, to achieve a maximum HP peak at 6,750 rpm. The camshaft needing the most attention because of the perceived shortcomings of the M&A heads. Mainly, the small valve size.
In my instance, which was to be drag racing only, I knew that the transmission shift point would be somewhere past the peak HP level. In my case, 450 to 1,000 rpm past the engine's peak HP rpm. This is done to maintain the highest average HP level throughout the track run. This shift point is different in every case depending mainly on how quickly the HP level drops off past peak HP rpm. Since I had picked a maximum redline rpm of 7,800 rpm, I would need to adjust all my engine specifications to obtain a peak HP level at somewhere around 6,700 to 6,900 rpm. The crankshaft stroke and camshaft specifications that I picked for the engine put the upper limit of the target intake air speed (discussed in previous post) at about 6,750 rpm. Notice I said crank stroke and camshaft. Actually, it was a matter of matching stroke, cam specs and rocker specs (ratio), intake runner size and dimensions (degree of taper), intake plenum size (pulse tuning or not), exhaust primary tubing size and style (straight, 2 steps, 3 steps, equal length, staggered lengths), exhaust collector size and style, and turbocharger turbine housing A/R ratio. Every single breathing system of the engine optimized, around the heads abilities or shortcomings, to achieve a maximum HP peak at 6,750 rpm. The camshaft needing the most attention because of the perceived shortcomings of the M&A heads. Mainly, the small valve size.
Camshafts!
:biggrin: This could be interesting with some input from others. I am by no means experienced with different camshaft grinds. I can basically only pass on what I have learned from books, catalogs, engine analyzing software and by limited personal experience with what most people would think are long (too long) duration cams for a turbocharged application.
Let me start by laying down some basic truths about camshafts.
The intake duration will dictate the rpm at which the engine develops maximum HP.
To make big HP, big duration numbers need to be used.
There are two schools of thought when it comes to turbochargers and camshafts. One school says that because of the turbocharger, you can use less camshaft duration. Another says that turbocharged engines will react to camshaft timing in the same manner as naturally aspirated engines. There are important truths to both statements.
Camshaft timing can be manipulated to adjust for shortcomings of the cylinder head to a small degree. This would include duration, lift, lobe separation and the use of dual patterns (different durations on the intake and exhaust).
:biggrin: This could be interesting with some input from others. I am by no means experienced with different camshaft grinds. I can basically only pass on what I have learned from books, catalogs, engine analyzing software and by limited personal experience with what most people would think are long (too long) duration cams for a turbocharged application.
Let me start by laying down some basic truths about camshafts.
The intake duration will dictate the rpm at which the engine develops maximum HP.
To make big HP, big duration numbers need to be used.
There are two schools of thought when it comes to turbochargers and camshafts. One school says that because of the turbocharger, you can use less camshaft duration. Another says that turbocharged engines will react to camshaft timing in the same manner as naturally aspirated engines. There are important truths to both statements.
Camshaft timing can be manipulated to adjust for shortcomings of the cylinder head to a small degree. This would include duration, lift, lobe separation and the use of dual patterns (different durations on the intake and exhaust).
(dramatic music) Camshafts. More often than not, a closely guarded secret among the elite members of our small, but effective community. :tongue: Sure, the tiny cams are well publicised. You can find them here. You can find them there. But what of the real pony makers. In what small garage, across what ocean might the ellusive cam spec be hiding? Will it ever be found? More tonight on the 11:00 news. 
I have to wait until 11:00? That's not nice. 
I don't hold any hope that the heavy hitters in our community will want to freely share their cam specs. It is the black art of engines. Just like torque converters are the black art of transmissions. The good thing is that anyone who will take the time to study camshaft design and function can figure out a good cam grind for their particular application.
To me the camshaft is the brain or soul of the engine. The heads being the heart. In a strictly high performance point of view, if you're looking to extract every bit of HP from a set of heads, you'd better look at the engine as a whole when selecting specifications for your cam. So much plays a part in making that camshaft work to its best. Another thing. To me there is no such thing as a generic, one size fits all cam.
I have to wait until 11:00? That's not nice. I don't hold any hope that the heavy hitters in our community will want to freely share their cam specs. It is the black art of engines. Just like torque converters are the black art of transmissions. The good thing is that anyone who will take the time to study camshaft design and function can figure out a good cam grind for their particular application.
To me the camshaft is the brain or soul of the engine. The heads being the heart. In a strictly high performance point of view, if you're looking to extract every bit of HP from a set of heads, you'd better look at the engine as a whole when selecting specifications for your cam. So much plays a part in making that camshaft work to its best. Another thing. To me there is no such thing as a generic, one size fits all cam.
There are a multitude of decisions that must be made when selecting a cam. The main ones being the intended use of the engine and the anticipated rpm limit of the engine. In a turbocharged application, there is another decision thrown into the mix. Turbo size and the amount of acceptable turbo lag time.
Let me back track a little here. There are some small duration cams that will seem to give you a high rpm limit with your engine. Let me explain what I mean. The stock cam in the GN has a drastic fall off in HP after 5,200 rpm. And when I say fall off, I mean like a cliff. Some small duration cams will flatten and broaden the HP curve which is real nice for a street/strip application, but will also let the engine rev higher with what feels like good power. Every cam will give your engine a peak HP rpm, which can be much lower than the rpm limit of the cam. It becomes unproductive to just rev the engine to say 7200 rpm if the peak HP was at 5750 rpm. A dyno reading becomes invaluable at this point to help you pick the best shift point for your setup. It's just undo wear and tear on your engine to pick a shift point higher than is really necessary and can in fact be slowing you down. Remember. Best average HP throughout the run.
Back to the subject at hand. Some of the other factors that need to be taken into account when picking out a camshaft.
Is there an important HP level that needs to be met? And how flexible is it?
How well sized are the heads for the intended use of the engine?
Will the heads need a little help from the cam to fulfill the target power level?
Do we need to be concerned with smog testing?
Are we running a catalytic converter?
O2 sensor?
Are we willing to change out the O2 sensor and cat more often?
How well will our engine management system handle a large cam?
How often do we want to change spark plugs?
Will we be changing the oil often?
Will it just be me driving the car?
How often do we want to be servicing the valve train? Inspection, valve adjustments and changing out valve springs on a certain schedule.
The durability of the cam drive system we plan on using?
How well will the intake and exhaust manifolding be tuned to the target power level and the cam?
Open exhaust? Full exhaust system?
Indeed a lot of questions that must be answered first before the best cam for the job can be picked out. And believe me, there are more.
Let me back track a little here. There are some small duration cams that will seem to give you a high rpm limit with your engine. Let me explain what I mean. The stock cam in the GN has a drastic fall off in HP after 5,200 rpm. And when I say fall off, I mean like a cliff. Some small duration cams will flatten and broaden the HP curve which is real nice for a street/strip application, but will also let the engine rev higher with what feels like good power. Every cam will give your engine a peak HP rpm, which can be much lower than the rpm limit of the cam. It becomes unproductive to just rev the engine to say 7200 rpm if the peak HP was at 5750 rpm. A dyno reading becomes invaluable at this point to help you pick the best shift point for your setup. It's just undo wear and tear on your engine to pick a shift point higher than is really necessary and can in fact be slowing you down. Remember. Best average HP throughout the run.
Back to the subject at hand. Some of the other factors that need to be taken into account when picking out a camshaft.
Is there an important HP level that needs to be met? And how flexible is it?
How well sized are the heads for the intended use of the engine?
Will the heads need a little help from the cam to fulfill the target power level?
Do we need to be concerned with smog testing?
Are we running a catalytic converter?
O2 sensor?
Are we willing to change out the O2 sensor and cat more often?
How well will our engine management system handle a large cam?
How often do we want to change spark plugs?
Will we be changing the oil often?
Will it just be me driving the car?
How often do we want to be servicing the valve train? Inspection, valve adjustments and changing out valve springs on a certain schedule.
The durability of the cam drive system we plan on using?
How well will the intake and exhaust manifolding be tuned to the target power level and the cam?
Open exhaust? Full exhaust system?
Indeed a lot of questions that must be answered first before the best cam for the job can be picked out. And believe me, there are more.
Thanks Nearing. With the lack of feedback or participation, sometimes I have to wonder if anyone is getting anything out of this. I hope this is causing some wheels to turn so that your own projects can benefit. I would love to start seeing some new and different projects that might, in some small way, have been inspired by this thread.
Amazing what some people will resort to when having to wait for parts to come in.
Amazing what some people will resort to when having to wait for parts to come in.
