Advanced Engine Theory and Design
- Thread starter Alky V6
- Start date
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Some info I thought I'd put out there. Food for thought.
4 main ways to increase engine power.
Increase cylinder pressure. P
Increase crankshaft stroke length. L
Increase cylinder bore diameter. A
Increase engine rpm. N
Those well read may recognize the above.
Engine rpm limit is directly tied to cylinder head efficiencies and intake valve duration.
Required cam durations and overlap directly tied to cylinder head efficiencies and ?
4 main ways to increase engine power.
Increase cylinder pressure. P
Increase crankshaft stroke length. L
Increase cylinder bore diameter. A
Increase engine rpm. N
Those well read may recognize the above.
Engine rpm limit is directly tied to cylinder head efficiencies and intake valve duration.
Required cam durations and overlap directly tied to cylinder head efficiencies and ?
Tuning homework
I had an interesting tuning scenario come up last night at the stadium drags.
I was helping out a fellow racer with a tuning problem he's having. I belong to a racing club and there were a few of us adding in our 2 cents here and there throughout the night. Let me give you some simple specs on his engine.
360 some odd cubic inch small block ford.
Single plane intake with a dominator adapter weld fitted to it. The plenum was worked to provide simple flow turns into the runner. Runner dividers unmolested and protruded into the central plenum area. The configuration provided for a built in 1 inch riser for the carb.
Dominator carb with modified venturis for better signal reaction from the small engine.
Car fitted with an O2 alert system. Provides engine cutoff if a pre-entered A/F ratio (lean) is encountered.
250 shot of nitrous on for the whole run. Under carb plate distribution.
Intermittent re-ocurring problem: Engine is cutoff by the O2 alert system during launch in the middle of a big wheelie.
Ouch! O2 alert system is set to cutoff if 13s to one A/F is seen.
The nitrous system is setup rediculously rich. 4 something to one. Can't remember the exact ratio.
On the motor only the A/F records as high elevens at the end of the run (1/8 mile).
The funny thing is the A/F at the start of the run will record lean and drop (richen) in a fairly linear line until the end of the run. I feel it is the O2 sensor warming and changing reading and not a carb tuning issue. He was only testing last night and was not doing any warmup burnouts. I asked him to do a burnout the next run, which he did, and the record showed a little richer at the start of the run with the same linear richening until the end of the run. Still recording the same A/F at the end of the run as previous runs showed.
A new O2 sensor was installed last night, because I felt the readings were lazy. Readings were more active with the new sensor. Finally started to see slight A/F stepping between gear changes. Nothing outrageous. We recorded some graphs to test the accelerator pump tune and no leaning was occuring. A smooth slow richening was recorded.
During one run we caught a lean spike right at the launch. It was at the edge of setting off the O2 alert system. Obviously we had captured the very thing that was his main problem.
I will give clues if no one comes up with the answer. Razor will probably get this one.
I had an interesting tuning scenario come up last night at the stadium drags.
I was helping out a fellow racer with a tuning problem he's having. I belong to a racing club and there were a few of us adding in our 2 cents here and there throughout the night. Let me give you some simple specs on his engine.
360 some odd cubic inch small block ford.
Single plane intake with a dominator adapter weld fitted to it. The plenum was worked to provide simple flow turns into the runner. Runner dividers unmolested and protruded into the central plenum area. The configuration provided for a built in 1 inch riser for the carb.
Dominator carb with modified venturis for better signal reaction from the small engine.
Car fitted with an O2 alert system. Provides engine cutoff if a pre-entered A/F ratio (lean) is encountered.
250 shot of nitrous on for the whole run. Under carb plate distribution.
Intermittent re-ocurring problem: Engine is cutoff by the O2 alert system during launch in the middle of a big wheelie.
Ouch! O2 alert system is set to cutoff if 13s to one A/F is seen.The nitrous system is setup rediculously rich. 4 something to one. Can't remember the exact ratio.
On the motor only the A/F records as high elevens at the end of the run (1/8 mile).
The funny thing is the A/F at the start of the run will record lean and drop (richen) in a fairly linear line until the end of the run. I feel it is the O2 sensor warming and changing reading and not a carb tuning issue. He was only testing last night and was not doing any warmup burnouts. I asked him to do a burnout the next run, which he did, and the record showed a little richer at the start of the run with the same linear richening until the end of the run. Still recording the same A/F at the end of the run as previous runs showed.
A new O2 sensor was installed last night, because I felt the readings were lazy. Readings were more active with the new sensor. Finally started to see slight A/F stepping between gear changes. Nothing outrageous. We recorded some graphs to test the accelerator pump tune and no leaning was occuring. A smooth slow richening was recorded.
During one run we caught a lean spike right at the launch. It was at the edge of setting off the O2 alert system. Obviously we had captured the very thing that was his main problem.
I will give clues if no one comes up with the answer. Razor will probably get this one.
Thanx Don. Had a similiar problem a few years back. Which route are you planning to take to cure it? I myself am considering a small, dry setup on my current configuration and was going to fatten the overall tune to compensate. Any negatives with this idea? The fogger will be placed approx 8in from the t-body and I was anticipating the possibility of the same split-second lean condition. What are your thoughts?
Scott Wile
Scott Wile
What engine management are you using?
With the carb setup, I suggested he tee in a signal delay box from NOS that has adjustment to delay the opening of the nitrous solenoid only, in increments of .1 second up to, I think, 2 seconds. I think it would be much easier than playing with different length hoses. He most likely only needs one or at the most two tenths delay.
With the carb setup, I suggested he tee in a signal delay box from NOS that has adjustment to delay the opening of the nitrous solenoid only, in increments of .1 second up to, I think, 2 seconds. I think it would be much easier than playing with different length hoses. He most likely only needs one or at the most two tenths delay.
Why? Have you decided not to inject?Disregard
One observation I've learned about injecting nitrous for the whole run. You've got to have monster wastegate capacity. Maybe even two wastegates. If you don't, the extra exhaust energy will have to go through the turbine housing and you will overboost. WFO!
Make sure you setup your system to give the O2 sensor enough authority if you plan to dry inject. Start out with a small amount of N2O injection and check your data.
No, it works great! Just a matter of wiring in the power adder enable on the XFI. I guess the stock WG puck is going to take a beating! You gonna make it to Phoenix Don? Last time I spoke with you in Vegas I broke the rear end and a few min later you popped a motor. Do we have bad luck when far from home or is it just me??
-Scott Wile
I'm re-designing my cam thrust system. Had a big boo boo. I sure do wish I could have made it. Make a good show of it for me.I've been thinking of how to finish the last question in the above post. Let me throw in a few possibilities.
Target rpm band.
Target HP level.
Either one or both could be used to answer it. Generally, the more rpm you push from an engine the more HP you reap.
That brings up another interesting argument that seems to keep coming around in the drap racing arena. In drap racing, what is more important? Torque or horsepower. Or maybe a combination of both? How does this work in a small engine, heavy car application?
Thoughts anyone? This one is always a thought provoking argument.
Torque for a heavy car(3000+) and HP for a light car. Trans ratios and rear end gearing also come into play where a light car, (high HP) benefits from low gearing and several gears, while a heavy car benefits from taller gears and is possibly more efficient with an automatic trans and 2 or 3 gears(dependant on a good convertor). Technology today utilizes both HP and torque, IE the new Lexus LS( 8 speed auto) Wouldn't that be nice?
In a small engine/heavy car application I think the question should be narrowed down. Are we talking turbo, N20, or naturally aspirated apps? They all have there place.
BTW- They always mention the HP output of a Top Fuel car(8000+), but has anyone ever heard some torque numbers?
-Scott Wile
In a small engine/heavy car application I think the question should be narrowed down. Are we talking turbo, N20, or naturally aspirated apps? They all have there place.
BTW- They always mention the HP output of a Top Fuel car(8000+), but has anyone ever heard some torque numbers?
-Scott Wile
I think that when you have an overabundance of torque, HP becomes the main focus.Torque for a heavy car(3000+) and HP for a light car. Trans ratios and rear end gearing also come into play where a light car, (high HP) benefits from low gearing and several gears, while a heavy car benefits from taller gears and is possibly more efficient with an automatic trans and 2 or 3 gears(dependant on a good convertor). Technology today utilizes both HP and torque, IE the new Lexus LS( 8 speed auto) Wouldn't that be nice?
In a small engine/heavy car application I think the question should be narrowed down. Are we talking turbo, N20, or naturally aspirated apps? They all have there place.
BTW- They always mention the HP output of a Top Fuel car(8000+), but has anyone ever heard some torque numbers?
-Scott Wile
A perfect drag engine would be one that has enough torque to take the car's traction to the limit for out of the hole performance without having to rely on low gearing and then the HP to give top end performance and high MPH.
For now, let's narrow the discussion to an engine with any combination of power adders. Since most of us are not using blowers, let's look at turbos and nitrous. I think I'm getting excited.:tongue: Forgive me.
I lose control of myself. :frown: We can discuss our own engine configurations and the logic behind picking certain specifications to get the desired performance result. Specifications that have an important factor on the characteristics of an engine would be; bore, stroke, compression, fuel, head flow and volumes, cam specs, intake manifolding, exhaust manifolding, turbo compressor and turbine housing sizes.
2700lb car,tube chasiss, 10"w tire,1000hp. I'm thinking about a lower gears set for the th400 in first gear with a 3.55 or 3.73 rear gear with 29" tall tires. The debate on HP vs torque is maybe alittle outdated as you can make more power now than you could ever have traction for. Where in the past this wasnt true.
I'm in the old school thinking under 3000lbs run a glide and the rear gears to trap at the desired RPM. For heavy cars it depends on overall power...heavy car not alot of power or heavy car with tons of power.
One of the funnest cars I drove was a 350hp crate 350 but had a closr ratio rockcrusher with 3.73 gears. Fun as hell on the street. By the way if my car/nova was a total drag car I'd runa glide for sure.
I'm in the old school thinking under 3000lbs run a glide and the rear gears to trap at the desired RPM. For heavy cars it depends on overall power...heavy car not alot of power or heavy car with tons of power.
One of the funnest cars I drove was a 350hp crate 350 but had a closr ratio rockcrusher with 3.73 gears. Fun as hell on the street. By the way if my car/nova was a total drag car I'd runa glide for sure.
