Nascar engine specs vs. others

[Koncretekid]

In compiling information on pushrod engine specs, the Nascar Sprint Cup (or their carburetted predecessor), produces gobs of reliable horsepower relative to my old BSA.  My single cylinder big bore short stroke 500cc motor is not much different than one cylinder of the Nascar V-8, so the hp to cubic inch produced is a formidable challenge.

One cylinder of the Nascar motor is 4.185" x 3.25" for a bore to stroke ratio of 1.29 with a rod/stroke ratio of 1.9, vs. my BSA of 3.66" x 2.95" for a b/s ratio of 1.22 and a rod/stroke ratio of 2.03.  I'm using cut down Nascar titanium valves of 1.875" intake and 1.6" exhaust.  Piston is JE ceramic coated and rod is steel Carillo. Of course, mine is an air cooled hemi compared to Nascars water cooled wedge head.  Compression ratio of the Nascar motor is listed at 12/1 while mine is similar (I need to re-check it, but I got around 12.5/1 at last check).

My intake passage is opened up to about 40mm and I'm running a 42mm Mikuni HSR carburetor on about an 8" total intake length (bell of carb to intake valve).  The cam is a Megacycle with 282 degrees of overlap and about 109 degree lobe centers and about .440" valve lift.  On the most recent Dyno run with about a 24" exhaust pipe length (1-7/8"), I achieved a hp reading of 44 at about 7800 rpm (this motor can turn 9000 rpm if necessary -- I've seen that in 3rd gear), for a hp to cubic inch ratio of 1.44.   Nascars hp to cubic inch ratio is about 2.3.

Can anyone tell me more specifics of the Nascar carbureted motor, such as cam specs, intake diameter and length, exhaust length to the collector, valve lift, ignition timing, and any other pertinent performance specs that may be helpful in optimizing power for a NA pushrod gas motor such as mine?  I may be overly optimistic, but I believe more hp is possible for this motor.

Tom

[RansomT]

Try this ...

Heads flow 425+ CFM, cams 270* range, / .800+ lift, rockers 1.7-2.2.  Bryant 3.33 crank, 6.2" Carr rods, CP/Mahle/JE pistons with a dish or whatever to make 12:1 with 40-50cc heads. 2.180 intakes 1.625 exhausts.  Uni-Boring blocks with 50-65mm cam bearings, 4.100-4.200 bores.  Also I know that the cranks use Honda sized bearings to reduce drag.

[Rex Schimmer]

NASCAR is also big into big time vacuum in the crank case, they seperate all of the cylinder sets and then the scavenger pump is a high displacement "roots" style pump that pull the case pressure down, not sure what pressure they go down to, but when Roush started doing this they claimed a 45 hp increase, divide by 8 and your single could see an additional 4-6 hps. Again assuming all other things equal. NASCAR engines are also big rpm(ers) and turn north of 9400 rpm pretty consistently. The basic horse power equation is:

BHP=PLAN/33000
P= Brake mean effective pressure (BMEP) in PSI
L= Piston stroke in feet
A= Area of one piston in sq. inches
N= Number of power strokes per minute. i.e. strokes per minute= rpm for two strokes engines, power strokes per minute = rpm/2 for four stroke engines.

Using Ransoms info and assuming that a "typical" NASCAR engine makes 850 hp, 106.25 hp/cylinder we find that the BMEP= 200 psi and using your info your BSA has a BMEP of 143.95. BMEP is basically a measure of intake and exhaust and combustion efficiency so from this info it shows that your engine is about 75% as efficient as a NASCAR engine. It is the continuous incremental improvement of these basic engine functions that has raised NASCAR engines from the 600 hp range at 7000 rpm, which amazingly has a BMEP also of about 200 psi but they have been able to maintain that BMEP at 35% higher engine speed which requires improvements in the basic engine functions. So you need to improve breathing, and combustion but also need to be able to maintain that improvement at over 9000 rpm. No problem right ? just break out the check book!

Rex

[wobblywalrus]

Tom, automotive HP numbers are often from an engine dyno.  I use a 1.1 multiplier to convert rear wheel HP to engine HP for comparisons.  Some folks might have a better number than this.

There are well over 100 dyno runs on the Triumph that were used to develop different things and find optimum combinations.  In the beginning when the motor was standard most things that were tried worked.  That ratio reversed as the engine was developed.  It is hard to get those last few HP.  Your engine is putting out good numbers for an air cooled push rod single cylinder engine with two valves and side draft ports.  You might be at nirvana now.  Do not make changes that cannot be unchanged if they do not work.

The engine does have a small crankcase volume for its size.  The crankcase pressure deal might be worth pursuing.

[John (Maryland)]

A couple ideas on gaining robust HP per cubic-inch:  Ring selection, configuration, and bore seal quality; piston configuration and high bore-skirt aspect ratio; oil intakes to clear oil off the crankshaft (vacuum cleaning); valve spring selection as a critical element for power, endurance, and reliability; and, of course, ultra-premium engine assembly.

R.
John.

[WOODY@DDLLC]

Wobbly, you have become acquainted with the law of diminishing returns!  But, hey, we can bend the rules and break that law!  You have a serious mission! I learned many years ago that the hardest engine to super tune is a single! There is simply no forgiveness or other cylinders to carry a weak one! You are getting lots of good suggestions here! 

IMO the next step for dyno testing is in-cylinder pressure recording. You will not believe the differences that you will see from one stroke to the next. A series of three articles [Beyond the Dyno by Levon Pentecost] starting with #1 is here: http://www.aera.org/ep/epQ112.html [#2 & #3 are not on-line yet!]

Levon's webpage: http://www.isystemsperformance.com/index.html

These guys are suppliers of the necessary goodies: http://tfxengine.com/

[panic]

Displacement > power doesn't "scale", even if the proportions match.
Lanchester's original prediction (1906?) of power per inch is still useful, after a minor tweak by Phil Vincent.
N = # of cylinders, C = a constant for state of development, quality of materials, fuel etc.
P ~ B^1.65×S^.5×N×C
For the Nascar 44.71" cylinder (N=1) and C = 4:
4.185^1.65×3.25^.5×4= 77 hp
The B50's 31.04" cylinder: 58 hp

The B50 case volume is a terrible problem. A V8's pressure amplitude and frequency are very small by comparison because of the other cylinders. Just my guess: a big reed valve with a big connection to the case interior (substituting for the existing breather assembly) will allow the case to pump itself down to its leakage-based pressure.

[Dean Los Angeles]

The variables are endless. All engines are air limited. The bulk of the work is to get more air into the cylinder.
Can't forget fuel either. That Mikuni is squirting huge drops of fuel. Trying to get that atomized and mixed for optimal power is tough. EFI can show some real gains.
Intake tuning, exhaust tuning, spark plugs, EGT, everything else listed above, the list is endless.
How much dyno time have you spent?
Oh, and carve 3 lbs off of the engine, 10 off of the frame and 20 off of you.

[jacksoni]

Assuming you mean 282 duration (at 0.050) (not overlap) plugging your engine into Pipemax it suggests your exhaust pipe is too big and too long. 1 5/8 x 29" better (for that rpm, higher would want shorter- to be determined as power and rpm  goes up) Intake is too short as well being at about the 5th harmonic. Lengthening to range of 12" puts at 3rd harmonic, a stronger pulse. At 9000 your 8" intake is 3rd harmonic, not bad. These are pretty easy things to change without going into the engine. Pretty much all HP is about getting air into (and out of course) with the proper fuel to go with. More RPM makes more air in and out. All the hard parts are to make it live with the RPM. Yes, CR and chamber shape and piston shape etc are part of that also. Ports and valves etc are all part of getting the air in and out. Panic's formula suggested that if you can manage Nascar level tuning, 58hp is what you could get. 9000 RPM short term is one thing, will it live there for 3 miles is another.

[Koncretekid]

Assuming you mean 282 duration (at 0.050) (not overlap) plugging your engine into Pipemax it suggests your exhaust pipe is too big and too long. 1 5/8 x 29" better (for that rpm, higher would want shorter- to be determined as power and rpm  goes up) Intake is too short as well being at about the 5th harmonic. Lengthening to range of 12" puts at 3rd harmonic, a stronger pulse. At 9000 your 8" intake is 3rd harmonic, not bad.

Starting at the last reply, yes, I meant 282 duration, but actually at .040" (Megacycle). You say my pipe at 1-7/8" x 24" is too long; that 1-5/8" x 29" would be better??  I wish I had more dyno time, but unfortunately everything so far has been done with 3 dyno runs of an hour or so.  Dyno back in N.S. which is where I'll be headed in a week is about an 8 hour drive, so is difficult.

The variables are endless. All engines are air limited. The bulk of the work is to get more air into the cylinder.
Can't forget fuel either. That Mikuni is squirting huge drops of fuel. Trying to get that atomized and mixed for optimal power is tough. EFI can show some real gains.
Intake tuning, exhaust tuning, spark plugs, EGT, everything else listed above, the list is endless.
How much dyno time have you spent?
Oh, and carve 3 lbs off of the engine, 10 off of the frame and 20 off of you.

Carb too big, maybe, no fuel injection in near future, lots of other variables, I know and will try to address one at a time because we know what happens when two or more changes are made at the same time.  As for 3lbs of the engine, it only weighs 85 lbs with the transmission, and the frame is all .060" x 1" tubing so only weighs 50 lbs, bodywork made by boat builder so weighs as much as the frame, and me, at 150 lbs, I'm 15 lbs lighter than when I was younger, but then I did wrestle in high school at 129 lbs, so ...maybe!

The B50 case volume is a terrible problem. A V8's pressure amplitude and frequency are very small by comparison because of the other cylinders. Just my guess: a big reed valve with a big connection to the case interior (substituting for the existing breather assembly) will allow the case to pump itself down to its leakage-based pressure.

I'm using a PCV valve on my breather, but not sure how well it is working.  Generally, If a BSA is not blowing oil out somewhere, it must be doing something.

IMO the next step for dyno testing is in-cylinder pressure recording. You will not believe the differences that you will see from one stroke to the next. A series of three articles [Beyond the Dyno by Levon Pentecost] starting with #1 is here: http://www.aera.org/ep/epQ112.html [#2 & #3 are not on-line yet!]

Levon's webpage: http://www.isystemsperformance.com/index.html

These guys are suppliers of the necessary goodies: http://tfxengine.com/

I will be checking that out before my next dyno run.

A couple ideas on gaining robust HP per cubic-inch:  Ring selection, configuration, and bore seal quality; piston configuration and high bore-skirt aspect ratio; oil intakes to clear oil off the crankshaft (vacuum cleaning); valve spring selection as a critical element for power, endurance, and reliability; and, of course, ultra-premium engine assembly.

R.
John.

I can get a better ring package (perfect seal?), and I'm sure my piston doesn't qualify as "high bore-skirt" ratio, so maybe I can lop off a couple of inches (see photo).  Then it will be off to the balancer again to try to get the thumper to stop breaking things (like my frame.) I don't have oil intakes but I do have an oil scraper (second photo).  I'm also running an oil squirter with a .025" hole, which may be flooding piston with too much oil, but WTF, I'm not blowing it up at 8500 rpm, so I don't think I'll eliminate that.  Valve springs are RD and two years old.  Ultra-premium engine build may not be the case, so I'll just defer to my previous statement.

NASCAR is also big into big time vacuum in the crank case, they seperate all of the cylinder sets and then the scavenger pump is a high displacement "roots" style pump that pull the case pressure down, not sure what pressure they go down to, but when Roush started doing this they claimed a 45 hp increase, divide by 8 and your single could see an additional 4-6 hps. Again assuming all other things equal. NASCAR engines are also big rpm(ers) and turn north of 9400 rpm pretty consistently.
 So you need to improve breathing, and combustion but also need to be able to maintain that improvement at over 9000 rpm. No problem right ? just break out the check book!

Rex

The BSA does have dry sump with a two sided gear pump, but I'm quite sure it doesn't suck hard enough to pull a vacuum.  As Panic suggested, I am using a (small) PCV valve to get some reduction.  I've read about using an exhaust extractor (sound familiar?) to draw down the crankcase pressure, and that seems quite doable, so maybe I'll try one.  And yes, just throw cubic dollars at it and hope they land in the right place.  This year I gained 18 mph with the bodywork, but that cost about $5500, so about $300 per mph.  Does that sound about right?

Try this ...

Heads flow 425+ CFM, cams 270* range, / .800+ lift, rockers 1.7-2.2.  Bryant 3.33 crank, 6.2" Carr rods, CP/Mahle/JE pistons with a dish or whatever to make 12:1 with 40-50cc heads. 2.180 intakes 1.625 exhausts.  Uni-Boring blocks with 50-65mm cam bearings, 4.100-4.200 bores.  Also I know that the cranks use Honda sized bearings to reduce drag.

The big numbers here are 425 cfm head flow and .800" valve lift.  I'm flowing about 225 cfm with .430" lift.  I have some re-ratioed rocker arms for .530" lift I can try but I'll still be a long way off these numbers!

I suppose other numbers such as actual port areas and lengths as well as valve timing are still somewhat secret for Nascar motors.  Just knowing what they use would still be interesting so we don't have to guess whether or not there are some new ideas there.  Otherwise, it will be incremental changes, as Rex suggested, and hope for the best.  Wish I had my own dyno.  Maybe I could make one........
Tom

[jacksoni]

Sorry, I mistyped. I meant too big and too short! For 7800rpm and that size engine.
I think RansomT was suggesting what the cup motors spec out at, more or less, not what you might be able to do with yours.

[Koncretekid]

You're excused.  It boils down to more dyno time and lots of intake and exhaust lengths, and maybe smaller diameter as well.  As a matter of interest, I will be posting additional info about my latest dyno run, and I gained a horse and a half by reducing the length from about 29" to 24".  And yes, I know what Ransom was offering, just the Nascar specs.  I'm just replying that I don't think I can get there, but maybe closer.
Tom

[Milwaukee Midget]

I'm flowing about 225 cfm with .430" lift.  I have some re-ratioed rocker arms for .530" lift I can try but I'll still be a long way off these numbers!

You flowed the head - excellent!  Okay, there's your peak number at max lift the way it sits today, but what does the graph look like?  Did you flow bench past that .430 lift?

The bigger rocker ratio get's you .530, which about 20% more lift through the entire range of motion.  Compare that to the graph from the flowbench.  How much more air will that lift provide, and equally as important, at what point in the stroke will it provide it?

You only need as much CFM as the engine will handle, but it needs to be there when the engine needs it.

Fordboy's been pounding this into my head for about 9 months - Area under the curve.  I'm no expert, but I'm getting good at asking questions.

[Koncretekid]

I'm flowing about 225 cfm with .430" lift.  I have some re-ratioed rocker arms for .530" lift I can try but I'll still be a long way off these numbers!

You flowed the head - excellent!  Okay, there's your peak number at max lift the way it sits today, but what does the graph look like?  Did you flow bench past that .430 lift?

The bigger rocker ratio get's you .530, which about 20% more lift through the entire range of motion.  Compare that to the graph from the flowbench.  How much more air will that lift provide, and equally as important, at what point in the stroke will it provide it?

You only need as much CFM as the engine will handle, but it needs to be there when the engine needs it.

Fordboy's been pounding this into my head for about 9 months - Area under the curve.  I'm no expert, but I'm getting good at asking questions.

"You only need as much CFM as the engine will handle, but it needs to be there when the engine needs it."  I think this is the $64,000 question.  When my head was flowed (at 10" H2O), the flow at .400" lift was 127, at .450", 132, and at .500, 135.  Using a simple conversion to 28" H2O will yield 212, 220, and 225.  So I don't actually have 225 at .430" (I misquoted), but it appears that increasing the valve lift is producing diminishing returns.  This is why I haven't tried the new rocker arms yet.  Does this mean that my head is now port restricted?  And how do I know how much my motor will handle?  I could probably work on the head to give higher flows, but might that reduce the velocity of the airflow and possibly reduce atomization of the mixture?  As Bo (Wobbly) said above, I don't want to do anything that is irreversible, as I might already be at Nirvana 

[jacksoni]

With respect to your statement that power went up 1.5 with shorter pipe, was the RPM of peak power different between the two runs?( was the power better at a higher RPM) Sometimes due to other engine design parameters, someone will want peak power at a certain RPM (and then a bit more for shifting above that).  The program I quoted was set up for the numbers you gave us and it is reputed to be very accurate- but testing to prove of course needs to be done. What I am trying to say is, if you want peak power at 7800, 29" pipe should be better. If you made 42.5 at some other RPM and the 29" pipe and you shortened it to 24 and made 44 at 7800, there is not necessarily a  conflict with the prediction. (I think- could be a GIGO issue  )

Airspeed in the port goes up and down with port size, other things (displacement, RPM) being equal. If the port is "too big" and is lazy, performance goes down. My engine has a head that is "too big" for the displacement. Made up for with much higher RPM's than usually considered (peak power is 9500+) requiring very good parts to survive, which it does reasonably well though I am discovering limits on valve, lifter, spring etc life. Yes, you can get to the point where port is too small by same token. All the parts- valve sizes, port sizes, valve timing and lift etc all have to match displacement and RPM goals and capability to make the engine work best.