94bird

Keep in mind also that for a ring to seal it needs unit pressure. That's generally how ring designs are rated when we compare engines of different bores and their ring sealing efficiency.

Thus, if you increase the bore diameter, and have to keep the ring's unit pressure the same to seal against the bore, your friction goes up right with it. As Erik says, if you don't need the bore diameter to allow more air in, this may not get you more power.

SStrokerAce

This just gets longer and longer doesn't it...

"So if it's not induction limited (which it's not) valvetrain limited (which it's not) and gear rule limited (which it's not yet) friction limited (which it's not) what keeps the engine speeds to where they are now in Cup racing? Why do they have bore size limits on the motors? Why do they have minimum mass requirements on the pistons/pins and rods? Do ya think that is all connected someplace?"

A Cup spec 4150 carb is not going to supply the motor with all the cfm it needs obviously, they probably see around 2" of Hg at HP or more with that carb on there. With another 400cfm they would find 30-40hp for those motors. Still it's not a RPM limit for the motors it's a restriction to the production of HP.

A 390 Truck Carb flows a bit more than that obviously, but like a Cup 750 based 4150 it still has a limit to how much it can flow.

The valvetrain systems have been tested to 10,000rpm or more, they survive and work up that high. Advances like spintron testing, lighter Ti valves (till they put a weight rule in for that) and better spring material allowed them to get the results they are looking for.

The friction is not an issue that limits RPM either. Small main and rod journals, roller cam bearings (for both spring load and friction), low drag seals, dry sumps and low drag rings all might add up to maybe 100-140 friction HP @ 9000rpm. Still not more than what the motor is making nor enough to limit the HP peak of the motor.

In 2002 they instituted the bore limits on the motors since the Mopar block allowed those teams to run much larger bores than the Chevy and Ford guys. I don't think this was just because they wanted to limit the airflow of the P7 heads, they did it because guy like Penske were turning 9000-9500rpm at places like Pocono. When Ryan Newman goes around that track without shifting and is going fast as or faster than the rest of the guys that motor is REALLY turning some RPM.

The minimum mass requirements are for money, but it's not the lighter weight steel rods that are what costs more I'm sure the rods cost the same price or more than they did now and not because steel is more expensive. RPM costs money plain and simple. The teams that still have that money spend it. (I.E. Hendrick) It's the same thing as a port that has the same volume and CFM as another head but makes more HP, a connecting rod with the same length and mass as another rod might not be as strong as another rod. You still spend the money making better parts, going to better grades of steel, spending money on better design of the parts etc..... just so the heavier rods can stay together at higher RPM. If they really wanted to save money they would put in a gear rule to keep RPM down, and low and behold they did.

RPM costs money everywhere and that's what the want to limit. NASCAR did things over time to try and limit RPM, first the bore limits, then the minimum masses of the parts, and finally they are saying it's enough, you only can turn the motor this fast because you are now going to run out of track to turn it any higher. Gear rules are the only way to limit RPM until the power increases enough to make the motor turn faster, then they just back off on the gears.

The part that was banned was the Be content, so now you know.

My point was that the parts just aren't going to live given known masses and piston speeds and accelerations with pistons that have 275-300g mass with that many piston speeds.

As for what the old man wrote....

FWIW, using the 19200 peak rpm, 40 m/s peak piston speed and 25 m/s avg. piston speed on a 10 cylinder engine of just shy of 3000 cc, I got the following:

Stroke:
39.065 mm (1.538 in.)

Bore: 98.75 mm (3.888 in.)

Displacement: 2992 cc

Rod length: 98.0 mm (3.858 in. )

R/S ratio: 2.51:1

And what you said about it...

Your dad also posted a combination of max and mean piston speeds that would only happen if the rods were shorter than the stroke.

Those numbers all relate. The rod is not shorter than the stroke, and the speeds are directly from Mario Thiessen engine development director of BMW F1 as stated in Racecar Engineering. They make sense too since the looks of the F1 motors 5.8-6" deck height is would be right.

Actually I'm not making any assumptions here.

That's a fact. I never said piston speed wasn't linked to the stroke and RPM.

Piston speeds of F1 motors and Cup Motors are almost identical. Around 5000 ft/min.

19,200 RPM, 1.538" Stroke = around 5,000 ft/min (ex 4922 ft/min)
9,500 RPM, 3.25" Stroke = around 5,000 ft/min (ex 5146 ft/min)

Seems to be about the same limit don't ya think?

Now the G's on the pistons are much higher around (9,500-10,000 for F1, 5000-5300 on a Cup motor) that’s due to the higher RPM, makes sense to both of us obviously. My point is that the Force on the parts is relative to all of this. If the F1 parts can take more g's than the Cup parts but they have the same piston speeds then the motors are probably working with around the same max F at max RPM. That's where the whole piston weight thing comes from, I figured you would have worked that out but I guess not.

So actually it's not the RPM that "KILLS the parts" as you say it's the Force acting on them that does. So you basically proved my point. The issue is why they break, it's not RPM alone that does it. RPM and piston speed give you the G's, the mass of the parts with the G's give you the Force and that's what makes the car go BOOM!

The problem here is that I talk about the motor in terms of a set cube limit, not the same bore longer or shorter stroke. If you have the same swept volume and same chamber volume you get the same compression ratio.

In the same instance you are stating

They can run short stroke smaller stuff but you will lose power in friction

Like a 406 vs. a 377 the 377 doesn't have more friction HP, it has less friction HP per RPM. It's pretty much a set ratio.

As for the BSFC there is more of a relationship in with the compression or lack there of than there is with the stroke. Given the 377 and 406 with the same compression ratio, they would be very similar given that we don't have stupid domes and decent chambers in each motor. Now if you look at say a Busch motor vs. a Cup motor that drop in compression from 12:1 to 9.5:1 shows a loss in BSFC efficiency. If you can't compress the air/fuel charge as much so it makes much less power per pound of fuel consumed.

Continued.............

SStrokerAce

Yeah but I think this is more of a combination of things than just XXX amount of air and XXX amount of cubes.

If given XXX amount of air from a restrictor it seems obvious that you need more cubes to make more power with the given amount. Problem is that more cubes with said restriction will lower the RPM the motor turns and produce about the same amount of HP. A smaller motor with the said restrictor will turn more RPM but the loss of TQ probably can't be made up by the extra gear given to the motor, but then again Super Stock racing is a good example of what can happen here.

The endurance motors don't want RPM for the whole piston speed, piston G's and force reasons we have talked about, they want TQ and a useable RPM band for the drivers to use for 6,12,24 hours at a time.

My thought is that stroking a motor to gain cubes is done when bores can't be enlarged any more. If you can use a bigger bore to get the same cubes then you do that as we see in tons of racing situations where there is a set cube limit (F1, Cup, NHRA Pro Stock) When you don't have cube limits or the cube sizes you need to run are huge for the block you are using then you add stroke to gain the cubes (IHRA Pro Stock and Sprint Cars) More on that down the page when I get to the Engine Masters stuff.

Again, we are talking about a set amount of CUBES per set amount of CUBES. Without changing the displacement of the motor. The short stroke reduces power BECAUSE it is a reduction in displacement, not because it's a shorter stroke. Take that same Cup motor with a 4.128" bore / 3.25" stroke and change it to a 4.040" bore / 3.48" stroke, same 358 cubes. Which one will make more power and last longer with the same mass parts?

So you agree that the 4.185" bore / 3.25" stroke is going to make more power.

Power output is the goal here not just RPM. Taming the lobes would produce less lobe area reducing output for a given duration cam, same thing with reducing lift (even though you could run a shorter spring and valve and same valvetrain mass) and less valve are would just reduce airflow and that's never going to help HP.

That's a interesting thought (no not that you actually think that there are people are smarter than you lol)

The less surface area that the ring puts on the bore is obviously an issue here. Looking at the 4.185" and 4.040" examples with a .043"/.043"/3.0mm Ring set. We have to account for the expander in that ring set so let’s say that gives you .130" of vertical on that ring stack, which translates into 1.788 sq in of ring surface area with a 4.185" bore, and 1.666 sq in of ring surface area on the 4.040" bore. That's a 7% increase in ring surface area, which should relate to 7% more drag but...... Then you need to account for the piston speed and the distance it has to travel (stroke) to figure out how much drag you actually have here. The smaller bore has less ring surface area (7% less), but a longer distance to travel (7% longer distance) and it has to do it much faster (7% faster) given the same RPM. Now I would say that for a given piston speed the smaller bore motor will have less friction HP, but for a given RPM which is the real limit we have here the motor will have more piston speed and therefore more friction. It's going to be very hard to test these things and we are talking about very small differences in HP output if everything else was the same, but you can't do that since the drastic change in bore size would obviously hinder the cylinder heads in the case of cup motors or your average motor. There are some cases were it is not a problem..... again down the page.


The pin loading might increase, that depends on the piston design. The rod loading in compression is still going to be a given for the pressure in the cylinder which is related to HP level. That's another long story that we can talk about later.

I luckily got to go this year and watch the EM as the only spectator that was not an employee of Bill Mitchell, or of Primedia or a sponsor or contestant. WJ wasn't there but Sonny was and I did get to talk with Kaase about his motor.

Kaase's bore was 3.970" with a 4.125" stroke and a 6" rod, a lot like last year, just with a smaller bore. Now sitting down and talking to the man was very interesting, and I did get to learn some thing but at the same time I knew some of his answers were more of a redirection than an answer. Asking the right questions and getting a real answer was the key here.

In his situation or any guy who is in a position to like that of a guy working on a Cup team in the engine department or a Pro Stock team you have to look at what they actually tell you and wonder if it's "declassified".

A good example I can give is one of OldSStrokers flying buddies from the Air Force was a test pilot in the 70's into the 90's. He flew things that he can't even tell his wife about, and just until a few years ago he couldn't even say that he crashed one of the test planes in the Have Blue program (Stealth Fighter) and that was in the mid 70's! We have no idea what things he flew, and what we do know is 25 years old. Racing is a lot like that but it's not as long of a timeframe. I'm sure the things that people can tell us are not what happened yesterday, but some of the things are just depends on how important they are and if it's not a new or recent thing.

Going back to talking with Kaase and then reflecting on the design and answers gets you someplace. The first thing I asked him when he mentioned the bore size of 3.970" was if the heads flowed at that bore size. He said they flowed really well on a 4.00" bore so it wasn't an issue. The way he welded up the chambers, which in turn moved the valves closer together and farther away from the bore walls (because it's a canted valve Cleveland) is obviously going to make the bore size less important. The next question is obviously why the longer stroke? His simple answer was that the longer arm is better for TQ. Again he answers what he wants and doesn't answer what he doesn't want.

The one thing you have to remember with Jon is that his business is building motors with very large strokes relative to other racing motors out there. The bore/stroke ratio of his 408 cube Cleveland was REALLY close if not the same to his 815 cube Mountain Motors, and his 468 cube SCJ BBF was really close to the same bore/stroke of his 698 cube Sportsman motors. Honestly I think he's sticking with what he knows. He understands motors that work with those combinations, and in that challenge development time is at a premium. Just look at his site to see how many ported Cleveland intakes he has for same in the overstock section. No doubt his combos work , but that's not the whole story.

Also one little known fact out there is that Jon has been beat in the Engine Masters arena. Norm Grimes in 2003 built a big bore short stroke BBC and actually put down more average with the legal contest mufflers than Jon did, he just screwed up and ran the race mufflers that were not allowed. The funny thing is that the race motors made less power, so he would have not been DQ'ed and would have one with the legal mufflers.

It's been real and it's been fun but has it been real fun?

Bret

OldSStroker

Good point. Of course if you want to keep displacement and max rpm the same, the displacement is increasing at the second power of the bore diameter, but directly with stroke/piston speed. The motoring power curves I've seen are not linear; they increase slope a little with piston speed.

For sure one would have to balance friction hp increases against brake hp increases when increasing bore size/ring drag, stroke/piston speed, and rpm/gs/part mass. Obviously OEM designs also have many more parameters involved.

It will be interesting to see what direction Cup engines go if NASCAR implements a "gear rule" which is really a "max rpm rule". My guess is that if it's around 9500, we won't see longer strokes.

IF Cup "plate" engines have the same bore/stroke sizes as unrestricted engines, mean p/s is closer to 4100 than 5100 fpm for plate engines due to the 1800 or so less rpm. That's a lot less ring friction, so my guess is that the b/s dims are about the same to keep the p/s as low as possible. These guys will sell their mothers for a couple of brake hp on a plate engine, and friction is a good place to find it. I'll bet the "plate" engines have the smallest journals and bearings possible.

I wonder about rotating inertia on plate engines, because at speed they don't vary much (a few hundred rpm) during a lap. If inertia is high, could that help when they have to llift a little to avoid bumping? With a momentary lift, might not high inertia keep the "momentum" up? Anyone have any knowledge of this?

racer7088

Bret,

Nascar Cup motors are limited by the valvetrain. Some of us know this and some of us obviously don't. They don't make more power or power any higher because of this and they also have airflow limitations of the single 4150 carb. This is not hard to understand. Friction also rises with rpm and some of it's components are exponential and some are more linear but none get BETTER with rpm.

Your dad said that the F1 engine had a max piston speed of 45 m/s and then an average of 25 m/s. He edited it then later after I said that couldn't be possible. You must have already forgetten in one day? I'm sure it was just a misprint as I said and I was right.

You can't say that STROKE is hurting or helping anything unless you hold everything else CONSTANT like bore etc. What you are doing is changing multiple things at once and then saying the longer stroke is bad. This is not true and it is known not to be true. When holding CID constant you can make more power with a BIGGER BORE generally because of increased valve area NOT because of the shorter stroke. Shorter strokes on their own REDUCE power and efficiency.

You also can NOT say that because you are spinning more rpm at the same pistons speed that the forces will be equal when they are DOUBLE. You are plain wrong. You can't assume that you can't run just as light a parts in the long stroke engine because you CAN. Also high rpm engines as per your example HAVE TO HAVE parts with 1/2 the weight if they turn double the rpm. This shows again how wrong it is to use piston speed as a stress indicator!

You can't make statements about his stuff if you are changing multiple variables at a time.

racer7088

Bret,

It's not anyone's opinion that you have more pin loading and compressive loading with a bigger bore and the same inches! If you make 1000 psi cylinder pressure at TDC on both then the bigger bore motor has exactly it's bore difference SQUARED more force going down on the piston top. This is simple stuff. MORE bore area mulitiplied by the same cylinder PSI equals MORE force. That's the way that works. The shorter stroke knocks the force the cranks sees right back down though since it has less leverage on it now. The rod though sees more compressive stress plain and simple with a bigger bore.

Jon Kaase builds all sorts of motors as does WJ and so do the other guys and they did the exact opposite of what you say must be done to make good power and they won as did most of even the first sets of engine builders. Ask some of these guys why they didn't all build 4.200 bore and 3.700 stroke motors? Maybe they just don't know as much about engines as you do?

racer7088

Have you ever seen the cup cranks for sale all over the place? They are known to come in two distintive stroke ranges? I wonder why this is?

They change stuff all the time. It all depends on the rules and budgets. People thought that you could have too much exhaust only a while back with those things etc.

Usually when trying to make all out power though you run as big a bore as possible when the rules are unlimited to allow the largest possible intake valves and with a set displacement limit that also means a shorter stroke. It doesn't get any more simple than that.

SStrokerAce

This is a dead horse already.... When are we going to get a smiley with a hammer on here beating a dead horse?

I'm sick of writing the same thing time and time again because you don't take the time to read it fully the first time. I give you that respect and it's just something I think people should reciprocate.

Good point..... I had a good talk today about this exact topic with someone who actually knows how fast they can go and what they can do, I think you would be surprised what the answer is. Then again it's a dead horse, I'm not going to change your mind and actually I don't really have any interest in it.

Said all that already. 2" of Hg vacuum etc..... Friction etc....

Dead horse point again. It was a mistake, he fixed it. Hey I don't get on you for not changing the oil on Rick's motor when the turbo went so give up already. WE ALL MAKE MISTAKES, I do, he does and so do you And anyways it would be much more manly of you to say that to him (but not 3 times like you have) and not bring my family into this, this is one of those times it's better to be on the net rather than sitting next to each other in a bar. Personal = Not Cool, Professional = Proper. As I said Dead Horse, you look like an *** brining it up again and again. I might be stepping out of line with this statement but I'm not one of those people who will let his values be stepped on, period.

Basically what this thread seems to be about anymore. You being right. Good luck with that.

Now back to the topic at hand..........

Actually I've said you have to hold it constant and change one thing this entire thread. Just because you brought it up here doesn't mean you invented this idea. Go back, reread the posts (for the first time) and you'll notice that I mentioned stroke length changes using the same displacement numerous times.

OTOH, the thought of changing a bore and not seeing what goes with that is dumb. If there is an increase in airflow with an increase in bore size that needs to go with it. It's the chain of events that needs to be recognized and added into what is changing the situation. Your examples of changing the stroke only in a motor don't isolate what we are looking at, similar cubes and compression are factors that have to be isolated when you are talking about things that change the power curve less drastically.

You might want to think about the "shorter strokes on their own REDUCE efficiency" thought. Is the reduction in mechanical drag, reducing efficiency?


Forces don't = G's, G's are part of the equation for F (i.e. F=MA)

That's the point. The forces should be equal, BECAUSE the mass should be cut in half every time the piston G's double. Therefore the force is the same. The force is the key here and it's what states the limit of the motors RPM, the piston speed just shows you what the physical limits of the materials at hand in the different racing classes.


Continued.............

SStrokerAce

Actually that was my point with this..........

I was assuming the same mass (not weight, different things W=M x g) for the parts since the example was a Cup motor with a set mass for all the parts in the motor. Actually you could run lighter parts in the long stroke motor, unless you change the deck height.

Actually, if you are going to say that you have to get it right. It's that they turn double the RPM with the same max piston speed. Therefore the piston G's with be double, therefore for the F to be constant the mass has to be 1/2.

Everything is linked together. I'm not saying x is what counts it's a bunch of things added together.

BTW again with the mass = weight thing, I made my point about the company namesake before. Engineers don't screw those two up.

You can't cheat physics. Try running a motor with the same mass at twice the G's for the same length of time. How is that going to turn out? They only have to have the same requirements for durability, if you throw that out the window you can cheat the numbers at bit more but in time Mother Nature will bite you in the ***.

I made a mistake (actually another value you might want to pick up, humility it comes with self image)

PSI x Surface Area = Pounds of Compressive Force pushing on the parts.

Again this is another long topic that maybe we can talk about when you are not picking on a guys family.

Jon does build other motors, getting outside of Drag Racing for him as he said "is more for fun to see what I can do than anything" I was lucky enough to have this talk with him face to face and get in the guys head to see why he did what he did. I also have a ton of respect for that guy and a bunch of the guys in that contest, he would be one guy that if you beat would be a great accomplishment.

Can you do me a favor and find WJ on this page for me? http://www.popularhotrodding.com/eng.../2004/results/

Guy has never touched an EM motor. Now there are rumors as to other guys doing it, but never once did I hear WJ or KJ mentioned.

Eric, I really think that saying that the jury is out on the best combination for an Engine Masters motor is Kaase's way is very narrow minded. Knowing the real story as to what is going on here will say a lot. I've been there, talked to the people and got the story that they can't print. How can they say that Grimes made a score of 1182 to 1178 for Kaase but got kicked out because one place said his mufflers were street mufflers and one place said they were not. That just takes away from Jon's accomplishments and actual win which he deserved. It doesn't prove the point that small bore big stroke is the best way to go. In fact the #4 guy did a bunch with the opposite setup with much less knowledge, money and technology than Kaase, Tony and the Williams boys had. I think a lot of what is going on now is that since Jon did the small bore big stroke in the Big Blocks guys want to follow the leader because he won. Sad fact is nobody is going to beat that guy if they keep doing the same thing as him, he's just going to be much better at it than they are. It's like Greg Anderson, they're not going to beat him coping him they can only beat him if they think outside the box and fix whatever he is doing wrong, which apparently is not much.


Hey I'm done with this thread. It's beating on a dead horse back and fourth, and personally it's wasting time for me. Its good reading material for everyone else but it's just pointless if the guy on the other end is waiting to talk so he doesn't read what you write. I can see that in your writing and when it happens to me with a person in real life I cut the conversation short, as I'm doing now. We can continue this in another thread in some other time.

Bret

rskrause

Lots of good stuff posted here, especially by Bret and Jon, but also others. But the discussion got very complicated. I think is because of the number of variables introduced by the various contrbutors to the thread. The following scenarios are very different when it comes to engine design. Modifying an existing production based block for max hp produces a vastly different combo than a purpose built race motor. Displacement limits, $$$ available, rpm limits, intake area limts, etc. all will change the equation. But most of the people here are interested in modifying production blocks for max performance. In that situation, the answers are clear: first bore it as much as practical and then stroke it as much as practical. Displacement rules and that is why you NEVER see a competitive engine that has anything less than the max cubes allowable or feasible. The only exception is the circumstance where someone can throw enough cubic money at the problem to trump cubic inches. But all else being equal, cubes rule.

Rich

Boost It!

72* ATDC huh?


FWIW: friction is a HUGE deal to F1. HUGE. If you dont think it is, think again.

from my limited understanding, its a big part of the reason why the theory of best layout bounces from V10 to V12. but I only get to pick at the race guys brains, I dont have them so I'll leave it at that.

doesn't friction increases to a power of 2 with respect to velocity? I know air drag is anyway.

racer7088

Bret,

No one is making fun of your family. You and your dad often double team people on here like you two have all the answers. Your dad even mentioned it in jest but most of the CamaroZ28 crowd here was suprised since many didn't know that you two were related until recently. I know it makes a lot more sense to most of us after knowing that, as obviously you have a common mind set which is not to say your always wrong.

The problem is that people get their physics wrong as in the piston speed being a prime stress indicator when it is not. Another one you just mentioned being that you doubted that short stroke engines in general are less efficient than longer stroke engines. What is the average bracket 632 CID BSFC numbers and what is a mega dollar <300 CID Comp engine that makes over 2.7 hp/inch? I think you routinely interchange the word efficiency for hp/inch which are NOT the same and any engineer would know that or should. Unless we are on different planets weight and mass are almost interchangeable but they are different so I agree that mass is the right word (even though we are obviously in the same frame of reference).

I don't usually see your dad, OldSStroker saying that type of stuff but rather you and then you defend it with strange "science" that no one understands?

I say that big engines are usually more efficient and more powerful and that is true with all else equal.

I say that longer stroke engines also are usually more efficient and powerful which is also true all else equal.

I say that bigger bore engines make more power due to bigger intake valves which is also true all else equal.

I say that shorter strokes usually decrease power and efficiency which is also true all else equal.

I said that when MMC(some fiber based) was banned earlier in F1 that they went right back to aluminum and that the pistons weighed from 275g to 300g which is also true since I know several people in F1 and several piston companies that do F1 pistons or did back then. I know that earlier some even weighed 320g and that was in the 90s and was on a V12 of even smaller bore size.

I said that I didn't know if MMC of all types were banned which was true and your dad, OldSStroker, pointed out correctly that they are now using many "other" MMCs that are legal and I totally believe him that he is right even though I haven't checked yet.

Lastly I am not in the least perurbed or angry at all but it certainly seems that you are? I would say that you need to sit back and just breath and think a bit about what you are saying. Tell me if anything I said above is wrong because I see you saying that and so do others and these are things commonly seen, documented and agreed on.

racer7088

Rich,

All you say is true except at the end because there will always be another Bill Gates spending the big paper on the BIG engine and he will take the other Bill Gates with the SMALL engine every time!

racer7088

Bret,

I don't change Rick's oil and I was not even there when this happened in the first place? These kinds of posts are just bizzare? None of this really matters that much so don't get so worked up about it. Hell Rick's doing stuff to go even faster and I'm sure he will. We need more people doing this stuff rather than talking about it anyway. We need to get together at PRI if you aren't still so mad because I am one jolly person in real life! I think Danno would love to meet you guys too if you are there.

Boost It!

Can someone fill me in on the drama?

Whos related.
who changes whos oil
whos rick?