Ben R

Im sure Erik will get on here eventually and tell you exactly what I did, but I was just trying to clear up the miscommunication before an arguement started.

Ben R

I'm all for it, but I'm not gonna let Bret take shots at me personally without defending myself.

SStrokerAce

iTrader: (2)

Well at least you know why I said what I said. I'm know you went to SAM Ben. The point of that comment is that YOU should question what you "learned", Since Erik obviously isin't teaching anything with any basis in physics and math over there. It doesn't suprise me that you don't understand how the units on both sides of that equation have to equal out for the formula or math to work. No wonder Erik never got the Engineer certification. I really love how you guys all blindly follow this guys words like they are gospel, without ANY thoughts as to how the world works.

Good Luck


Intake Port Cross Section Area x Average Intake Port Velocity = Displacement x (RPM/360)

Intake Port Cross Section Area x Average Intake Port Velocity = Piston Area x (Piston Speed/60)

Either one will give you the port size or velocity you just have to figure out what you want to solve for.

So to find:

CSA = ((Bore x Bore x Stroke x .7854) x (RPM/360)) / Ft/Sec

RPM = ((CSA x Ft/Sec) / (Bore x Bore x Stroke x .7854)) x 360

Ft/Sec = ((Bore x Bore x Stroke x .7854) x (RPM/360)) / CSA

This is also helpful.

Port Volume in cc = (CSA x Port Centerline) / .061

CSA = (Port Volume x .0061) / Port Centerline

Math.... it's just the facts.

Bret

SStrokerAce

iTrader: (2)

Ben, the only shot I'm taking as that you are close minded, maybe you need to question what you learned.

If you want to take that as hostile, go ahead.

I'll take shots at Erik all day long for all I care. He has to represent both HPE and SAM.... which I don't think he does a good job of at all. JMHO.

Bret

Ben R

Bret, you should email Jon Kaase and ask him about this whole piston speed, you'll learn a lot from it. I did.

racer7088

In our world Old SStroker they are almost the same. BMEP is almost directly related to specific Tq. which is almost directly tied to BSFC. I thought you knew that? What kind of dyno do you and Bret have? You should see that kind of stuff when you are testing all these different combos. Great BMEP is what you are trying to create at all rpms you are racing in.

Ring drag on both and ring flutter is not a major concern at 6500 rpm on either so the ring drag is not way higher on the long stroke engine at such low rpm. You are forgetting that the rings also have greater circumferential surface contact by PI times the difference in the big bore too and that the piston has more downward loading and more side loading due to the larger bore (more surface area) at the same cylinder pressure. Why do you think all the engine builders that do these engines run so much stroke and a smaller bore?

Why do you think GM has a 3.780 bore LS1? Why not make them all 4.000 or even 4.125 because they can if they want. Does GM also not understand what you are saying when they build these engines? Why doesn't Honda build engine like you say. They've also won F1 world championships. Maybe they both know something that you don't about making efficient and powerful engine that run under 6500 rpm? Why aren't there 4.500 bore 2 inch stroke engine in everything since you think they are so much more efficient at any rpm?

SStrokerAce

iTrader: (2)

Eric,

How about that it's packaging.... larger bore sizes extend the length of the engine block?

How about that it's emissions..... smaller bores are more efficient in combustion, so there are less emissions.

In the OEM it's not about specific power output per cube/L..... If power was their main focus the world would be a different place.

Racing and OEM engines are not working under the same circumstances.

I know you are married to piston speed Erik but it's not the be all end all reason for anything in a motor.

Bret

racer7088

Bret,

Fortunately for them the average SAM student is smarter than you probably know. They don't blindly follow anyone. Quite a few are also degreed mechanical engineers and they see this stuff the easiest. I don't know why you are your dad can or can not understand the relation ship of piston speed to breathing but I don't think you've been around much racing engine stuff anyway for the most part after reading your endless quoting of the Reher and Morrison web site.

Many of the guys winning these contests are engineers and they do it the "wrong" way according to you. Why is this? Can you explain this in your "bret math" way? Just because you and your dad do not understand why piston speed is used by so many engine builders and engineers is no reason to spread the incredible misinformation and mumbo jumbo that you do more often than not.

Why couldn't you guys do any better in these same contests with all you supposedly know about this stuff? Why aren't you out building any real racing engines with all your knowledge? At SAM we have people in almost every race shop in the land and many overseas as well and guess what Bret, they all do real well. I know whats going on all over the place and we see what people are REALLY doing. I don't think any of this is that hard if you understand it.

Quotinga bunch of simple formulas like you do below is redundant since everyone already knows this stuff. What we are talking about is how this stuff interacts dynamically. In the scientific world you hold as many variable constant as possible and that's what piston speed talk is about. It's all about physics and math.

racer7088

Bret,

The EMC is about 2500-6500 rpm so it's basically in performance OEM engine range.

I am married to piston speed so don't be jealous! I just understand heads and their relationship to power and rpm. It's all good.

Ben R

I'd also like to add that SAM is racing against some of the best engine builders in the world as we speak. The SAM Mustang is down in Florida competing in NMRA Hot Street. Some of the other engine builders in that class include Kuntz And Company, BES, and Roush. After yesterday's qualifying session we are qualified #1, and we're also the only car to run in the 8's. We've also run in the top of the field back in the old NMCA days. BES even protested us because they didn't think a vocational school could play by the rules and win. The NMCA tore us down and we were 100% legal. Today BES hires SAM graduates. They just hired one of my classmates less than a month ago. People from my class have gone to A.J. Foyt's, Steve Schmidt's, BES, and a bunch of other places.

Basically, the proof is in the pudding. When was the last time somebody with a Bauer Racing Engine was the low qualifier or won a big event like the school has done many times over?

Old SStroker

racer, thanks for the response. We do agree on some things! BMEP is absolutely related to torque/cube. In my world that is directly related to how efficiently the engine injests air for each cube. BSFC is the amount of fuel burned per hp per hour and is a measure of how efficiently the fuel is being used to produce power at the cranskshaft. Am I correct that if the engine is running a tad richer than optimum for MBT, the BSFC (which is calculated from fuel flow and hp) will increase even though the BMEP remains nearly the same?

I can't reply without some math.

For three 434 cubic inch engines:

4.500 bore x 3.41 stroke = 433.87 cubes (the SShort stroker)
Cylinder bore area that a ring sweeps = circumference of bore x stroke or (4.50 x PI x 3.41) or 48.20 sq. in.

4.030 bore x 4.252 stroke = 433.89 cubes (the long stroker)
Cylinder bore area that a ring sweeps = circumference of bore x stroke or
(4.03 x PI x 4.252) or 53.83 sq. in.

3.750 bore x 4.91 stroke = 433.83 cubes (smaller bore/even longer stroke)
Cylinder bore area that a ring sweeps = circumference of bore x stroke or
(3.75 x PI x 4.91) or 57.84 sq. in.

The last one has 20 % more area that the rings rub on than the first. That's the inverse ratio of the bore diameters as you would expect. Couple that with more mean piston speed for the long stroke, and I see more friction hp.

How much? Holdling everything else equal, EAPro said about 13 more friction hp loss for the 4.03/4.252 than the 4.50/3.41 @ 6500. If you shortened the rod for the longer stroker (to get it in the same deck height) there was more difference.

As to side loading, there are a probably a few other factors involved, including rod angularity which is worse on longer stroke/shorter rod engines.


For EMC builders I think it was mostly for detonation resistance when using very high SCR to make power, at least in the last 3 years. A couple of the guys who placed fairly well had larger bore engines.

Most of the competion engines we discuss here are built for performance, so we have different priorities on meeting emissions, cost of parts, manufacturing economies, etc. Note that the racing versions of the LS1 tend to be larger bore/short stroke engines until thy get to 7L where the 4.40 bore spacing sort of limits things.

For example: CTSV-R 5.7 race engine was 4.125 x 3.268(83 mm). The 5L LS1 deriviatives used in Daytona Prototypes are restricted by the rules to a maximum bore of 4.00 (wonder why?) which means a 3.03 or so stroke. I don't believe any of the front runners are using small bore/long stroke versions, but I will ask around.

GM probably had displacement growth in mind when the LSx engines were designed. 5.7L was the first and was the initial desired size for the C5 and then the F-bods. 6.0L. now 6.2L and 7L were in the plans. A lot of that is coming from bore.

As for Honda race engines, look at their F1 engine. Bore is about 2.5 times the stroke, which is even more than your (4.500/2.00) 2.25 bore/stroke ratio. It would be higher yet if max bore size wasn't limited.

In this exotic area of F1 engine design, BSFC is CRITICALLY important, to the point that a lower BSFC means a measurable amount less fuel can be added at a stop and the lap times drop just form a few fewer kilos of overall weight. They don't have a big detonation problem with their fuel. Their most difficult problem with SCR is physically getting it much beyond 12.5:1 or so because of the very short stroke. The valve reliefs are most of the combustion chamber. I don't think you'll see small bore long stroke F1s soon.

Thanks for asking for my thoughts.

DavidNJ

Erik,

This wasn't a good one. Everyone knows you know about the packaging, cost, emissions, economy, and manufacturing issues. The performance resume was quite impressive.

One of the big topics in this tread on the parasitic losses from rings and sidewall loads in trading long stroke/poor rod angularity engines vs. their advantage in combustion and managing detonation. It would be great to add some more real world trade-offs that were made and the reasoning behind them.

For instance, if it isn't to secret, what were the decisions with the school's race car? How did it affect cylinder head and piston selection and modification?

Thanks,

David

racer7088

OldSStroker,

We are not building an F1 engine remember.

This is ALL piston speed related though so it is a good example.

To get good breathing the F1 engine uses a stroke that results in about the same old 5000-ish mean fpm piston speed as everyone else even though they are now turning 20,000 rpm.

To get the displacement you make the bore as big as you can till you hit the displacement limit.

This ensures enough valve area vs bore area to not overspeed the ports.

This has been said 2 million times now.

No ever ran a 1.000 inch stroke in F1 before and the bores were not always limited.

racer7088

David,

All the winners were the exact opposite of what some are saying here. Power is what matters and smaller bore engines make more power at lower rpms. We have been talking about that.

The EMC challenge is very much based on OEM style rpm ranges and uses OEM style fuel therefore they are VERY comparable in thinking as well to OEM engines.

The schools race car engine is made to turn 9500 rpm and it has the biggest bore we can get in it since we are going to run out of air even at that bore size and 9500 rpm! The difference here is that we are unlimited in rpm.

I build big bore engines and probably more so than the others talking here. There's a reason though and that's to meet the air demands to make the power that we desire.

The EMC engines are only going to turn 6500 rpm and you only need so much airflow and the smaller bores easily support that.

Running a way bigger piston and chamber just sucks away more power with it's larger "quench" area basically at TDC. We want a tiny spherical combustion chamber with the plug and the fuel right in the center of it if we could! This would be optimum but is not really acheivable. We want minimum surface area to volume basically to minimize heat loss and maximize pressure.

We don't want a ridiculous pancake shaped combustion chamber 5 inches across where half the chamber can't even see the plug and tons of heat and pressure is lost into these piston and deck surfaces. This will also be a "slow" chamber requiring more spark timing which will further reduce power and BMEP.

We want a fast burning low thermal loss chamber that MAKES BMEP HIGHER not lower. We want to minimize surface area at this critical point so we maximize the pressure here. 90% of the power is in that top inch of travel so we want the pressure to act on our piston here and not anything else.

DavidNJ

If I understand correctly, the trade-off is better combustion with a smaller quench volume with a smaller bore providing better combustion vs. improved flow with larger, unshrouded valves in a big bore and more dwell time at TDC with the longer rod allowed from a shorter stroke allowing more pressure and better translating it to power out of the engine.

What are the indicators that you are reaching the stage where increases are better accomplished with more bore? Are there any rules of thumb?

Thanks,

David

racer7088

David,

I can not answer that question with any authority unless I know I have tested it myself but the tests I have been around and read did not support the idea of a big bore short stroke being very efficient in any lower rpm engine.

The main thing good about big bores is big ports and valves and if you don't need them for breathing then the engine is usually not going to pick up any power at all and may even lose power due to the bigger chamber.

Race engines right now have the smallest and tightest chambers they have ever had. Most decent race engine have chambers twenty CCs smaller than the people on here probably think they are. Domes are really bad!

Ben R

It is a big bore/short stroke combination. There is no RPM limit on the Camaro or the Mustang, so we put the biggest bore into it that we can so that we can get the most out of the cylinder heads. Then we put whatever size crankshaft into it that we need to to get to the displacement we want.

All of the information for all of our racing projects can be found at http://www.samracing.com/docs/projects.htm

DavidNJ

Does this mean the bore is determined by the valve size? 2 intake + 1.57 exhaust + .33" margin = 3.9", 2.20 + 1.60 + .33=4.13". This would seem to favor canted valve heads like the Chrysler Hemi, which has a very large combustion chamber, or the Ford Cleveland derived heads, which don't.

Would the LS7 have been better with 4x4.25 dimensions and a Cleveland like canted valve head? In the school's Camaro, if it had been a Cleveland headed engine (which I believe can get 2.25x1.71 valves in a 4 inch bore at 9 deg angles and sub-60cc chamber sizes) would you have used a smaller bore?

Thanks,

David

P.S.
Ben, an interesting link, but with only external pictures, high level specs, and no dyno sheets. Adding pictures with captions, maybe of the students doing the machining, flow testing, etc., a dyno sheet, more detailed parts list would make a more effective marketing tool. Probably not much more information than in the linked articles.

Ben R

The website is undergoing a complete facelift. The new site will be awesome. We've had video people in and out of the school recently taking video footage for the 'virtual tour' section of the site. All of the new stuff should be up pretty soon.

ShaunSG

SStrokerAce, you are assuming wrongly, that everything Ben says was picked up at SAM.