Small powerhouses and old school

[ESH]

I asked in the other thread if it is possible to reach the 100hp/l limit without having to spend a fortune and I have received info that this is impossible to reach - especially if you want a true street engine.

The answer to the first part of that question is obviously yes, Formula Vee engines of 1600cc have put out something in the order of 180bhp for years but the answer to  the second part is go try it, Lee/Kalle talk to G.A.C. (I can get you the phone number) who have been building this type of motor for quite a while and let us know how it's doing in 5 years (or let's say 30K miles time). It'll be a interesting experiment and I'm pleased to see someone's going to try it!

 

[John Maher]

In my experience I find it’s possible to achieve an output of 90bhp/litre on what I regard as a perfectly streetable engine eg 2276cc making 204bhp... i.e. a street/strip motor. That’s equivalent to a 1679cc engine making 150bhp while still retaining a semblance of drivability. Is that possible with a 1679? Definitely, but it won’t be as relaxed a drive as the 2276cc motor.

Stepping up to 100bhp/litre is certainly achievable but will start to stretch the boundaries of what might be regarded as streetable by some, most definitely in the case of the 1679cc motor. All depends on your definition of 'street motor'. If both engines were being built purely for the strip, you should be aiming a lot higher than 100bhp/litre but there’s no way they’d be getting used on the street.

Larger motors will always make for a better street/strip engine because you can build in a good mix of mid-range torque and peak bhp. For best performance on the track you need power rather than torque and the mods required to get really good power out of a small n/a motor (big valves and ports, long duration cam etc) will push the rpm range sky-high, which has the effect of killing torque in the low and mid-range rpm—exactly where you need it for good performance on the street.

The small cc, high hp motors from the ‘70s and early ‘80s mostly came about as a result of NHRA class rules, where permitted engine size was dictated by vehicle weight, which gave a lighter car with a well designed small capacity engine an advantage over the larger engined heavyweights. IMO it’s only when we see a racing class with a well defined set of restrictive rules that great developments take place. It focuses the mind and encourages people to push things to the limit. We saw it again with the introduction of PRA Pro Stock and Super Street. That was the first time VW n/a engines were being built where 48IDAs became the restricting factor and prompted the development of larger carbs and even some alternative induction systems etc etc. Racing technology always ends up trickling down to the street.

As an extreme example, take a look at NHRA Pro Stock 500 cubic inch engines. Normally aspirated, pushrods, two valves per cylinder and a pair of 4 barrel carbs. Working within those restrictions for decades has seen continual development push power towards 1400bhp….. that’s more than 165bhp/litre. That’s equivalent to a n/a 1679cc engine making 277bhp!

Only problem with working within a very defined set of rules is the optimised combinations that work so well on one particular engine won’t necessarily transfer across to another engine being built to a different specification. Take British Formula Vee. They use a 1285cc single port engine, with stock valve sizes and make around 100bhp. They work incredibly well considering the limitations of the rules and are a good example of what continued development can deliver, but bolt one into a road going car and you won’t get very far. Also, apply the bhp/litre formula and you fall well short of what might be regarded as a great performing street engine i.e. approx 80bhp/litre so it doesn't work as a great model for a high powered street car.

Sometimes the focus is too much on the peak bhp figure. The car that performs the best on the track is the one that makes best AVERAGE power in the rpm range it sees through each gear. It's the area under the curve that counts.

[folkevogn]

Sometimes the focus is too much on the peak bhp figure. The car that performs the best on the track is the one that makes best AVERAGE power in the rpm range it sees through each gear. It's the area under the curve that counts.

This is a VERY VERY good point John!
Alot of people seems to forget this(including me)

[Jon]

Stepping up to 100bhp/litre is certainly achievable but will start to stretch the boundaries of what might be regarded as streetable by some, most definitely in the case of the 1679cc motor.

First of all, THANKS for a brilliant post!

I'm curious as to why a smaller engine would suffer more from "efficiency" than a bigger one? Surely the weight of the reciprocating parts must be less in a engine of smaller volume? (If this isn't so there must be a optimal size somewhere where the weight of the parts (wear) meets optiamal output?)

What do you think the "next level" is John?

[John Maher]

First of all, THANKS for a brilliant post!

I'm curious as to why a smaller engine would suffer more from "efficiency" than a bigger one? Surely the weight of the reciprocating parts must be less in a engine of smaller volume? (If this isn't so there must be a optimal size somewhere where the weight of the parts (wear) meets optiamal output?)

Generally speaking, reducing the weight of components won't make any difference to power output (assuming all parts concerened are capable of doing their job). Lighter parts, such as rods, crank, flywheel, pistons have less rotational inertia which allows the engine to accelerate more quickly from one rpm point to another, so performance on the track is improved while measured power remains the same. That's why one 200bhp engine can be faster than another 200hp engine. Same goes for vehicle weight and aerodynamics. An improvement in either will make for better ETs with no change in engine power.

What do you think the "next level" is John?

It all depends on intended use for the engine. From a racer’s point of view I believe a major limiting factor is the VW’s stroke to bore ratio. Look at any serious n/a professional race series (F1, NHRA Pro Stock etc) and you’ll find they use a large bore in comparison to crank stroke.

Increasing bore and reducing stroke delivers two significant benefits to a high rpm race engine…  the shorter stroke reduces piston speed and the larger bore makes room for bigger valves…..

Imagine a theoretical drag race series dictating a maximum capacity of 2276cc (normally 82mm x 94mm). If the rules allow any combination of bore and stroke I’d be looking at say a 101.6mm bore rather than 94mm, and reducing stroke from 82mm to 70mm (2270cc).  A set of suitably modified 101.6mm heads would easily outflow anything you could fit on a 94mm bore engine.

Second major gain is a reduction in piston speed. At 7000rpm, an 82mm stroke motor has an average piston speed of 3766 feet per minute. Reduce stroke, the piston has less distance to travel in the same time and speed falls to 3215 feet/min for the 70mm crank at the same rpm. Therefore higher rpm is on the cards with the 70mm stroke and the bigger ports and valves of the 101.6mm heads can make some serious power, assuming they’re teamed up with suitable cam, induction, exhaust etc

Horsepower lost to friction is also a factor with approx 75% of an engine's friction hp being caused by ring to cylinder contact. The reduction in stroke more than offsets the extra contact area of the larger diameter rings so more power is being used to turn the engine than being lost as heat.

Currently there’s no real incentive to persuade someone to build a short stroke, big bore n/a engine because having a higher bhp/litre ratio isn't going to win you the race if the guy in the next lane has more total bhp. But if you're looking to maximise bhp/litre, IMO this would be the route to explore.

In the meantime max stroke/max bore engines will dominate but at the expense of bhp/litre and unless something comes along to cap engine size, the obvious route is to increase capacity by whatever means practical so naturally people will continue to opt for the longest stroke crank they can physically fit in the block. The fact remains, for a tractable street motor you can't beat an increase in displacement.

If you want an easy route to force more air through your engine, make lots of power, have good driveability on the street and bump up bhp/litre, fit mappable EFI and a turbocharger. 

[louisb]

Wow, there is some great information there. Thanks for posting that.

--louis

[richie]

If you want an easy route to force more air through your engine, make lots of power, have good driveability on the street and bump up bhp/litre, fit mappable EFI and a turbocharger. 

Afternoon John

So you think that would work

cheers richie,uk

[louisb]

If you want an easy route to force more air through your engine, make lots of power, have good driveability on the street and bump up bhp/litre, fit mappable EFI and a turbocharger. 

Afternoon John

So you think that would work

cheers richie,uk

  

Anyone can make a turbo engine go fast. 

--louis

[BeetleBug]

If you want an easy route to force more air through your engine, make lots of power, have good driveability on the street and bump up bhp/litre, fit mappable EFI and a turbocharger. 

Afternoon John

So you think that would work

cheers richie,uk

Probably would but thats cheating you know 

Thank you for your post John. Very interesting info!

[Peter Shattock]

All very interesting this, clearly enthusiasm for small cc engines is alive and well in these parts.

For my part I think you need to have a realistic expectation if you’re going to head down the small cc na rapid street car route. It’s a fairly obvious thing to say but the faster you want to go the more difficult it becomes to keep the car streetable (not that this is unique to small cc engines). That said personally I’ve always thought when I want to drive my car its to go for a raz not just bumble about in it wishing it was more tractable comfortable, quiet etc. Its not that the car is unreliable but you need to want to drive it. As with all things there are compromises to make and we all draw the line at a different point, hence the constant argument about what a street car is.

I for one am keen to chase the na 100bhp per litre mark on pump gas, if for nothing else just for the achievement. Although as John has suggested above it’s not all about bhp. To turn a good ET particularly when you chose a small cc option, maximising other areas is even more important then when you choose a more powerful combination.

Interestingly though I’m not quite sure it’s as difficult as most people might have you believe to get to a point where you can go quicker than most people with a similar combination. I think most people are content with a combination once it’s in the back of their car and running ok. Then there’s the likes of the people that frequent this forum who take a strange fascination in spending lots of time, effort and often money to achieve more with less.

I run a na 1776cc because I like the small engine combination and it’s a common boring old size that most people pass by on there way to bigger and “better” things.

The biggest problem we all face is the lack of R&D as the majority of us developing our combinations do not have hours of backed up results at the track and dyno. All in all though looking at some of the numbers people are turning on here looks like people are doing pretty well.

Just for the record does anyone know how fast people have been with a na 1776cc motor (regular 69 x 90.5 combination) in a race or street car in the past, as it would be nice to know what to aim for.

Glad to see the small motors are still chasing down the big guns!

[BeetleBug]

Glad to see the small motors are still chasing down the big guns!

Still chasing?.... Soon they will be ahead.   

[Lee.C]

Glad to see the small motors are still chasing down the big guns!

Still chasing?.... Soon they will be ahead.   

Dam Right 

also some very good points Peter - I willbe doing a LOT of research for my mouse motor 

[Jon]

Generally speaking, reducing the weight of components won't make any difference to power output (assuming all parts concerened are capable of doing their job). Lighter parts, such as rods, crank, flywheel, pistons have less rotational inertia which allows the engine to accelerate more quickly from one rpm point to another, so performance on the track is improved while measured power remains the same.

This is obviously both right and interesting, but its not really a answer to what I asked about, or rather what I tried to ask about (English is hard). I find everyone saying that a smaler engine would suffer more from being efficient, and by efficient I'm talking about good cylinder filling and thereby realizing the power and the torque the engine size is capable of.

higher rpm is on the cards with the 70mm stroke and the bigger ports and valves of the 101.6mm heads can make some serious power, assuming they’re teamed up with suitable cam, induction, exhaust etc

I think this also could be used as a pro "short stroke engine" argument, but what I really is aiming at is the later part of you sentence, the "teaming" up sentence.
As soon as you mention rising the efficency, people reach for the Alarm button, maked drivability/long-livety.

Are we really at the breakpoint for efficiency and longlivety?

[Johannes Persson]

Hello!

After following this very interesting thread I have decided to build a "mouse motor" with almost only original parts and by using some simple math and sience.

Engine spec:

Case: original AS41
Crank:German stock
Rods:German stock
Pistons:JE 86mm 24mm comp hight
Cylinders:Stock 85,5mm honed to 86mm
Heads:043 40x32mm valves
Compression:12,0:1
Rockers:Jpm two stud 1,5:1 ratio
P-rods:Manton 3/8" cromoly
Cam:Fk45in/Fk44 ex
Cam gears:Magnum
Oilpump:26mm
Deepsump:1,5lit
Flywheel:180mm stock lightend
Clutch disc:cush lock
Pressure plate:Kennedy
Header:Custom made 1 5/8" tuned length
Manifolds:Custom made tuned length(second order)
Carbs:IDA 48

The most expensive parts in this concept is the JE pistons, but I feel they are nessecery if the calculated power should be optained.

All the parts will of course be inspected and modified(linebored,shuffle pinned,balanced,fullflowed etc..........) to take the higher output.

Heads:

The heads will recive a little welding in some areas and ported to achive as high flow as possible in the limitations of the calculated port size.

Cam:

I will use a cam with split duration, fk45 intake and fk44 exhaust.The less ex duration will give a superior midrange without loosing top end, if the ex port flows enough, a good choise when using a "Hi-Po" engine on
the street.

I have decided to use a 40mm intake valve because of the 86mm bore, and the valve will not be moved to the center of the cylinder,a bigger valve will be to much shrouded from the cylinder wall.

Calculation:

The formula I will use to see how much rpm the 40mm valve will be good for is:

RPM=3300000xPort dia xPort dia/BorexBore xStroke

This formula is based on a mean port velocity at 110m/s or(360ft/s), and the Port dia is the smallest area in the port.

As this engine is going to be used as a street engine the smallest port size I will use is 0,88 x valve dia(0,88x40=35,2mm)

RPM calculation:3300000x35,2x35,2/86x86x69=8012rpm

The teoretical rpm where peak power will be is 8012 rpm.

Now we have the RPM,diplacement but not the Bmep, a realistic Bmep is between 12-13 bar(171-185psi), so I choose 12,5bar Bmep.With this information we can calculate the POWER of the "mouse motor".

Formula:

P=Displ x rpm x Bmep/910

POWER=1,603 x 8012 x 12,5 / 910 = 176,4hp

This is the power that could be expected from the "mouse motor" if everything is properly done.


With properly done I mean everything like heads,compression,cam timing,exhaust length,intake length,friction etc.....................  .

I will start on this project in the next week but as I run a company it will take some time to finish it, probably in mars 2008.

During that time I will keep you updated with pictures and info as the project continous.

When the "mouse motor" is done there will be som serious dyno testing and tuning, hopefully we will see the numbers that i come up with in the calculations above.

To me,this is what I belive is "Thinking outside the box" and "The next level".


With Best Regards

Johannes Persson
JP Motorsport
Sweden

[lawrence]

Way to go, Johannes and everyone else who is attempting to build a mouse motor! Everyone, please keep the lounge updated with pictures, specifications, etc. This is interesting stuff. While not trying to sound emotional, attempting to build a mouse motor that will survive is a fitting tribute to our cal-look forefathers who did the same with less technology at their finger tips.

I want to do something like this one day.

[Jon]

WOW, what else can I say? That sounds like a hefty output of such a small capacity!
I just hope you keep us informed when you start building this powerful dwarf. This small/original parts approach has old school written all over it, except for those nice pistons, (BTW how much would one loose by using stock pistons with their fat piston rings? Or is it to avoid "ring flutter")
And it's just what I expected, the big guys use simple formulas to "home" in on the target, but you are the first one that has been willing to show them. I will have a good time checking over my engine with these formulas when I have an night free.

attempting to build a mouse motor that will survive is a fitting tribute to our cal-look forefathers who did the same with less technology at their finger tips.

I think you are right Lawrence, another big thing was the lack of over the shelf parts, it will be cool to see all these Mouse motors beeing built, and that makes me wonder about thing John Mahler said about racing beeing one of the most impotant ways to push the limits.
How about a MOUSE class? Alternatively could we design a class that would push forward the "street" engine? Limit both the RPM and the volume?

[christophe]

Like JHU said....WOW!!!!

But where the 3300000 are coming from in your formula?

[BeetleBug]

Johannes, this is for sure one build thread I`m really looking forward to read and study. For us not so familiar with the formulas used could you please take some time to explain them. Thanks,

Best rgs
BB

[Jim Ratto]

Johannes, this is for sure one build thread I`m really looking forward to read and study. For us not so familiar with the formulas used could you please take some time to explain them. Thanks,

Best rgs
BB

a great read on this topic...and overall engine tuning techniques.... Four Stroke Performance Tuning by AG Bell. Covers more subject matter than any other book I have gone through. Excellent chapter on camshafts and why we advance, retard, and so on. Seat duration vs. .050", etc. Valve diameter vs. cylinder displacement and use of engine....I highly suggest it.

[folkevogn]

I`m speatchless!!
MAN...I love this tread! 
I hope that one day, I also will be able to build an engine without to mutch "swaging"

But where the 3300000 are coming from in your formula?

I`m just guessing but 3300000 in the rpm equation and 910 in the power equation is probably constants(a locked number) that gives you the desired term after the answer in your equations(f.ex rpm or hp)

[JS]

175hp in a  1600ccm 
I´m REALLY looking forward to this! 

[Jon]

Four Stroke Performance Tuning by AG Bell. Covers more subject matter than any other book I have gone through. Excellent chapter on camshafts and why we advance, retard, and so on. Seat duration vs. .050", etc. Valve diameter vs. cylinder displacement and use of engine....I highly suggest it.

Thanks, thats a good tip!

[Johannes Persson]

Hello,

The 3300000 and 910 are constants created from many other formulas which have fixed numbers in them.

Exemple:

To calculate the area of a circle I use this formula : dia x dia x 3,14/4, the 3,14 and 4 are always there so you could "bake" them together 3,14 / 4=0,785 and there you have a constant,the new formula is: dia x dia x 0,785=area.

Regards
Johannes

[christophe]

OK. Thanks.
Will you put this engine on your blue sleeper and race it this summer?

[n2o]

Hi Johannes,

Is there any smartness behind your choice of compression height? What does it mean if you move the weight of the piston up or down over the rod? I do understand choice of compression height, when you have long stroke, but in this engine is there any gain?

Thanks

Roar Lunde

[Johannes Persson]

Hi Roar,

Perhaps you already no about this, but this is the reasons.

1: You do not get that much piston "rattle" when the the piston pin is closer to the rings,means less blow by.
2: It is very important to get as short push rods and cyl studs as possible, when rpm is going up a shorter(stiffer,lighter) is extremely important and the rgidity of the cylinder and heads are improved a lot, (better valve control).You also end up with a narrower engine that fits better in your car , win win situation.

Regards
Johannes

[folkevogn]

Now we have the RPM,diplacement but not the Bmep, a realistic Bmep is between 12-13 bar(171-185psi), so I choose 12,5bar Bmep.With this information we can calculate the POWER of the "mouse motor".
Is it possible to calulate the Bmep?Whats the reason that you estimate the Bmep to be 12-13bar(why not 10 or 15?)Is it link between CR and Bmep?

[John Maher]

Now we have the RPM,diplacement but not the Bmep, a realistic Bmep is between 12-13 bar(171-185psi), so I choose 12,5bar Bmep.With this information we can calculate the POWER of the "mouse motor".
Is it possible to calulate the Bmep?Whats the reason that you estimate the Bmep to be 12-13bar(why not 10 or 15?)Is it link between CR and Bmep?

BMEP (brake mean effective pressure) is a useful way of comparing efficiency of various engines, regardless of capacity or manufacturer.

BMEP formula below calculates AVERAGE pressure (psi) acting on the piston during the entire four stroke cycle.

BMEP =(2471.174 x Torque) / engine cc

To find torque from Johannes calculations (176.4bhp @ 8012 rpm)....

Torque (ftlb) = (bhp x 5252) / RPM

so....... 

Torque = (176.4 x 5252) / 8012 = 115.6ftlb  i.e 115.6ftlb @ 8012rpm

Plug the torque value into the BMEP formula and you have...

BMEP =(2474.174 x 115.6ftlb) / 1602cc = 178.5psi = 12.3 bar

The maths and physics used to calculate the engine's power potential are sound. Now it's simply a matter of making it reality.

Very interesting project. Looking forward to the seeing the results.

[K-Roc]

The formula I will use to see how much rpm the 40mm valve will be good for is:

RPM=3300000xPort dia xPort dia/BorexBore xStroke

This formula is based on a mean port velocity at 110m/s or(360ft/s), and the Port dia is the smallest area in the port.

Hi, this calculation above ( I believe) is used to determine the port velocity as compared to a measurment on a Pitot Tube not the actual .55 Mach, or  613 Ft/second that some other caculations use,

 Like this Example

RPM = ( FPS * CA ) / ( Bore * Bore * Stroke * .00353 )

where;
RPM = point of desired Peak HP
FPS = Feet per Second  or 613.975
CA = Cross-Sectional Area in Square Inches (smallest measured)


FPS = ( Bore * Bore * Stroke * RPM * .00353 ) / CA


CA = ( Bore * Bore * Stroke * RPM * .00353 ) / FPS


( I just wanted to point that out in case some folks are confused by reading various formulas...)

Thanks,

[Udo]

We had 1600 cc engines up to 130 hp and 1776 cc up to 150 hp in the mid 80's . That was a lot of fun to race against the bigger cc engines . But at that time we only worked with german camshafts . Today there should be some more power on those engines  

Udo