Transmission gear ratio and engine / wheel size.

4.12 is the ring & pinion ratio- lower number (3.88, 3.44) means slower acceleration (which you won't notice as much with a bigger stroker engine) but higher top speed (provided you do have enough engine to push the car that fast). Higher number (4.37, 4.62, 4.86) means the car is quicker through the gears but slower top speed (with the same 1-4 gearset). 4.12 is a good place for a small (less than 1900 or 2,000 cc) engine- the car's still reasonably quick around town and has a decent cruising speed for the highway.

"I live in north Georgia mountains and the shift ratio is a challenge.  Big gaps in the power band."

That's because the 4 speed in your car was originally designed for a low powered, low budget commuter car that had to be able to haul around 4 people and 100 kph (60 mph) was 'fast enough'. I'm guessing your 1st through 4th gears are 3.80, 2.06, 1.26 and 0.89, which is the standard later VW gearstack. You're probably feeling that when you shift from 3rd to 4th (and even from 2nd to 3rd) it would be nice to be a little higher in the rpm range so you can take more advantage of the powerband of the engine- this is typical, and what close ratio gears do, but it comes at a big cost- a much lower (in this case, 14mph lower) cruising highway speed. Click on the link below- 

http://www.teammfactory.com/ca.../0/0/3600/3600/1/0/2

_{before we continue, special note- any one who feels that their head is getting too full and may explode may break this into 2 (or more, if needed) sessions}

Transaxle 1 is what you have now, and what was in millions upon millions of VW's for gearing. To just change that highway speed without changing the gear spacing, click on the 'Final Ratio' box and see what happens when you put in any of the r&p ratios I mentioned above, remembering that higher cruising speed means slower off the line performance, and vice/versa. Don't play with any individual gear ratios just yet.

Now, with the r&p ratio in trans 1 back to 4.125, look at trans #2 and compare the tops speeds of the 2 examples in both 3rd and especially 4th gear. The close 3rd and 4th gear ratios in #2 are so much fun to drive, as the shifts put the engine significantly higher in the powerband- change the 'Max Rpm' for both to 5500 or 6,000 rpm and compare shift points into 3rd and 4th to see for yourself. Again, compare cruising speeds, 'cause that's the downfall of all this fun- and anybody who's ever driven close ratio gears will tell you that they are FUN!

Now, just for sh*ts and giggles, put that stock 4th gear number (0.89) in 5th spot in trans 2. That's your 5 speed.

Transaxle class 1 dismissed... _{(and you can thank Gordon for the poke at yours truly, although he didn't capture my likeness at all!)}

 @ALB types faster than me!! but here it is anyway.

The long transmission "what's going on in that box?" explanation (from kindergarten to college in 9 paragraphs):

There are multiple ratios in a transmission and they are expressed differently. There is the gear ratio of each gear and the final drive ratio.  It helps to think of it in steps; power goes from the engine into the transmission, out of the transmission into the final drive, and out of the final drive to the wheels. To wit:

The transmission has an input shaft that spins at whatever speed the engine is turning. That rotation goes through the ratio of the gear selected and that turns the output shaft of the transmission at a different speed based on the ratio.  That speed of the transmission output shaft then goes to the final drive and goes through the final drive ratio (the ring and pinion gears) and spins the axles/tires at the road speed of the car. If we know the circumference of the tire, we can multiply the axle rotation speed by the circumference and get the road speed for a given engine speed. Our transaxles combine the transmission and the final drive into one unit, which makes it seem confusing, but it all works the same as if we had a transmission, a drive shaft and a rear end like a pick-up truck.

Let's make up a super simple imaginary transmission to illustrate. Let's make it a 2 speed transmission to keep it simple. First gear ratio is 2:1 and top gear ratio is 1:1(say 2 to 1 and 1 to 1 out loud).   If the engine is spinning at 1,000 RPM the transmission input shaft is also spinning at 1,000 RPM. After going through 1st gear the out put shaft is spinning 500 RPM.  In top gear at the same engine rpm the input shaft is spinning 1,000 RPM and the output shaft is spinning 1,000 RPM.  If we were buying this gear stack from a catalog the gears would be sold as a 2. first gear and as a 1. top gear. The second half of 2 to 1  or 1 to 1 is implied as only the first number is given. We hear .82 used frequently for a type 1 transmission 4th gear. It means .82:1 (point 82 to 1) or that the output shaft spins .82 times slower than the input shaft. This is called an overdrive gear.

Now let's add a final drive. Let's make that final drive ratio 4:1. That means the axles will spin a 1/4 the speed of the output shaft from the transmission.  So all together if the engine is spinning 1,000 RPM and we select first gear, the output from the transmission spins at 500 RPM and the tires will spin at 125 RPM. In top gear with the same engine speed our axles will spin 250 RPM.  If we bought this final drive from a catalog it would be sold as a 4 (with the to 1 implied as with the gears). We hear folks say "I have a 3.88 ring and pinion" and that means a final drive ratio of 3.88, or 3.88:1 (3.88 to 1).

So that's the simple explanation of what's happening to the engine RPM getting to the RPM of the tires.  Once we've got our heads around that, we can start to talk about torque multiplication.  We know that in first gear of our transmission the engine spins 8 times faster than the tires and so it has an easier time moving the car.  We can think of gears like being levers and the lower the gear (1st in our transmission) the longer the lever.  It's multiplying the torque of the engine at the tires.  This is where designing a transmission gets interesting and difficult.  As we move through the gears the engine drops RPM at each up-shift.  If we go back to thinking of levers and we're moving a big rock, we don't want to suddenly switch to a lever that's too short so the rock stops moving. That what having too big a drop in RPM at a shift feels like. Getting this right is what makes a transmission feel right...or wrong.  I'm guessing your transmission this is the feeling you're getting particularly between 3rd and 4th, but maybe 2nd and 3rd, also.

Now to get what we want we need to know several things; 1) Tire size    2) Engine max torque RPM or torque curve    3) Number of speeds    4) Intended use.  There is no use in our cheating on any of these if we want to make ourselves happy.  A car designed to make the most of a curvy road with max speeds of 80 MPH will make us very unhappy if we spend 75% of our time on the highway. 

Once we know these things we need design tools. We need a gear calculator like this Weddle Gear Calculator.  We need to know our tire size for that so we need a tire size chart to find circumferences and heights to enter into our calculator. We also need to know what gearing is available, so a catalog like the Weddle site is handy, too.  

I referenced Stan's transmission above ( @Stan Galat you got a link? I can't find it) and we see it's a 4 speed designed for the engine characteristics and his intended use.  His conversation around it is very useful to illustrate the thought process at play.  My transmission is very similar with tweaks for the different characteristics of my engine and not surprisingly it's really close to being the same.  We are always limited by what is available, and the budget, and what we want. But this is the 101 on getting there. Probing the brain trust here is a huge part of getting there, too.  There's a ton more to explore like drivetrain losses, and other stuff, but in our case it's not really necessary to go there to get something good.

There...I think we only got as far as 12th grade, but it's far enough I think. Oh, I almost forgot, @MotoCarlo your final drive would be written 4.12:1 or sold as a 4.12 ring and pinion. That should work pretty well for back roads.  I think what you might be after is a close ratio gear set dropping 3rd and 4th gear down and closer together, and keep that 4.12 if you're not doing much cruising at 70+. 

@JMM (Michael) wrote- " @ALB types faster than me!!"

Trust me, Michael, I don't; you just put in so much more. Between the 2 of us there'll be a couple of exploding heads for sure...

ALB posted:

@JMM (Michael) wrote- " @ALB types faster than me!!"

Trust me, Michael, I don't; you just put in so much more. Between the 2 of us there'll be a couple of exploding heads for sure...

It's Sunday morning and time for some transmission theology with brother @ALB!  Let us study the book of ratios while we're here together at The Angels of The Air Cooled Monastery. How can we make a smooth shift from here to the astral plane?  

Can I get an AMEN from my brothers?!?!?

Work your rosaries and repeat after me:

Hail Mary, full of grace, the lever is in three, let not the clutch fail us in our hour of need for blessed are you among ratios and the fruit of your math, acceleration!  Mother of gears pray for us drivers in our hour of need and as the guardrail looms close upon exit.

(Yup, I'm heretic )

Boooooom!

You may be a heretic, but I guess I'm joining you 'cause I'm Catholic, know the prayer (oh so well) and found it funny!

And btw, there are 2 fruits- the other being top cruising speed. It's always (especially with a 4 speed) such a fine balance!

I'm sure Brother @Stan Galat will pop in as well..

The four speed will always have a too high of a gear or too low. that really shows up on a twisty road. it's in those situations that you either learn how to push the car harder and drive it faster in to the turns, but if your car or yourself is not there it makes for a scary ride.  Unless your driving around town in a mostly flat area you need to step up to the five speed. Five Speed=driveability

@MotoCarlo-- I reread your post, and realized that you answered a lot of my questions in your original post. I'm sorry about that. I deleted my post above asking questions you already answered.

You live in the mountains. You have a smallish engine. You probably have stock transmission ratios. One GIANT question--

Are you satisfied with the final drive (how the car runs in 4th). If you are, then there's something that can be done with a 4-speed. If not, then that's another matter altogether.

FWIW - When your BMW 2002 is finished, that can be your mountain road blaster.

For everything else enjoy the IM for what it is and it's current capabilities . Save lots of money (for other adventures or endeavors), avoid engine/trans angst, switch engine/trans build time and sorting through a mountain of information for drive time. Use your short time on this earth to enjoy the fresh air, scenery and top-down driving. 

Oops I did not notice that question Stan.
Yep, we  live in north Georgia mountains. Twisty and hilly. But there is distance to drive between cool places to go, ie long sweeping rural state roads. (I avoid the interstate like the corona virus.)
That means twisty and a good 0 to 60 torque and a comfortable 70 is needed. But also I am not looking for a hot rod. This is a Roadster and I have her decked out like a Roadster... so  punchy with torque and power, but comfortable at 3.5k rpm / 70 mph.

Perhaps I will try the stroker and see how she performs with the current transmission. 
Am I correct in thinking the 2110 would be more reliable than the 2332? 

Input on those engines is appreciated too.Is there more of a tendency to chew up cvs with the 2332. Or is it really a mute point at that level engine?

Photo of our driveway.

Happy with 4th gear final drive. But getting there can be "wanting".

(Wise words Jim. Of course I am a lunatic ,or I would not have gotten one in the first place.  :-)  )

^ 

MotoCarlo posted:

Oops I did not notice that question Stan.
Yep, we  live in north Georgia mountains. Twisty and hilly. But there is distance to drive between cool places to go, ie long sweeping rural state roads. (I avoid the interstate like the corona virus.)
That means twisty and a good 0 to 60 torque and a comfortable 70 is needed. But also I am not looking for a hot rod. This is a Roadster and I have her decked out like a Roadster... so  punchy with torque and power, but comfortable at 3.5k rpm / 70 mph.

Perhaps I will try the stroker and see how she performs with the current transmission. 
Am I correct in thinking the 2110 would be more reliable than the 2332? 

Input on those engines is appreciated too.Is there more of a tendency to chew up cvs with the 2332. Or is it really a mute point at that level engine?

Photo of our driveway.

And this is the problem with a 4 speed- robbing from the low end to enhance the high.

To keep 4th gear but shorten up the 2-3 and 3-4 shift you'll either have to go to a custom mainshaft ($1100) and different 3rd gear (3 or $400) OR you could do close ratio 3rd and 4th gears with a longer (3.88 or 3.44) r&p. The stroker engine will help, but to really feel like you're getting the most out of those mountain roads you'll still need to shorten up the gear ratios. Stock cv's and axles will live just fine in your car- there are street Beetles running 11 second quarter mile times on the stock parts.

Anthony is right- joining the way of the 5 is truly the answer- Amen!

2110 vs 2276 vs 2332- later (I've gotta go grocery shopping) Al

I had a 2110cc for 5 years before I built my new car and it was event free.

@MotoCarlo,

What you've got is likely a stock gear-stack with a stock R/P. I'm supposing that your tires are 185/65R15s, but I don't know for sure. If this is what you have, you'd be turning about 3500 RPM at 70 MPH. If that is the case, this is what you have:

If you are happy with the final drive (.89/4.12) you could use a non-stock mainshaft (1st and 2nd gears) with a 3.44 R/P, and a short 3rd and 4th. Every single gear in this box would be non-stock, but I happen to know somebody with a used but nice custom 3.10/2.07 mainshaft that was just taken out.

This 4-speed has very nearly the same final drive as what you have, but it's a lot tighter spacing between gears. Of course, nothing comes for free, and you'd give up the drag-racing first gear:

... and here they are on top of each other:

The blue is what you have, the red is the closer gearstack. Somebody might have a better idea, but that's as good as I know how to get it on a Sunday afternoon. 

You are correct sir. I have the 185 65 r15, I like the idea of the ratio you mapped out Stan.
A longer first gear would actually be helpful around here.
But this is all over my head, so I  will need to reread all this and Google to reference your info to get an idea of what is going on.
But this is really helpful.  Thanks.
To give you an idea of how much I don't know :
The "custom mainshaft" , does that mainshaft already have the gearing you mentioned? 

Stan comes up with some good working combos. ...I just look at the cost to build a good  combo like Stan stated, but putting that towards five gears is better overall.

MotoCarlo posted:

You are correct sir. I have the 185 65 r15, I like the idea of the ratio you mapped out Stan.
A longer first gear would actually be helpful around here.
But this is all over my head, so I  will need to reread all this and Google to reference your info to get an idea of what is going on.
But this is really helpful.  Thanks.
To give you an idea of how much I don't know :
The "custom mainshaft" , does that mainshaft already have the gearing you mentioned? 

I do.

As I understand it, the size of the 5 speed makes it quite tough to install in a pre- existing car.  Cold build ,not too bad.

y/n?

Also we never have mentioned price yet. Hummm?

And last I still might wait and see what a stroker does with my existing trans.  I canot even get back to my aircooled until this fall anyway.

Thanks guys for all the great info!!

Berg5's are designed to fit between type 1 frame horns without much issue- it's the custom chassis'd cars that would have to be put together specifically with the extra space requirements in mind. I thought I'd mentioned cost earlier, but here it is again- plan on spending 5- $6,000- if there's money left over, great. 

A custom 1-2 mainshaft is just that: non-stock. To change 1-2 gears is an extra 1000 bucks into a transmission. 

IMHO, you can have a mountain-carver OR an interstate cruiser with a 4 speed. But definitely not both. 

As far as reliability and power-handling: I have 175 hp, and as long as you don't jam the shifter or miss a shift it will be plenty reliable with welded 3-4 synchro hubs(factory VW are pressed-on and can spin on the shaft) and a "super diff" which has 4 spider gears instead of 2.

I've beat my trans up pretty well, and paid the price. I didn't push the clutch in far enough on a 4-3 downshift at high rpm, and toasted a 3rd gear slider. I also banged into second at Autocross and broke the synchro. Not a lot of money to repair, I did it myself, but it takes time. A complete disassembly is necessary for both repairs. I've had my trans apart 4 times, I got 35k on it before rebuilding. You won't see yourself getting 100k on a trans in a Speedster replica, if you drive it like it was meant to be driven.

Yes, you CAN do it yourself, but there are some special tools you need. You'll need a shop press. You'll need various bearing pullers. You'll need some pushing tools for the press, various sockets work well. The biggest tool you'll need is a pinion nut wrench. I made one, but it wasn't easy making a 16 point socket of about 35-40 mm that can take a few hundred ft. lbs. A dial indicator and a depth gauge are needed. Maybe some feeler gauges.

Your biggest problem will be the shift fork adjustment. Most guys cut up an old trans case to do this job. If the forks aren't adjusted properly, it will pop out of gear at best.

Danny's right, of course, as is Al and Tony. A 4 speed can't do it all, unless you have a small block Chevy under the hood, and then you can get away with a Powerglide 2-speed.

A 5-speed is fantastic, and not a ton more money than a 4-speed transaxle with a custom mainshaft, 2 non-stock gears for 3rd and 4th, and a new R/P.

The problem comes in trying to put a Berg-5 in a tube-framed IM. It's a lot of work, and you'll be a few thousand dollars into that as well. Tony's done it, but Tony is on the other side of the country. I know of nobody else who has.

I've got the mainshaft for the 4-speed I plotted above. New, it's about $1000-- but I'll not be using it again and it'd be priced well below that when i list it for sale, and that will be soon.

The advantage to a 4-speed is that it slides right in without any undue muss or fuss. If @MotoCarlo's car was a pan-car, we wouldn't be having this conversation-- I'd say, "so the 5-speed, and don't look back".

As it is not... it's more "complicated". 

I came across this nosecone late last night. It supposedly allows a 915 trans to fit in a Bug with little to no modifications. Of course, it mounts differently with the two-rubber mount crossmember, like in a 911. That obviously isn't a bolt-on but I wonder if this might fit in Stan's car or Motocarlo's without too much trouble.

https://www.bugat5speed.de/en/...che-transmission-915

The German-to-English translation leaves a little clarity out, but opinions please?

More clarity this morning. This is the best 4-speed I can think of for @MotoCarlo.

The red plot is what is in the car now, the blue is the new gearing.

This one uses a stock mainshaft, custom 3rd, 4th, and a 3.44 R/P. @Anthony could build one of these in his sleep. The final drive would be slightly longer than what's in there, but the reach to 3rd would be much closer. If you wanted it closer yet, a guy could always use a 1.09 4th to get this:

That's a canyon-carving 4-speed right there. I like the first one better, as I think it'd be nicer on the highways, but either one are worlds closer to what Carlos was after than a stocker.

Stan, you nailed it. That is exactly what I come up with for a 3.44 final drive canyon carver. You can get almost the exact same ratios with a 3.88 final(more in a minute) but it's more expensive($$$$ 1-2 custom mainshaft).

I'd really like to use a Quaife Torsen-style differential in my Spyder. Conventional wisdom says tallest final drive with a Quaife is 3.88. There is a guy I know who says a 3.44 will fit IF you machine a little off the face of the pinion. We'll see, but I really don't want to ruin a R & P to find out.

The 3.88 version uses a 1.30 third and a .93 fourth, both stock ratios(less $$$) but has to use that custom(more $$$) 1-2 mainshaft to get there.

Great info . I am aghast at how much I don't know about transmissions and  how much you guys do know .
Thanks so much for taking the time to help out.
(I have copied most of it and put it in a folder.)
This has been very helpful. A costly big deal from any angle  and again this car is not a Speedster but a Roadster.
So again, Jim's response is ringing true.

But the little car is still wanting power with its 1835.

Now on to engine size, if I leave the trans as is?
(1st through 4th gears  3.80, 2.06, 1.26 and 0.89 with 4.12 ring and pinion)

2110 2276 or 2332. 
+ / - ?

Torque is king. I'd build a 2332. But with that shortish final drive you kind of want a revver. Decisions, decisions........

The absolute sweet-spot (IMHO) is a 2110 with a W120(ish) cam. If I were doing it, I'd buy a CB Builder's Choice 2110 kit, and never look back. Bolt on a set of 40s and a 1-1/2" header, and you'll have a reasonably powerful, happy, cool running, long-lived Type 1. It'll make 140-150 hp, and be happy pulling a highway gear or revving in the mountains.

I'd couple it with a stock geared transaxle, but swap the 4th with a .93 and put in a  3.88 R/P-- again, that's the sweet-spot that doesn't break the bank. The gears "feel right" and can happily pull you all day long on any 2-lane highway in America. Yes-- there will be times you wish for a gear between 3rd and 4th, but on the whole you can think of the $3000 you saved on the 5 speed, and the $3000- 4000 you saved not trying to make the 5-speed fit your car, and just be happy.

You'll note I used the word "happy" or some derivation of it 4 times and "sweet-spot" twice. That's because this is the one that isn't super-expensive to build and provides (by far) the most bang for the buck. 

Danny...Over the years I've heard "torque is king" or similar comments and never understood why some people think this way. Would you mind explaining why you think it is ? I have never been the sharpest knife in the drawer and just don't get it.

Bruce

Well Bruce I'll give it a shot.  I like to keep it simple. 

Torque is what moves you, HP is a bit more nebulous as it is a calculation. 

I always think of it this way, you have a 100hp diesel and 100hp gaz vehicle.  

in a Diesel Torque is what gets you humongous off the line pull.  It's a lot less in a gas engine for a number of reasons which Danny and others can elucidate.  

Definition

In my simple mind, I always thought horsepower gives you speed, but torque gives you acceleration.  I wait to be corrected...

DannyP posted:

 

I'd really like to use a Quaife Torsen-style differential in my Spyder. Conventional wisdom says tallest final drive with a Quaife is 3.88. There is a guy I know who says a 3.44 will fit IF you machine a little off the face of the pinion. We'll see, but I really don't want to ruin a R & P to find out.

 

yes you can machine the pinion slightly. but who knows how well that will hold up?

you can also clearance the diff but not very much. We have clearanced a IRS super diff to make it work and had no issues. To modify the quaife or TB unit can be risky due to that area being important for the internal gear operation.

Stan Galat posted:

The absolute sweet-spot (IMHO) is a 2110 with a W120(ish) cam. If I were doing it, I'd buy a CB Builder's Choice 2110 kit, and never look back. Bolt on a set of 40s and a 1-1/2" header, and you'll have a reasonably powerful, happy, cool running, long-lived Type 1. It'll make 140-150 hp, and be happy pulling a highway gear or revving in the mountains.

I'd couple it with a stock geared transaxle, but swap the 4th with a .93 and put in a  3.88 R/P-- again, that's the sweet-spot that doesn't break the bank. The gears "feel right" and can happily pull you all day long on any 2-lane highway in America. Yes-- there will be times you wish for a gear between 3rd and 4th, but on the whole you can think of the $3000 you saved on the 5 speed, and the $3000- 4000 you saved not trying to make the 5-speed fit your car, and just be happy.

You'll note I used the word "happy" or some derivation of it 4 times and "sweet-spot" twice. That's because this is the one that isn't super-expensive to build and provides (by far) the most bang for the buck. 

well said, but I still save for that five speed

As Danny said, Stan's got it covered, and is what I was referring to (but never got back to map out) yesterday. Either version (with or without aftermarket mainshaft) will be fun to drive!) 

@DannyP- I have heard that the end of the pinion only needs about a millimeter taken off to clear the Quaife- people I've talked to say it won't affect it's life. Look into it though- there are guys who have bought Quiafes and then sent them back because of poor machining tolerances, so if you buy one check it out thoroughly before installing.

Carlos- a 2110- 82x90.5 (or better yet, 2180 with  thickwall 92's) will rev to 6,000 rpm, make 150 hp all day long and with an auxiliary cooler/fan (with thermostat for quick warm ups) and enough air into the engine compartment should be pretty trouble free. With tons of torque throughout the rpm range there will always be power on tap at almost any rpm. This would be (relatively) easy to build, last 70 or 80,000 miles if operating parameters are always kept within reason and make a really fun engine in your Roadster. A 2276 is the same engine with 94's- some more displacement so potentially a little more power, but 94's are known for only going 40- 50,000 miles, so depending on how many miles you drive a year...

A 2332 (84 mm crankshaft) and 2386 (86 mm) are the same engine with more stroke. Now there's a little more work (or $$$ if someone else is building it) to put it together, you have to keep a more vigilant eye on oil and cylinder head temps and make damn sure it's getting enough fresh air (or temps will skyrocket), but there is also the opportunity for substantially more power, especially if set up to go to 6500 or 7,000 rpm. 200 hp or more is possible. Some guys can successfully run this much engine in a driver on the street while for others it's just too much work. Always choices...

@aircooled- Horsepower is high end power, Bruce, while torque is the power everywhere else. Think of it this way- a small engine (1776, 1835 or 1915) might make 140, 150, or even 160 hp at 6500 or 7,000 rpm, but it's all high end power with not a lot of torque/power 'below the curve, or in the area where we do most of our driving. I've run an engine like this in a street car (a Cal Look Beetle, at times my only transportation) and although (with close ratio gears) the car was reasonably fast, if I was loping along at 2800 or 3,000 rpm and wanted to really step on it I had to drop a gear as power was 500- 1,000 rpm away. 

A stroker engine will have substantially more power on tap from idle on up, and it it's set up to peak at 6,000 rpm the 3,000-3500 rpm 'sweet zone' will be that much lower and way more fun to drive.

If you look at a torque and horsepower curve it can help you choose an engine with more drivability.  

ie: Subaru here is a sample of a BRZ engines, look at where the torque starts and how high the engine has to spin, not my favourite. 

Hey look at this torque curve, pulling curve of what a Turbo can do when applied to a V6 F150... the torque starts right away at 1000rpm and goes to 5000.  Now you can pull that trailer easily. 

I'm pretty sure Bruce knows how this works.

I believe his point is that an engine needs to make torque to make horsepower, as HP is a computation based on torque.

While this may be true, total HP numbers don't tell you all that much about how powerful an engine feels. If the torque peak doesn't occur until 6000 RPM, and the HP peak is at 8000 RPM, it's going to feel like a 2-stroke-- all soggy and soft until the engine is REALLY spinning. Johannes Persson (Sweden air-cooled deity) made some crazy amount of HP with a 1776 a few years back (250+ HP), but I think the engine redlined at something like 14,000 RPM. That's astounding as a proof of concept, but not very useful as a street engine. One would need a 1000 lb car, or a 10 speed transmission, or both to make use of that kind of power.

The dirty secret? Total torque (as a number) isn't very useful either-- because it doesn't tell you anything about how flat the torque curve is, or where the peak occurs. We need a dyno graph to see that. The sooner the peak occurs, and the longer it hangs in there, the more useful the power is. This is what most guys just call "torque", or "twist", or "pull".

But even a dyno graph doesn't tell you everything you need to know. You've got to have a good torque number to have a good HP number, and a nice flat torque peak to feel powerful-- but there's another factor that almost nobody considers, because there isn't any number for it (although a 5-60 mph time in a high gear pull comes close):

Throttle response. Throttle response makes an engine feel "snappy".

Turbochargers are almost miraculous-- modern turbo engines start producing peak torque at about 1500 RPM, and carry it through until about 5500 RPM or so. The dyno curve looks fantastic. Still, car magazines and people in general miss the feel of larger displacement, higher compression engines which make similar power. Why? Throttle response-- what happens when you romp on the fun pedal? Does the engine gather it's skirts, draw a breath, and go-- or does it go from domesticated to "hang onto anything you can find" in less time than you have to think about it.

Great progress is being made here-- with dual scroll turbos, etc. Soon, there will be electrically assisted turbos, which are more interesting to me than any other technology under development right now.

But throttle response is not a number. That is where the magic of good combinations come in. That's why I wax all lyrical about Panchitos, and why an 8:1 engine feels a lot different than a 12:1 engine. It's why a (current) turbo 4 is as fun to drive as a NA 6 (I'm looking straight at you, Porsche)-- even though the 4 has better numbers.

Numbers don't lie, but they don't tell the whole story. 

Bob: IM S6 posted:

In my simple mind, I always thought horsepower gives you speed, but torque gives you acceleration.  I wait to be corrected...

In my simple mind, horsepower is how fast you crash into a wall. Torque is how far you push that wall when you do. 

MusbJim posted:

Bob: IM S6 posted:

In my simple mind, I always thought horsepower gives you speed, but torque gives you acceleration.  I wait to be corrected...

In my simple mind, horsepower is how fast you crash into a wall. Torque is how far you push that wall when you do. 

Smiling like he always does and cruising down PCH 1.