Topic: Engine Building Goals

[754]

2 Questions;

1..What do you expect to achieve when you modify your egine??

(Topend power , midrange etc)

2... What Rpm range do you spend most of your time??


From what I have read on here an lot of the riders are building for  high RPM power, but do they use it enough.

Greater torque and midrange would appear to be quite useful to a lot of riders.

Tell us what you expected, what you actually got, motors you loved, motors you did not like etc.. Tell what you loved or hated and have changed..

[mattcb350f]

Well, being this is my first "streetbike" engine that I am attempting to build I'm hoping that it runs when I'm finished 

My bike's a little 350F so I think you want to here from the 750 riders...

Anyway, the theory's the same. I hope to gain a raise in peak horsepower by means of porting the head and installing a mild cam. Already have a 4-1 exhaust so I'm hoping that will help too.
Doing this will sacrifice some bottom end and midrange power but will make it more responsive at powerful at RPM's above the 6k mark... I hope.
At 50 mph my bike is at around 5k on the tach and that's where I will spend most of my time. I'd just like to have enough HP to allow for comfortable cruising at that speed and and more juice up high when I want more. More power down low isn't really necessary...and hard to find on such a small mill.
The real trick is to gain power over the entire HP curve which would require much more than just what I'm doing and would be much more complicated. Especially since I'm sticking with the stock bore.

It would be nice having greater torque and mid range but that's not exactly what a small inline four wants to do... better job for a large twin. On that note, I think most builders go to find HP where it's easiest to get; high up in the RPM range on a SOHC/4.
 Matt.
 

[754]

I had one motor that I really disliked..

Was sold to me as a 900 but in fact was 812 or 836..cut skirt 350 pistons with a bit too much on top.

Cam of undetermined origin.

This bike would come on at high rpms and pull like crazy.. but.. down low it sucked.. not much below 6 K, in fact after a while it wasnt even fun to ride around on.. unless you were running it hard in the upper rpms.

Really got sick of it and it would sometimes need good fuel or rattle.. took it on a 1000 mile roundtrip 2 up once.. it was quick if you would downshift, but otherwise did not pull that great at cruising speeds.

I was glad to see that one go..

 Then We built one  with gobs of torque and midrange and great topend power.. a world of difference..

I know what I like now.. and sure dont miss that old motor..

[mkramer1121]

If it had the 350 pistons, it would be an 812.  Yoshimura made their 812's from the CB350 pistons.  I've actually got a set (used) w/ new rings and head gasket if anyone is interested....

So what are some tips and tricks to maintaining the midrange power and torque compared to the high RPM engines?  I think a number of people just buy the wildest cam they can get, strap it in and hope for the best.  Couldn't you also reclaim some of the midrange by dropping down a size in carbs (say, from 31's to 29's), or does this only work if the smaller size is the correct size for the bike?  After speaking to a former road racer, he stated that on certain tracks he would up the carb size to get more top end on tracks like Daytona.

[754]

4th over 350 =836cc..(It was probably an 812)


What I found makes a big difference in response was accelerator pumps..even the 77/78 carbs felt better in that regard.

 On my 836, my cam has  310 deg duration. I am running 30 mm carbs, have tried 32mm but found it much harder to ride off the line on the dragstrip. The Webers have huge accelerator pumps, actually a choice of several sizes.

[mlinder]

I commute at 2 to 4k. I ride at 7k to 10k.
Dun need much power to commute. Need more power to ride.
My changes will reduce low end slightly. I hope to increase my 7k+ power. Substantialy.

[scondon]

   Just adding the Wiseco 836 pistons to the engine seems to have added a nice bump to the low- midrange power. I added a streetable hot cam to it and timed it to spec, which gave me a bike that handled the city street and highway speeds equally well. Nothing TOO crazy while navigating 25-40mph traffic and lots of power on the freeway. A good all around commute bike that I have been very happy with.

  Though this first bike really turns up the power in 6000+ rpm range, I wanted my second bike to have the power a bit higher up the band. I used a similar cam, but retarded the timing a bit. It doesn't make much sense for daily riding and getting going faster "quicker" to do this, but for the riding I intended this bike for it is working out well. Twisties, long sweeper turns, etc.. This is where this engine seems to work really well for my riding style. At high rpms I find it much easier to regulate speed through the turns and am almost always "on" the throttle through the turn and using much less brake. At lower rpm's I have to brake more before entering a turn in order to dust off speed and a lot of torque tends to pull me wide when accelerating out of one. Again, it may just be my style of riding but the high rpm motor has definitely improved my handling and decision making at speed.

   I've got to get my first bike back on the road though since it IS more sensible for my daily riding conditions.

[scondon]

I commute at 2 to 4k. I ride at 7k to 10k.
Dun need much power to commute. Need more power to ride.
My changes will reduce low end slightly. I hope to increase my 7k+ power. Substantialy.

 

[Short Round]

currently I am rebuilding the topend of my 550K1.  All of the internals were fine and within functioning condition, I just had worn rings on the #4.  I bought a bit bigger pistons for it figuring it would last a bit longer than putting oversized rings on.  Its the 500 big bore kit, only jumped my ride up 11cc but I'm really not looking for a rocket, I merely want soemthing that is going to last onother 20 some odd years, something that my kids will remember and maybe redo again later on in life.  I just want something that is going to last and is why I am building it myself.  I could have bought a replacement for a couple hundred bucks but figured I would be in the same boat wondering what was done to it and when and how long was it going to last.  This wat I am going to know exactly what has been done to my motor, when it was done, and it will keep my mind at ease when I am on long rides throught the countryside of South and North Carolina next Spring.  In the process of putting the motor back together now,  and will be tackeling the frame in the coming winter.............should be back on the road by late winter or early spring.

[Jerry Rxman Griffin aka MuthaF'er]

754,

What cam are you running with 310 degrees? I gotta come up with something for the 1080 project that will allow plenty of time to fill the cylinders to go along with Mike's 33.5mm intake head and CR31's.

I really like the way my 812 Yoshi kit with the Daytona race cam pulls above 6K. Strong and quick. I'd love to have more mid range but I figure if I'm going to race someone I'm going to be doing so at 10K. Rev it and keep it there. That's what the shift lever is for. Do more cruising than racing anyway. It stays in 5th gear from 25mph and up unless I'm in a hurry. 

One downside we have is that we can't degree the cam with the engine in the frame. Too difficult to see what different cam timing will produce. I have one of Gordon's frame kits. Wish it was already installed so I could play with my Yoshi Daytona cam and see what it would do. When it gets taken down the kit goes in and I'll be able to see what can happen to a 900 by playing with the cam. I'll probably go with a cam that is more of a street racing cam rather than a full race track cam.   

[S-Dog]

I love mid-range grunt.  4k-7k ... My bike is stock(I think) cb750k and pulls real nice in the 4-6k range and a bit harder up high 6k+...

I have driven a CB750k with some porting and a hotter cam and it just doesnt have the flexibility my bike has... It feels like its missing something until about 6k... then it goes like the dickens.  Give me a bike that is consistent from 3.5k on and I am a happy man.

[MRieck]

 Build some compression in the engine and you'll get torque. You don't have to lose all your torque with a high performance cam. Use something with more lift but shorter duration, get a port to take advantage of it and keep the lobe center around 105.

[mlinder]

Build some compression in the engine and you'll get torque. You don't have to lose all your torque with a high performance cam. Use something with more lift but shorter duration, get a port to take advantage of it and keep the lobe center around 105.

MRieck, I'll be somewhere between 11:1 and 11.5:1. Hotter cam, and higher redline. 2nd size over. Headwork, titanium retainers, peened rods, etc. I'm hoping this will give me reasonable torque and a bit more HP.

[paulages]

i love the 550 powerband, but hate how fickle it is. my main desire in building the 718 is to improve the overall grunt so that i don't necessarily have to use the turbo button (upshift) every time i find myself too low in gear and needing to get out of a situation. i consider this power a matter of safety in urban riding, and not just thrill seeking. that said, i can't help but want to squeeze as much HP out of this engine as possible, just to see how much i can get. my 10.5/1 CR pistons and 37% displacement increase ought to give me plenty of torque, regardless of what i go for top-end wise.

man, i love that feeling on a 550 when you hit 7K or so, and get right where you want to be speedwise, just past hard acceleration... the engine just purrs. 

[eurban]

Build some compression in the engine and you'll get torque. You don't have to lose all your torque with a high performance cam. Use something with more lift but shorter duration, get a port to take advantage of it and keep the lobe center around 105.

MRieck, I'll be somewhere between 11:1 and 11.5:1. Hotter cam, and higher redline. 2nd size over. Headwork, titanium retainers, peened rods, etc. I'm hoping this will give me reasonable torque and a bit more HP.

What kind of gasoline do you plan on using?  At those CRs street gas might be out?

[sparty]

When Mike and I were planning my engine build I had one goal.  "To build the most powerful streetable (as in reliable) Hot Rod engine."  So now I have a engine that runs in the low 90s for HP, is a monster in straight line acceleration, has gobs of torque believe it or not, and will catch a small airplane above 8000 RPMs.  But all this comes with a price.  It isn't for daily commuting or just riding within the speed limits, so get your priorities in order.  Once my bike is in third gear and above 7000 RPMs I am illegal as all hell unless I am on a drag strip.  Fourth gear at 7000RPMs forgetaboutit and I can't even touch 5th gear for fear of the sonic boom.  But I love it and the goal was more than accomplished.

Sparty

[USN20]

1..What do you expect to achieve when you modify your engine??

Different schools of thought apply here ... For the street I would expect an engine that will run smoother, give snappy throttle response, have quicker acceleration, better shifting and deliver more power to the rear wheel across the power band. The engine will have stock reliability, run on pump gas and require no additional maintenance actions. This can be accomplished by addressing the detail items that did not get done on the assembly line due to time, machining and production costs. Just to name a few examples:

1. Precision valve jobs, professional porting, camshafts that are degreed in.
2. Crankshafts, rods and piston assemblies that are weighed and balanced.
3. Transmission gears undercut.
4. Lightening, polishing or coating select internal components.
5. Fine tuning the ignition timing and the fuel system on a engine dyno.

An engine built correctly with attention to detail will out-perform their production line counterparts. The trick is to pick up where the factory left off and modify the parts that are already paid for. Not a very exciting or winning recipe such as aftermarket big bore kits, cams, carbs and exhaust but it works.

[754]

The part I hated about my high revving, no bottom end motor was.. the only time it was fun.. I was usually doing something illegal..  which meant 80% of the time it was no fun.

Now the other motor I have is way more fun.. even if you shift at 3 grand and pour it on it pulls harder than my other ones did right through to the top. With a light rider like 140 lbs you could run it up  quickly to about  20mph, back off and nail it and have the tire starting to break loose.

Early 1080 motors in a stock frame could often wheelie and spin the tire at the same time in first... which would be a lot of fun on the street.

[mlinder]

Build some compression in the engine and you'll get torque. You don't have to lose all your torque with a high performance cam. Use something with more lift but shorter duration, get a port to take advantage of it and keep the lobe center around 105.

MRieck, I'll be somewhere between 11:1 and 11.5:1. Hotter cam, and higher redline. 2nd size over. Headwork, titanium retainers, peened rods, etc. I'm hoping this will give me reasonable torque and a bit more HP.

What kind of gasoline do you plan on using?  At those CRs street gas might be out?

Many bikes run 11:1 or 11.5:1 on street gas. I'm not terribly worried about it.

[MRieck]

1..What do you expect to achieve when you modify your engine??

Different schools of thought apply here ... For the street I would expect an engine that will run smoother, give snappy throttle response, have quicker acceleration, better shifting and deliver more power to the rear wheel across the power band. The engine will have stock reliability, run on pump gas and require no additional maintenance actions. This can be accomplished by addressing the detail items that did not get done on the assembly line due to time, machining and production costs. Just to name a few examples:

1. Precision valve jobs, professional porting, camshafts that are degreed in.
2. Crankshafts, rods and piston assemblies that are weighed and balanced.
3. Transmission gears undercut.
4. Lightening, polishing or coating select internal components.
5. Fine tuning the ignition timing and the fuel system on a engine dyno.

An engine built correctly with attention to detail will out-perform their production line counterparts. The trick is to pick up where the factory left off and modify the parts that are already paid for. Not a very exciting or winning recipe such as aftermarket big bore kits, cams, carbs and exhaust but it works.

Well stated and completely on target in my experience. The only thing I'd add is precision measuring of crank/rods/cases for optimum bearings and optimum squish.

[MRieck]

Build some compression in the engine and you'll get torque. You don't have to lose all your torque with a high performance cam. Use something with more lift but shorter duration, get a port to take advantage of it and keep the lobe center around 105.

MRieck, I'll be somewhere between 11:1 and 11.5:1. Hotter cam, and higher redline. 2nd size over. Headwork, titanium retainers, peened rods, etc. I'm hoping this will give me reasonable torque and a bit more HP.

It's at the limit but with chamber work and good squish....it's achievable. Like I said....it's really at the limit. You will need a very good ignition system with that combo. That said and that included....it will be a really fun and fast ride.

What kind of gasoline do you plan on using?  At those CRs street gas might be out?

Many bikes run 11:1 or 11.5:1 on street gas. I'm not terribly worried about it.

[mlinder]

Running dyna-s and 3.0hm coils. Should be reasonable, I think.

[amemoryoncelost]

 I'll be rebuilding my 400f this winter and my main goal is a reliable engine that doesn't leak oil. If I can manage that, job well done. I'd like to find a 550 or 750 to put some money into over the winter. Or at least find the bike this winter, than sink some money into the engine over the summer.

 I'll be pulling her apart sometime soon. Weather has been cold as hell, but dry, so I'm waiting...

[scondon]

Many bikes run 11:1 or 11.5:1 on street gas. I'm not terribly worried about it.

   Here in California, street gas only goes as high as 91 octane. This seems to be just at the margin of compatibility with my 10.25:1 pistons with .012" decked off the head (sorry, don't know final comp. ratio). Just did a test yesterday and bumped to 93 octane using Toluene, man what a difference

[Leino]

Engine building goals... to make a lot of noise and kick some hitech ass on
the way.Simple as that