top speed 114mph, What the F&*(?

[TADracer]

Remember, you have multiple reduction gears in these bikes. The 'primary' ratio is 1.657 (engine to clutch), then the trans at .882 (5th gear), then the trans output at .936, then the middle drive at 1.056. Multiply all these out, and you end up with a 'driveshaft to crankshaft' ratio of 1.44.

Looks like the 'primary' ratio of 1.657 throws the wrench in my gears.

[Crazcnuk]

Most companies, car or motorcycle, set the redline where the engine runs out of power, regardless of whether engine damage would occur at that rpm or not.

In fact, many companies, Dodge being one of note, often made redline occur at a certain spot (early) by putting in soft valve springs.

Most people believe that the mfg puts redline where engine damage will occur, when, in fact, they tested the engines, made sure they wouldn't hurt themselves, then put a red mark on the tach where power drops off due to valve float. Sort of a a built-in safety switch.

The XS bottom end will handle a lot more than 8500rpm, as several in this forum can attest. Small block dodges (318, 240, etc) had redlines of 5500rpm or so, but the engine will handle 8,000rpm easily, with the right cam and springs.

That being said, top speed is set by power. Power reqs increase exponentially as speed and wind res increases. Many people get caught by the 'I was doing xxx and still had 1/4 throttle left' even though that 1/4 throttle wouldn't do the same as the bottom 1/4 throttle.

If I changed the rear end gearing in my Monte Carlo I could easily take on the XS for top speed. With 500+hp and 38000lbs it actually has a better power to weight ratio and a lot more down force (weight).

I can't remember the actual numbers, but it takes around 500hp to do 160-170mph, 850hp for 190mph and over 1000hp to get over 200mph in a 3500lb car.

[oseaghdha]

Most companies, car or motorcycle, set the redline where the engine runs out of power, regardless of whether engine damage would occur at that rpm or not.

In fact, many companies, Dodge being one of note, often made redline occur at a certain spot (early) by putting in soft valve springs.

Most people believe that the mfg puts redline where engine damage will occur, when, in fact, they tested the engines, made sure they wouldn't hurt themselves, then put a red mark on the tach where power drops off due to valve float. Sort of a a built-in safety switch.

The XS bottom end will handle a lot more than 8500rpm, as several in this forum can attest. Small block dodges (318, 240, etc) had redlines of 5500rpm or so, but the engine will handle 8,000rpm easily, with the right cam and springs.

That being said, top speed is set by power. Power reqs increase exponentially as speed and wind res increases. Many people get caught by the 'I was doing xxx and still had 1/4 throttle left' even though that 1/4 throttle wouldn't do the same as the bottom 1/4 throttle.

If I changed the rear end gearing in my Monte Carlo I could easily take on the XS for top speed. With 500+hp and 38000lbs it actually has a better power to weight ratio and a lot more down force (weight).

I can't remember the actual numbers, but it takes around 500hp to do 160-170mph, 850hp for 190mph and over 1000hp to get over 200mph in a 3500lb car.

Not so much.
Redline is mostly a function of piston speed, which is dependant upon stroke. 68.6MM stroke at 8500RPM is about 3800 FPS. A typical number is usually around 3600FPS.

The mass of the piston/rod factors heavily, of course.

Once you know redline, you design so all the power is in by then.

Top speed is a function of HP vs Drag Coefficient and rolling resistance. Weight only will affect how long it takes to get there, and back.

[DenyP]

Just a note. Having read the posts and loving the subject matter, a little clarification. IMHO you will not gain top end speed with the 750 rear end mod. You will however gain on MPG at normal crusing speed.

Deny

[Ivan]

Just a note. Having read the posts and loving the subject matter, a little clarification. IMHO you will not gain top end speed with the 750 rear end mod. You will however gain on MPG at normal crusing speed.

Deny

I have found the opposite to be true. I get better MPG in 4th than 5th. If I keep the engine wrapped up, before I shift to 5th, it will keep pulling through 7k rpm, which has got to be close to topping out an 11 FD, I haven't had the room or the guts to let her wind out any further.

[DenyP]

Not being scientific - just riding and enjoying. My bike would wind up tighter b/4 the change but I don't see a higher top end now. But I do get better milage at crusing speeds. I am considering changing back to the 1100 rear end as I enjoyed the additional acceleration and the gas mileage is no longer as important to me.

Deny

[Crazcnuk]

"Not so much.
Redline is mostly a function of piston speed, which is dependant upon stroke. 68.6MM stroke at 8500RPM is about 3800 FPS. A typical number is usually around 3600FPS."

Not at all. You can design your engine to handle whatever piston speed you want. Think of the Honda inline 6's that can turn 21,000 rpm, or indy engines or whatever.

When your thinking of an actual fucntional redline, your talking race engines, where they want to use all the available rpm range.

This does not apply to off-the-rack consumer vehicles where the mfgs used a fictional redline to help thier vehicles reach the max warranty mileage w/o major repairs.

[Ivan]

Not being scientific - just riding and enjoying. My bike would wind up tighter b/4 the change but I don't see a higher top end now. But I do get better milage at crusing speeds. I am considering changing back to the 1100 rear end as I enjoyed the additional acceleration and the gas mileage is no longer as important to me.

Deny

I am willing to bet we have totally different riding styles. Out here in the flat lands of Kansas where a road will be straight as an arrow an not change a foot of elevation for 100 miles, most of my riding is at 75 mph or greater. I get better mileage in 4th with the engine wrapping about 5k, and with the obligatory headwind that can equal running at 100 mph wind speed fairly often and for quite a while.

If you live where the roads are "funner" and keep it at more sane speeds, and have trees around to block the wind, I would bet you do get better mileage with the engine unloaded and just cruising. I'm still willing to bet if you let it wind up a little more before the shift into 5th, you will see the top end come alive more than you'd be inclined to think.

[trbig]

I have the 750 FD. I didn't get any better fuel mileage, or top end. I do get a much better cruising RPM in 5th on the highway though. When I ride with guys that have the stock 11 final drive, listening to the motors side by side, my 4th gear is almost exactly the same as their 5th.

I have made many many top speed runs. My bike has a top end that is the same in 4th gear as it is 5th. There's no speed change, just rpm change between the two. It just gets to the point that it doesn't have the HP to push any more wind aside. I'm willing to bet that my 4th gear wound out is within one or two MPH of a stock FD in 5th.


Tod

[Ivan]

Yeah, the guys with the stock FD will set up a wah-wah-wah sound with a 75 FD in 4th. It startled the heck out of me when I heard it the first time riding with Lee. Thought something was coming apart.

[MindWebs]

speed kills, ride a harley.

hmm, bummer.. i was hoping for better top speed, with a 750FD

aarrgg, now i'll just have to install the 750FD AND Nitro injection...

or not....

nitro would be fun, but to much like work... lenthen swing arm, installing the kit, blah blah blah....

I prefer to ride more then wrench.. (it just never works out that way)

thanks gents

[BIG MIC]

got and 82 xj and just today i pegged it at 80 mph at 5600 with plenty of throttle left only problem no way to varify the actuall speed would like to know if anyone close would like to help me find out let me know

[Ivan]

got and 82 xj and just today i pegged it at 80 mph at 5600 with plenty of throttle left only problem no way to varify the actuall speed would like to know if anyone close would like to help me find out let me know

There's these guys that have these cars with funny headlights on the roof. For a nominal fee, they will tell you exactly how fast you are going. Shoot, they will even give you a free room to sleep in until some guy in a black dress decides on how much the price for your speed test is going to set you back. Nice guys really, they are there to help.

[CatatonicBug]

There's these guys that have these cars with funny headlights on the roof. For a nominal fee, they will tell you exactly how fast you are going. Shoot, they will even give you a free room to sleep in until some guy in a black dress decides on how much the price for your speed test is going to set you back. Nice guys really, they are there to help.

LOL!! Cute! I like that one!

Mic - you could try using a GPS to verify speed. might not be "Exact", but it's a lot more accurate than the speedos on these bikes.

[DenyP]

I am willing to bet we have totally different riding styles. Out here in the flat lands of Kansas where a road will be straight as an arrow an not change a foot of elevation for 100 miles, most of my riding is at 75 mph or greater. I get better mileage in 4th with the engine wrapping about 5k, and with the obligatory headwind that can equal running at 100 mph wind speed fairly often and for quite a while.

If you live where the roads are "funner" and keep it at more sane speeds, and have trees around to block the wind, I would bet you do get better mileage with the engine unloaded and just cruising. I'm still willing to bet if you let it wind up a little more before the shift into 5th, you will see the top end come alive more than you'd be inclined to think.

The improved mileage is with a cruising speed of 60 - 65, which is the majority of the time in the area I live. My trip to Utah I ran 80 + most of the time as I-80 is posted 75. My mileage dropped to low to mid 30's ( I did have a load on with all the gear I hauled) As far as top end is concerned, I shift when she won't clime no more. I am satisfied considering my weight and the windjammer. It will do 120+ which is where I usually back off.

Deny