If you end up switching the cylinder heads an opening up the flow of the engine then you may want to look at an annular version of the 750 when it comes time to change the carburetor out. It will have airflow similar to a 650 but have the top end performance of the larger 750 all while having good drivability and throttle response.
curiousity: 383 ci, intake ? and carb size
- Thread starter MYBAD79
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SmokinBBC
Well-known member
Welcome Tech at Barry Grant:hi:
MYBAD79
Moderator
Time to update this old thread..... Lol.... I have since then installed a polished RPM air gap intake and a Edelbock 800cfm carb, played a little with the advance springs in the dizzy and re-jetted the carb a few times.... Now it runs great, lots of power and I am seriously considering a rev limiter as it just wants to keep going, had it to 7000 a few times 
DeeVeeEight
Fast Pedalphile
Time to update this old thread..... Lol.... I have since then installed a polished RPM air gap intake and a Edelbock 800cfm carb, played a little with the advance springs in the dizzy and re-jetted the carb a few times.... Now it runs great, lots of power and I am seriously considering a rev limiter as it just wants to keep going, had it to 7000 a few times
And you can't wipe the grin off of your face...
I never had mine to 7K but I am told I should push it there. When are you taking it to the track?
:drink:
MYBAD79
Moderator
Just replaced the body mounts so now it's finally back on the road..... I really don't have to push a lot to get it near 7000.... it's not really intentional either, in first and second it's just very quick reving that high...... I really think I need a rev limiter, no point going past 6200 or so, I'd hate blowing up this engine.....
mrvette
Phantom of the Opera
I come from the old Pontiac school of engineering gimme 550 ft lbs at idle.....I want to move NOW not wait till 8000 rpm's come along.....
:shocking: call me impatient.....
Twin_Turbo
Der Maulwurf
- Joined
- Mar 5, 2008
- Messages
- 7,579
Time for some nice 200cc heads
MYBAD79
Moderator
Yeah, better heads would be awesome but for I have to say I'm really happy how it runs..... Now that the body mounts are replaced I can actually drive it again.... Might change the oil this weekend and put a few miles on it
BangkokDean
Well-known member
Time to update this old thread..... Lol.... I have since then installed a polished RPM air gap intake and a Edelbock 800cfm carb, played a little with the advance springs in the dizzy and re-jetted the carb a few times.... Now it runs great, lots of power and I am seriously considering a rev limiter as it just wants to keep going, had it to 7000 a few times
One question, I thought the cam has a point where the HP drops off, so what advantage is it to rev past that point?
MYBAD79
Moderator
BangkokDean;111661 One question said:No point reving past that, it's just that in 1st and 2nd gear it revs up so fast that i sometimes don't shift quick enough ..... Rev limiter would make it safer
Stroker-427
Well-known member
Revving an engine over the max power rpm, sometime make a big sense!
Remember that the acceleration is comin from the torque, so you have to analize the torque curve of the engine, not the power curve.
If I well remember the gear ratio of a TH350 is 2.52 - 1.52 - 1
The step between first and second gear is 40% so you will have 40% less torque at the wheels in second.
If the torque of the engine at full power is more than 40% lower that the torque after the shift.... you don't have to shift!
For example let analyze this engine (a tipical 383 with 450Hp)
Max power is @ 5500 rpm
Max torque is @ 4500 rpm
If you will shift (first to second) @ 5500 rpm the engine will drop to nearly 3300 rpm (40% drop).
Torque @ the driveshaft before the shift is some 1108 lbs/ft (440*2.52)
Torque @ the dirveshaft after the shift is some 700 lbs/ft (460*1.52)
Analizing again the torque curve is easy to notice that the max torque is some 480lbs/ft @4500 rpm. The theoretical best shift point should be where the engine have some 290lbs/ft of torque....... well over the max permitted rpm.
Different thing if you have to shift from second to third with a drop of ratio of 35%....
As much drop you have between gears, as much you have to rev you engine before to shift.
This is why with a close ratio gearbox your average torque at the wheels will be higher.
Hope this help....
Remember that the acceleration is comin from the torque, so you have to analize the torque curve of the engine, not the power curve.
If I well remember the gear ratio of a TH350 is 2.52 - 1.52 - 1
The step between first and second gear is 40% so you will have 40% less torque at the wheels in second.
If the torque of the engine at full power is more than 40% lower that the torque after the shift.... you don't have to shift!
For example let analyze this engine (a tipical 383 with 450Hp)
Max power is @ 5500 rpm
Max torque is @ 4500 rpm
If you will shift (first to second) @ 5500 rpm the engine will drop to nearly 3300 rpm (40% drop).
Torque @ the driveshaft before the shift is some 1108 lbs/ft (440*2.52)
Torque @ the dirveshaft after the shift is some 700 lbs/ft (460*1.52)
Analizing again the torque curve is easy to notice that the max torque is some 480lbs/ft @4500 rpm. The theoretical best shift point should be where the engine have some 290lbs/ft of torque....... well over the max permitted rpm.
Different thing if you have to shift from second to third with a drop of ratio of 35%....
As much drop you have between gears, as much you have to rev you engine before to shift.
This is why with a close ratio gearbox your average torque at the wheels will be higher.
Hope this help....
MYBAD79
Moderator
Never looked into the numbers but I admit, this is very interessting stuff......m
TKO 600 ratios are 2.87, 1.89, 1.28, 1.00, 0.64
From 2nd to 3rd that's a drop to 68% or a drop of 32%, if I shift at 6500rpm in 2nd I end up at 4433rpm in 3rd....
It seems that shifting at 6000 is a good idea
TKO 600 ratios are 2.87, 1.89, 1.28, 1.00, 0.64
From 2nd to 3rd that's a drop to 68% or a drop of 32%, if I shift at 6500rpm in 2nd I end up at 4433rpm in 3rd....
It seems that shifting at 6000 is a good idea
glen242
Active member
Where did the HP info come from?