A. Graham Bell

**TZ350** · 15th November 2008, 21:34

Diall a REV

Graham Bell in his book Two-Stroke Performance Tuning. He studied a lot of engines and give’s some port timing figures that he has found to work. His basic idea is that at a certain RPM a motor needs a certain port timing to work well. Graham Bells approach is quick and dirty but puts you on the money quickly.

Port Time Area is a later refinement.

I have copied the 100 and 125 info that he gives. The figures are in degrees of duration that the port is open.

To get the exhaust and transfer port opening after top dead centre ATDC subtract the duration from 360 and halve the resultant this gives you degrees opening ATDC.

For a piston port inlet halve the Duration gives you degrees opening before top dead centre BTDC.

Exhaust Port Duration

2 x 62 Road Race 13500 206-208 exhaust degrees duration.
1 x 100 Moto X 11200 198-200
1 x 100 Go-Cart 10800 176-178
1 x 125 Moto X 10000 190-192
1 x 125 Moto X 11000 196-198
1 x 125 Road Race 12000 202-204
1 x 125 Road Race 12500 203-205

Transfer Port Duration

10000 128-132 degrees duration
11000 130-134
12000 132-136
13000 134-140

Inlet Port Duration

9500 165-170
11000 185-190
12000 195-200

Examples of Rotary Valve Timing

Engine Capacity opens BTDC closes ATDC Transfer Opens ATDC
C-75 Kart 100 155/43 124
K96-3 Kart 100 155/60 123
FC-52 Kart 100 115/60 120
Can-Am MX-6 125 140/85 113
DAP T81 Kart 100 132/58 117
DAP-JM T71 Kart 100 120/55 113.5
Komet K78 Kart 100 132/60 118
Komet K78 TT Kart100 132/60 117
Morbidell 125 Race 2 x 62 150/79 109
MZ Bike 125 135/70 112
Rotax LC Kart 125 120/87 113
Sirio ST50 Kart 100 134/75 116.5
Sirio ST504 Kart 100 135/65 120
Siro ST52 Kart 100 134/75 117.5
Zip ZED1 Kart 100 140/66 121.5

My own GP125 Ex opens 86 ATDC Trans opens 114 ATDC Inlet 145/55 for Mt Wellington and Ex opens 81 ATDC Trans opens 114 ATDC Inlet 145/85 Taupo.

**TZ350** · 15th November 2008, 21:44

Diall a REV

Graham Bell in his book Two-Stroke Performance Tuning. He studied a lot of engines and give’s some port timing figures that he has found to work. His basic idea is that at a certain RPM a motor needs a certain port timing to work well. Graham Bells approach is quick and dirty but puts you on the money quickly.

Port Time Area is a later refinement.

I have copied the 100 and 125 info that he gives. The figures are in degrees of duration that the port is open.

To get the exhaust and transfer port opening after top dead centre ATDC subtract the duration from 360 and halve the resultant this gives you degrees opening ATDC.

For a piston port inlet halve the Duration gives you degrees opening before top dead centre BTDC.

Exhaust Port Duration

2 x 62 Road Race 13500 RPM 206-208 exhaust degrees duration.
1 x 100 Moto X 11200 198-200
1 x 100 Go-Cart 10800 176-178
1 x 125 Moto X 10000 190-192
1 x 125 Moto X 11000 196-198
1 x 125 Road Race 12000 202-204
1 x 125 Road Race 12500 203-205

Transfer Port Duration

10000 RPM 128-132 degrees duration
11000 130-134
12000 132-136
13000 134-140

Inlet Port Duration

9500 RPM 165-170
11000 185-190
12000 195-200

Examples of Rotary Valve Timing

Engine Capacity opens BTDC closes ATDC Transfer Opens ATDC
C-75 Kart 100 155/43 124
K96-3 Kart 100 155/60 123
FC-52 Kart 100 115/60 120
Can-Am MX-6 125 140/85 113
DAP T81 Kart 100 132/58 117
DAP-JM T71 Kart 100 120/55 113.5
Komet K78 Kart 100 132/60 118
Komet K78 TT Kart 100 132/60 117
Morbidell 125 Race 2 x 62 150/79 109
MZ Bike 125 135/70 112
Rotax LC Kart 125 120/87 113
Sirio ST50 Kart 100 134/75 116.5
Sirio ST504 Kart 100 135/65 120
Siro ST52 Kart 100 134/75 117.5
Zip ZED1 Kart 100 140/66 121.5

My own GP125 Ex opens 86 ATDC Trans opens 114 ATDC Inlet 145/55 for Mt Wellington and Ex opens 81 ATDC Trans opens 114 ATDC Inlet 145/85 Taupo.

**SHELRACING** · 15th November 2008, 22:28

I'm confused I thought Graham Bell had summit to do wiv telephones, was he into two strokes as well ??

**bucketracer** · 16th November 2008, 05:47

Port Timing. Now that rings a Bell!!!!

**koba** · 16th November 2008, 15:00

He also has books on 4 stroke tuning, forced induction and "modern engine tuning" all are really good and easy to read.

**gav** · 16th November 2008, 21:59

So interesting that you needed to post this twice?

**TZ350** · 17th November 2008, 07:59

Originally Posted by gav

So interesting that you needed to post this twice?

Yep. I don't know how it happens (has happend before), pushed a wrong key and bingo, a duplicate that I can't get rid off. Bugger

if any one knows what I got wrong and how to correct it I would love to know.

**CM2005** · 17th November 2008, 15:18

Hi TZ, why do you use different port timing for taupo??

**bucketracer** · 17th November 2008, 17:41

Originally Posted by CM2005

Hi TZ, why do you use different port timing for taupo??

EX85, In 145/55 gives good drive at Mt Wellington, EX81, In 145/85 gives a little more topend on the same pipe for Taupo's relatively longer straights.