I’ll start by saying this engines development over 25-30 years has been a learning curve and experience has been gained in that time. I’ve had this vehicle since 1981 and started in the usual fashion by fitting extractors, camshaft and 350 holley carb to the standard 250 log head engine. Although doing this without any real knowledge of what I was doing, also young with lots of dreams but no money to do anything.
The head gasket blew so I removed the head and thought I would give it a birthday. I removed the valves and cleaned them up and found the margins too thin to reface so re-assembled and put back on the engine. At this point I realised I had to Either rebuild the standard head properly or look out for a 250-2V head. As luck would have it I found a 250-2v head at the local wreckers.(remember this was in the early eighties) I promptly fitted the head to the engine and drove the car in this form for sometime.
Sometime later decided I should rebuild the engine still with no real knowledge but was a qualified Mechanic now so I thought I knew stuff. This rebuild was basic rebored new pistons, bearings and the cylinder head checked out and valves faced and seats cut. Fitted new extractors and fitted a new “25-65 cam” with the timing chain lined dot to dot. Fitted a Bosch Electronic conversion kit to the distributor. Now I thought I had it all worked out.
I changed jobs and went to a small workshop who did some performance work and had a chassis dyno. After many lunch time discussions with my boss I realised I needed to change a few things with my engine. The fuel we were getting then was leaded but the octane was dropping. We put the car on the dyno and checked the HP as the engine was. It produced 113HP. Before I go on I must specify the chassis dyno I used (READS CLOSE TO ENGINE HP) so don’t get confused about the HP readings.
I removed the engine and fitted deep dish pistons from the unleaded crossflow engine and gapless second rings. This when cc’d gave a true static compression ratio of 8:1 (to suit the crappy fuel) and zero decked the block. I then removed the camshaft and fitted a smaller camshaft 205@.050 and .273” lift on 108deg L/C and dialled the cam in on 106deg on the inlet. (Note I now know the correct camshaft terminology and how to set it correctly) The cylinder head was then ported by myself under the supervision of a very experienced cylinder head porter who worked next door and fitted 1.750 Inlet valves and 1.500 Exhaust valves. We never flowed the cylinder head even though he had an airflow bench as he said I had done all I could do and what I got was what I got. I re-assembled the engine using the same carb and extractors. Ran the cam in and put it straight on the dyno to bed the rings in, set Ignition Timing and check the Jetting to make sure it wasn’t running lean or rich. Drove the car for a few weeks to run the engine In and put it back on the dyno for a proper tune. We did a Timing map to work out what advance curve was required then modified the distributor to give the advance curve the engine wanted. Checked and Jetted the carb to optimise the fuel. This time the engine produced 126HP (note with smaller cam, ported head and much less compression)
About a year or so Later I realised the carb was holding the engine up so I had a good friend modify the inlet manifold to accept a Nikki 4barrel carb off a Mazda Rotary. I airflow tested the carb and it flowed 160hp so I rebuilt the carb and Hotrodded it by blending the sharp edges around the top and narrowing the throttle shafts then re-airflow tested it. Now it flowed 165hp. I fitted this to the modified manifold and back on the dyno. After about 40 Hours on the dyno getting the carb jetted correctly The engine now produced 160HP. I droved it quite successfuly for some time as this was my every day driver.
In the year 2000 I decided I’d like to do some track work hillclimbs and street sprints so bought some sticky rubber and had a go. I was soon to find the Nikki carb I fitted was a problem when cornering around LH sweeping bends where the engine ran lean and lost power due to the floats getting fuel surge and holding them closed. Time to change again. A good friend said to get a 500 holley carb kit and put together a 500 out of parts he had as this has the centre hung float bowl at the front of the engine. So I did and re-tested on the dyno to see if the engine still made the same HP and it did. So removed the carb and gave it back to my friend to modify ie, screw in air bleeds different aux.ventruis and modified carb top. Refitted the carb and he came in to tune it. When we got the fuel mixture correct the engine now produced 180HP much to his surprise. He thought that perhaps the extractors were holding up the engine so I got some custom extractors made to sizes calculated by another friend. We ran it on the dyno with no HP gain however the peak HP now held on for another 500 rpm. This is how I ran the engine for another 7 years. Driving to events, racing , driving home and then to work on Monday.
The next saga. One day I was about to leave work and drove up the road about 200 metres and a knocking sound came from the engine, so idled back to work to check it out. It sounded like a bent pushrod or the like. Removed the rocker cover to check but everthing was ok. Removed the spark plugs and found No.3 plug mechanically damaged. So removed the cylinder head and found the engine had detonated and the noise was from a small piece of broken top ring hitting the cylinder head. Removed the engine and dismantled. Found All the top rings broken and the pistons ruined. Time to rebuild again. Located another engine and bored to suit new ACL race series pistons .020” over size. Fitted 200 falcon rods and beamed polished. Ground the crank .010” on mains and Big ends. CC’d and checked the compression Ratio and found too high at 10.3:1 so dished the pistons to achieve 9.3:1. Balanced the rotating assy. The shop I worked for now had an airflow bench so it was time to find out what the cylinder head flowed. Found the Inlet flowed 230hp but the Exhaust percentage was a little low. Wasn’t game to do anymore port work for fear of going through to water. Turned up some different shape valves to test the exhaust port but found the valves I had were the best. More out of good luck than good management I recut the valve seat and changed the throat and top cut angles and re-flowed tested. Too my suprise the exhaust flow went up to the desired %. Fitted a new cam this time 205@.050 .272” lift on the Inlet and 220@.050 .286” lift on the exhaust on 110 L/C and fitted to the engine on 106 L/C on the Inlet. Re-assembled the engine and run in on the dyno and checked timing and fuel. Drove for about 2 weeks then put on the dyno and tuned properly. Being paranoid about detononation we paid particular attention to the Ignition Timing. Before it ran 32degs Total timing but now it only wanted 26degs. Now it made 230HP. Thats a wopping 50HP more. To say I was happy was an understatement this was noticeable when driving and far better when I competed on the track. ( Remember the Dyno reading is near to Engine HP)
I’m currently building another engine with Mikes head but this will be another story when I get it finished.
So this is what Ive found over many years of persisting with this engine I hope it may help some of you modifying your ride.
The head gasket blew so I removed the head and thought I would give it a birthday. I removed the valves and cleaned them up and found the margins too thin to reface so re-assembled and put back on the engine. At this point I realised I had to Either rebuild the standard head properly or look out for a 250-2V head. As luck would have it I found a 250-2v head at the local wreckers.(remember this was in the early eighties) I promptly fitted the head to the engine and drove the car in this form for sometime.
Sometime later decided I should rebuild the engine still with no real knowledge but was a qualified Mechanic now so I thought I knew stuff. This rebuild was basic rebored new pistons, bearings and the cylinder head checked out and valves faced and seats cut. Fitted new extractors and fitted a new “25-65 cam” with the timing chain lined dot to dot. Fitted a Bosch Electronic conversion kit to the distributor. Now I thought I had it all worked out.
I changed jobs and went to a small workshop who did some performance work and had a chassis dyno. After many lunch time discussions with my boss I realised I needed to change a few things with my engine. The fuel we were getting then was leaded but the octane was dropping. We put the car on the dyno and checked the HP as the engine was. It produced 113HP. Before I go on I must specify the chassis dyno I used (READS CLOSE TO ENGINE HP) so don’t get confused about the HP readings.
I removed the engine and fitted deep dish pistons from the unleaded crossflow engine and gapless second rings. This when cc’d gave a true static compression ratio of 8:1 (to suit the crappy fuel) and zero decked the block. I then removed the camshaft and fitted a smaller camshaft 205@.050 and .273” lift on 108deg L/C and dialled the cam in on 106deg on the inlet. (Note I now know the correct camshaft terminology and how to set it correctly) The cylinder head was then ported by myself under the supervision of a very experienced cylinder head porter who worked next door and fitted 1.750 Inlet valves and 1.500 Exhaust valves. We never flowed the cylinder head even though he had an airflow bench as he said I had done all I could do and what I got was what I got. I re-assembled the engine using the same carb and extractors. Ran the cam in and put it straight on the dyno to bed the rings in, set Ignition Timing and check the Jetting to make sure it wasn’t running lean or rich. Drove the car for a few weeks to run the engine In and put it back on the dyno for a proper tune. We did a Timing map to work out what advance curve was required then modified the distributor to give the advance curve the engine wanted. Checked and Jetted the carb to optimise the fuel. This time the engine produced 126HP (note with smaller cam, ported head and much less compression)
About a year or so Later I realised the carb was holding the engine up so I had a good friend modify the inlet manifold to accept a Nikki 4barrel carb off a Mazda Rotary. I airflow tested the carb and it flowed 160hp so I rebuilt the carb and Hotrodded it by blending the sharp edges around the top and narrowing the throttle shafts then re-airflow tested it. Now it flowed 165hp. I fitted this to the modified manifold and back on the dyno. After about 40 Hours on the dyno getting the carb jetted correctly The engine now produced 160HP. I droved it quite successfuly for some time as this was my every day driver.
In the year 2000 I decided I’d like to do some track work hillclimbs and street sprints so bought some sticky rubber and had a go. I was soon to find the Nikki carb I fitted was a problem when cornering around LH sweeping bends where the engine ran lean and lost power due to the floats getting fuel surge and holding them closed. Time to change again. A good friend said to get a 500 holley carb kit and put together a 500 out of parts he had as this has the centre hung float bowl at the front of the engine. So I did and re-tested on the dyno to see if the engine still made the same HP and it did. So removed the carb and gave it back to my friend to modify ie, screw in air bleeds different aux.ventruis and modified carb top. Refitted the carb and he came in to tune it. When we got the fuel mixture correct the engine now produced 180HP much to his surprise. He thought that perhaps the extractors were holding up the engine so I got some custom extractors made to sizes calculated by another friend. We ran it on the dyno with no HP gain however the peak HP now held on for another 500 rpm. This is how I ran the engine for another 7 years. Driving to events, racing , driving home and then to work on Monday.
The next saga. One day I was about to leave work and drove up the road about 200 metres and a knocking sound came from the engine, so idled back to work to check it out. It sounded like a bent pushrod or the like. Removed the rocker cover to check but everthing was ok. Removed the spark plugs and found No.3 plug mechanically damaged. So removed the cylinder head and found the engine had detonated and the noise was from a small piece of broken top ring hitting the cylinder head. Removed the engine and dismantled. Found All the top rings broken and the pistons ruined. Time to rebuild again. Located another engine and bored to suit new ACL race series pistons .020” over size. Fitted 200 falcon rods and beamed polished. Ground the crank .010” on mains and Big ends. CC’d and checked the compression Ratio and found too high at 10.3:1 so dished the pistons to achieve 9.3:1. Balanced the rotating assy. The shop I worked for now had an airflow bench so it was time to find out what the cylinder head flowed. Found the Inlet flowed 230hp but the Exhaust percentage was a little low. Wasn’t game to do anymore port work for fear of going through to water. Turned up some different shape valves to test the exhaust port but found the valves I had were the best. More out of good luck than good management I recut the valve seat and changed the throat and top cut angles and re-flowed tested. Too my suprise the exhaust flow went up to the desired %. Fitted a new cam this time 205@.050 .272” lift on the Inlet and 220@.050 .286” lift on the exhaust on 110 L/C and fitted to the engine on 106 L/C on the Inlet. Re-assembled the engine and run in on the dyno and checked timing and fuel. Drove for about 2 weeks then put on the dyno and tuned properly. Being paranoid about detononation we paid particular attention to the Ignition Timing. Before it ran 32degs Total timing but now it only wanted 26degs. Now it made 230HP. Thats a wopping 50HP more. To say I was happy was an understatement this was noticeable when driving and far better when I competed on the track. ( Remember the Dyno reading is near to Engine HP)
I’m currently building another engine with Mikes head but this will be another story when I get it finished.
So this is what Ive found over many years of persisting with this engine I hope it may help some of you modifying your ride.
