What makes a good rally engine?
Discussion
"Mechanics dream": I was asked to build a historic rally mini.
Happy and hurray and... well... I am lost in the wilderness.
I have some ideas but would like to hear Your opinion. What makes a good rally engine?
How to build a good 998 rally engine (post 70 mkIII mini)?
Greatefull on any comment.
Happy and hurray and... well... I am lost in the wilderness.
I have some ideas but would like to hear Your opinion. What makes a good rally engine?
How to build a good 998 rally engine (post 70 mkIII mini)?
Greatefull on any comment.
Thanks for the input soo far.
I have a "donor" engine I would like to alter to suit the rally needs.
It is a Mini Se7en engine done by a well-known specalist.
The spec of the engine as far as I seen now:
- Omega forged (?) pistons with not very high compression (not measured yet).
- MG Metro cam (252in/268ex)
- MED crankshaft lightened quite well
- lightened std conrods
- 12G940 head well modified with 31mm ex and 36mm in valves - done by a very good specialist
- bronze guides
- 1.3 forged rockers
- very light flywheel
- sintered clutch
- grey diapragm
The engine did 97Bhps. Redline at 8K.
I will put the engine on a SC/CR box with the BMC ST ratios and a 4.57:1 sc/crosspin diff.
I would like to modify it to suit a rally car. No matter if we sacrifise some of the peak power. I dont think we will use it at 8k on a rally. I plan to get the switclight set somewhere at 7300.
Things I was thinking about to do:
- replace the head with a more mundane item (rimflow 31mm, 35,6mm and only port it slightly - in order to get a decent idle and some low-down torque.
- replace the sintered clutch with a normal heavy duty item, and also replace the diapragm with a normal 1275S item (green?).
- Is it mandatory to replace the flywheel with a heavier one?
- any other ideas?
I have a "donor" engine I would like to alter to suit the rally needs.
It is a Mini Se7en engine done by a well-known specalist.
The spec of the engine as far as I seen now:
- Omega forged (?) pistons with not very high compression (not measured yet).
- MG Metro cam (252in/268ex)
- MED crankshaft lightened quite well
- lightened std conrods
- 12G940 head well modified with 31mm ex and 36mm in valves - done by a very good specialist
- bronze guides
- 1.3 forged rockers
- very light flywheel
- sintered clutch
- grey diapragm
The engine did 97Bhps. Redline at 8K.
I will put the engine on a SC/CR box with the BMC ST ratios and a 4.57:1 sc/crosspin diff.
I would like to modify it to suit a rally car. No matter if we sacrifise some of the peak power. I dont think we will use it at 8k on a rally. I plan to get the switclight set somewhere at 7300.
Things I was thinking about to do:
- replace the head with a more mundane item (rimflow 31mm, 35,6mm and only port it slightly - in order to get a decent idle and some low-down torque.
- replace the sintered clutch with a normal heavy duty item, and also replace the diapragm with a normal 1275S item (green?).
- Is it mandatory to replace the flywheel with a heavier one?
- any other ideas?
Okay Master!
You are maybe one of a dozen species on this bare planet whom I take every lesson as rockhard fact.
But may I try to tell You my "whys"? And You will tell me why I think wrong
.
Soo.
The ports of the head is huge. Realy. It is much bigger then I ever seen. Even on well modified 1380 engines.
I was told that theese race engines idle around 2k. The cam is mild - I accept. Soo I thought that the gas speed in the ports at low prm is low, soo the fuel atomisation would suffer. This engine was built for track racing (Mini Se7en), soo no real problem with idle/low torque.
The same applies to the flywheel: it was built to rev high. But idling speed may suffer, and also the negine may be hesitant to pick up reves from low rpm. But I would be happy to use the light flywheel, just would like to make this engine idle at around 1000.
Padavan is waiting for the force-transition
.
You are maybe one of a dozen species on this bare planet whom I take every lesson as rockhard fact.
But may I try to tell You my "whys"? And You will tell me why I think wrong
. Soo.
The ports of the head is huge. Realy. It is much bigger then I ever seen. Even on well modified 1380 engines.
I was told that theese race engines idle around 2k. The cam is mild - I accept. Soo I thought that the gas speed in the ports at low prm is low, soo the fuel atomisation would suffer. This engine was built for track racing (Mini Se7en), soo no real problem with idle/low torque.
The same applies to the flywheel: it was built to rev high. But idling speed may suffer, and also the negine may be hesitant to pick up reves from low rpm. But I would be happy to use the light flywheel, just would like to make this engine idle at around 1000.
Padavan is waiting for the force-transition
. I must rebuild the engine as
a, this block does not meet the homologation of our class
b, on one cylinder bore I found a nasty casting error, which I would never accept in a race engine
c, the tranfer gear failed apperently on its first race, soo it needs sorting out.
Thus if I have to rebuild the negine, I would like to make the changes which looks promissing.
a, this block does not meet the homologation of our class
b, on one cylinder bore I found a nasty casting error, which I would never accept in a race engine
c, the tranfer gear failed apperently on its first race, soo it needs sorting out.
Thus if I have to rebuild the negine, I would like to make the changes which looks promissing.
As I told before, I intend to move the engine containment into a homologed block. It is mostly straight forevard. I think the best would be to copy the clearances of the original engine.
Though some controll may not hurt.
Soo I measured the clearances.
Piston-bore clearance - 0.09-0.1mm. The piston is forged. Do I realy need such a huge clearance?
Piston ring end gaps: 0.6-0.8mm. Same question here.
Crankshaft main bearing clearance 0.03mm.
Big end bearing clearance 0.04mm.
Valve-deck clearance 0.15-0.2mm, plus head gasket (app. 0.8mm).
Valve stem-guide clearance with bronze guides 0.7-0.9mm.
The honing pattern is "shallow", maybe 25-30degree and quite fine. Is it ok?
Were do I need to take care if I am building a high reving engine?
Though some controll may not hurt.
Soo I measured the clearances.
Piston-bore clearance - 0.09-0.1mm. The piston is forged. Do I realy need such a huge clearance?
Piston ring end gaps: 0.6-0.8mm. Same question here.
Crankshaft main bearing clearance 0.03mm.
Big end bearing clearance 0.04mm.
Valve-deck clearance 0.15-0.2mm, plus head gasket (app. 0.8mm).
Valve stem-guide clearance with bronze guides 0.7-0.9mm.
The honing pattern is "shallow", maybe 25-30degree and quite fine. Is it ok?
Were do I need to take care if I am building a high reving engine?
There are no mini specialists in my country.
I contacted Omega Piston for information, but they could not help. I was told that "depends on application".
OK. Although they suggested the clearance between 0.05-0.1mm.
The engine was originaly built for Mini Se7en track racing, to be reved up to 8k. I convert it to rally use, and will set the rev limit to 7200.
Soo I decided to reduce the piston-bore clearance to 0.07mm.
I am still not sure about the honing patern. Call me a foul, but after my last engine, which developed that nasty smoke for the sole reason of a bad honing, I am overly keen on this.
The honing of the original race block was very shallow - 25-30 degrees at max, with a very fine surface. Shall I order my machinist to duplicate this, or shall I go for a "normal" 45 degrees pattern?
I contacted Omega Piston for information, but they could not help. I was told that "depends on application"
.OK. Although they suggested the clearance between 0.05-0.1mm.
The engine was originaly built for Mini Se7en track racing, to be reved up to 8k. I convert it to rally use, and will set the rev limit to 7200.
Soo I decided to reduce the piston-bore clearance to 0.07mm.
I am still not sure about the honing patern. Call me a foul, but after my last engine, which developed that nasty smoke for the sole reason of a bad honing, I am overly keen on this.
The honing of the original race block was very shallow - 25-30 degrees at max, with a very fine surface. Shall I order my machinist to duplicate this, or shall I go for a "normal" 45 degrees pattern?
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