Hiya guys,
Right, i'm kinda starting from a funny angle here but i'm not really certain on the direction i'm heading with this yet.
I want to build my E30 into something quiet nice. I'm aiming for a grand tourer style more than anything.
I want comfy seats, cruise control, air con, electric windows all round etc etc etc.
Obviously, with all the toys it'll need some power, and thats where you guys come in.
I've wanted to build an engine for a while, it might as well be the M20. I've gone through all the ideas of 3.2 specials with custom pistons etc but after reading into side thrusts and whatnot i reckon i would be better sticking with smaller capacity? Also, with a well built 3+ litre M20, i reckon i'll be struggling to top much past 240hp???
So i'm thinking of building a 2.8l M20 probably with forced induction.
I dont want the surge of a turbo for a car of this nature,
I do like large power NA so maybe a supercharger would suit better?
I've read that Eaton's produce a lot of heat but produce linear boost like i want?
Maybe a centrifugal (vortech, rotrax) would suit better? How is the boost produced on these sort of chargers?
I'm thinking of aiming for somewhere a little over 300hp with buckets of torque to pull a long top gear.
Do you guys reckon that will be enough? Too much? I dont want the engine to become untractable (peaky cams, paddle clutches etc)
Any advice or opinions on the above ramblings would be much apprieciated.
Cheers guys, and sorry for the disorganised rambling nature of the post.
Cheers
Chris
Help with ideas please.
Moderator: martauto
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goosiegander
- Zonegoose
- Posts: 2544
- Joined: Sun Nov 19, 2006 11:00 pm
- Location: East Anglia
That read fairly well Dude,
For a 2.8 thread see here:
http://www.e30zone.net/modules.php?name ... c&t=174097
This is a low compression M20B28 that was spec'd for FI and the rotrex kit as supplied by Ant,
Have a read and if you can get up to BBB's BBQ on the 25th i'll take you out in my car.
I think your target of 300hp is very attainable -but will not be cheep
For a 2.8 thread see here:
http://www.e30zone.net/modules.php?name ... c&t=174097
This is a low compression M20B28 that was spec'd for FI and the rotrex kit as supplied by Ant,
Have a read and if you can get up to BBB's BBQ on the 25th i'll take you out in my car.
I think your target of 300hp is very attainable -but will not be cheep
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E30BeemerLad
- Married to the E30 Zone
- Posts: 16806
- Joined: Mon Mar 28, 2005 11:00 pm
- Location: Norfolk
If you want more of a GT feel, why not go V8 but keep the auto box, it'll still be silly quick, but less of a frantic drive
Wo wo wo, who said anything about an auto box? I still want to be able to drive it 
.
To be honest, i like the M20. I have thought a couple of times about putting an M52 in it just for simple power, but i like the old lump. And i've bought a BTB3 for it so would be a shame to waste it
Do we think 2.8 is a good size for the numbers i'm hoping to get? My thinking was, that any bigger and you seem to get a sort of diminishing returns thing with the power, and if nice 2.8's can get 220hp, it's not a huge leap for the charger to make up.
Any idea what sort of boost i'll need for around 300hp (obviously very rough)
Oh, and i learnt long ago that cars are never cheap
Cheers
Chris
.To be honest, i like the M20. I have thought a couple of times about putting an M52 in it just for simple power, but i like the old lump. And i've bought a BTB3 for it so would be a shame to waste it
Do we think 2.8 is a good size for the numbers i'm hoping to get? My thinking was, that any bigger and you seem to get a sort of diminishing returns thing with the power, and if nice 2.8's can get 220hp, it's not a huge leap for the charger to make up.
Any idea what sort of boost i'll need for around 300hp (obviously very rough)
Oh, and i learnt long ago that cars are never cheap
Cheers
Chris
Chris,
Contrary to what the zone wiki says, the CR of the 2.8 stroker (M20B25 block + 84mm crank + 130mm rods + low CR B25 pistons + stock gasket) is 9.3:1. Add 0.5mm to your gasket and that falls to 8.9:1. Add a whole 1mm and it drops further to 8.6:1. Both the latter two values are ripe for supercharging.
If it's a grand tourer that you're after then an Eaton supercharger, such as an M62 (see here) pulled from a Jaguar, would be ideal. Eaton superchargers are technically what are termed ”aroots pumps”a and provide (in theory at least) a constant (not linear) boost pressure in accordance with the chosen pulley sizes. In practice, however, boost falls off somewhat at low rpm due to leakage around the rotors. The thing to be aware of with roots pumps is that they are highly inefficient, which means that they put a substantial amount of heat into the pumped air (over and above the usual due to adiabatic heating, which you cannot get away from) and also consume a large amount of your engines hp in order to operate. The fact that they generate more-or-less constant boost does however make them a very attractive proposition provided you can afford the fuel bill. To make sure a roots pump operates at least near to its zone of maximum efficiency (which admittedly is still only around 65%) you want to aim for around 0.5 bar of boost.
Rotrex superchargers, on the other hand, are basically belt driven turbochargers, termed centrifugal pumps, and will quite happily do a bar (and more) of boost. Their boost is, however, a linear function of engine speed. The disadvantage of these is that boost is low at low rpm. Choosing the pulley size to give decent boost at low rpm will result in too much boost at high rpm. Various systems have been devised to work around this problem, but none are simple. The advantage of a Rotrex, however, is it’s improved efficiency over an Eaton, so it won’t hit you as hard in the pocket when it comes time to refuel. If it’s a Rotrex that you are interested in then the C30-94 will work well on a 2800cc engine.
Be aware, however, that roots pumps and centrifugal pumps do not drive or feel the same. If it’s low rpm cruising that you want, the Eaton is your best bet, but will hit you hard in the pocket. Nothing beats the low rpm torque of a roots pump compared to a centrifugal blower, and if you can afford to fuel it then fair enough. Otherwise opt for the Rotrex, but be aware that your torque will effectively climb as your boost climbs with rpm. The two pumps produce VERY different torque curves.
FYI, to make 300hp at your flywheel your 2800cc engine will need to flow roughly 34 lbs/min of air in the case of the Eaton, and 32 lbs/min in the case of the Rotrex. This is because it will easily cost your engine ~40hp just to run the Eaton, so to have 300hp ”aleft-over”a at the flywheel the engine needs to produce a total of 340hp. Since the Rotrex is more efficient it will cost your engine only ~20hp (roughly) to make 300hp at the flywheel. As a rule of thumb, every pound of air you flow per minute generates 10hp, provided you mix it with fuel in a ratio of ~12:1. The result of this is that you’d need to boost a 2800cc stroked M20B25 engine to at least 0.9bar to make 340hp at 6000rpm, provided you keep your intake air temperature to 37’C or below using an intercooler. You could do this with an Eaton M62 but I wouldn’t recommend trying given the amount of heat you’d put into the pumped air (requiring a very large intercooler to get the intake air back down to 37’C). Running a constant 0.6bar of boost on an Eaton M62 will get you to 280hp total at 6000rpm. That should leave you with roughly 260 hp at the flywheel to play with. Be aware right from the outset, however, that you will need a mother of an intercooler to get the heat out of the air pumped by the Eaton. Do not underestimate this challenge! If you fit an M62 without an intercooler you will need to run at much lower boost in order to avoid detonation, and hence your hp output will drop and you will wonder why you bolted the damn thing to your engine in the first place. There are zoners here who have removed their Eaton superchargers in favour of a Rotrex because of exactly this problem.
With a Rotrex you will be able to achieve more peak power than with the Eaton (provided your engine can deliver). At 8.5:1 CR I wouldn’t recommend that you exceed 1bar of boost on 99RON fuel, but that should see you good for 330hp at the flywheel, no questions asked. Take note, however, that with a Rotrex your engines torque will peak at roughly the same time as the boost pressure. Below peak-torque rpm your boost, and hence torque will decline. As with the Eaton, you will need to run the Rotrex with an intercooler. Any supercharger or turbocharger that does not employ an intercooler is destined to run at low boost and will not realise its full potential.
HTH
Geoff
Contrary to what the zone wiki says, the CR of the 2.8 stroker (M20B25 block + 84mm crank + 130mm rods + low CR B25 pistons + stock gasket) is 9.3:1. Add 0.5mm to your gasket and that falls to 8.9:1. Add a whole 1mm and it drops further to 8.6:1. Both the latter two values are ripe for supercharging.
If it's a grand tourer that you're after then an Eaton supercharger, such as an M62 (see here) pulled from a Jaguar, would be ideal. Eaton superchargers are technically what are termed ”aroots pumps”a and provide (in theory at least) a constant (not linear) boost pressure in accordance with the chosen pulley sizes. In practice, however, boost falls off somewhat at low rpm due to leakage around the rotors. The thing to be aware of with roots pumps is that they are highly inefficient, which means that they put a substantial amount of heat into the pumped air (over and above the usual due to adiabatic heating, which you cannot get away from) and also consume a large amount of your engines hp in order to operate. The fact that they generate more-or-less constant boost does however make them a very attractive proposition provided you can afford the fuel bill. To make sure a roots pump operates at least near to its zone of maximum efficiency (which admittedly is still only around 65%) you want to aim for around 0.5 bar of boost.
Rotrex superchargers, on the other hand, are basically belt driven turbochargers, termed centrifugal pumps, and will quite happily do a bar (and more) of boost. Their boost is, however, a linear function of engine speed. The disadvantage of these is that boost is low at low rpm. Choosing the pulley size to give decent boost at low rpm will result in too much boost at high rpm. Various systems have been devised to work around this problem, but none are simple. The advantage of a Rotrex, however, is it’s improved efficiency over an Eaton, so it won’t hit you as hard in the pocket when it comes time to refuel. If it’s a Rotrex that you are interested in then the C30-94 will work well on a 2800cc engine.
Be aware, however, that roots pumps and centrifugal pumps do not drive or feel the same. If it’s low rpm cruising that you want, the Eaton is your best bet, but will hit you hard in the pocket. Nothing beats the low rpm torque of a roots pump compared to a centrifugal blower, and if you can afford to fuel it then fair enough. Otherwise opt for the Rotrex, but be aware that your torque will effectively climb as your boost climbs with rpm. The two pumps produce VERY different torque curves.
FYI, to make 300hp at your flywheel your 2800cc engine will need to flow roughly 34 lbs/min of air in the case of the Eaton, and 32 lbs/min in the case of the Rotrex. This is because it will easily cost your engine ~40hp just to run the Eaton, so to have 300hp ”aleft-over”a at the flywheel the engine needs to produce a total of 340hp. Since the Rotrex is more efficient it will cost your engine only ~20hp (roughly) to make 300hp at the flywheel. As a rule of thumb, every pound of air you flow per minute generates 10hp, provided you mix it with fuel in a ratio of ~12:1. The result of this is that you’d need to boost a 2800cc stroked M20B25 engine to at least 0.9bar to make 340hp at 6000rpm, provided you keep your intake air temperature to 37’C or below using an intercooler. You could do this with an Eaton M62 but I wouldn’t recommend trying given the amount of heat you’d put into the pumped air (requiring a very large intercooler to get the intake air back down to 37’C). Running a constant 0.6bar of boost on an Eaton M62 will get you to 280hp total at 6000rpm. That should leave you with roughly 260 hp at the flywheel to play with. Be aware right from the outset, however, that you will need a mother of an intercooler to get the heat out of the air pumped by the Eaton. Do not underestimate this challenge! If you fit an M62 without an intercooler you will need to run at much lower boost in order to avoid detonation, and hence your hp output will drop and you will wonder why you bolted the damn thing to your engine in the first place. There are zoners here who have removed their Eaton superchargers in favour of a Rotrex because of exactly this problem.
With a Rotrex you will be able to achieve more peak power than with the Eaton (provided your engine can deliver). At 8.5:1 CR I wouldn’t recommend that you exceed 1bar of boost on 99RON fuel, but that should see you good for 330hp at the flywheel, no questions asked. Take note, however, that with a Rotrex your engines torque will peak at roughly the same time as the boost pressure. Below peak-torque rpm your boost, and hence torque will decline. As with the Eaton, you will need to run the Rotrex with an intercooler. Any supercharger or turbocharger that does not employ an intercooler is destined to run at low boost and will not realise its full potential.
HTH
Geoff
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
Food for thought, and something similar to what i was thinking (but with justification rather than hunches)
I'm probably completely off base here but would running the rotrex on a smaller pulley produce more boost? so that i could bleed more off at higher levels to keep things safe, but produce a lot more heat and waste a lot more energy to produce the higher boost?
Can you run a housing size larger on rotrexes to allow for higher boost while keeping the effieciency? or do these then fail to deliver lower down the revs like a large turbo?
Cheers
Chris
I'm probably completely off base here but would running the rotrex on a smaller pulley produce more boost? so that i could bleed more off at higher levels to keep things safe, but produce a lot more heat and waste a lot more energy to produce the higher boost?
Can you run a housing size larger on rotrexes to allow for higher boost while keeping the effieciency? or do these then fail to deliver lower down the revs like a large turbo?
Cheers
Chris
See here for Tim_Haynes M20B25 powered track car with C30-94 Rotrex. Just keep in mind that he runs this on high octane race fuel ONLY.
FYI, don't discard the Eaton as an idea just yet. If it's low rpm grunt that is your objective you will at least have to consider it as an option. However, for all the effort to fit an Eaton M62 to an M20 to get that low rpm grunt you would do well to consider E30Beemerlad's suggestion of a V8. Since boost climbs linearly with rpm on a centrifugal blower it will still kick you in the back much like a turbo does. Not quite as bad since the rate-of-rise of torque is much more controlled, but it's still not considered ideal for a GT car.
FYI, don't discard the Eaton as an idea just yet. If it's low rpm grunt that is your objective you will at least have to consider it as an option. However, for all the effort to fit an Eaton M62 to an M20 to get that low rpm grunt you would do well to consider E30Beemerlad's suggestion of a V8. Since boost climbs linearly with rpm on a centrifugal blower it will still kick you in the back much like a turbo does. Not quite as bad since the rate-of-rise of torque is much more controlled, but it's still not considered ideal for a GT car.
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
Get a turbocharger sized in accordance with the power goal you want OP and you can have the low end grunt you like no problems.
Electronic boost control will be your friend if the low end is to much
Electronic boost control will be your friend if the low end is to much
All the electronic boost control in the world won't turn a turbine driven centrifugal compressor into a constant displacement pump. This fundamanetal difference between the two is the reason the roots pump still finds commercial application, despite its inherent inefficiency.Gunni wrote:Get a turbocharger sized in accordance with the power goal you want OP and you can have the low end grunt you like no problems.
Electronic boost control will be your friend if the low end is to much
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
Thats true. But there are turbochargers that are capable of giving full boost very fast when you aren´t demanding much HP/liter from your turbo engine. Even if they are old technology. So given todays turbochargers and their associated technology a turbocharger that will reach the same goal as a old one that was fast can now be tiny bit smaller and will actually be significantly faster.
My friend had a small T3 once, at 2500rpm the boost gauge was like a throttle gauge , basically the more you pushed the more boost you got, if you floored it right off the boost gauge only tailed after minutely.
I know this picture is very old but it shows a little test we did ages ago.
View it to see it better.
Those Gtech HP numbers when compared to HP numbers always came out a KW´s, so that HP number * 1.35 was the closest approximation to measured HP from those vehicles. The M3 was down on power the M30 worked very well and the 325i turbo had about 255ish hp. The torque then multiplied by 1.35 and again shows Newtons.
It didn´t even have electronic boost control or high boost at that time.
My friend had a small T3 once, at 2500rpm the boost gauge was like a throttle gauge , basically the more you pushed the more boost you got, if you floored it right off the boost gauge only tailed after minutely.
I know this picture is very old but it shows a little test we did ages ago.
View it to see it better.
Those Gtech HP numbers when compared to HP numbers always came out a KW´s, so that HP number * 1.35 was the closest approximation to measured HP from those vehicles. The M3 was down on power the M30 worked very well and the 325i turbo had about 255ish hp. The torque then multiplied by 1.35 and again shows Newtons.
It didn´t even have electronic boost control or high boost at that time.
Ant is the man for Rotrex I think he fits them..this thread might be of interest.
http://www.e30zone.net/modules.php?name ... &start=100
.and if you want a how to I have the instructions from Rotrex
http://www.e30zone.net/modules.php?name ... &start=100
.and if you want a how to I have the instructions from Rotrex
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goosiegander
- Zonegoose
- Posts: 2544
- Joined: Sun Nov 19, 2006 11:00 pm
- Location: East Anglia
Next time dudeChris wrote:Yeah, but a turbo will never fit on my BTB he he.
Unfortunatly i'm flying away for a week on the 25th, otherwise i'd pop over to BBB in my nasty Jap daily and have a chat with Mr Gander.
Lets not forget that boost is only a measure of how restrictive the engine is to the inducted air.
What about a Whipple then? Twin screw.
All the joys of the roots but without quiet so many inherant inefficiences????
Chris
What about a Whipple then? Twin screw.
All the joys of the roots but without quiet so many inherant inefficiences????
Chris