I want a low-output, high economy engine that can make big power if i stomp on it.Properly tuned, the car should as economical as stock. Maybe better with full time wide-band sensor.Matt wrote:Fantastic
Here's a random question - how do TCD kits affect fuel economy in off-boost situations? Assume Megasquirt engine management. I imagine economy would go up from the finer tunability of the standalone system as long as no boost was involved? Is it easy to stay out of the boost at ~80mph cruise?
I'm collecting ideas for what kind of E34 TCD car I want..
Maybe a conservative 350hp M30 E34 with a 2.93 axle or something for comfortable highway cruising but plenty of wake-up power as the occasion calls for
Motronic I believe has to run at 14.7 as it only has narrow band to reference.Matt wrote:Peter,
do the M30s do ok with a lean low-load cruise map? Does motronic run this way or would this be a potential advantage for standalone systems in terms of fuel economy?
I think in a theoretically perfect state of tune, cooling and lubrication, there will be no difference between how long an engine lasts naturally aspirated or at 20psi of boost.Soco wrote:so, with 17psi, how long do you expect this motor to last before something catastrophic fails? I'd like to force induce my motor, with about 199 on the clock, and i wanted to know how long the stock bottom end would deal with the abuse.
btw, those are some real nice numbers. you guys really do know your shit inside and out.
I agree that the state of tune, as long as it's within reasonable limits will have a minor effect on longevity.russc wrote:While a perfect state of tune is very desirable, your putting to much emphasis on its correlation to longevity. Yes, its' improtant, but the engine design is improtant also.
The reason a 20psi M30 engine does not last as long as a NA M30 engine at a reduced horsepower is because the cooling and lubrication systems break down. You are correct to say "engine design is improtant also" - the M30 engine design in not sufficient, without increased wear, to withstand the bearing and thermal loads that 20psi of boost put the engine under. But again, the REASON the engine does not last is because of cooling/lubrication break down. It should go without saying that by keeping a sufficient oil film between moving parts and controling thermal loads, wear will be minimized. If the lubrication and cooling system did their job perfectly, wear would not exist, or in other words, wear would amount to zero and there would be no difference in the life expectancy of a NA verses an engine running 20psi.russc wrote:A 20psi engine wont last as long as a NA engine. Your not going to get 250k from a 20psi M30. Your not going to get 150k either. I would say 100k or less.
RussC
How is that? The M88/S38 and M30 have the same bottom end and same oil pump. I say due to the more complex head that has much more oil lubricated surface area, the M30 will last longer.M635CSi wrote: Though some may not agree, I believe a correctly built M88/S38 engine will last longer per unit output of horsepower than an M30 engine. But that's another discussion...
You may be correct Duke, but I believe otherwise... and here's why: while the bottom end of the M30 and M88/S38 are essentially the same, they are not identical. The M88/S38 engine has a rod/stroke ratio which produces less side load on the piston skirt. This is part of the design of a higher speed engine which of coarse the M88/S38 engine is. Also, while the M88/S38 engine *may* have more lubricated surfaces (I'm not sure) the M88/S38 cylinder head is a superior design with increased cooling capabilities to remove the heat of combustion. The lateral and thermal load on the intake and exhaust valves, I believe will be less. The M88/S38 engine also has a water pump designed for higher speed, or so I've been told but that may just be a bearing design. So those are the basic reasons why I believe the M88/S38 engine will last longer than an M30 engine for a given horsepower.Duke M535ti wrote:How is that? The M88/S38 and M30 have the same bottom end and same oil pump. I say due to the more complex head that has much more oil lubricated surface area, the M30 will last longer.M635CSi wrote: Though some may not agree, I believe a correctly built M88/S38 engine will last longer per unit output of horsepower than an M30 engine. But that's another discussion...
I chose the phrase "last longer" rather than "wear out" to indicate my belief the M30 will expire, grenade, blow up or come apart before the M88/S38 engine for a given load. In other words, put both engines on a dyno and turn up the boost...The horsepower at which the M30 engine fails will be less than the horsepower at which the M88/S38 engine fails. Or in other words, for a given high load, the M30 will fail sooner. While a hole in the piston, broken rings, snapped connecting rods or a blown head gasket may not meet the definition of to "wear out", I think you would agree the engine has still reached the end of its service life. And because of the inability to sufficiently cool and lubricate the M30/M88/S38 engine under those loads, the end of its service life at maximum horsepower will come long before someone is able to "wear it out" IMHO... So, the take away here is if someone wants to make a lot of horsepower (600-800) from an 80’s era BMW 6 cylinder engine, the M30 can do it, but the M88/S38 is probably the better choice… boring or not…T_C_D wrote:I challenge anyone to build a new motor and actually wear it out. That isn't going to happen. Nobody will actually drive their car and/or own it long enough to actually find out. Arguments like this are boring.
????? When you say "given load" you mean the same HP or Torque right? Your “in other words” statement contradicts the statement before it.M635CSi wrote:
In other words, put both engines on a dyno and turn up the boost...The horsepower at which the M30 engine fails will be less than the horsepower at which the M88/S38 engine fails. Or in other words, for a given high load, the M30 will fail sooner.
Given the same horsepower or torque demand, yes.Duke M535ti wrote:????? When you say "given load" you mean the same HP or Torque right? Your “in other words” statement contradicts the statement before it.M635CSi wrote:
In other words, put both engines on a dyno and turn up the boost...The horsepower at which the M30 engine fails will be less than the horsepower at which the M88/S38 engine fails. Or in other words, for a given high load, the M30 will fail sooner.
Of course the M30 will fail at a less HP level than the S38/M88. The S38/M88 will make more HP at any boost level due to the much better flowing cylinder head. However, the M88/S38 will fail much sooner due to the delicate and over taxed timing chain and associated guides. You also have 2X the moving valves and associated parts that can fail too. That is a 200% more chance of those components failing than a M30.
The M30 is a much better choice.
200% is meaningless, I have never heard of a broken rocker arm on an S38/M88. The S38/M88 is not delicate, it is just designed for higher rpm use than the M30, an inherently more stressful task. Sure, an S38/M88 valvetrain needs to be rebuilt more often than an M30, but that does not make it fragile.the M88/S38 will fail much sooner due to the delicate and over taxed timing chain and associated guides. You also have 2X the moving valves and associated parts that can fail too. That is a 200% more chance of those components failing than a M30.
That's a tidy bit of information Russ but it has no bearing on the discussion and is, at least somewhat, unqualified. If we adjust for the M88/S38 final drive (3.91) gearing, the M88/S38 has to go about 180,000 miles to "last as long" as an M30 with 3.25 final drive gearing that goes 216,000 miles. In fact, because of the higher RPM, if road/driving loads were equal, the M88/S38 that goes 180,000 miles withstands more stress than an M30 engine that goes 216,000 miles. Your statement "This would be the same whether theres (sic) a turbo or not" is similarly unqualified and does not withstand scrutiny. It is not correct to say an engine produces 180 hp and lasts 100,000 miles so at 360 hp it lasts 50,000 miles. Quite often, it may last 20,000 miles. As an engineer you know wear does not increase in a linear fashion with stress and fatigue. Triple the stress and it may well result in a part failing instantly. The point here is that it is not possible to make a blanket statement that installing a turbo on an M30 and M88/S38 will result in similar wear patterns to their NA counterparts. But the current discussion and question is which would last longer, an M30 or an M88/S38 under the same extreme load. For example, if called to produce 800 horsepower, would an M30 engine last as long as an M88/S38 engine that was called to produce 800 horsepower? It’s been my position that the M88/S38 engine will withstand the call better than an M30 engine for reasons already set forth.russc wrote:It seems well known to me that the S38s don't last as long as a M30 for mostly one reason, RPM. The S38 runs at higher RPM, so it dosen't last as long. Most get rebuild before 200k, were M30 almost always go past that with the same maintenance level. This would be the same whether theres a turbo or not.
RussC
Yes, I agree. Would it last longer at that HP/Boost level? No one knows.M635CSi wrote:Due to its better volumetric efficiency, the M88/S38 engine would be running at lower RPM and or boost than the M30 engine to achieve the same work output
It is possible to extrapolate knowledge from what we know to what we don’t know. To this end, we know the M88/S38 is essentially equal in longevity on a true basis with the M30 while operating under increased stress/load. You agree the M88/S38 would be running at less stress (RPM/boost) than an M30 to achieve the same specific output. There is no reason to believe increasing the stress on an M30 engine will increase its longevity. In fact, all the evidence supports the conclusion that increasing stress on an engine reduces its longevity. Given this information, I know of no reason to believe an M88/S38 engine able to withstand greater stress but operating under a lesser stress would somehow fail before the M30 engine operating under the greater load.Duke M535ti wrote:Yes, I agree. Would it last longer at that HP/Boost level? No one knows.M635CSi wrote:Due to its better volumetric efficiency, the M88/S38 engine would be running at lower RPM and or boost than the M30 engine to achieve the same work output
Yep, the M30 wins big over the M88/S38 on price.Duke M535ti wrote:From an economic stand point, the M30/M106 with its MUCH lower parts costs is ahead. Then there is maintenance, example - special tools and valve "plate" replacement X24 to adjust vs. a wrench and coat hanger. Then weight, the M30/M106 is lighter (53 lbs) and smaller (head).
The M30/M106 wins X3.
I do not agree........how many S38/M88 run past 100K miles without a timing chain and guide change? How many have run to 200K miles without malfunctioning.........not many if any. Just ask RichM635CSi wrote: To this end, we know the M88/S38 is essentially equal in longevity on a true basis with the M30 while operating under increased stress/load.
