Green Sally

[B33 ENN]

That's what I keep saying - go for maximum power. The risk with highly tuned NA engines is that they will get a narrow engine speed range - nothing much happens except at max RPM, so it might actually end up less drivable than a turbo. So, when tuning your NA engines, don't go overboard. Finding the right balance between power and drivability takes a lot of skill and experience.

<{POST_SNAPBACK}>

I thought I'd stick this in its own thread as it is the next project we have been working on after Black Betsy and Red Sonia. It's also the next project that is nearing completion after the successful debut of Red Sonia.

The Engine Guru is very experienced in tuning Lotus motors, and specifically more so in NA applications.

It was his idea to develop a 2.5ltr version of the NA 4 pot. Bibbo and I established some initial specs from the Guru which were reasonably cost friendly.

1. We have a race spec gas flowed head.

2. We have a increased stroke race developed crank.

3. Flowed downdraft carbed heads (EFI would be pretty costly to add)

4. Light weight H section steel rods, half the weight of standard ones.

5. New lightweight pistons.

6. Lightweight flywheel is being considered.

7. Tubular manifold has been aquired.

Thats the main stuff so far. Aside from this, the working parts would be balanced to high tolerance by professional balancing chaps.

Recently we have had the option to ammend and add other bits. We are really at the parts accumulation stage looking for what we can get for how much.

Personally, I'd supercharge it, but it depends on cost and complications.

With a carbed arrangement we will be limited in top power, but I'm assured the driveability will be the main focus and the real increase I'm looking for is the torque output.

Welcome ideas.

[scoule]

This sounds perfect as an upgrade for my Excel too ... it needs more torque but without the trouble of fitting a turbo. I'm already part way through fitting a mapped fuel injection / ignition system.

Any idea on prices of parts?

[B33 ENN]

I don't think you really want to know the answer to that...

But as soon as we collate our costs, I'll let you know.

[scoule]

You're probably right, but the car is already at 132k miles with no rebuild, so it's going to need some work at some point .. maybe in another 30k or so!

I was considering building up a spare engine over time - that way, you forget how much each bit costs! At least I have all the injection stuff already, although I expect I'd need larger injectors at the 2.5 ... I expect the 300cc ones will max out at around 60bhp per cylinder ...

How much are you gaining on stroke & bore?

[hovgaard]

Does that race spec head include upper range cams?

[B33 ENN]

You're probably right, but the car is already at 132k miles with no rebuild, so it's going to need some work at some point .. maybe in another 30k or so!

I was considering building up a spare engine over time - that way, you forget how much each bit costs!  At least I have all the injection stuff already, although I expect I'd need larger injectors at the 2.5 ... I expect the 300cc ones will max out at around 60bhp per cylinder ...

How much are you gaining on stroke & bore?

<{POST_SNAPBACK}>

If you've added an EFi system to the engine (which I assume it didn;t have originally) then you must have spent a fair bit already? That avenue was quoted at around 3k to me when considering all the electronics that would go with the hardware on the motor itself.

A good crank is around 1500 to fabricate IIRC. The new rods I think are under a grand but not too far shy of it, same with the pistons. Bibbo got the Manifold imported from some chap in the USA, since its already made, it was cheaper than a commissioning one from scratch.

Overall, I'm expecting a few grand more worth of expenditure and keeping it under control by trading in a few bits that we won't need. Also, the motor will need to be dynoed and tuned which has to add at least another 1k or so I'm assuming.

I have a pretty complete spare 2.0 ltr GT3 motor which I thought I should keep for spares. Any use to you?

When you say gains in stroke and bore, what do you mean?

[B33 ENN]

Does that race spec head include upper range cams?

<{POST_SNAPBACK}>

Haven't got as far as cams yet, still to come. Waiting to see what Guru suggests.

[scoule]

If you've added an EFi system to the engine (which I assume it didn;t have originally) then you must have spent a fair bit already?

<{POST_SNAPBACK}>

I think the injection parts came in under 2k, but this was a few years ago when I bought them and I'm still only part way through the fitting! It does run an ignition as a test, but this is a simple 2d curve at the moment because there is no throttle sensor on the carbs. Hopefully I'll find a couple of days without work, kids etc to get everything else hooked up!

When you say gains in stroke and bore, what do you mean?

<{POST_SNAPBACK}>

I was wondering if any part of the increased capacity was due to a larger bored size, or if it was "just" a stroked crank. With the standard bore, the stroke will increase from 76.2 to 87.6 to go from 2174 to 2500cc ... what does your engine guy think the effect of this will be on a reasonable max rpm of the engine? With the new pistons and lighter rods, will the standard 7250 rev limit be about right?

[hovgaard]

Increasing the stroke without reducing the redline, will increase the maximum piston speed. This can cause dramatic increases in liner wear, and should not be done unless one is prepared to rebuild the engine at regular intervals.

If ignored, this problem will lead to piston seizures, and conrods will become visible outside the block.

Piston speed, rather than reciprocating mass, should determine your redline.

[mchlrodrigues]

Increasing the stroke without reducing the redline, will increase the maximum piston speed. This can cause dramatic increases in liner wear, and should not be done unless one is prepared to rebuild the engine at regular intervals.

If ignored, this problem will lead to piston seizures, and conrods will become visible outside the block.

Piston speed, rather than reciprocating mass, should determine your redline.

<{POST_SNAPBACK}>

The 2.2's have a reasonably short stroke at 76.2mm. The 2.5L conversion increases that to around 88mm. I've seen built up Alfas rev to 7500 without a problem. The pistons/liners may have to be refreshened at 50K miles, but that may be OK for a car driven just on weekends.

[hovgaard]

I suppose it all depends on how you drive, and what your expectations are in terms of durability. It is the time you spend with a max piston speed above 25 m/s that counts. Already stock, the Esprit can reach about 30 m/s. Go further, and you should drive with discipline and only use max RPM on occasion, and you should be aware that the engine won't last forever. Particularly on an NA I suspect it might be difficult to keep the revs down.

[lotusmotors]

Have you considered the engine builder may be using longer rods that will keep the mean piston speed at acceptable levels? Add to that a lighter & stronger piston and rod and the whole rotating assembly will see reduced levels of stress.

An 86mm stroke is almost standard for most 2.0L 16v engines these days and mildly tuned "rally" versions will see 8000 rpm quite regularly. The Honda 2.2 VTEC has an 88 mm stroke and will do very high mileages as well as very high rpms. Lets not forget we are in the 21st century now and metalurgy and design principles have moved a long way since the early 70's when these engines debued: a little modern thinking applied to the internal components and there is no reason they will not be able to rev hard and be reliable.

That said the mid range punch of a long stroke big capacity motor; will make for easy cross contry driving: no turbo to spool up to wait for and no revvy VTEC sytem to manage.

Just my opinion....

I suppose it all depends on how you drive, and what your expectations are in terms of durability. It is the time you spend with a max piston speed above 25 m/s that counts. Already stock, the Esprit can reach about 30 m/s. Go further, and you should drive with discipline and only use max RPM on occasion, and you should be aware that the engine won't last forever. Particularly on an NA I suspect it might be difficult to keep the revs down.

<{POST_SNAPBACK}>

[hovgaard]

Have you considered the engine builder may be using longer rods that will keep the mean piston speed at acceptable levels?  Add to that a lighter & stronger piston and rod and the whole rotating assembly will see reduced levels of stress.

An 86mm stroke is almost standard for most 2.0L 16v engines these days and mildly tuned "rally" versions will see 8000 rpm quite regularly.  The Honda 2.2 VTEC has an 88 mm stroke and will do very high mileages as well as very high rpms.  Lets not forget we are in the 21st century now and metalurgy and design principles have moved a long way since the early 70's when these engines debued: a little modern thinking applied to the internal components and there is no reason they will not be able to rev hard and be reliable.

That said the mid range punch of a long stroke big capacity motor; will make for easy cross contry driving: no turbo to spool up to wait for and no revvy VTEC sytem to manage.

Just my opinion....

<{POST_SNAPBACK}>

The engine builder, that would be you...?

It's quite possible that metallurgy has moved on, only we don't know about it around here. The engines we make where I work are pretty much required to last forever, and we would never go beyond 25 m/s in piston speed during normal operation, because then it won't last forever anymore. It's quite possible that engines that exceed this speed limit don't wear out as fast as they used to, but they will wear, and it will get worse with higher speed. Another example to bring up would be the Judd V10 with 33 m/s and a 3000 race km rebuild interval that I assume to be the result of the high piston speed.

Rod length has only minor influence on piston speed, but I can imagine that the reduced side force on the piston that results from longer rods would help reduce wear a little bit. Can you fit longer stroke and longer rods within the same engine?

I have no doubt that a larger capacity engine will be a real pleasure to drive and that it will be reliable. My concern is only with the durability. I'm not saying don't do it, I just wanted the boys to know what the implications are, i.e. it will wear faster. How fast? I don't know. Is it a problem? Not for me to decide. I merely wanted to help them along to forming their own opinion on the matter.

[B33 ENN]

I was wondering if any part of the increased capacity was due to a larger bored size, or if it was "just" a stroked crank. With the standard bore, the stroke will increase from 76.2 to 87.6 to go from 2174 to 2500cc ... what does your engine guy think the effect of this will be on a reasonable max rpm of the engine?  With the new pistons and lighter rods, will the standard 7250 rev limit be about right?

<{POST_SNAPBACK}>

Engine Guru says we going for both increased stroke and larger bore pistons. He is quite confident of the slant four having more capacity than we normally expect. The proviso is that we use better quality internal components like bearings and so forth.

He has successfully made 2.2 turbo 910 motors go to 800bhp and pull 10,000 rpm. Ok these are extreme drag racing conversions, but he is confident we can get 500bhp+ four pots, especially at 2.5ltrs.

I'd say that rpm choice is something we haven't gone into detail with, we talked about it for the supercharged V8 (Black Betsy) last year, lets see what we get.

[B33 ENN]

I suppose it all depends on how you drive, and what your expectations are in terms of durability. It is the time you spend with a max piston speed above 25 m/s that counts. Already stock, the Esprit can reach about 30 m/s. Go further, and you should drive with discipline and only use max RPM on occasion, and you should be aware that the engine won't last forever. Particularly on an NA I suspect it might be difficult to keep the revs down.

<{POST_SNAPBACK}>

Well, Bibs usually doesn't drive below 7000 rpm... ever... at all... no exceptions... even when parking... ask my neighbours...

Could this be a problem?

I guess, once I get some info on the expected rpm range I can tell you more about what the durability expectations are.

I know when I drive, I am quite careful about bringing the load on the clutch and box in gradually rather than suddenly. That's because we all know our drivetrains are the weak link.

In an NA 300 bhp, gearbox issues wont be a problem because a) it's top power is within Lotus design tolerence, and B) it has no turbo, so no punchy impulsive loads on the clutch/box.

On my Red Sonia, this is my constant worry and am looking for measures to sort that. Also, though, I realise that below the waist, Red Sonia is stock Lotus crank/bearings/ rods etc - at the moment. This has worried me since Brian Angus commented that Lotus bargain basement component choices effect the durability when pushing the engine beyond the stock, because those bits wear out prematurely. If they go, the whole engine can go with them.

That's another reason I'd like to re-do the bottom end on Red Sonia.

ON Green Sally, the difference is we are changing all that for custom made parts at the very top quality available, including Honda size bearings rather than Lotus.

I'm interested to know what Guru will say about your comments here...

[Bibs]

"double aero-counterweighted plasma nitrided billet steel crank"

^ that is car sex

[lotusmotors]

The engine builder, that would be you...?

It's quite possible that metallurgy has moved on, only we don't know about it around here. The engines we make where I work are pretty much required to last forever, and we would never go beyond 25 m/s in piston speed during normal operation, because then it won't last forever anymore. It's quite possible that engines that exceed this speed limit don't wear out as fast as they used to, but they will wear, and it will get worse with higher speed. Another example to bring up would be the Judd V10 with 33 m/s and a 3000 race km rebuild interval that I assume to be the result of the high piston speed.

Rod length has only minor influence on piston speed, but I can imagine that the reduced side force on the piston that results from longer rods would help reduce wear a little bit. Can you fit longer stroke and longer rods within the same engine?

I have no doubt that a larger capacity engine will be a real pleasure to drive and that it will be reliable. My concern is only with the durability. I'm not saying don't do it, I just wanted the boys to know what the implications are, i.e. it will wear faster. How fast? I don't know. Is it a problem? Not for me to decide. I merely wanted to help them along to forming their own opinion on the matter.

<{POST_SNAPBACK}>

Your point about piston speed is valid; and there is nothing wrong with constructive criticism; but I think to compare Engine Developments V10; which began life as an F1 engine; then evolved into a sports prototype engine; with a "warmed up" road car engine is stretching the a point a little. That is like suggesting the EDL V10 can't do 3000km because a Top Fuel dragster has to be rebuilt after every 1/4 mile...

Regular rebuilds and "life-ing" of components in a race engine go with the teritory; the weak link that mandates the rebuid may vary from engine to engine; I would suggest in the case of the V10 it has more to do with the valve return system than the piston & liner. In general I think it is fair to say race engines are rebuilt regularly due to the percentage of time spent at wide open throttle; rather than simply mean piston speed.

If Nick is trying to make his dream a reality; then there are any number of engineers out there capable of giving him the advice he needs; personally I think it's better to applaud his enthusiasm and commitment than to play "devils advocate" with him. No offence intended; I just think we should give the guy a bit of credit.

Edited November 23, 2005 by lotusmotors

[hovgaard]

Those guys deserve all the credit they can get and more. I don't mean to be the advocate of anything in particular, what I want to do is to try to understand what it actually is they are trying to accomplish, and to offer what ever advice I can give to help them get there. If that means pointing out risks that may not be obvious to everyone, then so be it. And I'm not saying that any engine with a maximum piston speed of 33 m/s will only ever last 3000 km, naturally things like nicasil coatings and road driving with lower RPMs and load can stretch its life almost indefinitely. Again, it all comes down to how the engine is to be used and what the expectations are. I don't think I'm stretching the point; any engines, from the smallest motorcycles to the biggest supertankers, are designed with the same piston speed in mind, and they are equally at risk if they exceed the limit.

[lotusmotors]

So you don't think the quality of the components will have any impact upon the piston speed an engine can sustain? Why the suggestion for Ti rods then? Steel ones are cheaper, Cast iron ones are cheaper still...

AAARGH - look what's happened: now I'm playing devil's advocate! We could go round and round with this one; so I am going to bow out now.

I hear what you are saying; but.....

I don't think I'm stretching the point; any engines, from the smallest motorcycles to the biggest supertankers, are designed with the same piston speed in mind, and they are equally at risk if they exceed the limit.

<{POST_SNAPBACK}>

[hovgaard]

I don't mind going round and round like this!

My short answer to your question is 'no'. The titanium rods have no impact on the piston speed and cannot influence what happens between liner and rings, but they will reduce the need for counter balance on the crank, making for a more responsive engine and a less flexing crank, they will reduce the load on the crank bearings, they will reduce the power the engine expends making them reciprocate, and they will never fatigue.

[scoule]

I think this is all very healthy discussion ... keep it up, so I know exactly the spec I need for my Excel's next engine!

Does anyone care to comment whether my 45mm (Jenvey/Lumenition) throttle bodies will be restrictive on a 2.5 with around 250 bhp? I guess they are a lot better than the DHLA 45 carbs since there is no 37mm? choke in there .. but will they strangle the top end?

What kind of cams will be required feed the engine? Would a pair of 104's (SE inlet spec) be ok for mostly road use with a few track days?

[lotusmotors]

A 45 throttle body will flow around 185-200cfm (at 10" water) per butterfly; if you are staying with standard valves then the head will make at best 170cfm with a very good porting job (a stock head can be as low as 135 cfm). Plus 1mm valves will be neeeded to take you close to 180cfm and over that you will need plus 2mm valves; they will require new valve seat inserts, but even then heads flowing over 180cfm are few and far between. So 45 throttle bodies should be just fine for your 250hp target; and won't restrict the engine's performance. 104 cams may be just a little on the conservative side; I would put your 104 cam (currently in the inlet) in the exhaust and use something with around 0.450" lift and 285 duration on the inlet side - I can steer you in the right direction for that if need be. The exhaust valves on the 907/910/912 flow comparatively well; so a milder cam in there will not hurt power and usually helps keep the mid range torque up.

[B33 ENN]

I think this is all very healthy discussion ... keep it up, so I know exactly the spec I need for my Excel's next engine!

<{POST_SNAPBACK}>

I assume you have seen this Lotus Bits Engine Upgrade offer on LEW?

[MKE40]

I don't mind going round and round like this!

My short answer to your question is 'no'. The titanium rods have no impact on the piston speed and cannot influence what happens between liner and rings,

-----------------------------------

Explain please,.............

Titanium equals lighter /stronger, therefore centrifugal force of the "smaller " end of the rod is reduced and thereby reducing the load on the cyl. wall.

Cannot therefore, the pistons accept more revs/piston speed by virtue of oil film strength which must be where most breakdown starts ?

I am not accounting for crank reciprocationin this query or metal fatigue.

I remain ,

A thicko boatbuilder,

Just askin'

Mike

[hovgaard]

Titanium equals  lighter /stronger, therefore centrifugal force  of the "smaller " end of the rod is reduced and thereby reducing the load on the cyl. wall.

Cannot therefore, the pistons accept more revs/piston speed by virtue of  oil film strength which must be where most breakdown starts ?

<{POST_SNAPBACK}>

I think the effect would be marginal at best. The oil film begins to break up at 25 m/s, and there is not a lot that can be done about it. Below that speed, wear is negligible, provided the air and oil is clean. And a lighter rod would only have minor influence on the side force on the piston, that force stems mostly from the fact that the rod is at an angle to the direction in which the gas press down on the piston. When increasing the stroke, the rod usually becomes shorter, the angle greater, and the side force larger.

Lightweight components should be used to reduce the power used to make them go up and down, although some might also class that effect as minor. Lighter components do reduce the stress, thus the engine can attain a higher speed without breaking up instantly, while incurring wear. All very useful in racing, where the next rebuild is never far away. And titanium has the added bonus of being immune to fatigue.

Sustaining high speeds is another matter (sustaining here taken to mean clocking up many hours of high speed use, not necessarily all in one go). High piston speeds bring wear. There are medicines with which to postpone certain death (such as nicasil), but as far as I know there is nothing to bring immunity. A stock 4 pot Esprit is capable of reaching 30 m/s, but since the majority of driving is done on the road with much lower revs, wear seems to occur at an acceptable rate.

Increase the piston speed, and wear builds much quicker. Use the range above 6200 rpm often, and wear builds much quicker.

Can you increase the maximum piston speed? Can you increase the usage of the high speed regime? That depends on how long you want the engine to last.

What kind of boats do you make?

Edited November 29, 2005 by hovgaard