Esprit Turbo project car - part3 - the further continuation

[CHANGES]

Fabian you must do what you feel is right...  When you put forward the data as you do then you can make the figures produce the SCR you desire.     I can only point out what I see in you pics, plus what you have written , then base this on what  I have experience in ..  A standard combustion chamber is between 40- 42 cc depending on valves and details etc ,   I always use the 40 figure a reasonable guide .  So using your own logic that 8.0:1  SCR is your set up with a 1.2 gasket..    You now have a 1.651 gasket.  The difference in volume  between the two gaskets is 3.3 cc ...  Your combustion chamber  has reduced by at least 3.0 cc  based on your measurements of 37 cc .  So taking out 3 cc from the head  and adding in 3.3 cc from the gasket ,  This will put you SCR at back to 7.98:1..    This is just basic logic  nothing else . 

2 hours ago, Lotusfab said:

This is the figure to be expected from Daves estimate of skimming effects (0.25) and 0.5 drop due to a thicker gasket. Its also the same as the figure that was guesstimated by the expert.  So 8 - 0.5(gasket) + 0.25 (skim) = 7.75.1. 

The 0.25 figure i was referring to in my post was the deck height , not head skim ...  0.25 is only 0.0098'' 

  Looking at your pics I notice the head is skimmed to the inlet seats.   I have skimmed a head to just past that point which was 0.045''.  This gave me a head volume of 33cc and a final SCR of 8.5:1 on that build.  However that is all irrelevant.   I only mention it because the head volume is crucial ,  I just wondered, did you remember to subtract the extra volume caused by the valve recess voids in the pexiglass, when you made your measurement.  It all adds in to the final figure ..  If you did not then you can still get a basic measurement off your plexigless plate .. and recalculate..  Also did you remember to allow for the meniscus curve on your burette .  

2 hours ago, Lotusfab said:

Its also the same as the figure that was guesstimated by the expert. 

I'am not a fan of guesstimates,  which is why i have tried to go into detail so you can have the most accurate assessment of your engine SCR..   Only you have done the measurements and if you are confident with your chamber volume at 37 cc and have allowed factors mentioned then regardless of what the head was skimmed too we still come back to 8.0:1 ..   Personally I can not put any more input to this subject ,  if you still feel i am wrong with all this then disregard my comments .   As i said before putting it on a dyno when done will help match any anomaly and give you piece of mind..   good luck with the rest of the build ..   

     

[Lotusfab]

Yep, I think its a good idea to Dyno so will plan on doing that

[Lotusfab]

This will fly back together when the shimming is done. Trouble is you need a box of shims and some smaller ones when doing this from scratch.Its pretty easy when there is practically no wear and you have an accurate digital micrometer, oh and you have done it before! Enough said, this should be complete by the end of the week. I should have the output shafts done with new bearings and back on the gearbox. Then a simple matter of bolting all the bits on. Will be much quicker than before as all the parts are new or refurb, labelled and nothing is missing! So maybe two weeks at the worst and this car should be driving. Then is 110 percent effort on the ski racks. I have the lab test colour paint ready to go, so just the machanisms to build. Then I need to hire a test track for speed trials!

[Chillidoggy]

Why did you buy new cam followers, then buy another set of new ones? What was wrong with the original new set?

[Lotusfab]

Good question. The originals were adequate for our application.The Arrows ones are more expensive but lighter and I like  the quality.

[sailorbob]

How much do the Arrow cam followers weigh and what is their skirt length?

[Lotusfab]

Hi Derek, I weighed them all. The cast iron ones 56g, the stainless ones I had 47g the Arrows 35g. The skirt length on the arrows 24.3mm. The machining on the Arrows is much better - but they cost more. They are cheaper from Mike than elsewhere.

[sailorbob]

Thanks, a smidgen lighter and shorter than Garry Kemp's followers (48.5 +/- 0.5 grams and 25 mm).

[Lotusfab]

Saw a second S3 today with the Lotusbits upgraded 2.5 litre NA engine today pushing out some  245 BHP, thats 35 HP more than the Turbo! Awesome stuff. I’m a bit concerned though, if you ever come up against these S3 lads, theres a shock waiting for you under the bonnet! 

http://www.lotusbits.com/upgrades_engine.html

[andydclements]

Even more so than just the headline figure, because there's no turbo lag, so from a slow/standing start the NA really has the edge.

[Lotusfab]

Wastegate

I have been having a long think about this I want a totally reliable engine and am not interested in getting every last HP. The engine I have I believe can sustain full HC boost, but it will run slightly hotter due to differences in the cooling arrangement. The HC wastegate is set to 9.5 psi. The wetsump wastegate 8 psi. So in effect I am already limiting the final pressure. I have been told by told by two of the best authorities on this who have already built the spec its not necessary to change anything. I am sure they are correct. As I don’t need the extra power I am going to build a safety factor in and ensure the carbs are operating as they were designed by reducing the wastegate operating pressure to achieve the final pressure of a wet sump. I calculate this is about 6 psi. I have allowed for a SCR of 8.1, just in case Dave is correct and 7.7.1 is wrong.  I have a compressor and a variable pressure regulator. So when the wastegate comes back I will measure the opening pressure and reduce it to 6 psi. I believe these wastegates have a large tolerance, so I’ll investigate. I believe the best way to change the pressure is to change the spring. If the replacement spring is narrower I will have to machine rings to hold it in position. All theoretical at the moment until I get the wastegate back. With this reduced pressure the engine will be operating at a significant margin below Its maximum.

[Andyww]

10 hours ago, andydclements said:

Even more so than just the headline figure, because there's no turbo lag, so from a slow/standing start the NA really has the edge.

What is the downside though, why did Lotus not do this?

Reliability springs to mind but thats never been a great priority for Lotus and in fact the early Turbo engines were not that reliable, suffering from cracked manifolds, sticking wastegates which could potentially cause piston melt etc.

6 minutes ago, Lotusfab said:

The wetsump wastegate 8 psi.

I thought it stated 7.5 on the plate on the side?

[Lotusfab]

Maybe it starts to open at 7.5 PSI to achieve fully open at 8 psi? From what I have heard its very variable! I have had no conformation so will have to test it and will write down here what I find.

Harrys HC article is in Octane magazine. Theres much more info than in the video, all round excellent. Just annoyed he did it before I did having said about it a long time back!

[Lotusfab]

Shimming almost done just awaiting three final shims. I have got them all spot on, but in a fraction of the time it took before. Decent digital micrometer and a bit of practice makes all the difference, oh and a thin magnet to remove  the torx  Bolts from the cam towers before lifting the cam tower off between shim changes.
 Inlet manifold and carbs back on. The spacers on the carbs are suppose to be set at 1.5 to 2 mm. A 20 pence piece is about 1.7, ,so I used this to set the spacing Quick and spot on. .
All of the final parts should arrive tomorrow except my Wastegate which is up with Pete at PNM. Pete seems to be the premier Wastegate  expert in the UK and probably the world for the Esprit, not that he doesn't know just about everything else as well! 
Should be able to fit the cam towers and finsh the engine build Tomorrow if the shims arrive and work. Then its an oil pressure test. Data to follow. I hope to have this car running again within a week. But I’m not rushing, just taking my time and trying to get it the best standard I can.

[andydclements]

12 hours ago, Andyww said:

What is the downside though, why did Lotus not do this?

Reliability springs to mind but thats never been a great priority for Lotus and in fact the early Turbo engines were not that reliable, suffering from cracked manifolds, sticking wastegates which could potentially cause piston melt etc.

I'd say the most basic reason Lotus didn't do this was cost,  Back in the 80s the way to gas flow a head was to get a person with a hand grinder to use skill on each and every port of each and every head, now once the design has been determined it's a matter of replicating via CNC milling. It's not cheap now, but back then it would have been horrendous costs, so bolting on a turbo was relatively cheap. In some ways a tuned NA should be less problematic than a TE, less parts to go wrong.

My Europa Special had head work back in the 80s (before I owned it) , IRC it was about £9k then, and added...... an estimate of 5-10 HP.  

[snowrx]

Rumor has it that an extra aluminum spacer ring was fitted to some wastegates to extend the existing spring and reduce the opening pressure back in the cast piston days.  Easy to fabricate, and would be a reversible tweak in order to use your stock spring. 

 

[drdoom]

The reasons for pursuit of power via turbocharging were largely due to emissions considerations. The high peak cylinder pressures associated with high SCR conventionally tuned engines yield unacceptable levels of NOx in the exhaust whereas turbo boosted engines manage to increase power by way of breathing as if of larger displacement. Perhaps the low SCR turbo configuration pays dividends more so in the moderately loaded states typically the focus of emissions testing protocols as opposed to full boost.

One other big cost of the 2.5 spec engine would be the bespoke long stroke crank.

[Andyww]

Another factor is if Lotusbits are getting 245 hp this even further disproves any unfounded worries Lotus had at the time about block strength. 

The worry was the reason they went to dry-sump which must have been very expensive to tool-up for as its all bespoke. To enable a strong solid bottom casting rather than a ladder. It suggests they tried to rush through the turbo engine launch rather than fully test a wet-sump design before launch. Seems an odd decision.

Not forgetting of course that Bell & Colville designed the first Turbo Esprit engine!

[Lotusfab]

I think its quite an achievement by Lotus bits to get that much horsepower.

12 hours ago, snowrx said:

Rumor has it that an extra aluminum spacer ring was fitted to some wastegates to extend the existing spring and reduce the opening pressure back in the cast piston days.  Easy to fabricate, and would be a reversible tweak in order to use your stock spring. 

 

Thanks for posting this, I hadn’t seen that thread. A spacer ring might be a simpler solution.

[andydclements]

2 hours ago, Andyww said:

Another factor is if Lotusbits are getting 245 hp this even further disproves any unfounded worries Lotus had at the time about block strength. 

The worry was the reason they went to dry-sump which must have been very expensive to tool-up for as its all bespoke. To enable a strong solid bottom casting rather than a ladder. It suggests they tried to rush through the turbo engine launch rather than fully test a wet-sump design before launch. Seems an odd decision.

Not forgetting of course that Bell & Colville designed the first Turbo Esprit engine!

The block weakness was real, it twisted blocks. Those however were the old 907 engine blocks, the 912 blocks used for the Lotusbits engines were the reason dry sump was no longer needed to overcome the twisting problem.

[Lotusfab]

Output shafts

Tricky! Why, well getting 108 lb ft on the nut without the correct tool. I don’t have a fixed vice or welder, so I had to be creative. The original bearings were still in after 64000 miles. They were just about Ok so for the small cost now was the time to replace them. The new ones are a serious upgrade. Very very smooth.I have had five of these output shafts now and to honest all of the bearings needed replacing. I also replaced one of the seals. The originals are better than the replacements but if they are worn you have to replace them. I found the torque on both the nuts was wrong. As a professional gearbox place had this I’m not impressed! Still they are perfect now.

I cut slits in the end of the box wrench and used the little metal bar in the picture to tighten the bearing nut. It got to 72 lb ft no problem, once I thought of locking the body in the press, before that no chance! My tool worked really well considering. Another small step forwards. Shims didn’t arrive so a break to enjoy the sun till Monday!

[910Esprit]

Interesting. I've only had to replace one of those bearings in almost 35 years of running an Esprit!   Although as mentioned previously I've had several seals fail.   How much are you paying for the bearings (i.e. are they a standard size or Citroen unique expensive?)

[Lotusfab]

Hi Steve, I tried simply bearings but they couldn’t match the size. So got them from the usual source. They were about £80 each. The original bearings were running ok in my car but when I took the shafts off you could feel and hear they were past their best. These new ones are really so much smoother and will be very quiet.

[drdoom]

Whilst agreeing with comments regarding the 907 block stiffness limitations I'd also suggest that oiling reliability issues leading to big-end failures had been identified by the time of Turbo development, thus pointing to the costly drysump solution. The 911/912 sump redesign reflects attention directed toward a less costly path to reliability.

Regarding the 245 HP build, it would surely afford ample grunt with cracking response ( right in my wheelhouse! ) but 100 HP/litre is fairly unremarkable for a well-tuned street engine of modern design. No assurances offered on the bottom end durability of such a beast but likely tolerable if properly put together and maintained without undue usage at top revs. Probably better on S3 forward chassis, owing to mounting limitations of our earlier cars.

Cheers

[Lotusfab]

Well nearly back to where I was five months ago!