Lotus Elan

Cosworth BDP Block Lotus 2.0L Twincam

PostPost by: knockoffnut » Fri Oct 14, 2016 7:47 pm

Hi All,
I am beginning to build a 2.0L alloy block Lotus twincam motor, based on a Cosworth BDP alloy block sleeved at 90mm, a 77.62 stroke crankshaft, and a ported Lotus twincam head with oversized valves. I know that there are a few people out there who have already done this in the past, and I am hoping to learn from their experience before I begin, to avoid making mistakes, as much as is possible. This engine is intended for fast road use, so torque, and smooth power in the normal road range is preferred over high end horsepower. I realize that a full BDA head is likely an easier option, but I also want the engine to look stock(ish) in the car. I plan to machine the block to accept a stock oil pickup, and to run a wetsump. I understand that I need to run an external oil line to the exhaust side oil gallery. I plan to modify the block with an inserted plate to run the stock Lotus waterpump. I know that there is a bit of a mismatch in the watercooling ports between the block and the head. My first question to those of you who know these things is; Should I be planning to enlarge or modify the cooling ports in the block to more closely match the Lotus Twincam setup? Are there other block modifications I need to perform to make this combination work well, all bearing in mind that I have no plans to race this engine, but I do want it to be as bulletproof as possible. All knowledge, comments and info gratefully accepted.
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PostPost by: john.p.clegg » Sat Oct 15, 2016 6:26 am

Looks like you're preparing it for some "spirited driving" Try to include a swinging pick-up or gated/baffled sump..

John :wink:
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PostPost by: nmauduit » Sat Oct 15, 2016 6:39 am

Hi,

that sounds like an interesting exercise, the stock look approach must appeal to a number of enthusiasts : please post photos of your progresses as you go (esp. water pump adaptation)...
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PostPost by: knockoffnut » Sat Oct 15, 2016 11:17 am

Hi John,
For my current 1600 motor, which runs forged pistons, L1 cams, 1.625/1.375 valves in a ported and polished head, polished rods and polished/nitrided crank, I build a fully baffled big sump oil pan which holds 7 liters. It worked out well but its a little heavy so this time I am hoping to build a similarly baffled smaller pan in alloy. I will try to post some pictures of the head and block and progress (as and when that happens).
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PostPost by: rgh0 » Sat Oct 15, 2016 9:36 pm

The starting point for designing an engine like this is to determine your usage and how much money you want to spend :shock:

For a road usage engine you want a short duration cam - higher lift and shorter than your current L1 cam which is probably 0.410 lift and 305 degrees seat to seat.

So as i say a lot on this forum, you need the highest lift you can get into a 280 to 290 degree seat to seat cam. This is around 0.420 to 0.440 depending on your cam supplier. If the porting, carbs and exhaust are all very good this will give you close to 200 hp at the 6500 rpm rev limit on the standard Ford crank with a very strong torque curve all the way. A new SAS or Dave Bean or McCoy converted head will give you a bit more than the best ported original head at additional cost. If you have additional money to spend then with steel crank and rods and forged pistons and a higher rev limit it will pull strongly to 8000 rpm and make a bit more power again above the cast iron crank 6500 rpm rev limit.

cheers
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PostPost by: knockoffnut » Sun Oct 16, 2016 11:46 am

Hi Rohan, Thanks for your info. I have read that 200 HP (and the torque available from a 2L) may be too much for a cast iron crank regardless of RPM, so I am looking for a used Steel 77.62 crank and rods. I expect to use new JE forged pistons. I already have a well ported head with very large valves so I plan to use that. It is ported for 45mm intake so I plan to run 45mm webers. I have also heard that longer cam durations work well with no downside on a 2.0L engine, as breathing restricts them at all times. Effectively the dispacement ensures that port flow velocity is always high enough that there are no flat spots. Do you have experience with a LTC head on BDP block Rohan? I am hoping to find someone with direct experience on this combination to check details on cooling ports and oil ports; what modifications are required and/or recommended to make it work well. As this block was never intended to go under this head I know there are extensive mods required, but I also know it has been done a few times already by other people so I am hoping to find folks with direct experience.
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PostPost by: promotor » Sun Oct 16, 2016 5:41 pm

Interesting project you've got going there!

My first thoughts with making the block suitable for wet sump is does the block have any/enough casting "meat" in it to be able to take the oil pickup pipe drilling, and is there also a provision in the casting to allow you to drill the hole needed to take the oil from the oil pump up into the main gallery. As the blocks look to be designed with the intention of only ever needing a simple face for a dry sump pump to be mounted then would the extra meat be even put into the casting?

I will be taking into my possession (only for a short while - I would like it to be permanent though!) a Novamotor 2litre F3 Twincam in the next week or so (although it's special iron block with plate mounted on the top to allow room for extra stroke so has some differences to the alloy block you will be using) which was reputed to be making 200 bhp so I'll be interested to see what cams that has in it! Not sure what info I will be able to divulge regarding spec though as the owner may wish to keep it private! What I do know though is that the ports aren't as big as I would expect (at least not at the very outside of them!) so there will likely be some other tricks in there to make it as special as it is!
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PostPost by: knockoffnut » Mon Oct 24, 2016 2:55 pm

Hi Promotor,
Thanks for the input. I believe that my BDP block has the meat required to machine it for a normal wetsump oil pump. (my info says that the earlier BDR etc blocks do not, but that the BDP was desigend to be more of a "universal" replacement) I will do some accurate measuring to check... My block is sleeved for 90mm bore, so there is no room between the sleeves for the horizontal cross oil passage. I am thinking I will run an external hardpipe around the back of the block to connect the oil pump on the right hand side to the oil gallery on the left hand side of the block. I had a look at Bill's block, and his has a new bung welded into the forward end of the RH side oil gallery so that the external fitting doesn't interfere with his TTR header. That was helpful information as I hadn't been focused on clearance to the header. I am awaiting a cometic 91mm head gasket to begin checking oil/water port allignment and relative sizes between the BDP block and the LTC head. The information I have been given so far indicated that no changes are required here, but I want to investigate further and may choose to do some matching to improve flow.
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PostPost by: promotor » Tue Nov 01, 2016 7:26 am

Sounds like the BDP block might just do the trick for you. Fingers crossed.

One thing that I've just thought of that will be applicable to your engine are the size of the water jacket holes in the head - the original ones will be too big (if unmodified) and will intrude into the fire ring of the head gasket at 91mm. The holes that foul will need to be welded up and drilled with a small hole, or drilled/machined to take a sleeve/bush type assembly to take the size down. I've seen brass ones put in which helps with stopping the feathering of corrosion around the holes like that which can be found on most aluminium heads. I'd prefer the brass insert as it looks tidy and doesn't require putting any unnecessary heat from welding into the head but it might not hold/not move against the fire ring so weld really should be the option to go for. All depends on what room etc you've got work with though.

The engine I've just stripped has an 86.5mm bore and is just on the limit of not needing smaller holes - the edges just touch the outer edge of the fire ring. That's something that has to be compromised on when running a big bore twincam engine.

Regarding how many holes and placement of them I can't make any suggestions as I've seen all sorts of combinations of holes on blocks working with twincams - original twincam blocks and early crossflow blocks have more holes than the late crossflow blocks but all have been used in twincams at some time or other with seemingly few issues. The engine I've just stripped is very custom and doesn't have the hole at the front of the block that drains down into the water pump aperture. That's possibly to help promote water flow towards the centre and back of the block.
Last edited by promotor on Wed Nov 09, 2016 7:16 am, edited 1 time in total.
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PostPost by: jono » Wed Nov 02, 2016 12:55 pm

...make sure you build it right :shock:
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PostPost by: theelanman » Wed Nov 02, 2016 2:04 pm

now that's what you call failure......

holy smoke Jono....who's was that?
talk about the bottom falling out of stuff.....

:shock:
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PostPost by: CBUEB1771 » Wed Nov 02, 2016 4:44 pm

jono wrote:...make sure you build it right :shock:


Now that is a proper mess. Seeing the rubber tube at the front I take it this was a BD series engine. Possibly the crankshaft torsional resonance failure common to 1600 stroke length crankshafts?
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PostPost by: jono » Wed Nov 02, 2016 5:26 pm

Croft circuit - a friends Modsports Elan, first time out.

Cause never established but very expensive :shock:
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PostPost by: rgh0 » Wed Nov 02, 2016 7:42 pm

Jjudging by the end of the broken crank it looks like a crack was present there and when the crack finally let go the rest of the block was torn apart.

Crack checking critical components is well worth the extra time !

cheers
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PostPost by: knockoffnut » Tue Nov 08, 2016 9:11 pm

Thanks for that info Promotor! Jono I bet folks heard that "BANG" miles away. My 2.0L will be built as an entirely spare engine, and is not intended to be raced so engine stresses and my stresses will both be lower.
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