Removal and rebuilding of a Twincam

[rgh0]

Mahle OC21 is one of the shortest filters I've seen - you might want to check them out while looking into other filters.

Thanks for all the suggestions. I have ordered some of the Mahle OC21 from Amazon UK - cheap and free shipment if I ordered 4 ! and 6 to 10 days delivery. I will start and test run the engine with the current filter and swap in the Mahle one before my first race in March (Covid permitting). My stock of larger Ryco Z62 will last me a while on my Plus2.

The smaller filter certainly not an issue on a race engine given the frequent changes and limited miles done between them.

cheers
Rohan

[promotor]

Mahle OC21 is one of the shortest filters I've seen - you might want to check them out while looking into other filters.

Thanks for all the suggestions. I have ordered some of the Mahle OC21 from Amazon UK - cheap and free shipment if I ordered 4 ! and 6 to 10 days delivery. I will start and test run the engine with the current filter and swap in the Mahle one before my first race in March (Covid permitting). My stock of larger Ryco Z62 will last me a while on my Plus2.

The smaller filter certainly not an issue on a race engine given the frequent changes and limited miles done between them.

cheers
Rohan

Cheers for the update. They certainly don't break the bank like some brands out there, which is unusual for a big brand such as Mahle!

[rgh0]

Almost done

Topped up the engine oil and filled the gear box. The installed and static timed the dizzy.
With the plugs out I cranked then engine. It all sounded good and I got oil pressure after about 20 seconds.

Then fitted radiator

Filled radiator, fitted breather and ignition coil and the engine is complete

Fitted exhaust and engine was ready to start

Ignition on, electric pump filled the carbs, 3 pumps of the accelerator, turn the key, and it started and ran in 5 seconds of cranking
A quick check to ensure no leaks and listening for any bad noises ( there were none) then adjusted the carb balance while it warmed up.


Now to refit the front roll bar. With the suspension on full droop fitting the 22mm front bar is a challenge. I use a ratchet strap to pull the arms of the roll bar in a few mm to get it over the shock mounting pins whose track is less on full droop. Then I use a jack to compress the mounting pin rubbers so I can get the nut on.

Chassis cross brace and wheels fitted and I am done.

Off the hoist and its off on the test drive. Running perfectly and the new gearbox with the Quaiffe helical gears is no more noisy than a standard box. Only one fault, I pulled on the headlights to test the vacuum system and the RH light only came up half way. A quick inspection showed the inner pivot bobbin had shear off the fibreglass flange that supports it. Oh well a bit of fibre glass work next week.


I will test drive a couple more times to bed in the new cam followers and run in the new gears, then check the head bolt torque and change the oil in the gearbox and engine ( with the new smaller OC21 Mahle filters I should have soon) and the car will be ready for its next track day.

A long build and finally done. Finished the day by preparing to put my spare race engine on the stand to start a new project .... reducing the compression on this engine from 13.5:1 to 11:1 for use on pump unleaded.

cheers
Rohan

[alan.barker]

Looks like a wide Triumph Rad you are using in your Baby Elan that "Floats like a Butterfly and stings like a Bee"
Alan

[rgh0]

Looks like a wide Triumph Rad you are using in your Baby Elan that "Floats like a Butterfly and stings like a Bee"
Alan

Yes, I had the standard radiator modified like Lotus did to move the filler to the side and to turn the top outlet around. Lotus used a slightly different profile top tank from the Spitfire one I sourced. I don't know if Lotus had a different one made for easier fitment of the cap on the RH side or if there were various Spitfire tank versions.

cheers
Rohan

[USA64]

Rohan
First thank you for the rebuild post. I feel much better now about the money I spent having someone else rebuild my engine. I have a radiator like yours and was wondering about cooling. I see you have two small fans unshrouded and assume they are adequate. Have you made any modifications to the engine bay to facilitate the airflow out? The vent holes Lotus put in the fenders suggest is was a problem.

[rgh0]

Rohan
First thank you for the rebuild post. I feel much better now about the money I spent having someone else rebuild my engine. I have a radiator like yours and was wondering about cooling. I see you have two small fans unshrouded and assume they are adequate. Have you made any modifications to the engine bay to facilitate the airflow out? The vent holes Lotus put in the fenders suggest is was a problem.

The fans are shrouded and blow through the radiator well. Absolutely no problem with the larger radiator ( with a three row core and the two fans.

I ran with the narrow S4 radiator ( with a 3 row core) for many many years and a similar single fan. That was fine in all situations except when coming off the track after a race on 40C days when the temperatures would creep up a little on the slower drive back to the paddock. On the road absolutely no problem. When the narrow radiator needed some work a few years ago due to a split soldered seam, I bit the bullet and got the wider radiator set up so I could just do a quick swap over.

I have some holes in the body that I cut to enable the upper front suspension arms to be easily removed and would have a similar open area to the holes that Lotus added in later cars. I don't think these holes do much for aiding engine cooling as plenty of room for the hot air from the radiator to flow down and out under the car but may assist with cooling of the generator / alternator. I have never measured it but I suspect cool air may in fact flow in these holes to the vicinity of the generator / alternator air intake at their rear rather than hot air flow out from the radiator into the wheel arch ?

cheers
Rohan

[Andy8421]

Rohan,

Just been looking back through the pictures. No sign of air trunking or air filters.

What's the plan?

Andy.

[baileyman]

... I have never measured it but I suspect cool air may in fact flow in these holes to the vicinity of the generator / alternator air intake at their rear rather than hot air flow out from the radiator into the wheel arch ?

cheers
Rohan

I, too, so suspect. It would be fun to put some tufts there and a go-pro camera to see for sure. Meanwhile, the Le Mans prototypes have huge vents at the top of their wheel wells to let the air out.

[h20hamelan]

Rohan,

Just been looking back through the pictures. No sign of air trunking or air filters.

What's the plan?

Andy.

If you look 3 or so posts above by Rohan, with the nice plaid picnic blanket. You can see red foam over the trumpets?

[Andy8421]

Rohan,

Just been looking back through the pictures. No sign of air trunking or air filters.

What's the plan?

Andy.

If you look 3 or so posts above by Rohan, with the nice plaid picnic blanket. You can see red foam over the trumpets?

Good grief. These things?

https://www.uniflow.com.au/contents/en-us/p1653.html

I thought they might have been some old socks to stop something falling into the air intake while Rohan fitted the engine. I having nothing but admiration for Rohan's engine build, lets hope the next installment has him fitting a proper intake system.

[rgh0]

Responding to comments on my air filter choice ....though I am not sure about the seriousness of the questions ..... always hard on email , easier in the pub

You have a range of choices around intake air when building a developed engine. My assessment of these choices based on lap times and dyno results and user experience are as follows:

1. Standard inlet air box with standard or other style filter .... my dyno tests show the standard box cost you power of about 5 hp in a 150+ hp engine but the standard versus fancy filters on the end of a stand box makes no difference at least up to around 170 hp, have not tried it with 180+ hp engines

2. Bigger air box regardless of filter or open end into nose to pick up cold air .. works better as provides better flow to rear cylinders . Worth 5 HP in a 150+ HP engine and reverses loss seen in 1.

3. Open trumpets .... same as bigger air box appears, no advantage to cold air pickup versus just let the air flow past the radiator to the trumpets where the cold air duct would run

4. Open trumpets with sock foam filters - same as bigger air box.. but less risk of nuts and bolts getting in and less dust and wear. socks same as open trumpets in terms of power

In the end for my purposes I have chosen option 4. This makes access on a race day easy to items below the carbs and appears to have no power loss issues while protecting the engine compared to the big air box approach

Just my logic ... no criticism intended and others may differ in opinions but I have done the dyno and lap time tests to gather the data.... have others more data to bring always happy to listen and learn from people who have done it ????

cheers
Rohan

[Evante]

Rohan,

Any thoughts about how ITG or Piper foam filters would affect performance? They are made of the same stuff as socks.

JAS

[Andy8421]

Rohan,

That's a helpful reply. Just a few comments:

- With the standard design of inlet system, you are picking up cold air from the highest pressure part of the car, where the inrush air through the grill stalls against the radiator.

- By having a large gap down one side of the rad, you are allowing air to bypass the rad, potentially lowering its cooling ability.

- A twink in racing trim at WOT produces a lot of standoff - which will soak into your filters creating a fire hazard.

You clearly have found a solution that works for you, but it would be interesting to compare the performance of the engine in race conditions with the two approaches - Mr Chapman's original (plus a larger airbox) vs. the trumpet mounted filters. I am not sure that a dyno test with a static car fully captures all the differences between the two approaches. When you mention lap times, did you try to compare the two approaches?

When I still raced, all the cars I looked at (and I may have missed a few) in the HSCC roadsports series were running standard design of airbox / filter - although the filter can was usually substituted for a K&N or Pipercross cone replacement. This may have been a series requirement to be fair - I can't remember to be honest.

Andy.

[vstibbard]

Rohan,

From the dyno testing I've done on 105 Alfa i raced in Sb the 26R and S1 Elan Group M car that I completed a few years ago, what noted on dyno is a drop off in power when the air is sourced after the radiator, or drawing air from alongside/through radiator, less of issue on days in low to high 20 deg's, the power drop off was especially noticeable on hot 30+ deg days.

When back to back tested ITG (single element for both carbs, and large airbox with trunking and quality filter in front of the radiator and routed the hose to airbox through a blanking panel either side of radiator, this stopped air passing other then via radiator the power drop off showed minimal variation run to run.

The last test was ITG filter with trunking feeding air from nose, using blanking panels and it closely mimicked the top number we achieved with airbox albeit with slightly different torque and power curves.

Another interesting fact we found was, if idle down and stopped for a reasonable period after dyno runs in the hot conditions, the heat sink to the Webers was enough to affect the next power run, if it was not allowed to idle/operate at part throttle cruising speed for a few minutes prior to power runs. We put this down to fuel temps, as I had used steel lines to run front to back then steel braided lines to Webers. I also added fire guard tubing over the flexible fuel lines and steel lines exposed in the engine bay/gearbox area to limit heat sink.