Converting a Zenith/Stromberg Head to a Twin 40 DCOE Head

[4129R]

So a gradual taper from 45mm down to about 34mm from the flange where the DCOE bolts on to the manifold to the valve seat.

As the manifold is accessible from both ends, and as the ports in the head are now much shorter, that should be easier than normal to achieve.

Alex in Norfolk.

[BDA]

For the little I know, I think your logic is pretty good. I know that there are more choices for weber chokes than you mentioned and a weber throat is not completely open as there is an auxiliary venturi but for round numbers I guess you can ignore it. However as Alex and John have said, porting heads and intake runners is something for the experienced.

If this is an experimental project to expand your knowledge or just have fun at or it is something you might try to market (if it works out), I'd say, go for it. Otherwise, it sounds like you're getting to a cost level that is a significant portion of one that you can assume is right off the self and you haven't factored a development effort. That being the case, the "off the shelf" option would make more sense from a financial point of view.

But then when we're talking about your motivation, I'm probably not telling you anything you haven't already thought about.

[buzzer]

Question, why 45DCOEs not 40DCOE. If you are going for 150 bhp or less 40s are fine and will perform better lower down the rev range.

Dave

[4129R]

Question, why 45DCOEs not 40DCOE. If you are going for 150 bhp or less 40s are fine and will perform better lower down the rev range.

Dave

Max possible choke for a 40DCOE is 36mm. I have 38mm chokes in my 145BHP engine as suppied by Quorn who did all the head work.

45DCOEs have "future tuning" possibility, 40DCOEs are limited.

[buzzer]

45's verses 40's always an interesting discussion. Richard Winter says he gets 150 with 40's and 32mm chokes and a very tractable motor. I have 40's with 34mm chokes, the largest size chokes for historic racing production class. I think 40's will get you to up to 170ish on bhp but the limitations are the head gas flow work, and the use of steel crank etc.
I question how tractable 45's would be low down, compared to 40's. run ok but not the best.

On inlet manifolds have you looked at off the shelf one's and converting? the crossflow manifolds for twin side drafts may be worth a look at with an adaptor plate and save a lot of grief. I suspect close but not Carling!  I think the stromberg head port direction will be offset too much but would be easy to measure up to check

Dave

[EuropaTC]

45's verses 40's always an interesting discussion. Richard Winter says he gets 150 with 40's and 32mm chokes and a very tractable motor. I have 40's with 34mm chokes, the largest size chokes for historic racing production class. I think 40's will get you to up to 170ish on bhp but the limitations are the head gas flow work, and the use of steel crank etc.
I question how tractable 45's would be low down, compared to 40's. run ok but not the best.

Interesting comment there from Richard Winter, it ties up with my (hazy) knowledge on the topic. I have the old "Tuning Twin Cams" book by Dave Vizard and his comments were that it wasn't worth changing from DCOE40's until you were north of 155bhp. 

I think you're right on the low speed running aspect with 45's, I could imagine the air velocity being significantly lower through a 36mm choke than a 33mm one and maybe not getting as good atomisation. Perhaps that's how Richard gets his 150bhp and tractability, by retaining the smallest choke practical for the top end power ?

SidedraftCentral on Yahoo groups is the place to go for weber tuning, the guys there lose me very easily !

[4129R]

I have both 40s and 45s, so I will try both to see which gives better low down tractability, and if this affects top end power 5500-6500.

I can see the argument for both scenarios, which is similar to the 8 valve versus 16 valve head argument.

Specialist milling shop was useless, so the hunt for a 160mm long end on cutter continues.

I bought a 6ft length of 3/8" x 4" ally to make the carb end of the manifolds. Cost £40 and it should make 5 ends. So cost of ally for 1 manifold is likely to be in the region of £25 + welding + gas flowing. Just bought a pair of 40 DCOEs for £250 which will need cleaning and jetting, so costs look like around £350 plus the machining time/cost for head adaption.

Alex in Norfolk. 

[EuropaTC]

Not wishing to drift too far off topic, by coincidence Kieth Franke has just posted a message on Sidedraft Central about getting 181bhp from an Elan TC engine with DCOE40's at 7000rpm. It's not a 1558 engine but 1700cc and with a later head, but the principle illustrates just how much you can get through a dcoe40. I suspect this has Kieth's own design of jets, which do seem to be an improvement on OEM Weber parts.

Back on topic, I see there are hiccups on the machining front. The chances of me being able to suggest a way forward are minimal but I'd like to see a photo of where you are and what the issue is when you've got a moment ?

Brian

[andy harwood]

Alex -
concerning the cutter chattering and coming loose in the chuck - have you tried using a collet? some wd40/lube on the cutter may help with the buildup.

[4129R]

I have bought a different chuck which takes up to 16mm diameter cutters. It has collets to grip the shaft of the cutter, rather than the 3 moving thingies on a standard drill chuck tightened with the gear key thingy.

Tomorrow morning, Cromwell Tools will have a 150mm long end cutting mill bit at their Norwich branch for me, which has a 16mm shaft. So by the time I get home, progress on milling starts around midday.

Meanwhile a replacement MGB fuel gauge sender for about £20 has arrived but the arm is too short. Otherwise identical, so I have to try to get the longer arm off the old sender, and put it on the new sender. 1/2" UNF bolts have arrived to plug the drain holes in the tanks, so I can continue restoring a pair of rusty tanks, full of sh1t. I think chipmunks have been nesting in the left tank. Luckily, access with the gauge sender removed is much easier.

Photos of progress this weekend to follow.

Alex in Norfolk (about a 90 minute drive from Brian in Lincs !).

P.S. Changing the arm on the fuel tank sensor is very easy. Bend 3 retaining tabs up, remove cover and spring, remove float from arm, change arms, replace spring, replace cover, bend back 3 tabs, replace float in shepherds crook on end of arm, job done.

[4129R]

Here are the progressing photos of milling #3 & 4 inlet ports to get a large flat plate to bolt a flange to.

Two holes appeared. I was a little concerned that I had cut into the waterways. The last photo shows the holes from the other side. Easily welded or plugged up from either side.

Next task, make up 4 x head to manifold plates based on standard gaskets in the head gasket set. Then make up the one piece manifold to 40 DCOE plate from 4" x 3/8" ally plate.

Alex in Norfolk.

[4129R]

I have started making up the manifold plates/flanges, to see fixings to the head, using a standard gasket.

1 & 2 cylinders were fairly straight forward, using a 60 degree slant on the studs.

3 & 4 cylinders were more difficult. A 60 degree hole struck the hole where the valve spring goes, so I am drilling 90/270, rather than 60/240. I have hit a waterway, but there is sufficient metal to tap a thread with 6 turns +.

Cutting the 32 and 40mm holes for the flanges is proving a challenge. I have found a decent type of cutter, and with 10mm ally plate, you have to cut from both sides, as the cutting blades quickly fill up with cut swarf.

I have ground the end off a tap to make the 5/16th UNC threads in blind holes. I am assuming 6 complete turns is enough stud in the head.

Next, I continue making the flanges, and make the stud holes flat. I will have to mill and pack with a washer to get the surface of the stud hole in the same plane as the inlet port.

The Weber flange I am copying from a manifold I cut up, placed on a 10mm ally plate, sprayed with black paint, and now I am cutting the black bits to get the right shape.

Alex in Norfolk.

[BDA]

You're making great progress! Congratulations!

Six turns of a screw should get you most of the possible strength of the joint. A thread insert like a helicoil or timesert would be better.

I'm not a machinist and I they may not work in your situation and it may not help since you've already ground a tap, but they make bottom taps to get threads at the bottom of a hole - basically what you made yourself.

This is getting exciting!

[4129R]

I think the 90/270 studs on 1 & 2 may not offer enough support to the Webers vibrating, so I will make the flange for the 90/270 lower below the port so that it will stop vibration snapping off the weld or straining the studs too much. This would also need a bigger gasket.

I will explore drilling and tapping a hole at 180.

The 60/240 studs do offer greater stability for up and down vibration on the studs.

Alex in Norfolk.

[EuropaTC]

Cutting the 32 and 40mm holes for the flanges is proving a challenge. I have found a decent type of cutter, and with 10mm ally plate, you have to cut from both sides, as the cutting blades quickly fill up with cut swarf.

If you are using a hole cutter in a drill to make these holes, then it's similar to what I was doing recently with steel. I picked a tip up from Youtube to prevent swarf build up. What you do is start off the hole and then drill another hole, say 9mm or so, at the edge of the circumference. That broke up the circle and although not perfect for me it did slow down the swarf build up.

https://www.youtube.com/watch?v=jTj8JVWDV6Q