Modern-day Miura

[Joel Heinke]

Alternator Mounting

So after figuring out a decent serpentine belt routing, it was time to fabricate alternator mounts. There are only M8 sized bolts on the engine top front, which aren’t all that big, so I had to figure out a mount that would include some bracing to spread the weight out between the few bolts located there. As a reminder, the alternator is being mounted with the pulley facing the engine as there isn’t room to mount it in a standard manner. Here’s what I came up with.

3/8” thick aluminum plates anchor to the engine with long mounts going out to alternator. The alternator only has two mounting lugs so triangulation is definitely required. An idler pulley mount on left side of engine provided a good downward triangulation point.

I had to use McMaster-Carr to source the long bolts used throughout this alternator mount. With the triangulation in place, the alternator is very solid showing no movement when I press on it.

 

[Chris Kouba]

I was just able to find a Dayco dimensional reference catalog online and it does look like they make this idler pulley in 59mm OD where what I have is 76mm OD. It's plastic instead of metal but that's not a show stopper. So I think the smaller pulley will give more clearance and resolve the rubbing part of the issue.

Joel,

Sometimes it takes someone to say something because you might be overlooking the obvious, so please forgive Captain Obvious here...

Given the skills you have displayed already, have you thought of turning your own idler pulley and swapping it onto the tensioner? That's got to be an option for you, no? Do you have a lathe, or a friend with one? If not, send me the tensioner and the OD of the pulley you need and I'll turn you one if you want.

 

[Howard Jones]

I've had quite a fight with alternators on my track SLC. I have used three different types with the second being the one you have in the pictures. The problem with it was the case broke. The large 2-inch wide tab with the bolt hole through it completely came off the larger case casting. I believe that the cause was a very rigid lower mount and a double rod end/ tubing adjusting link. The link allowed the main casting fore and aft movement and to flex, ultimately failing.

I am now using a solid 1/4 thick adjusting link with a slot. It is very rigid and I am also using the newest iteration of the standard gm alternator that looks to have a more robust case.

The first one just shook all the pieces apart internally and burnt up. I'm pretty sure its the curbs at the track that is imparting all the shock loading into the alternators as well as turning them at too high a speed. I have since changed the pullies to achieve a much slower alternator shaft speed as well.

 

[Joel Heinke]

Joel,

Sometimes it takes someone to say something because you might be overlooking the obvious, so please forgive Captain Obvious here...

Given the skills you have displayed already, have you thought of turning your own idler pulley and swapping it onto the tensioner? That's got to be an option for you, no? Do you have a lathe, or a friend with one? If not, send me the tensioner and the OD of the pulley you need and I'll turn you one if you want.

Chris: thanks for the offer. I do have a lathe and good enough knowledge on how to use it. If the belt contact surface for the idler pulley in question was just flat, I'd have made one already. The belt surface on this pulley is 6 grove along with flanged shoulders. I could probably make one if I had to but it would take a bunch of time and probably a scrap piece or two. I've now got the smaller OD replacement pulley (in plastic) and hopefully it works fine. If not, well then it just might be time to advance my machining experience by making one.

 

[Joel Heinke]

I've had quite a fight with alternators on my track SLC. I have used three different types with the second being the one you have in the pictures. The problem with it was the case broke. The large 2-inch wide tab with the bolt hole through it completely came off the larger case casting. I believe that the cause was a very rigid lower mount and a double rod end/ tubing adjusting link. The link allowed the main casting for and aft movement and to flex, ultimately failing.

I am now using a solid 1/4 thick adjusting link with a slot. It is very rigid and I am also using the newest interaction of the standard gm alternator that looks to have a more robust case.

The first one just shook all the pieces apart internally and burnt up. I'm pretty sure its the curbs at the track that is imparting all the shock loading into the alternators as well as turning them at too high a speed. I have since changed the pullies to achieve a much slower alternator shaft speed as well.

Yeah, hopefully this alternator is good enough for the mounting I've put together. I'd feel more comfortable if the alternator case had provision for a 3rd bolt for mounting. Everything feels nice and solid though, so hopefully it can hold up ok for this application.

 

[Joel Heinke]

Shift Linkage

Prior to fabricating the headers, I thought it smart to build out the shift linkage to ensure the space I had reserved for the linkage while mocking up the headers was actually going to be adequate. As a reminder, the custom transverse transaxle uses a Tremec TKO 5 speed transmission (which normally uses an integral H pattern shifter) and in this Miura application needs to be shifted via cables. I had already converted the transmission so it has a single horizontally placed shift shaft oriented to the passenger side of the chassis.

My original plan was to hook one shift cable to this shaft via a lever for the twist motion and the other shift cable directly to the shaft for the push/pull motion. After ordering up some custom made push/pull shift cables, I found a major flaw in the plan. There wasn’t enough room to route the cable to the end of the shift shaft without it rubbing on the passenger side rear tire.

Another wrinkle in that plan was that a non-standard shift pattern would result if the push/pull motion wasn’t reversed. In other words, I wanted first gear to be the leftmost and forward shifter position. First gear would be left and backwards on the shifter if the cable was run directly from the shifter to the shift shaft. To get the desired shift pattern, I’d need to reverse the push/pull motion with a set of levers. My original plan was to put the reversing lever adjacent to the shifter but with the lack of clearance between shift cable and rear tire, my original plan was out the window.

So I set about designing a shift cable mount on the engine that would also include a reversing lever for the cable with push/pull motion. First step was adding a shift shaft extension to get out of header heat zone and beyond the A/C compressor hose mounts. A linear bearing was integrated into the A/C compressor bracket to support the shift shaft extension.

Next, a direction reversing lever was built with a ½” shaft carried on pillow block bushings mounted on a stout piece of angle attached to the engine timing cover and A/C bracket.

The vertical lever gives a twist motion on the shift shaft and the push/pull direction reversing lever is connected to shift shaft via a pair of heim joints so the twist motion isn’t impaired.

A cable mount bracket fits snuggly between engine and chassis. It also provides triangulation for the other shift linkage bracket.

Some small notches were required in chassis gussets to provide clearance for cable connections to shift linkage levers.

My preferred design mantra is, “keep it simple”, but this shift linkage is very complicated, maybe overly complicated. There are 28 fasteners just within this shift linkage. It seems to work ok in some initial testing. I won’t really be able to test it until the transaxle is fully assembled and has been filled with oil.

 

[Joel Heinke]

Shifter Installation

I had chosen a shifter made by Numeric Racing for use in the Miura. The shifter is designed for use in Porsches so there were a couple of quirks with the install involved in converting metric pickup points to standard threaded cables. The shifter itself is very well made with all pivot points supported by ball bearings. Compared to the shift linkage I had just completed, the shifter install felt very easy and straight forward.

The shift lever ends with a 10mm ball on the bottom. I couldn’t find any connectors that accepted a 10mm ball that didn’t also have metric threads. I did find however that gas strut ends are made to accept a 10mm ball stud. I found some nice ones made of stainless steel that were reasonably priced on eBay. They came with a M6 thread which I drilled out and added a heli-coil to get to the ¼-28 thread for the shift cable.

The pick-up point for the side to side motion is 12mm round by 13mm wide. Starting from a ½” thick scrap of aluminum, all it took was to drill a couple of holes and tap one out to adapt this for cable hookup.

I think this shifter setup will benefit from some sort of gated arrangement but I’ll hold off in doing that until I’ve been able to take a test drive to try it out.

 

[Joel Heinke]

Header Fabrication in 304SS

After completing the header mockups, I had all the information needed to order up all the necessary U bends, double slip collector, Y pipe, V band clamps, and collector tabs in 304 stainless steel to fabricate the headers. It was all delivered in one big box (packing materials removed before picture).

The double slip collector does look like it will seal much better than the single slip variant.

I decided to fabricate the aft/passenger side header first since the engine was currently sitting in the chassis and this header needs the engine, transaxle, and chassis all in place to ensure clearance around all these items. The first step for this header was to port out the flange as the primary tubes connect to it at an angle. The flange was port matched to the head and then blended to ovals on the outboard side as the primary tubes connect to it at a 50 degree angle.

Next I had to turn up some special tooling on the lathe for stretching the ends on the mandrel U bends for proper fit up. A mandrel bender shrinks the tube a bit and distorts it out of round while making the U bends. I had to make three tapered stretching dies as the primary tubes are composed of three different sizes of tube.

I put my metal shaping skills and tools to good use in resizing tube ends to get a perfect match. A big ass hammer and sandbag were used to drive in the tapered dies and then a combination of body hammer and half round slapper were used to stretch out the metal. All of the metal stretching needs to be done on the inside of the curve as that is where the metal is thickest. After the mandrel bender finishes its thing, the metal on the outside of the curve is only about half the thickness as the metal on the curve inside. I also used a bench vise with rubber jaw protectors to persuade the out of round openings back into round.

I decided it would be much easier to fabricate, install, and remove this header as four separate primary tubes versus a single integrated unit so the flange was cut into four separate pieces. Then it was pretty much following the mockup header as a pattern to route the primary tubes. The primary tubes go to the next larger size tube every 9 ½” so from 1 5/8” to 1 ¾” to 1 7/8”. This gives the effect of a gradually tapered primary tube which makes for better exhaust flow.

The one new wrinkle not experienced when fabricating the mockups is that 304SS is not magnetic. I had made use of strong magnets to hold tube sections together for welding when I did the mockup headers. A tip I had been given was to use a special worm drive clamp to position tube sections that are stainless steel. These clamps are made for very large hose, are composed of the worm drive and extension sections where the extension section has small “windows” in it for connecting to the worm drive section. With a very steady hand on the TIG torch, you can make tack welds through the window. These clamps worked well where two fairly straight sections are to be joined but not so good for joints on curved sections as it was hard to keep the joints tight when the clamp was tighten.

I found aluminum foil tape to work best when joining curved sections. The joint could be positioned and then held with 2 or 3 small pieces of tape. The joint fitting could even be fine tuned after it was held with tape because the foil tape is semi-rigid. The aluminum foil tape tolerates a decent amount of heat so it’s good for use during tack welding.

Well after a few days work, I’ve transformed a bunch of U bends into half a header and tack welded it up.

Hopefully now that I’ve got the tooling and process figured out, the progress will go faster.

 

[Joel Heinke]

Header Fabrication in 304SS (cont.)

I was warned that when SS mandrel bent tubes are welded they would warp/move often in seemingly random ways. This is even when the joints are tight and held with 4 good tack welds. I’m sure the movement isn’t random but given this is the first set of headers I’ve fabricated, I was sure I couldn’t accurately predict where they would go. So I decided to weld up the butt joints first and reserve the slip joints for making adjustments if needed. With the butt joints welded on 3 primary tubes here’s what resulted.

These all started with 5/16” gap between them and the ends even with each other. I could easily slip the collector on and off of them. Needless to say, the collector won’t go on these as they are without some serious persuasion. So I’ll grind off the tack welds where needed on slip joints, make adjustments, and then complete the welding on them. Hopefully the slip joints will have less movement when being welded. I’m told the underlying cause of the warping is the different metal thickness resulting from mandrel bending and thus the welding induced shrink rate varies on different sides of the tube.

The other tip I received was to make full welds on the joints closest to the engine before tack welding joints further down the primary so that adjustments can be made along the way thus eliminating the need to break tack welds. I’m going to try that approach on the 4th primary tube to see if it goes better.

It’s all good, this whole Miura project is a big learning experience.

 

[Joel Heinke]

Header Fabrication in 304SS (cont.)

For the aft header, it was time to complete the full welds on the primary tubes. I ground out the tack welds on the slip joints to make adjustments for the warping from the initial welding. The welding schedule I chose to use is: weld butt joints starting closest to the engine working in sequence down the primary tube while skipping the slip joints, refit the primary tubes on engine/chassis; mark, tack and then weld the slip joints starting closest to engine and working down the primary tube.

Here’s the result where the primary tubes meet the collector.

The collector now easily slips onto the primary tubes after all joints are fully welded.

I now need to weld on the double slips and collector tabs to complete this header.

 

[Joel Heinke]

Header Fabrication in 304SS (cont.)

One header down, one to go. I welded on the double slips, collector tabs, collector extension, and O2 bung.

And with the rear chassis brace in place, only bits and pieces of the header are visible.

Now the engine and transaxle needs to be pulled from the chassis to build the other header.

 

[Vinny G]

Looking good Joel !

 

[Joel Heinke]

Header Fabrication – One step forward, two steps back

Given what I’d learned fabricating the aft header, I’ve been busy fabricating the header for the other side of the engine. The main difference between these two headers is that I was able to have the engine in the chassis while fabricating the first header, for this one it could only be done with the engine out of the chassis.

This header is located on the front side of the transverse placed engine between it and the firewall. So the only access is from underneath the car and with an 8 foot ceiling in my garage, the highest the car can safely lifted is jack stand height. My body just couldn’t take the many dozens of trips on a creeper under the car that would be needed to work out all the primary tube routing and bend placement.

I thought I had it all worked out with the mockup header, but upon final inspection it was hanging about an inch below the chassis bottom. So after making some changes to correct for that and making all the primary tubes equal to 28 ½ inches, here’s what resulted.

I was really proud of how it came out after welding up all the primary tubes and was about to TIG braze the primaries to the flanges when a niggling thought prompted me to put the engine into the chassis to double check the overall fit. Well long story, short, the header doesn’t fit. It hits on the passenger side motor mount base and also on a chassis rail. My first hope was that a couple of small tweaks could provide the needed clearance. But no, it’s pretty much start all over again as this one is all cocked up. The space constraints are so tight there is no margin for error.

I now see firsthand how helpful a car lift would be for this type project. Oh to be able to walk upright under the car to test fit pieces with the engine and chassis all there as a unit. I’ve been contemplating a move for a while and now a garage/workshop with a high enough ceiling for a car lift is definitely on the list of things for my next home.

 

[Joel Heinke]

Header Fabrication – Restart on Header Two

As tough as it is to cut up a just fabricated part, I’m over it and busy remaking the front side header. My approach this time is to positively locate the collector position/orientation and then route the primary tubes starting at the collector working back up to the engine. The best opportunity to position the collector was while the engine/transaxle was still in the chassis so that’s what I did. I determined that only 1 of 4 primary tubes could be reused and this one still required one of the welds to be ground away to reorient one of the bends. So I did this while the engine was in the chassis to use it to position the collector.

After pulling the engine again, here’s what I’ve got.

The collector is set at a 15 degree angle where in the prior version it was horizontal. This angled positioning puts the collector above the chassis rail while still keeping it about 1 inch below the oil pan. Routing the primary tubes into the collector is more challenging with this new positioning and that’s why I’m starting primary tube routing at the collector versus the engine.

 

[Davidmgbv8]

Did the Italians have this much trouble with the Muira’s???
fantastic patience you have!

 

[Joel Heinke]

Did the Italians have this much trouble with the Muira’s???
fantastic patience you have!

I've never had the pleasure of owning an original Miura so I can only speak to what I've heard. The Italians have a reputation for making beautiful sports cars but like many beautiful things, they can have their quirks.

For example, until the last couple of years of production, the Miura shared a single, common oil sump between the engine and transaxle. It sort of made sense given these were made in a single casting, but it really didn't work very well at keeping gear shavings out of the engine. And posi-traction wasn't an option as engine oil lubricated the final drive.

Also, there was a high Miura mortality rate from gasoline fueled car fires. In a Miura, the engine sits higher than the radiator. In this situation, a well meaning but uninformed person could easily introduce air into the cooling system leading to an overheating situation. The gasoline in the four Weber carbs tended to boil over when the engine overheated. Hmmm, hot gas running down a hot engine just needs a little spark and another Miura bites the dust.

Another quirky thing is they used a toothed Gilmer style belt for the alternator. These were known to pop off on occasion or get stripped if the alternator didn't turn freely. Hmmm, keep an eye on the amperage gauge on long trips.

I've been told the Miura ownership experience is somewhat like dating an Italian super model. The beauty makes it un-resistible but you better be ready to pay the inevitable high maintenance costs

 

[Joel Heinke]

Header Fabrication – Restart on Header Two (cont.)

To try to avoid repeating the situation where the completed header would not fit, I decided it worth the couple of hours work to put the engine/transaxle back into the chassis for another test fit. 3 of the 4 primary tubes are formed and tack welded so the collector positioning is locked in at this point.

The rightmost primary tube is equidistant between the oil pan and frame rail. It should have enough clearance for the engine to move in the mounts and not contact the frame rail. There looks to be enough room to route coolant pipes and A/C hoses by the header to their connections running up the center bottom of the chassis. I do think shielding will be required on this header for heat management purposes.

I also re-worked the collector outlet to reduce it in size. The collector was originally built with a 3 inch outlet and I decided to change to 2 ¾ inch secondary pipes given all the exhaust clearance challenges. Given the collector transition goes from an irregular rectangular shape to a round circle this resulted in some fairly advanced metal shaping to accomplish. By cutting about ½ inch off the transition outlet the vertical height in the middle was 2 ½ inches but the horizontal width was now about 3 ¼ inches as the transition tapers wide as it approaches the collector. Increasing the vertical height was easy as this was just changing the metal arrangement with hammer and sandbag. Decreasing the horizontal width involved shrinking the SS which is not easy especially once the metal work hardened. Using a small sandbag and body hammer I was able to shrink and reform the sides to a circular shape but the metal stopped moving prior to getting to the targeted 2 ¾ inches OD. The last bit of shrink required “hot working” the metal.

I feel good about the header fit now and am confident that it will have the needed clearance once it’s fully fabricated.

 

[Joel Heinke]

Header Fabrication – Second Header Completed

I’ve come to the conclusion that the people who build tuned length headers for a living must be of a different breed altogether. I’ve driven myself cross-eyed with fitting together all these different radius curves, measuring, fitting, re-measuring and joining all these tubes with the objective to fit them into a very constrained space while also making each the exact same length. Well mission accomplished, but I sure am glad this portion of the Miura project is done.

All the primary tubes are fully welded and the primaries are brazed to the flanges with silicon bronze. I chose to TIG braze the flanges in place instead of welding them to minimize heat induced warping and thus hopefully have leak free headers. On the good news front, I was able to remake this header with left over bend pieces and by cutting primary tubing bends out of my previous mis-guided effort. In other words, I didn’t need to buy additional mandrel bends for the second attempt.

 

[Andrew Robertson]

I’ve come to the conclusion that the people who build tuned length headers for a living must be of a different breed altogether.

Hi Joel, yep agreed! I think folks lose track of the fact that the length is related to a single RPM point where peak torque is expected, and that having a bit of variation (i.e. a few inches either side of "ideal") simply spreads out the torque peak a bit. I think any bundle of pipes with primaries between 32-36 inches with good design and flow is going to work pretty good on a sporting street engine. Cheers, Andrew

 

[Joyce]

Everything looks clean on this thread, I am so impress by this build.