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Discussion Starter · #1 ·
I have a 1956 750D Giulietta Spider that I have been restoring at home for a couple of years now. All the nasty, dirty work is pretty much done, and I am now getting into the fun part. The body shell is on a rotisserie at the paint shop getting finished up, and the rest of the car is in my garage in pieces. I have all the restored mechanical parts are on racks ready to be installed, all the hardware is plated and bagged, the chrome are done, and new rubber parts are all in a box waiting to go on. The car was all original, but I wanted something more fun to drive, so I am installing 4 wheel disc brakes, 5-speed close ratio trans, stiff springs and bar, Bilstein shocks, etc. I am keeping and restoring all the original parts so it can be converted back to stock is a later owner really wants to do it. I built a couple of Carrera Panamericana cars to this spec years ago, and they were a blast to drive.

The last part to this puzzle is the engine. I want more power, but I don't want the oil pan sticking out the bottom of the car like you have to do with bigger engines. My solution is to use a 1600, which will fit under the hood without too much tweaking, but bore and stroke it out to 1779cc. I am using a 1750 head as well. At the same time, I have installed 1 mm oversize valves in the head, mild porting, 45 DCOE carbs, big cams (high lift, short duration), lightened steel flywheel, etc. I have a 1750 crank, Mahle liners I will bore out to 80 mm, Crower rods to 1600 dimensions, and have just ordered a custom set of CP pistons to make it all work. I plan to run it on an engine dyno before installing it in the car, so I should be able to get a pretty good idea of how well this all works when it is finished. My goal is to get 150 hp with a tune mild enough for my wife to still drive the car to work and back (I forgot to mention this is her car).

Flow data for the cylinder head before and after big valves and port work is below. Basically a 15% increase in flow across the board.

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Rob
 

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Discussion Starter · #3 ·
Hi Otteud,

A stock 1300 Normale is a fine car, but just a little more tame than we were looking for. I have had the opportunity to enjoy many Alfas during my time as a professional restorer, but this car is one my wife and I want to keep for ourselves as a weekend driver. It is certainly financial suicide on my part to do a full rotisserie restoration to concours standards, then spend a small fortune on modifying the drivetrain, but again, I plan to keep the car for a long time. Everything I have done can be easily undone by a future owner. It is all bolt in, except for the section I cut out of the tunnel to clear the later trans, and even then I saved the old piece and welded in a lip and threaded inserts so it can be screwed right back in.

Rob
 

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Discussion Starter · #5 ·
Thanks Vic, that's very useful information. I am a little nervous about a 2 mm overbore on the liners, but I have gotten several reports like yours that give me confidence it will work for a street car. I also bought Mahle liners, which I am told are a little stronger material than the Borgos, just for insurance.

Rob
 

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Discussion Starter · #8 ·
Hi 180 Out,

The way I see it, I am just building the car Alfa, or at least Conrero, would have built in 1956 if they had access to the technology. I am using mostly original Alfa parts, admittedly from a decade later, but they all bolt into place. Similar to your friend Bob, I will be using a stock 750 Veloce airbox and filter, exhaust headers, yellow fuel line, etc. to keep it looking original.

Rob
 

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Discussion Starter · #10 ·
I just checked out the blue car on BAT; thanks for pointing it out. Seems it was incorrectly listed as a 750F Veloce initially and there have been a ton of posts about that. My guess is all that "noise" will depress the final selling price, so it might be a real bargain in the end. Sadly reinforces my opinion that what I am doing to my car is financial suicide. I think the blue car is not as nice as what I am going for, but if it is cheap enough, it could all be fixed. For example, I really hate the engine sticking so far out the bottom of the car, but I have an engine in process here that could fix that. I am sure I could find a convertible top frame without too much trouble.

Rob
 

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Discussion Starter · #14 ·
Hi Alfajay,

No more Panamericanas for me (I think I did four of them), but I did think that I might AutoX the car occasionally if I can get it away from my wife. To make a short story long, I did a bit of a study when I built the PanAm cars (we are talking 30 years ago). I bought several sets of aftermarket springs which I measured and compared against some stock Alfa springs I had in the shop. The results were:

Front spring rateFront free lengthRear spring rateRear free length
Stock 750 Giulietta Spider 170 lbs/in16"60 lbs/in17"
Stock Giulietta Sprint Zagato200 lbs/in15" 60 lbs/in15.4"
Alfa Ricambi Sport280 lbs/in14.4" 90 lbs/in13"
Ward and Deane Race410 lbs/in12.5" 115 lbs/in13.2"
John Norman Race560 lbs/in11.5" 150 lbs/in11.5"

For the first year we ran, I used the Ward and Dean racing springs (roughly double the stock spring rates). The car was great fun on smooth roads, but on the rough roads and huge speed bumps in the south of Mexico they were just too stiff. About halfway through the 10-day event the fuel tank strap mounts actually started to rip out of the trunk floor. We did very well (3rd place overall) but the next year we opted for the Alfa Ricambi sport springs (50% stiffer than stock), all with Spax gas shocks. The absolute grip limit of the car went down, but the driveability was improved. That car is still in road use today with the same springs, and it is remarkably nice to drive. Alfa Ricambi doesn't exist anymore, but I was able to purchase a set of springs with just about the same dimensions and rates, so I am hoping for a similar result.

As to the rear end hopping around, I never experienced that even with the Ward and Deane springs. I have had similar problems when I used KYB Sport shocks and some Bilsteins, so it may be that the KYB rates are just way too high. FYI, I misspoke when I said I was using Bilstein shocks on my car; I am actually using Konis. Hopefully they will work as well as the Spax shocks did back in the day.


Rob
 

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Discussion Starter · #16 ·
I am hoping to get back to the engine build here. My plan is that this will end up being a relatively low-cost but high output build that still looks stock on casual inspection. I am getting ready to have the Mahle liners bored this week, so I am getting the crank ready to install once the block gets back and cleaned up.

Photos show the liner retainers I used to hold them all in place so the boring and honing can be done on a standard machine. There used to be a motorcycle shop in town with a fixture to hold single liners in place, but they are out of business.

Automotive tire Bumper Motor vehicle Automotive exterior Toolbox
Material property Font Drinkware Cylinder Electric blue


I also drilled extra oil passages to the #2 and #4 main bearing saddles, as I never liked Alfa's idea of only supplying oil to #1, 3, 5 main bearings and then relying on the crank passages to carry oil to the other two main bearings. I realize that Alfa built a zillion of these engines and didn't have a lot of trouble, but we all have our superstitions. I figure it does no harm. Crank journals and bearing bores were measured to determine bearing clearances, which are all right about 0.0015". I always use Plastigage during assembly just as a final check, but I admit this is probably unnecessary. Interesting that the Plastigage and measurements seem to agree very closely, but I still do both.

Motor vehicle Product Automotive tire Automotive exterior Camshaft
Automotive tire Rim Engineering Automotive wheel system Auto part
Finger Tool Rotary tool Metalworking hand tool Gas


One thing I always do that I am convinced makes a difference is removing the plugs out of the crank so that I can run bore cleaning brushes through all the passages. I am surprised at the junk that comes out of there. It seems the centrifugal forces during running force any particles in the oil to pile up against these plugs and collect there. The only way I can see to get them out is to remove the plugs. I drill out the stock plugs, then tap the holes for either 1/16" NPT taper plugs or M8 x 1.0 straight set screws; I have used both in the past. You need to use a new, good quality tap and be careful. The cranks are hardened and if you break off a tap you will have to get it EDMed out, which is expensive and tricky.

Automotive tire Automotive lighting Alloy wheel Camera lens Audio equipment


I will post more photos when I get my block back from the machine shop and start assembly.

Rob
 

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Discussion Starter · #21 ·
I agree with all the above, primarily that I should look into making a torque plate. I am switching machine shops as all the other shops here in the Carlsbad area seem to have closed, and my new machinist is not an Alfa guy. I will meet with him tomorrow and see how he wants to handle it. It is getting hard to find anyone who wants to do anything "hands-on" these days. I can't recall the last time I met a restoration shop owner who didn't have grey hair.
 

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Discussion Starter · #22 ·
Hi Koenraad,

Neat trick with the 10 mm spark plugs, I had never thought of it. I opted to use off-the-shelf parts on this build in an effort to keep the cost down. I used 1 mm oversize intake and exhaust valves with stock stem diameters so I could use stock guides, seals, retainers, locks, shims, etc. The 1 mm oversize valves fit on the stock valve seats as well. If the engine output on the dyno is disappointing when I am done, the first place I would turn to try to make more power is the head, but I hope it doesn't come to that.

FYI, my cylinder head man told me that he can get better flow out of a 1750 head than a 1600 head. I believe that Mike Sperry of Sperry Valve works told me the same thing 30 years ago. The guy I bought my used engine parts from told me I could have either one for the same price, so I picked the 1750 head. The better flow thing might just be an "old wives' tale", but I figure the chambers might be shaped better for matching up to my 80 mm bore.

Rob
 

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Discussion Starter · #29 ·
Thanks everyone for your comments. I suppose that what I am trying to build is just a 1750 with a shorter block. As Ipalmer pointed out, I will end up with a 1750 with a less desirable rod length/stroke ratio, but it will fit under my hood. Everything is a tradeoff.

Thanks, Koenraad for the port dimensions. I was not aware of this book and will be interested to see how my port dimensions compare. Interesting that the dimensions are different for the 1600 and 1750, but I wonder whether that is due to casting differences or just an adjustment for larger displacement?

Rob
 

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Discussion Starter · #32 ·
I will have to get my head down off the shelf and measure the ports to see how well they correspond to Jim K's book. I will also have to get a copy of the book.

I don't know if anyone noticed, but the blue Abnormale we discussed earlier in this thread sold for $80k on Bring a Trailer ($84k including commission). That makes me feel a little better about all the work I am putting in.
 

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Discussion Starter · #33 ·
There has been a delay on my project due to the lead time for pistons from CP. Winter is always the busy season for these guys as all the race teams are ordering parts to build engines for the next season, but this year it got really crazy. 14-16 week lead time for new pistons. All I have been able to do is modify my intake manifold, order some parts, and try to make sure everything is ready to go once I have my pistons in hand.

I am using an (I think) early 105 intake manifold, but I want it to look more like a 750 part. I ground off all the sharp corners to get a more rounded shape, welded up all the holes and ports I will not need, then prepped the whole surface to give it a uniform "cast" look. I also cut the ears off my head for fastening the front of the cam cover, then filled the notches with weld and gave it the cast treatment. You can still notice it from below, as in the photo, but when it is installed in the car it will look good with a 1600 cam cover on it.

The cams I am installing are 286 deg intake duration with 11.0 mm lift and 282 deg. exhaust duration with 10.5 mm lift. I got these from Jon Norman and he reported great results using them in a similar engine recently. I was originally thinking of bigger cams, but it is a street car after all.

I also looked up the build sheets and engine dyno sheets for a pair of 1750 engines I built years ago for the Carrera Panamericana. They were similar spec to the one I am building now (low compression, ported heads, 45 DCOE carbs) but with slightly bigger cams. I got 157 hp out of one and 154 out of the other at 7000 rpm, but with slightly better peak torque (129 ft lbs @ 6000 rpm). I think that makes my goal of 150 hp @ 6500 rpm for this motor realistic, hopefully with better low end torque than the Panamericana engines. Can't wait to find out.
 

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Discussion Starter · #34 ·
So, a big delay in getting my liners bored due to making a torque plate, but it is all done now. Just cleaned the block, liners, and oil passages this morning, so I am ready to start assembly. I bored out the block to feed oil directly to the #2 and #4 main bearings while I was at it, something I used to do on race engines. Not sure whether it makes any difference in a street car. Photo shows running a bristle brush through the block oil passages while flooding with solvent in the tank. Have to get out all the debris from the machine shop before assembly.

I know most of this is boring detail, but I found something ineresting in my dyno records while doing my research. When I was building those 1750s for the Carrera Panemerica, I tested out a camshaft change on the engine dyno. I think it was interesting because normally you have to give up low end torque to get top end power gains. In this case, I improved both, or at least I didn't lose anywhere. The engine started with 300 deg, 10.5 mm lift cams both intake and exhaust. Peak power was 152 bhp @ 6500 rpm, which I thought was quite good for a 1750 on 87 octane pump gas. I then changed just the intake cam to a 280 deg, 12.0 mm lift cam. Much of the Panamericana is run at high altitudes, up to 10k feet if I recall. I was trying to reduce overlap to improve mid range torque and close the intake valve earlier to help build compression in the thin air at altitude. By using a cam with shorter duration but greater lift, I got an increase in area under the lift vs. duration curve while also reducing duration. The results was 158 bhp @7000 with no significant loss in power lower down. I wasn't able to simulate high altitude on the engine dyno, but the driver reported much improved performance all around on the actual event. I thought this was a good example of how increasing cam lift improves performance everywhere.

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Discussion Starter · #35 ·
I finally have everything I need to continue my build in-hand, so I am starting to assemble my engine.
Just for review, my plan is to use a 1750 crank in a 1600 block along with an 80 mm bore to give me 1779 cc in a 1600 block. The crank drops in because all the bearing journals are identical, so that part is easy. I also want to use stock 1600 length connecting rods, so the only custom part I need to accomplish this are the pistons. There are no off-the-shelf pistons that are going to work for this, so I had to design my own. First thing I had to do was to figure the dimensions of all the parts I want to use. Rod length is easy, as I found that published several places as 148 mm. The next thing I needed was the crankshaft’s stroke, which was also easily found, of 88.5 mm. The dimension I could not find published anywhere is the 1600 block height, the distance between the crankshaft centerline and the top of the deck. I was able to calculate this by using a large set of calipers and measuring the distance from the top of the front main bearing saddle to the head gasket surface. I could then take that distance and add half the main bearing bore diameter, which gave me 222.5 mm. This seems a funny number, but compared to the published 1750 block height of 235 mm, it sounds about right. This means the 1600 block is 12.5 mm shorter than the 1750 block, almost exactly 0.5”.

Since I knew that I wanted the edge of the piston to be exactly level with the top of the liner at TDC, this gave me enough info to calculate the pin height or compression height of the piston. This is the distance from the centerline of the piston pin to the deck of the piston at its outer edge. I needed the compression height to be equal to the block height, minus half the stroke of the crank and the length of the con rod center-to-center. 222.5 mm – (88.5 mm/2) – 148 mm = 30.25 mm, which is the compression height I need.

The next thing the piston maker needs is the piston dome volume. First, I needed to choose the compression ratio I want. The number I always heard for hot Nord engines in the past was 9.7/1 if running on pump gas. I have been told by smart people that if you use the flatter dome of the later Motronic pistons you can tolerate 10.5/1 on pump gas (91 octane is the best we can get in CA). Not wanting to push it, I decided to shoot for 10.0/1. The first thing I needed to do was to measure the volume of the combustion chamber. My head was already assembled with all its new parts, so this was relatively straightforward. I sealed a flat plate with two holes drilled in it onto the bottom surface of the head with a thin film of grease, then used a burette to add ATF until it was full. This test showed the combustion chamber volume to be 75.0 cc. I used this number to calculate the volume I would need to fill with piston dome to get the 10.0/1 compression ratio I was looking for. This gave me a piston dome volume of 32.8 cc. I now had everything I needed to order the pistons. I told them I wanted 80.0 mm bore Alfa 1750 pistons with a 30.25 mm pin height, a 32.8 cc dome similar in design to the newer Motronic pistons, and I paid a little extra to have the underside of the dome machined to reduce weight. That gave me the last piece that I needed to place my piston order.

I now have pistons in my hands and bored liners to match. I will give an update when I get a little farther along. In the meantime, if someone wants more detail on the piston design, I would be happy to provide it.

Rob
 
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