Super charger rods and pistons

[Limey]

Hi all,

A can of worms question. Not racing but sort of..I'm fitting a good old 1960 Judson super charger to my 1600cc S2 (As fitted to 1600cc MGA's, Corvairs, Jeeps, Volvos, Sprites, Beetles etc Stateside in period.. just not to Alpines strangely)

My question is, will the standard conrods and rings be OK at a compression of 11-12CR?

Here's the background (and a bit of 'sharing out loud' for my benefit as much as yours...)- I have a profesional classic race engine builder company doing the work for me here in the UK (they build engines for Goodwood classic racers and vintage blown racers as a speciality) I'm posting because I'm just trying to get ahead start spec wise.

I'll be building a thumper not a revver for the sheer challenge of it and hope to end up with an Alps touring/ Italian strada cruising Alpine that won'tbe asked to exceed 5500rpm on a typical day. An 11:1CR theoretical at 9lb boost so probably 10 - 10.5cr in real life, broadly speaking given engine and blower inefficiencies. I'm keeping it as period looking as possible, as close to other Judson engine bays of the '60s.

Probably 120-140lbft all said and done depending on driven pulley, head improvments, Carbs and extraction, theoretically. The boost gauge and the dyno read out will tell the real truth at the end of the day.

Everything from front to back and from top to bottom will be dynamically ballanced but I don't plan to radically lighten much as this is not a 'spinner'. Am I wrong in not lightening whilst I have the chance? Is it wasted cash for this application? I am open to persuasion. SCs don't like flywheels that are over light for example. Got to keep things spinning..So reciprocating mass may not be an obvious enemy at 9lb boost...? This is not a drag racer after all.

Judsons were a 'bolt on' but I'm planning improvments that are blower specific. would be daft not to,. For example I plan to keep the original valves (3 angle seats) but fit roller rockers to get that ratio uplift without resorting to heavy cam profiles., ( I may fit Datsun valves, not sure yet). The head will be semi-hemi/ softened bath tub, I will take advice from the builders. Definately a custom solid copper head gasket and larger diameter, top spec head studs plus the usual welded crescents etc

I have ditched the crap Judson 'original package' fixed jet Holley carb for an E type 2''SU with custom needle etc, plus a hidden SU pusher pump and pressure regultor in the boot recess, which will run through the original but gutted AC Delco glass domed pump to keep the period look in the engine bay.

I could get a special cam but I'll start with an S5 grind on a S2 donor cam and see how that goes as the specs look OK, I have a custom dizzy sorted as per SC specs (special curves, deleted vacuum), and also a nice ex Alpine racers exhaust as a pattern (4 into 1, equal length, 1 1/8 bore) to get the gas out.

So, thats the background. Con rods, pistons and rings - Leave as they are or what should I fit if thay're not? Any thoughts as I am in the dark, totally.

Thanks

Oliver

 

[puff4]

Sounds interesting, but I think the real problem is keeping the engine cool enough, particularly the #4 cylinder, since even in the stock configuration (9.2:1 compression) it tends to overheat back there. You've got to find a way to pull that hot water out of the back of that head.

 

[Limey]

Hi Kevin,

That was also a concern for me. I'm fitting a three core rad with Evans waterless and Le Mans oil cooler with an oil temp sender fitted into the base. Engine will be dipped to clear out the jacket. 6 blade fan. I was playing with a custom smaller fan pulley If I need to.

I'm considering a high flow oil pump (from Coltec I believe)

 

[alpine_64]

. Engine will be dipped to clear out the jacketl)

Oliver.

Scrub out the coolant passages with a stuff wire brush.. Especially around the rear most core plug. Might need a screwdriver to chisel at old casting flash amd accumualted junk

 

[alpine_64]

Amd re piston and rods... I wouldn't use stock.. If you domt wamt to racey.. The chev rods id have as a minimum.... Stronger and lighter

 

[Limey]

The following article is reprinted without permission from the Rocky Mountain Vintage Racing Ltd newsletter, date unknown.

This was written in reference to a 1725 engine. Would it work for a 1600 unit?

Can any one add or correct the info below??

The key to a reliable engine is the installation of 350 CI Chevrolet connecting rods. The Chevy rods are .075 inch longer than the Sunbeam rod and may be used with slightly modified stock Sunbeam pistons. The steps required to use the Chevy rods are:

1. Obtain 4 matched 350 rods with 3/8 inch bolts.

2. V8 rods have one side of their big end machined off so that they are narrower than the sunbeam's one inch. With the cap bolted to the rod, have the cut off side heli-arced with bronze to a height greater than one inch. The bronze doesn't need to be very uniform and it is best not to braze across the parting line between the rod and cap.

3. Using a stationary belt sander remove the minimum amount of metal parallel to the rod bolts so that the Chevy rods will fit in the Sunbeam cylinders. Don't remove any more material than is required to get the rods through the Sunbeam cylinder, so if the engine is to be rebored take this into account.

4. Have the bronze surfaced by an automotive machine shop to give .010 inch side clearance on the Sunbeam crank.

5. The wrist pin hole needs to be honed approximately .030 inch to float the Sunbeam wrist pins in the Chevy rods. The clearance should be .0005 inch and an oiling hole should be drilled to oil the wrist pin like on the Sunbeam rod.

6. Install new rod bolts and recondition the big ends of the Chevy rods.

7. Balance and glass bead the rods.

8. Grind the rod journals on the Sunbeam crank to 2.100 inch to provide .002 inch bearing clearance. Use Clevite 77 type Chevy rod bearings.

 

[husky drvr]

A can of worms question. (As fitted to ... just not to Alpines strangely)

Oliver,

The Judson S/C is driven by a belt from the front of the engine, correct?

The first weak point you, and your builder, should investigate is the limited engagement of the front pulley hub keyway and the key in the crankshaft. That connection will be required to transfer all of the power required by the S/C and can be problematic even on a stock engine.

If you're thinking about using the Chevy six cylinder rods in a 1600, keep in mind they are 0.050 inch shorter than the stock rods. If used with the stock pistons, the stock GM rods would drop the stock piston in the bore and reduce compression by adding about 6.7 cc's to the combustion chamber volume.

There are aftermarket 6.0 inch rods available, but that would only be possible with custom
pistons.

Using the six cylinder rods eliminates the need to weld/braze (destroys heat treatment) on the 350 rods because the six cylinder rods are a few thousandths WIDER than the Rootes rods. You get to choose if you want to widen the crankpin face or narrow the GM rod to match the Rootes spec. either way you can reset side clearances, if needed.

The crankpin in the 1600 is only ~ 2.00 inch - smaller than the 1725's 2.125 inch crankpin.

Just a few thoughts,

 

[Limey]

Oliver,

The Judson S/C is driven by a belt from the front of the engine, correct?

The first weak point you, and your builder, should investigate is the limited engagement of the front pulley hub keyway and the key in the crankshaft. That connection will be required to transfer all of the power required by the S/C and can be problematic even on a stock engine.

If you're thinking about using the Chevy six cylinder rods in a 1600, keep in mind they are 0.050 inch shorter than the stock rods. If used with the stock pistons, the stock GM rods would drop the stock piston in the bore and reduce compression by adding about 6.7 cc's to the combustion chamber volume.

There are aftermarket 6.0 inch rods available, but that would only be possible with custom pistons.

Just a thought,

Thanks Don. "
I'm compilling a list to discuss with the builder and your keyway reminder is very useful. Dropping compression is, infact what I want to do. I need to get down to 7 0r 7.5 static CR. I'll get part of the way with head mods and increasing the piston dish. I'd like to keep original pistons if possible.

 

[Limey]

Don - ''If used with the stock pistons, the stock GM rods would drop the stock piston in the bore and reduce compression by adding about 6.7 cc's to the combustion chamber volume.''

I would loose some 'Squish' with those rods but at 9lb /11CR do you think I would miss the squish?

 

[Alpine 1789]

If you're thinking about using the Chevy six cylinder rods in a 1600, keep in mind they are 0.050 inch shorter than the stock rods.

I think you have that backwards - the Chevy rods are longer than the stock ones. Mine were .060 taller. Jan Servaites posted very specific measurements of his rods in the old Marque (https://sunbeamalpine.org/wp-content/uploads/2017/10/issue_14.pdf) and found his Chevy rods were .075 taller than the stock ones. Jan attributed the difference to "how many times the rod was reconditioned because it gets shortened every time it’s reconditioned" which makes sense to me. In my case, the machine shop took .064 off the top of my pistons to compensate for the difference in the pistons and the deck work. https://sunbeamalpine.org/wp-content/uploads/2017/10/issue_11.pdf

 

[husky drvr]

I would loose some 'Squish' with those rods but at 9lb /11CR do you think I would miss the squish?

Oliver,

To be honest, I don't know. Articles I've read that touch on the squish subject, make me think it's much more beneficial to have "good" squish than not.

 

[husky drvr]

I think you have that backwards - the Chevy rods are longer than the stock ones.

Jim,

Oliver's original post stated his interest is for a 1600 three main engine. The rods are different to the 1725 rods because of the 1725's longer stroke. Since Rootes had to have a new design rod because of the 1725's larger big end bearing requirement, it seems they adjusted that rod's length to continue the use of the same basic piston design.

WSM 124 > ... C to C ... 5.751/5.749 inches
.............crankpin dia. > 2.0010/2.0005 inches

WSM 145 > ... C to C ... 5.626/5.624 inches
.............crankpin dia. > 2.125 inches

As you also point out, the GM rods are nominally considered to be 5.70 inches C to C and designed for a nominal 2.000 inch crankpin. No offset grinding opportunities available for a 1600.

Hope this helps,

 

[Alpine 1789]

Thanks, Don. I completely spaced out on the fact that he was talking about a 1600 engine. I'm glad I started with "I think you have that backwards" rather than "Don, you ignorant slut!".

 

[Aladin Sane]

I love a good Point, Counter Point reference.

 

[Alpine 1789]

You definitely have to be a certain age to get it.

 

[spmdr]

My $.02 here:

5500 RPM is quite conservative with better rods and pistons.


Check out the 1592/1600 engine build discussions on this forum.


consider the "New school" rods and pistons with a stroked 1592.


Links to check:

https://forum.sunbeamalpine.org/index.php?threads/1592-for-racing.28570

https://forum.sunbeamalpine.org/index.php?threads/h-beam-racing-rods.29544

https://forum.sunbeamalpine.org/index.php?threads/new-school-custom-pistons.29981

Also, consider some form of computer timing control to have half a chance of keeping the head gasket functioning.

DW

 

[husky drvr]

Thanks, Don. I completely spaced out on the fact that he was talking about a 1600 engine. I'm glad I started with "I think you have that backwards" rather than "Don, you ignorant slut!".

Jim,

Had to search for that one.

I think I'm of that age, but that is a reference that went right over my head. SNL was not a part of my life in those days. I was too preoccupied with working to pay for an expensive hobby - college.

Live long and prosper ,

 

[Limey]

hi Michael - So if I wanted to lay my money down today what Rods should I order?