Stupid, stupid SP1300 ideas

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petew
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Stupid, stupid SP1300 ideas

Post by petew » Mon May 22, 2017 3:20 am

I've got a 1300SP sitting my shed doing nothing. I bought it a few years back to convert into a blown motor for my bug. That plan changed, but I'd like to use it for something. What I'd like to do is have some fun with it... on the cheap.

I've got some Manton moly pushrod and AA 1.25 ratio rockers. I also have some pretty heavy duty double valve springs. I figure I could use these. My current bug is setup for MS EFI/ignition, so I'd use that too.

What I'd like to try and do is build it up a crazy mouse motor ala JPM, but with the SP heads. I know this seems crazy, but I want to keep as much stock stuff as possible. So some questions...

1. Could I balance the motor somehow (and save the case) WITHOUT having to use an counterweighted crank?
2. Would reducing the rotating mass a lot help it rev? I'm thinking of things like cutting down the skirts on pistons and the like.
3. Where would the heads run out of breath stock? How much porting could I get away with?

Thoughts?

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Re: Stupid, stupid SP1300 ideas

Post by petew » Thu May 25, 2017 11:08 pm

C'mon, no one? A series minis are single port too.

There are a stack of crazy 36'ers out there now. Surely the 1300 block is an upgrade past them and the 40hp 1200?

I came across some truly nuts 77mm piston on ebay from motorbikes. Come on, dream a little!

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Re: Stupid, stupid SP1300 ideas

Post by Marc » Fri May 26, 2017 3:11 am

Don't need to dream, just hearken back about 50 years - you're hardly the first one to think of this.

1300SP heads have smaller intake ports than 15/1600s; you could open them up as big as stock 15/1600 heads (even a bit more) but you'd then be limited by the valve sizes. 15/1600 carb'd engines (DP and SP) all use 35.5x32 valves; 1300 and L-Jet 1600DP use 33x30mm. Even the dualport 1300 (never offered in the US but popular in countries where they tax based upon displacement) had 35.5x32, the 33x30s are great for low-end grunt but undesirable for any kind of performance work.

Because the 1300SP was only sold in the USA for one year the heads are pretty rare. They actually work well for a daily-driver 1600, making it more responsive and netting better mileage than the 35.5x32 heads (they do need to be flycut for the larger-O.D. cylinders). But by the time you get to those little red marks on the speedo you may as well shift since the HP is already nearly peaked. So, there are a few folks out there who would like to have those heads - maybe for a Bus - but you'd be wasting your time with trying to build a hot-rod using them. Simpler to just do a little step-cut on some 15/1600 heads and get the bigger valves and intake ports with zero effort. The small bore does shroud the 35.5mm valves, in fact if you flycut the heads a lot and/or run a lot of lift the valves will actually hit the cylinders below 77.5 or 78mm.

The F0 1300 case is identical to the 1967 1500SP H0 case, and 1300 cylinders have the same bottom spigot diameter as 1500 and 1600. The metallurgy isn't bad (not cottage-cheese alloy like the `68/`69s were) but it's a small-passage, single-relief case. That's all people had to work with before 1970 so every classic VW dragracer used one like it, but it's nowhere near as good as the `71-up cases.

The way that the flywheel is sealed to the end of the crank was changed from a gasket to an O-ring setup midway through the `66 production year, so depending upon the vintage of yours it may not accept a 12V flywheel without a little modification. 69mm cranks didn't get cross-drilled rod bearing journals until late in `67, but IMO those aren't really a benefit with a small-passage case. If you still have the original rods you'll see that they look almost like 1200 parts (bolts rather than nuts) but with dimensions identical to 15/1600 rods - so they're already lighter (and weaker - but I've used 'em on bigger engines without a failure so unless your plans include nitrous or a turbo they'll probably hold up).

Slinging the lightweight rods and pistons the non-counterweighted stock crank shouldn't start flexing much until you're past 5500 RPM - and that would be an accomplishment with SP heads - so there's really no need to change it.

If you really want to get all you can out of the 1300, first step would be to graft on some DP heads. The chambers are bigger so the compression ratio would be about 6:1 without any flycutting, but you want a step of the correct diameter to center the 1300 jugs anyway so kill two birds w/one stone. To end up with even 8½:1 @.050" piston deck the DP heads will need to be reduced from the stock ~52cc to under 37cc so they'll have to be flycut ~.150" and have a fin removed (the engine just got narrower - not enough for a 1200 exhaust system to fit but too narrow for a 1600 system) and of course you'll need custom-length shorter pushrods to match. To get serious compression with such a small displacement you'll need pop-up pistons that'll fit the chambers or a lot more flycutting. I've been to 12½:1, that required cutting the heads clear to the sparkplug holes, milling off two fins, and notching the piston tops for the electrodes...but at least a 1200 header bolted up :)
And don't forget, unless the cylinders are bored at least .020" over (.040" to be sure) the intakes are going to hit the cylinderwalls...those can be notched too, but only down to just above the top ring's travel. Obviously, the pistons need valve notches too by that point. And now, with enough carburetion and cam, you'll be able to buzz it hard enough that the stock crank's going to start flexing and knocking out the main bearings and wristpin clips.

Are you sure this is how you want to spend your time & money?

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Re: Stupid, stupid SP1300 ideas

Post by petew » Fri May 26, 2017 4:02 am

Marc wrote:
Fri May 26, 2017 3:11 am
If you really want to get all you can out of the 1300, first step would be to graft on some DP heads. The chambers are bigger so the compression ratio would be about 6:1 without any flycutting, but you want a step of the correct diameter to center the 1300 jugs anyway so kill two birds w/one stone. To end up with even 8½:1 @.050" piston deck the DP heads will need to be reduced from the stock ~52cc to under 37cc so they'll have to be flycut ~.150" and have a fin removed (the engine just got narrower - not enough for a 1200 exhaust system to fit but too narrow for a 1600 system) and of course you'll need custom-length shorter pushrods to match. To get serious compression with such a small displacement you'll need pop-up pistons that'll fit the chambers or a lot more flycutting. I've been to 12½:1, that required cutting the heads clear to the sparkplug holes, milling off two fins, and notching the piston tops for the electrodes...but at least a 1200 header bolted up :)
And don't forget, unless the cylinders are bored at least .020" over (.040" to be sure) the intakes are going to hit the cylinderwalls...those can be notched too, but only down to just above the top ring's travel. Obviously, the pistons need valve notches too by that point. And now, with enough carburetion and cam, you'll be able to buzz it hard enough that the stock crank's going to start flexing and knocking out the main bearings and wristpin clips.

Are you sure this is how you want to spend your time & money?
:lol:

Have you seen the 1300DP motor a UK guy built for classic touring car racing? 9K rpm and 128hp.

https://forums.aussieveedubbers.com/vie ... 798&page=1

Then there are these pistons off ebay...

http://www.ebay.com.au/itm/HONDA-CRF-25 ... SwofxUlyez

I know it's ridiculous, but like I said. There are a stack of guys doing the 36'hp challenge with motors that we all thought were less than weed eaters a few years back. Why not have a go.

I think on your advice re DP heads. Maybe I can find some DP 1300 heads. ;)

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Re: Stupid, stupid SP1300 ideas

Post by Marc » Fri May 26, 2017 5:57 am

The way I read it he's claiming 126HP from 1285cc...before he wanders off into some fantasy land where various displacements all make the exact same power per liter (an absurd concept when you start taking into account the valve-size limitations and bore-to-stroke ratios involved). I'd like to know more about what's in that. My 1285 race motor was limited to a pair of 35mm 1-bbls, non-ported heads and a stock crank; it was undoubtedly the most powerful legal engine ever run in its class (one that gave me a good run some times turned out to be a 1585 when tech'ed). Never had it on a dyno but it'd be pretty optimistic to think it made over 70HP - pretty big jump from there to 126, they must have some magical dyno correction factors down there :)


Just because that piston yields 13.2:1 in its intended application doesn't mean squat. What's the compression height? (distance from top of piston to wristpin centerline). On a stock Type I piston it's approx 39.6mm. That's over 1½" - the piston in the picture looks like its pin height is about 1"....that would mean an extra half-inch of piston deck unless you spring for some aftermarket longer rods to compensate. That much deck would bring the 37cc head 8½:1 engine I mentioned above down to somewhere around 4:1.
Is it even a 22mm wristpin?

DP 1300 heads aren't worth the effort to locate, essentially they're just 1600DP heads that are bored to 89.8mm rather than 93.8mm. Since you'd no doubt need to flycut them for the desired CCs anyway, it's no biggie to just start with the common 1600DP head and cut an 89.8mm surface in the center - what I meant by "step-cut" above.

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Re: Stupid, stupid SP1300 ideas

Post by petew » Fri May 26, 2017 7:28 am

Marc wrote:
Fri May 26, 2017 5:57 am
The way I read it he's claiming 126HP from 1285cc...before he wanders off into some fantasy land where various displacements all make the exact same power per liter (an absurd concept when you start taking into account the valve-size limitations and bore-to-stroke ratios involved). I'd like to know more about what's in that. My 1285 race motor was limited to a pair of 35mm 1-bbls, non-ported heads and a stock crank; it was undoubtedly the most powerful legal engine ever run in its class (one that gave me a good run some times turned out to be a 1585 when tech'ed). Never had it on a dyno but it'd be pretty optimistic to think it made over 70HP - pretty big jump from there to 126, they must have some magical dyno correction factors down there :)
Watch the vids of him racing. I think you'll find it interesting. There's another thread on aussieveedubbers with more in it I think. Just look up his username "pompom". I don't see why he'd be lying and JPM is making 195hp out of a 1600 at about the same revs.
Marc wrote:
Fri May 26, 2017 5:57 am
Just because that piston yields 13.2:1 in its intended application doesn't mean squat. What's the compression height? (distance from top of piston to wristpin centerline). On a stock Type I piston it's approx 39.6mm. That's over 1½" - the piston in the picture looks like its pin height is about 1"....that would mean an extra half-inch of piston deck unless you spring for some aftermarket longer rods to compensate. That much deck would bring the 37cc head 8½:1 engine I mentioned above down to somewhere around 4:1.
Is it even a 22mm wristpin?
Yeah, there'd be work to do if I wanted to use them. Although, that's just one set. There are a LOT or 77mm motorbike pistons to choose from. All of them are lighter and more purposed for higher revs.
Marc wrote:
Fri May 26, 2017 5:57 am
DP 1300 heads aren't worth the effort to locate, essentially they're just 1600DP heads that are bored to 89.8mm rather than 93.8mm. Since you'd no doubt need to flycut them for the desired CCs anyway, it's no biggie to just start with the common 1600DP head and cut an 89.8mm surface in the center - what I meant by "step-cut" above.
Yeah, fair enough. Although I can probably find some over here easily enough. We had lots of DP1300s in the 70s.

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Re: Stupid, stupid SP1300 ideas

Post by farmer » Fri May 26, 2017 3:11 pm

Marc wrote:
Fri May 26, 2017 5:57 am


DP 1300 heads aren't worth the effort to locate, essentially they're just 1600DP heads that are bored to 89.8mm rather than 93.8mm. Since you'd no doubt need to flycut them for the desired CCs anyway, it's no biggie to just start with the common 1600DP head and cut an 89.8mm surface in the center - what I meant by "step-cut" above.
Erhm, no. Real 1300 dual port heads have smaller port volume. Some of the later ones out of AR engines have only 30 mm exhaust valves too.

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Re: Stupid, stupid SP1300 ideas

Post by farmer » Fri May 26, 2017 3:11 pm

And of course smaller chamber

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Re: Stupid, stupid SP1300 ideas

Post by Marc » Fri May 26, 2017 3:56 pm

farmer wrote:
Fri May 26, 2017 3:11 pm
Erhm, no. Real 1300 dual port heads have smaller port volume. Some of the later ones out of AR engines have only 30 mm exhaust valves too.
Yes, the chamber is a little smaller (if it wasn't they'd only have ~6.6:1 w/flattops). The domed-piston version increases the C.R. by ~.3 but I haven't been able to find those pistons available anywhere - they must exist in Europe but whoever's sitting on them doesn't have an online presence.
The intake manifold endcastings are smaller inside than 1600DP, and the center section is smaller in diameter with the smaller carb flange for the the 31PICT-3 carb they use.
Are you saying those late AR heads are 33x30 or 35.5x30? I've never seen either (although an L-Jet 1600DP is 33x30, with 9mm exh guides).

Regardless, IMO it wouldn't be worth the trouble to hunt down 1300DP heads for a high-performance build in the US, where they're rare as the proverbial hen's teeth. But if they're common where petew lives, the smaller chambers would make it worthwhile. IIRC they're about 4cc smaller than 1600DP.

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~

Post by Marc » Fri May 26, 2017 5:08 pm

petew wrote:
Fri May 26, 2017 7:28 am
There are a LOT or 77mm motorbike pistons to choose from. All of them are lighter and more purposed for higher revs...
I'd concentrate on ~78mm to eliminate the concern of the 35.5mm intake valves striking the cylinderwalls. The added cost of having the cylinders bored to match would be trivial compared to the overall budget if you're seriously after 100+ HP.
1200 connecting rods have a 20mm wristpin and would need to be narrowed at the big end to fit the stock journals of a 69mm crank - something to consider. They're not as strong as 15/1600 rods by a long shot, though - I'd be more comfortable with the latter (or aftermarkets) provided you can find pistons with a ~22mm wristpin.

I think the biggest challenge would be finding motorcycle pistons with a tall enough pin height for a stock-length rod - you'll need to do some research into that since it's not often published by vendors. Late 1200cc engines have cylinders that are the same registers top & bottom as the 1300 but are shorter - another item that's rare in the US but might be common where you are, shorter barrels might also be a way to achieve the desired piston deck. Even classic 1200 barrels that are only 87mm O.D. at the bottom can be used in a 90mm 13/15/1600 case by simply putting an O-ring around the skirt to hold them centered during assembly, once the head's torqued down they aren't going anywhere (old Formula Vee trick).

Another factor you could play with is rod length. Aftermarket replacement rods are readily available in 5.5 and 5.6" length, there are even 5.7s (stock is 5.394"). The higher rodlength-to-stroke ratio would be appropriate for a high-winding engine but IMO 5.7" would be too long if you're thinking of remaining streetable - I've run those on a 69mm stroke and while it makes a happy motor above ~5000 RPM, at idle the increased piston dwell near TDC causes so much slap that it sounds like a diesel.

You might even abandon the idea of using a rod intended for the ACVW and instead find one that can be modified to fit the crank. Stock journal size is 55mm (2.165") but those could be turned down for a smaller-I.D. rod; if done offset, you'd also have the opportunity to tweak the stroke...for example a 69mm crank offset-ground for 2.00" bearings can be 73+mm => 78x73=1395cc.

The more "customized" parts you incorporate, the harder it'll be to make repairs if needed since the same machining will be needed on any replacements, but I suppose if you've read this far you're past the point of caring about that. We're way off in the weeds compared to your original stated goal.
petew wrote:
Mon May 22, 2017 3:20 am
... I want to keep as much stock stuff as possible....

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Re: Stupid, stupid SP1300 ideas

Post by Piledriver » Sat May 27, 2017 1:07 am

Perhaps emulating the JPM 1600 plus boost would be more interesting.
I'd still stick a counterweighted crank in it on principle.

See if you can get in the 300 HP club.

IIRC Lancia make a 1700 at one point that made well north of 700 when turned up to 11.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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Re: Stupid, stupid SP1300 ideas

Post by petew » Sat May 27, 2017 2:41 am

Piledriver wrote:
Sat May 27, 2017 1:07 am
Perhaps emulating the JPM 1600 plus boost would be more interesting.
I'd still stick a counterweighted crank in it on principle.

See if you can get in the 300 HP club.

IIRC Lancia make a 1700 at one point that made well north of 700 when turned up to 11.
And then there was the Zakspeed capri. 1.4L turbo that shut down all manner of DTM hardware. :twisted:

Hmmmm... thinking, thinking... :?

P.s. I won't even start on my wetsump 2 stroke musings. :lol:

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Re: Stupid, stupid SP1300 ideas

Post by Marc » Sat May 27, 2017 3:18 am

petew wrote:
Sat May 27, 2017 2:41 am
...I won't even start on my wetsump 2 stroke musings. :lol:
That's been done, too. In fact the original powerplant that Ferdinand Porsche wanted to use in the VW was a 2-stroke, but that was abandoned because the available materials at the time weren't sufficient to reliably seal the crankcase. The engine we all know & love was NOT designed by Porsche, but by an assistant engineer who'd come up with it while in technical college - it was hurriedly stuffed into the VW prototype to make the deadline imposed by Hitler, at the time Porsche considered it to be just a stop-gap solution while he continued to attempt perfecting his 2-stroke...eventually he faced facts and got behind the 4-stroke motor.

Attempts to convert a conventional ACVW engines have been made but obviously none has been especially successfully or they'd be common knowledge. Conventionally aspirated with exhaust ports in the cylinders is the simplest (other than figuring out a way to plumb the exhaust) or you could go Detroit Diesel style with a Roots supercharger....either way takes a trick cam with double lobes or a 1:1 cam drive. On paper it'd be a great way to nearly double the specific output, but nobody's made one that works well enough to bother with (yet, anyway) ;)

Back in the `60s there was a small ad in the back of every issue of Popular Mechanix for a conversion kit that adapted a 2-stroke outboard motor to a VW transaxle. On my first submarine c1973 I served with the son of the guy who invented that - he had pictures showing him pulling a tour-bus out of the ditch in Idaho with a bare VW pan outfitted with one of those :)

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Re: Stupid, stupid SP1300 ideas

Post by Marc » Sat May 27, 2017 4:06 am

Piledriver wrote:
Sat May 27, 2017 1:07 am
...I'd still stick a counterweighted crank in it on principle...
The primary concern with a Type I crank is the max RPM - they just aren't stiff enough in stock form to keep them from flexing above ~5000 RPM or so, which beats the hell out of the center main bearing and case web. The resultant connecting rod misangularity also knocks out the wristpin clips - Spirolox or teflon buttons are a Band-Aid. Same goes for putting dowel pins in the center main web or sleeves around the center case bolts - the gain (if any) is minimal so IMO the money spent on the machinework is wasted since the case still ends up in the scrap pile.

I've used non-CW cranks for short-fuse engines intended only for establishing track records. The goal was achieved but at the expense of sacrificing the case...even had one that permanently yanked the crank out of true (by a LOT).

A stock, non-CW crank that's dynamically balanced and not extremely stressed is good to ~5500 RPM - beyond that, counterweights are mandatory IMO if you expect to run for more than a mile or so without terminal damage.

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Re: Stupid, stupid SP1300 ideas

Post by petew » Sat May 27, 2017 5:35 am

What if you swapped the factory crank over for a WB crank?

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