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1500 engine rebuild - part 1; planning

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This is what I've heard, but it doesn't answer one question: Were the pushrods the same length as on other years? Or were there 1976 specific pushrods?

There are numerous heads that came on the 1300 and 1500 engines, and they are all interchangeable, but that doesn't mean you should interchange willy nilly or you can end up with too high or too low compression or trade down to smaller valves. If you are keeping your basically stock North American market engine setup, then no point in looking for another head--just tidy up the one you have. But if you want to do a little more and will be improving the flow into and out of the head (better carbs and intake manifold, and a decent exhaust), then finding a "big intake valve" head from a world market late 1300 engine will yield 8.9:1 or so on a 1500 with dished pistons--an upgrade that'll require no messing with the bottom end to change to flat-top pistons. Shave about 0.040" off this same head, and voila--approx. 9.5:1 compression, which will do fine on ordinary premium pump gas and a reasonable ignition map and not knock. There are a few other "big intake valve" heads to choose from, but for most you'll also need to switch to flat top pistons to help raise the compression enough to help. But as has been said, without some other mods, this upgrade would yield little improvement.

The combustion chamber volumes of your 75 and 78 heads (I suspect stamped (not cast) with part numbers TKC 1409 and TKC 3239, respectively) are the same (on the order of 45cc per cylinder per head chamber only--not counting the deck clearance volume and piston dish volume). This and the dished pistons make a 1500 engine 7.5:1 vs. 9.0:1. If you decide to use the 75 head with the air ports, remove the little air injection tubes before you plug the holes to improve airflow.

This was posted by Paul Geithner some time ago somewhere, and I saved it for reference. Hope it helps!
 
Thanks guys! Lets keep this going, as I'm quite sure I wont be the last one to do a rebuild like this.
 
Pete,
Some more of the engine discussion on the NASS forum

The big journal cranks, while heavier, are also stiffer and stronger than the small journal cranks.
The real problem is the big journal rods, they are apparently made from the heaviest metal known to man.
Typically they they run 775-800 g (for a 48 HP motor!!!!)

The solution is straightforward, lighter rods, flat top pistons, the usual port'n'polish, cam, headers, dual SU's.

Turns out that the stock big journal rod are 1.875 stock.

You can find (on eBay) ex-Nascar H beam rods that use the very common 1.850 bearing, weighing about 500g, for about $200/set of 8. Each rod is capable of supporting 75-125 HP at 8K RPM.

So turn the journals to 1.850, and use the H beam rods


The stock Spitfire rods are 5.75 C-C, and the deck height is 8.75".

So you can use SBC 5.7 rods and stock 1500 pistons with a 1500 crank, or if you go with a 1296 crank, use 6.00 H beam rods, and 1500 pistons, they pop up about 0.020", so you might not even have to skim the head.

Why would you choose the 1296 over the 1500?

So you can turbocharge it and run higher revs, of course!

The longer rods yield a bit better mechanical advantage in a motor, which equals more torque.

The advice to fix up the oiling system is dead on, but you should also put 0.050" restrictor sleeves into the cam bearing galleries. This helps to maintain oil pressure/flow to the mains and rod bearings.

With these mods, even a 1500 can rev reliably to 7500 RPM.
 
Don_R said:
With these mods, even a 1500 can rev reliably to 7500 RPM.
Click to expand...

You sir are the first person I've ever heard say that!

I'm going to bookmark your information.

Now a stupid question. If you turn the crank that much, do you have to get it nitrided? I've read that turning cast iron causes it to harden anyway.

Never mind, My math skills are usually turned off on the weekends. It isn't that much.
 
Groovy Don, thanks! I keep on reading more and more about how the 1500 engine is the way to go. Right now I'm looking into bore options. I think I might be asking Michael Oritt (when he gets back) about the bore on his Elva's engine. It's a 1500 bored to 1600. His race engine seems really reliable, which should prove fantastically fun on the street, if I go with similar specs.
 
Just trying to do my part in helping you spend your money, Pete. :thumbsup:
 
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