914 displacement increase questions

[Slanski62]

Hiello. This is my first post to the forum. I recently bought a 1.8 liter 914 motor, and rebuilding it will be my winter project. I have a couple of real high level questions to start.

If I want to increase displacement, is there a big difference between getting there via increases to the bore versus the stroke?

How much can I bore the existing cylinders? EBS said 96mm isn't a problem, but what about 100mm or even 102mm, assuming I'm willing to machine the case?

How much displacement will the stock 1.8 liter heads support before they choke the motor? I realize I'll have to machine them if I use bigger bores.

Thanks everyone for your help

Steve Yeatts
Chapel Hill, NC

[racer]

How much HP are you looking for?
How much $$ do you want to spend?
How long does the motor need to last? (See #1 and 2)

[Dave at Pelican Parts]

In general, engines with longer stroke tend to be more torquey and less rev-happy. Short-stroke motors tend to be more revvy and less torquey.

It is reasonably easy to bore the stock 93mm cylinder from a 1.8 out to 96mm. Make sure that a "torque plate" is used to hold the cylinders; this puts a clamping force on them like they'd have when installed on an engine. Several outfits make 96mm pistons for the 1.7/1.8 crank and rod set. This gives you 1911cc, and with a decent cam makes for a nice zippy engine.

Going larger than 96mm means you have to flycut the heads to fit the larger cylinders, plus likely cut the case spigots as well. Most of the larger cast-iron ones (103mm and 105 were relatively popular; 100mm and 102 were uncommon at best) are not super high quality and won't tend to cool very evenly no matter what. Unless you go with the Nikasil-plated aluminum cylinders, which cost a pretty penny but are quality stuff.

Going with a longer stroke than stock means a new crank and rods. Few of those are available, so be prepared to pay. You can go with Type I journals on the crank to get a little more room, but no matter what you start getting interference between one rod (#2 maybe?) and a cam lobe when you get over about ~74mm of stroke. The folks who run 78mm cranks are using reduced base-circle cams for clearance, for example.

Your 1.8 used a 66mm stroke. To make the 2.0 liter engine, the factory offset-ground the same blanks into a crank with a 71mm stroke. 71mmx96mm = 2056cc, which is again a nice motor. You can just get a set of 2.0 crank and rods (even 2.0 Bus ones, actually!!) to make that work, rather than having a set made custom. (Note that the wrist-pin hole is in a different location in the 2.0 pistons, so if you go with the 71mm crank and rods you should get pistons made for a 2.0 engine.)

If you use non-stock parts, you also have to worry about things like rod ratios. A short rod makes things fit better, but wastes more power on side-forces and friction. A long rod gives you better piston dwell time and less side-forces, but you wind up making the overall engine wider and needing custom pushrods and pushrod tubes and engine tin and on and on and on.

Your 1.8 heads are better for flow than the 1.7 heads are. They have larger valves, at the very least. I am told they will feed a 2056 with a stock cam with no problem. Note that caveat--with a stock cam. The stock cam is very tame, and if you go more aggressive with the cam you will flow more air (at high RPMs) and will probably want heads that can support that. The stockers will work to some extent, but how much is a question. And is affected by lots of other variables, like induction and exhaust and fuel quality and compression and cam ramps and port shapes and on and on and on.

Cams are another set of variables. They also have a lot of influence on where in the rev range your power band is, how wide it is, and so on. They also have a nasty tendency to go flat, due to changes in the available cam blanks and in oil formulations over the past two or three decades. (Valvoline VR-1, or Brad Penn, or other "old-style" oils with high ZDDP levels will help but are not a magic cure-all.) Get your cam and lifters from the same manufacturer to have the best chance of having them live with each other.

Cooling can be a challenge on more powerful engines. Very nearly anything you can to do make more power will make more heat. You will have to deal with this heat, and oil cooling can only do so much for you. Things like piston squirters can help, spray bars up in the rocker boxes can help, but that adds more complexity and more expense and again it only goes so far.

OK, so all of that said:
- The simplest thing to do is to bore the cylinders to 96mm and get some rings and pistons to fit.
- The next simplest thing is to do that, and get a 2.0 crank and rods and make sure the 96mm pistons have the 2.0 wrist pin height.

After that, things get rather more complicated and expensive. If you're into trying stuff out, it's a journey worth taking as long as you can live with whatever problems your mistakes may cause. (Or random chance.) If you just want a motor to drop into the car so you can drive, use one of the simple options.

--DD

[Slanski62]

Hi Dave. Thanks very much for your thorough response. It's real helpful.

Steve

[mark 74 carrera]

I agree! Dave, this is a great answer to the question I have wanted to ask. What's a relatively simple way to bump my stock 1.8 liter's performance? For back road running and not racing, your plan sounds like a perfect and simple upgrade.

Mark

[Slanski62]

I read a VW 'expert' state we could expect 70 -75 ft. Lbs. of torque per liter of output. This was in the context of VW type 1 builds. Does this benchmark hold true for the T4? He presented the formula, which I've seen elsewhere, that HP = (torque x RPM)/5252. Assuming a 2 liter motor and peak output at 5000 rpm, output would be 133 to 143 hp.

Based on Dave's post above and this formula, it's apparent that getting 140 HP isn't difficult, but if you want more, it can be difficult or expensive. So a follow up for Dave is, if I want a solid 150 HP, hats the best way to get there?

[Dave at Pelican Parts]

HP is defined as torque*rpm/5250, so all motors will fit that.

I've never actually thought much about torque/liter. Some comparisons with various stock autos might prove enlightening. Keep in mind that our engines aren't nearly as developed as anything in the last couple of decades, though.

I have to run to a meeting; hopefully I can get back to this thread later.

--DD

[racer]

As point of references...
Original Customs 2056 Type IV
Original Customs 1911 Longblock
Porsche 914


1.8 heads can work, with some porting and polishing.. They just won't be as nice as 2.0 heads.

While prices may vary, you can likely pick up a lot of info from these type IV builders.

For many years, the "easiest" and reliable upgrade was to put a 2056cc in a 914. Depending on cam, and carbs vs FI, 110-130hp was possible. And it was also plug and play. These motors are only getting older and perhaps even more $$ to upgrade. Finding quality components is one challenge. Finding someone who knows the motors and what to expect is another.

150hp type IV motor would be a lot of fun in a 914 for sure.

[Dave at Pelican Parts]

A simple way to bump up a 1.8's performance is with a set of headers. Real tuned headers, such as the ones Tangerine Racing sells. His aren't cheap, but they are the best and most effective ones out there. You lose all semblance of cabin heat unless you opt for his heat exchanger box, which will help defog the windshield but probably not a lot more.

Bumping the engine up to 1911cc (96mm P&Cs) would generally be less money, but more work. Compression can be set to wherever you like; something on the order of 8.5:1 should still work with premium-grade fuel.

You can combine both of those for more power.

To get real power, you'll need to crack open the case. An aggressive cam that moves the power band up in the RPMs will definitely get you more power, but you will have to ditch the stock L-jet EFI and go with something aftermarket or a set of carbs. Much more involved.

I don't have a recipe for getting to 150 HP, in part because there are so very many variables, but also because I simply haven't done the in-depth research. I suspect that a 2056 with a hot cam, headers, carbs, high compression, and very good heads would do it. But spinning the engine fast enough to make that level probably means a reduced lifespan.

Lots of trade-offs you can make...

--DD