building a 1.7 big bore?
 

I bought a 1970 914 for $600 about a year ago, It finally runs (and stops) but has compression in the 95 psi area. So
I guess its time for a rering, if not more.

This winter I'm going to tear into it and have no idea what I'm going to find. If the heads and pistons are good, I'm thinking about putting in a 76 mm stroke crankshaft (1934cc displacement). Then I thought well maybe I should bore it out and put 94 mm pistons in it, then I'd have ~ 2100cc

Anyway long story short, at what point should I just start hunting down a 2.0 litre case? Or just buy an eninge prebuilt?

Any opinions, or anyone out there who has built a big 1.7 ??


Thanks, in advance.

Todd

How much money are you looking to spend to build a motor? Big Type IVs are not cheap to build. Anyway, here's some info from the aircooled.net site that applies to 96mm pistons - I'm not sure about 94s.

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"96mm Type 4 Piston and Cylinder Sets

Price: $ Varies according to options
Part #: EPS0007
These SLIP IN to all 1800 and 2000cc engines for a nice increase in displacement. VERY reliable. Choose forged or cast pistons, and 22 or 24mm wrist pin size. We now supply these kits with top quality cylinders (stock cylinders, bored and machined in matched sets) because the quality of the "budget" ones sucked.

It is important to note that we only carry kits for the 1.8 and 2.0L engines, the 1.7 kits are junk. You can use the 96s for a 1800cc engine on your 1.7L engine IF you bore the heads out to the larger 1.8/2.0L size. 1.7s use a smaller head opening then the 1.8/2.0 engines, though the case hole is the same. As a result, the cylinder is TOO THIN on the top of the 1.7s to reliably install 96s. If you go to 96s on a 1.7L, we recommend you either use 1.8/2.0 heads, or bore your 1700 heads to the 1.8/2.0L size."

The only difference (big difference that is) with your 1.7 is that your cylinders heads have a smaller register in them. Your case is the same as a 1.8 and 2.0, so no need to do anything there. I would recommend purchasing some used 1.8 or 2.0 cylinders, some keith black pistons (from aircooled.net), and have the cylinders bored out and match honed to the keith blacks. Then you will have to have your heads remachined to accept the larger register of the 1.8/2.0 cylinders. This will allow you to have a nice 2056 (with a crank and rod swap- call DPR machine, they will exchange your 1.7 crank and rod set for a .010/.010 2L set.). I would also recommend putting 42 x 36 valves on the heads, trying to mimick the flow #s from a stock 2L 3-bolt head as closely as possible. If anything, the exhaust figures could be improved upon.

If you're on a budget, this is a good combo to shoot for, albeit if you are planning on retaining your stock fi, it won't be so good. A set of 40 idfs will be a nice match.

I had a 2056 with 40 idfs and an 86 grind webcam and it was a nice engine in my 914, but didn't quite come on until 2500 or so RPM and would happily spin to 6500.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

So if I build a 2056cc engine, can I simply replace my current 1.7 injectors with 2.0 injectors, and turn the fuel pressure up? or is it not that simple?


p.s. Thanks for the feed back.

Todd

In a perfect world, yes. I've tried it, and it doesn't work as expected. Three options: ditch the fi and go for carbs, get a 2L injection setup and then start tuning from there, or take your current system and fit it with an aftermarket FI such as the kit carlson. The throttle body would be a limiting factor as well, and the 2L setup has better flowing components and would be a better starting point even with the kit carlson. All things equal, the carbs would be a much easier solution and the route I chose myself for the 2056. Otherwise, the 1.7 could be rebuilt back to stock specs to retain the stock fi.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

Without covering every combination (and me being a pest) what happens if I rering the current pistons, and change out cranks, to a 71mm or 74 mm stroke. Can I use the FI then?

The reason I ask is my budget it fairly tight, I'm gonna autocross it locally, and would like to spend most of my money on suspension componets. Maybe next winter do the engine, starting with a 2.0 (hopefully).

That's a wise choice to spend the money on the suspension and brakes. Save your money then go for a bigger engine later, once all the upgrades are done to the car. Just hone and re-ring, do a good head rebuild and 3 angle valve job, clean up the ports, and possibly even swap in a better cam (73 grind or something based on this cam - only if the rules allow for such a change). Have the heads flycut a tad to bump up the compression and run premium gas too. You'll still have to do minor tweaking of the FI, but it should be a cakewalk compared to going to a 2056. Don't do the crank change either, since that will just make it even more difficult to tune. You'll still be able to run circles around most people with a 1.7 once you master the car. Then it's time to shop for more HP, something like a 2270 or 2600 :-)

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

Step Zero is always: RTFR. Read The Rulebook. That will let you know what sorts of mods are legal for which classes.

The regular 94mm pistons have the wrong wristpin location for the 66mm crank and rods. I think you wind up with ~1/8" of deck height, which means a compression ratio of about 5:1 (exaggerating, but not by much). I may have it backwards, BTW, and the pistons may actually stick out of the cylinders at TDC instead.

Anyway, I would suggest honing and re-ringing and getting the heads done. That ought to hold you for a good while. And remember, you will learn better by driving a car with limited power than you will if you drive one with tons of power. That means that you'll be even faster if you then step up to a powerful engine! :D

--DD

5 to 1?
TURBO time....

That's one way to look at it :-) Or even better yet you can scavenge gas out of tanks at the junkyard, since it should run with anything you can pour into the tank. Reminds me of the time I ran straight diesel on my father in law's '74 thing.... and it idled (flames, smoke, and all).

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

1832cc 94mm x 66mm

So you've read about using the 94mm Type 1 pistons conversions in place of the Type4 pistons.

Here is how its done:
If you use the 94mm B pistons, with 136mm Type 1 connecting rods and your Crank big end reground for Type 1 VW journals.

The 1800 93mm barrels will be bored out to fit the 94mm pistons.

This will build a 1832cc's you will be getting about 100 HP, which will be totally reliable.

How big are Type I journals? If they're significantly smaller than the stock 1.7/1.8 journals, then why not offset grind them so you get a longer stroke?

--DD

You could do that. The T-1 are the same diameter but narrower. You could also use toyota rods and get away without grinding the crank but only with 66mm stroke.

if the T-1 rods are narrower, what do you do about the side clearance on the rods?

How long are the Toyota rods you use?

Inquiring minds want to know.....

To use the Type 1 You need to have the crank journal welded then reground to Type1 width.
The toyota rods are 137mm