Many questions about 1.7L rebuild/upgrade

[Mockmaw]

This is a long post. I hope it makes sense as I wrote it late last night..

Okay, I posted here a few weeks ago concerning my 72 1.7's engine failure. I've decided that I'm going to go forward with an engine rebuild. I plan on doing the rebuild myself (using our garage in San Diego and the aid of the local machine shop that we've been using for years.) I don't know the extent of the engine's damage, and I won't know until I've dropped the engine and taken it apart. I'm planning for the worst though, which means a complete rebuild.. I'm hoping that it won't be that bad and I may change steps if I find that some of my parts are still good (see below.)

I'm aiming for a larger displacement, carbed engine with aggressive cam. I've spent the last week or so doing research about the options for TIV rebuilds and what's involved in general engine rebuilds, including extensive reading of forum posts from here, the PP board, and shoptalk. I've also ordered two books which I've heard are excellent references the 'How to rebuild your aircooled VW' guide and the Dellorto tech book/reference.. I'm new to engine rebuilding, so I'm trying to learn as much as I can before I get my hands dirty (and start breaking stuff!)

I have several questions that I hope some of you could help me with (most of them are me asking about component X and you giving me anecdotal Y about your previous experience with it.) I recognize that a lot of what I may be asking has a certain "you find this information by spending years at the track" aspect to it, and I'm not asking anyone to divulge their voodoo secrets.. I'll just say that any assistance or guidance is greatly appreciated.

My choice of displacement is likely going to come down to the condition of my crank and rods (which are 66mm). If the crank and rods are in good condition (or at least good serviceable condition), I will likely stick with the 66mm rods.. I'll add 96mm pistons and depending on the condition of my current heads, either machine my current ones (if good) or purchase good condition ones to bore to 96mm. So the 66mm rods with 96mm P+C's should give me 1910cc's, correct?

If the crank is not in reusable condition than I'll acquire a set of 2.0 crank and rods (71mm), add 96mm P+C's and whatever headwork is necessary. This should give me the popular 2056cc displacement, correct?

My first problem: I don't know what to expect from each of the displacements/setups.. I've driven low-performance cars my whole life (nothing larger than the 96 2.0L Ford Probe and 97 2.0L Dodge Neon engines, my daily drivers since 16 include a 83 Volvo 240DL and a 86 Civic 1.5L FI.. Perhaps you can understand why I felt that the 1.7L 914 engine was quick!) Moving back on topic, I know that the 1910cc displacement is more of a 'stroker' engine, equating to higher revs (and more top-end power?) but with limited lower end torque. The 2056cc should be a more balanced engine. So some of my questions (and I realize how some of these may be 'unanswerable' without knowing all the other details of the engine..):

1. Will I obtain higher revs than the stock redline by going with the 96mm bore/66mm rods combination or just more power at the high end?

2. If I go with the 1910cc, will I have reduced torque as compared to engines with a more 'balanced' bore to crank ratio?

3. Now the broad question: What kind of performance difference will I see between the rebuilt 2056cc and 1910cc assuming all other components are the same?

4. Even more difficult: what kind of relative performance difference will I see between my old 1.7 (which is difficult to analyze since I know it's a tired engine) to the 2056 and 1910?

5. Is it worth it to even consider the 1910 displacement? It seems like such a rare combination compared to the 2056, a common displacement when people do upgrades/rebuilds for 914's. The 1910 does seem more common in the VW world, though.

6. Is there a displacement combination that I'm missing which I should be considering?

Two: I will be converting the car to carbs as I want to run a more aggressive cam, likely the webcam 86a (and I'm getting tired of fuel injection issues.. especially the increasing cost associated with FI components.) There's a lot of controversy associated with sizing carbs to engine displacement, and perhaps even more in which carb setup to go with. I've seen many recommendations for the Dellorto tech reference, so I'm hoping that will give me some answers, but I'd like to ask here:

1. Sounds like most people prefer the Dellortos to the Webers (including Jake Raby, who's engine building judgment I certainly trust), but I haven't seen a post on any forum explaining why. Can anyone provide pros and cons to the dellortos over the webers?

2. As for sizing, I've found the general rule to be: Weber 36 for 1.7/1.8, Weber 40 for 2.0, Weber 44 for 2.2, Weber 48 for 2.4+ (with Dellorto being one size down in all cases.) Is this a good rule to follow? Unfortunately, the displacements I'm looking at lie somewhere in the middle of these marks.. is it better to go larger or smaller in the case of the 1910cc and the 2056cc?

3. I've heard mixed opinions about purchasing carbs used (taking into account the fact that Dellorto DRLA's aren't even made anymore.) Is it 'okay' to purchase and use used carbs? When are rebuilds necessary? Any qualities that I should particularly look for to avoid bad used carbs?

Three: For the ignition, I'm looking at a Mallory Distributor with Vac. Advance combined with a Mallory HyFire VI. I've heard so many good things about the Mallory (especially coming from Jake) that it seems foolish to not go with it. Are there any reasons why I should not go with this setup? I recognize that it is fairly costly though, so I want to ask: how will the dizzy from my 1.7 handle in the 1910 or 2056?

Four: Sounds like the webcam 86a is the cam to go with for this application, any other recommendations or reasons I should not go with this cam?

I realize I may be leaving out quite a bit, but those are all the questions I can think of right now. Any and all help is sincerely appreciated! Thanks!

-Tyler

[Dave at Pelican Parts]

Oh boy, this is certainly a bunch of very big questions!

First, 66x96 will give you 1910 or 1911cc displacement, while 71x96 will give you 2056cc displacement. You are quite correct about that.

1. Will I obtain higher revs than the stock redline by going with the 96mm bore/66mm rods combination or just more power at the high end?

In general, short-stroke motors tend to be more rev-happy than long-stroke motors, which tend to be more torquey. But in the case of the Type IV motor, many other factors dominate over those. The biggest ones being the cam and the heads. With the stock cam, the only way to get the motor to spin faster than about 6300 RPM is to miss a shift... It makes absolutely zero power past about 5300 RPM. This is regardless of displacement.

2. If I go with the 1910cc, will I have reduced torque as compared to engines with a more 'balanced' bore to crank ratio?

Generally, no. All other things equal, the 1910cc engine should be as good as the 1.7 engine just about everywhere in the RPM range, or better.

3. Now the broad question: What kind of performance difference will I see between the rebuilt 2056cc and 1910cc assuming all other components are the same?

I would guess (and it is a guess!) that the difference would be quite noticeable, back-to-back.

4. Even more difficult: what kind of relative performance difference will I see between my old 1.7 (which is difficult to analyze since I know it's a tired engine) to the 2056 and 1910?

I hear that it is a sizeable difference. Depending on the rest of the build, of course, you can get 30% more power than a tired 1.7 makes from a 1910, or 60% more from a 2055.

5. Is it worth it to even consider the 1910 displacement? It seems like such a rare combination compared to the 2056, a common displacement when people do upgrades/rebuilds for 914's. The 1910 does seem more common in the VW world, though.

The 96mm cylinders that fit 1.7 heads are very very thin. I usually recommend that they either locate a 96mm kit that is intended for 1.8s, or find some 1.8 or 2.0 cylinders and have them honed (by a reputable shop) to 96mm. The heads will have to be cut to accept them. Otherwise, chances are not that bad that the cylinders will not last a long time for you.

6. Is there a displacement combination that I'm missing which I should be considering?

Strokes up to 76mm with Bug rods can be done relatively easily. (Mock it up a zillion times to check for clearance, though!!) It's about $500 for the crank, so it isn't cheap... But the rods are relatively cheap and light. You can use Type I 94mm "overbore" pistons, even. Those are also cheap and light! The motor starts to become more of a stump-puller, though.

1. Sounds like most people prefer the Dellortos to the Webers (including Jake Raby, who's engine building judgment I certainly trust), but I haven't seen a post on any forum explaining why. Can anyone provide pros and cons to the dellortos over the webers?

I hear that the progression circuits in the Dells are far superior. That means better transitions from off-throttle to on-throttle, and better performance at part-throttle. Which is where street cars do most of their driving.

2. As for sizing, I've found the general rule to be: Weber 36 for 1.7/1.8, Weber 40 for 2.0, Weber 44 for 2.2, Weber 48 for 2.4+ (with Dellorto being one size down in all cases.) Is this a good rule to follow? Unfortunately, the displacements I'm looking at lie somewhere in the middle of these marks.. is it better to go larger or smaller in the case of the 1910cc and the 2056cc?

Quite a number of people use carbs that are theoretically "too large" for their engine, and make them work very well. I'd probably consider Dell 40s for either of those two. Note that it's the overall flow capacity of the engine that determines what size carb is needed--so cam and valves and heads all enter into it, as does exhaust.

3. I've heard mixed opinions about purchasing carbs used (taking into account the fact that Dellorto DRLA's aren't even made anymore.) Is it 'okay' to purchase and use used carbs? When are rebuilds necessary? Any qualities that I should particularly look for to avoid bad used carbs?

If you want Dells, you've gotta buy used. I would want to rebuild any used carb I bought.

...Then again, I'd rather go with aftermarket FI...

Three: For the ignition, I'm looking at a Mallory Distributor with Vac. Advance combined with a Mallory HyFire VI. I've heard so many good things about the Mallory (especially coming from Jake) that it seems foolish to not go with it. Are there any reasons why I should not go with this setup? I recognize that it is fairly costly though, so I want to ask: how will the dizzy from my 1.7 handle in the 1910 or 2056?

It will work OK. Better than a 009, probably not as good as an 050 or stock 1.8 distributor. The Mallory, from the sound of it, is the thing to get if you have the budget.

Four: Sounds like the webcam 86a is the cam to go with for this application, any other recommendations or reasons I should not go with this cam?

Cam selection, valve sizes, and head work are three of the most important things to how the engine performs. They all work together, and are all inter-related. Keeping the stock small 1.7 valves is going to give you good flow velocity at lower RPMs, and start to choke off the volume at higher RPMs--particularly when feeding a larger-displacement motor. A cam with a lot of lift and/or duration can overcome that to some extent, but at the expense of needing stiffer valve springs and/or lighter valvetrain parts. The former will wear things faster and rob some power, the latter are more expensive and (especially if not done right) are weaker.

Trying to work out a combo like this very often is a whole mess of trial and error. I don't have enough of that to do much more than wave my hands and repeat what I have read. (That is what you have, above.) Also note that the "little things" can easily make or break an engine. Static & dynamic balancing, ultra-careful assembly and fitting, reducing obstacles to air flow and oil flow, and so on.

--DD