yet another engine rebuild..

[James Warren]

Hi all,

New to the site as a member (been lurking for several months).

This post is a bit long btw...

I need to replace the engine in my car.  After doing a bunch of research, and mostly having enough money to do it, I'm leaning towards rebuilding mine as a 2.3 stroker (100mm crank, 86 mm bore). That would be with a new 2.4 crank, wiseco pistons and eagle rods.

My car is a 92 tsi awd. My engine is a 6-bolt as far as I can tell (oil pan bulges out on driver's side) and shows no signs of crankwalk. Mileage is actually pretty good, I'm just getting a lot of blow-by and oil consumption.  Verified the blow-by with a leakdown test several months ago at L & R.

My car is mostly stock at the moment. K&N filter and 2g exhaust manifold (ported I think) is pretty much it. No add-on fuel control, has stock fuel pump, stock wiring, unmodified 1g MAS, stock boost guage, no boost control, stock IC, 14b turbo, etc.

Unfotunately, while having enough to do the 2.3 build up, I won't have enough to add anything else right away. I also don't have a lot of time to wait and save to get the engine replaced. That means trying to run the stroker on the stock fuel system at stock boost levels which is 10 psi roughly?

I'm looking for opinions (or experience) regarding if this is possible. Some of my immediate concerns are things like MAS overrun, fuel cut, boost creep, etc. From what I understand, most 1g's start running into problems when they try and go above 15psi boost (14b turbo). I tried to figure out the numbers and a stock 2.0L @ 15psi seems to flow about the same air as a 2.3 @ 10psi, which means it should be possible...

I'm not looking for the best tuned car or the most power right away. Just as long as it runs reasonably efficiently and doesn't damage the engine by running too lean or frying the turbo by making it work too hard.

I also wouldn't be surprised if I'm missing something important (see sig )...

James

[Chris Andrews]

I think you can get away with it, IMHO.   Not too many people put a stroker into a virtually bone stock car, so few people would have any actual experience.

You have a stock exhaust so you probably won't run into creep, overrun, etc.

Still, it would be wise to be careful. Keep the boost down, so things don't get lean and melt your new pistons.  You should at least get a mechanical boost guage to see if your boost creeps, as the stock guage won't tell you......

As for MAS overrun, if it happens, take your foot off the gas, the same goes for fuel cut.  Not dangerous to your expensive new engine, at least not if you are aware, and back off.  

When the 3" turbo back goes on, the shit will hit the fan.  :laugh:

I say go for it,  there's not enough strokers in this club.  

[Martin Raska]

Overly simplified calculations (we'll just assume all other variables are constant when applied to either):

2.3L @ 10 psi w/ 9.1:1 compression ratio:

(14.7+10) x 9.1 = 225 psi at top dead center compression stroke

2.0 @ 15psi w/7.8:` compression:

(14.7 + 15) x 7.8 = 234 at tdc

Then we factor in the displacements in, via remembering the high school gas law equation PV = nRT = the work that can be done by this gas.  I can't really get any units by using psi and litres, but the conversion is a constant I just don't feel like doing it, so it's just for your interest to see which is higher,

2.3L: 225 psi x 2.3L = 518

2.0L: 234 psi x 2.0L = 468

Plus I think you will have a better powerband since you're probably going to have that higher compression than the stock engine.

Also,  you'll notice that the 9.1 compression ratio at 10 psi which is a pressure ratio of 1.67 yields an effective compression ratio of 16.7:1 over atmosphere, and the 7.8 at a compression ratio of 2 is only 15.6 over atmosphere.

So I'd expect a 2.3L rebuild at stock boost and the higher compression rato to be much more enjoyable.

[Mike Schmid]

Boost on the 14b will build alot quicker too.  It should end up being a really nice car to drive.  Like Chris said no one really strokes a totally stock motor, that said, the 1G MAS, 450s, 14b and sidemount can go really far on a 2.0L motor so they should have no problem handling another 300cc.  Log it and even if you do lean out a little you can just mildly port the MAS and that should clean it up.

[James Warren]

Thanks for the feeback. The consensus that its doable is good :).

Just to clarify a couple of things to make sure I understand what was said.

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From Martin:

"(14.7+10) x 9.1 = 225 psi at top dead center compression stroke
...
(14.7 + 15) x 7.8 = 234 at tdc
...
Also, you'll notice that the 9.1 compression ratio at 10 psi which is a pressure ratio of 1.67 yields an effective compression ratio of 16.7:1 over atmosphere, and the 7.8 at a compression ratio of 2 is only 15.6 over atmosphere."

I understand what you're saying, but how did you get to the 16.7 and 15.6 values? If I do ((14.7 + 15) x 7.8) / 14.7, I get  15.7.  Doing the same for ((14.7 + 10) x 9.1)  / 14.7, I get 15.3?

Given I can't manage the fuel or boost, slightly less effective compression would be a good thing.  Using the above formula for stock gives 13.1.

That's one of things I'm looking forward to from doing this, flattening out the powerband and reducing lag.  Better fuel efficiency from the higher compression would be a nice bonus, especially at a freaking $1.08/litre for Chevron 94 (sheesh).

--------
From Mike:

"Log it and even if you do lean out a little you can just mildly port the MAS and that should clean it up."

By porting the MAS, do you mean removing portions of the lower honeycomb? Without being able to manage fuel on a stock system, doesn't that have the effect of making things even leaner? More unmetered air?

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The one thing I'm trying to understand is the effect of putting more displacement behind the turbo. I'm using information from http://www.stealth316.com to try and figure it out, but I can't quite get a handle on it.

Compressor maps for the turbos give a certain flow rating at a certain pressure rating (outlet to inlet), so what happens if an engine can flow more air at a given pressure rating than the turbo can supply? If I understand the stock wastegate (and this is very iffy for me), it bypasses exhaust gas when the boost pressure at the outlet exceeds roughly 10 psi. What effect does the engine flow capacity have on that pressure rating of the turbo outlet if it can outflow the turbo, if any? Am I even looking at this the right way?

I think I need to take a break from researching...

Thanks,

James

[Mike Schmid]

Well as long as you don't overrun your wastegate it shouldn't be a problem.  It should more or less just self regulate.  Chances are with the ~7% increase in displacement you will be processing and flowing say ~7% more intake/exhaust and hence you might be turning the turbo faster to process more int/exh at a given rpm which will make a little more heat... But.. with stock DP and exhaust I don't see wastegate overrun (causing boost creep) to be a problem and as far as pushing the compressor out of it's efficiency range or something I don't see that being a problem either because we are only talking 10psi... the 5psi drop from what you're running now will cool the intake charge alot more than the increased flow will heat it.  

I just really don't see anything being a problem because with stock extremities and appendages you're going to be choked off all over the place.  You might run into some problems when you start getting the BPUs done.  All that means though is you'll need a fuel system faster than most...