Thom

Very interesting article, thanks.

What is not mentioned is that increasing CR should help with transient response when varying load by opening the throttle. The curves posted all seems to be at WOT, and I suppose we would need 3D tables with TPS (or VE) as the 3rd dimension against RPM and Power to really get a picture of how CR and boost balance eachother.

refresh951

Interesting what the shop manual states:

Typical Crank Runout: 0.04-0.06 mm (0.0016"-0.0024")
Max Crank Runout: 0.08 mm max (0.0031")

0.003" does seem high especially considering main bearing oil clearance is spec'd at 0.0007"-0.0038" for new bearings. I guess this is where crank flexibility factors in. It is also easy to see why you would want a much tighter spec on a high performance engine.

refresh951

I know we can run lower than 9:1 CR on our motors without noticeable disadvantages as I demonstrated with my 2.85L. I would be interested in reading about the M50. Any links?

Agreed.

I am completely confident Rogue will have me covered from a tuning standpoint. I will be running his new Direct DME Tuning/Data package.

Rogue_Ant

Regarding CR.
For ultimate power, peak cylinder pressure must be kept within reason. If this means sacrificing some efficiency and low-end power, then that is the choice which the owner/builder is faced with.

That said, the added stroke & displacement more then makes up for lower compression (compared to a higher CR, smaller displacement engine). We've seen this on back-to-back dynos of a 2.8L stroker with low CR vs a 2.5L with higher CR.

Rogue_Ant

Obviously there is newer computer hardware out there, but what exactly do you think is limited by the stock ECU?

The best thing about computers is that we can rewrite software, change strategies and algorithms, and generally improve upon the original code (not to mention fix errors in the factory software...).

The factory DME utilizes some hardware brute-force to compensate for the limited computing power available.
For instance, new ECUs, which utilize a 24 tooth, or 36-1 trigger wheel (or similar), must have a predictive (possibly kalman-filter type) algorithm to guess (predict) engine crank-angle at any given time. This takes processing time, and if done in floating-point, it can take quite a bit of processing power. The DME, however, utilizes a very high tooth-count (132 for the 951). The hardware then has narrowed the crank-angle down to ~2.73° window of accuracy without needing any computing power. The microcontroller then only has to run a timer to get to the correct angle(time). This approach is much simpler than the approach used by new ECUs. And allows for quite accurate ignition/injection timing without needing much processing power.

The main limitations I see on the factory DME hardware:

Age (component failure).
The need for the cap&rotor.
Batch-fire injection.
Limited IO (input output).
Lack of engine knock knowledge (only the KLR knows knock).
Lack of non-volatile memory (for fuel/octane trims).


That said, really non of those are deal-breakers, nor do any contribute to a significant reduction in hp/tq potential. In-fact, I would be happy to put up my full Tuning solution against XYZ setup for a dyno session. I seriously doubt there would be any real power difference between the two.

Finally, you are correct, I definitely know the limitations of the factory DME - and I am working to correct them

Rogue_Ant

Yes, apples to oranges - though both are fruit aren't they

I would be happy to bet you that a low CR 2.8 can make more power without losing a HG than a high CR 2.8...

refresh951

+1 Exactly my point.

Thom

Will it be as fast or at least feel as fast though?

I suppose many people may prefer a crisp and responsive engine over a more powerful but slower responsive engine.

refresh951

Obviously there are trade offs. The key is to find a good compromise. My goal is to make the car as responsive as possible while still reliably meeting my power goals. I believe you can run around 8:1 CR (possibly even a bit lower) and still have a VERY fun car to drive. If you look at the dyno for my 2.85L (8:1 CR), you can see that a lower CR build can still perform well accross the spectrum. I can tell you for a fact that my 2.85L was VERY crisp and responsive. Josh B also drove the car and he can attest to this. The point is that if you are going to build a big power motor (>500hp) you must consider CR carefully and that higher is not always better. My goal is to build a 550 HP beast that is still very responsive and fun to drive, reliable, and low cost! It is a thin line but with Sid's concepts, Rogue's tuning, extreme stroke, and careful turbo selection I am hoping to pull it off.

RennBod

Wow, amazing project, I want to build one!

I have now read both this and the blown944 thread and am serious about having a go at building one of these, but not being on your side of the Atlantic, I am at a bit of a loss to a couple of things.

You mention that they are Mitsubishi Eagle con rods, but is there a specific Mitsubishi Eagle engine code that the rods were originally designed for? I expect you are using an aftermarket rod, such as a Carrillo, but can you narrow down some specifics of what engine these are used in?

You also mention Chevy pistons, again, what are the specifics?

Or is this a commercial thread and this info is a commercial secret?

blown 944

What would be considered responsive? My car, even at this high elevation will just shred the tires at the push of the throttle. IMHO, with the added stroke, Shawn's car will be borderline dangerous on the street. When you have 300# ft of tq at 3000 rpms and 500 shortly after it would seem to me that it is plenty.

@Rennbod, all the info is there. To build one of these you should be able to dis cipher the pats code. If we just throw out all the part numbers and say bolt it together there may be a few catastrophes. Read a few times through and you can figure it all out easy enough.

refresh951

Awesome post by mclarenno9 in Paulyy's build thread about fab work to install a GT Turbo:

https://rennlist.com/forums/9975192-post397.html

I think I am going to start a separate thread and detail my approach for installing the GT35 including adapters, oil, water, and fab.

Thom

... at least he's got one.

mclarenno9

Thanks man. I am going to be starting a build thread soon which will detail the plumbing, exhaust, etc.

refresh951

The sooner the better