Building a slightly tweeked 2v drysump motor

wow! great savings! that stuff makes a difference.

 

Dave,

We discussed this a while ago on the phone: You then said you were going to use the larger dia gudgeon pins. Have you since re-considered that idea, and if so, for what reason?

 

Hi hf,

Yup, that's exactly right. You'll know it when you hear it - sounds like the engine is missing on a few cylinders, sort of like you're running on 4 or 5 cylinders rather than the full complement. And, indeed, that's exactly what's happening because the vavle is failing to fully seat and seal during the compression stroke so you're losing compression. An air cooled 911 engine is particularly good at demonstrating this noise because there is no water jacketing around the cylinders and heads so it's really easy to hear!

 

Cliff,

If that is happening in your 308 engine at the rpm's you indicate, either your rev-counter is showing 1500rpm too low, or you have much bigger problems. There is no way this will happen below way over 8,000rpm on a good engine.
If you are sure that this is what is happening, I politely suggest you start a new thread about it, as it certainly merits being discussed properly -and cured.

 

Dave you have a PM.

 

Hi Jack,

Here's an interesting twist - I went out to the garage earlier today to study the situation in my 308 a bit more. I don't know this car that well as it was purchased relatively recently. It has an excellent service history, recent major service, and is a very clean and well maintained car. Poking around under the hood a little, I see a smallish box low down on the firewall - you wouldn't know it was there unless you're really looking. It says "MSD" on the side of it and after looking at it for a bit I realize what I'm staring at is a rev limiter - there's a small knob (wire tied) for setting the redline with graduated markings from between 5,000 and 8,000 rpm - wired into the ignition system somehow. The knob is set at 7,500. I clipped the wire, dial it up to 8,000, re-set the wire tie and viola, she turns happily well past 7,500 and only starts to cut out at the 8K mark.

At some point I'll sketch out the wiring diagram for this particular item and then remove it (I personally don't need a rev limiter) and set the wiring back to stock.

So, mystery solved!

ps. I have a lot of mechanical sympathy so it'll be rare that she'll turn anywhere near 8K to be honest....

 

Cliff,

Glad it's solved, and even without cost

Back to Dave's engine build!

 

Dave,

I am going to run a Hard Anodized Aluminum front pully.
308 motors are internially balanced,,, and after "blueprinting," need no Harmonic Balancer.
I will then trigger my Haltech Computer unit from the flywheel.

I am putting a Gold Pully on my 2V 308 Crank.
PM me if interested, I have two extra pullies on the shelf.
(oNLY, 1.3# ,choose, Red or Gold.)

Ciao,
Edwardo
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This is an entirely fascinating thread. I believe the factory uses Ti stuff to reduce the recip and rotating mass, thus to reduce the stress and enable higher revs???

Is this so??? Once again, you can build a better engine it just costs for the higher quality parts.

Tell me a bit more about the lack of need for the harmonic balancer. Isn't this needed to reduce or dampen the torsional vibrations in the crank. Aren't the internal parts on most hp engines fairly closely balanced??

I have heard of claims of "x" number of horsepower per unit of weight reduction. I think this oversimplifies the physics involved. Wouldn't the proper measure of improvement be in units of rotational inertia. For sure a light flywheel enables more of the engines power to go toward moving the car rather than expending energy on bringing the relatively high mass of the stock flywheel up to speed.

curious chris

 

Chris,

The energy used to bring the flywheel up to speed isn't lost: it is stored in the flywheel. Making the flywheel lighter frees the energy to go to propulsion directly, so it makes for a livelier engine, but it also makes the engine more 'nervous'.
It's hard to say where weight reduction of the rotating and reciprocating masses should stop. As far as rods and pistons are concerned, I'd say they can't be light enough, but the rotating mass is quite critical as to how the engine will behave, so should be made dependent on the intended use.
That said, the 308 flywheel is rather heavy, as is the clutch. Even for normal street use a diet wouldn't hurt it much.

 

looking fantastic! getting the crank in is always a moment where you feel progress has been made. good stuff

 

Looks great Dave.

 

If you have the room I say go for it. I am not mating the engine to the 'box yet due to wanting to keep the engine on the stand to degree the cams. Makes it easier for me

 

That's looking superb Dave!

 

The motor is looking good, keep up the good work.

 

nice pics and thanks for sharing.

Not to hijack but you're one of the few I've seen on here inside a dry sump motor.

How tight is that chain on assembly? ... don't know what kind of answer I expect with that so how about how much does the chain "deflect"? ... either one side or both squeezing at the same time? (if that makes sense)

How much wear on the guides? Any idea on miles?

cheers,

Sean

edit: for dry sump 308 junkies note the unique location of one of the studs on the timing cover ... makes the gearbox a little bit unique.

 

Thanks for the info.

Is there enough slop in the chain that you can rock the pump gear back and forth just a bit? Any chance you could give me an actual measurement on that if there is some? You could just put an indicator on one of the sprocket teeth ... I know what a PITA that can be though when you have a laundry list of more important things to do.

Thanks if you can and thanks again for what you've shared,

cheers,

Sean