First 911 questions

[chrisbalich]

240psi is a ton of cylinder pressure unless the cylinder walls were wet with oil like after a fresh rebuild.

It's worth noting that the car would have to have been spec'd to run some sort of race fuel with single plugs and very high cylinder pressures. This would mean that if you're running 93 octane, you're probably knocking and the pre-detonation is the cause of the high temps. The jetting would also be for the race fuel and that would lead to the poor running at certain RPM and tip-in.

[colingreene]

Since I dont know anything about the inside of the motor its impossible to know what the compression numbers are, without bore/stroke and chamber cc. but its a lot.
Ive taken to putting about half a tank of 100 oct in it to try to knock back any chance of it detonating
I am considering pulling the motor down and checking it out and while im at it twin plugging it, just not sure whats the best way to do that.
I also want to sort out the suspension, I have brakes sorted out thanks to PMB and some pelican members.
Its going to be Late S calipers up front and some fresh new rears with all new soft lines and brand new master cyl.

The over heating is largely in check now thanks to the working thermostats and 3.2L cooler as well as a electric fan on a thermostat.

[colingreene]

Heres some crappy video from last night of the car up and running.

https://www.youtube.com/watch?v=W8igflj0MhI

Did a leak down with a porsche engine builder friend and the leak down numbers are not good so we may be pulling it out this weekend.
Might uncover some of the mystery's of this motor.
other than that i am just collecting bits to put on the car.
bilstein front struts, late s calipers, and some new control arm bushings. oh also adjustable spring plates and shocks all around.

[colingreene]

So not so long ago this happened.
It was in effort to find out what was going on with this motor not ever wanting to run right.

[MichaelSJackson]

"So my car seems to have difficulty going into 5th/Reverse."

Start in reverse; instead of in 1st. Because of the catch protecting reverse it is the tightest position. Put trans in reverse, shifter in reverse, loosen rear coupler. Now move the shifter around while staying in reverse. You should feel the motion limits forward and back and side to side. Sort of defines a rectangle? Place the shifter in the middle of this box and tighten the coupler. Now shift into 1st. Is it good? If it's too short to slide into 1st, go back to reverse, loosen the coupler and pick a spot in the rectangle a little closer/forward to neutral. Test again. Likewise, if the shifter won't move left enough to reach 1st, pick a location a little more to the left in the rectangle. When finished, the shifter should not be pressed against any of the walls of the rectangle, nor should it "trapped" in 1st. If those two opposite corners are good, everything else will be also.

This assumes all the bushings are in decent shape.

[colingreene]

well were way past that now.... I did replace all the bushings when i bought the car.
motor is torn down to the case going to hopefully split the case tomorrow.
turns out it was 11:1 on single plug and 3.3L

[colingreene]

So here is where I am at currently.
As of right now we have learned the motor was set up like this.
70.4 crank
100mm pistons that were a 105mm bore in register
11:1 compression
single plug
Solex center oiler cams
and SC oil pump.
heads are from a 80 that have been ported to 40mm ports.
The bores have some pitting pistons measure out good
crank looks good

So what this tells me is no matter what it was never going to run correctly on 11:1 and single plug.
It was a weird choice to go with solex cams and 46mm carbs.
Also 3 bearing rather than the 4 bearing it came with.
So we are getting a plan together to get the motor back together and working properly.

[Trackrash]

How did you determine the 11-1 CR? I don't see a lot of dome on those pistons.

[colingreene]

By CC'ing the combustion chamber and then doing some extensive math.
The person helping me is/was a Engine builder for PMNA and was trained in Germany by a well known engine builder so I am extremely lucky to have him as a friend and guide on this engine build.

[Trackrash]

58cc for the combustion chamber is probably not correct, if that is what is shown there.

SC heads usually are 90cc.

If you post your deck height and piston dome volume, someone here can verify your CR.

[colingreene]

58cc is what the chamber measures out at with the piston at TDC because of the dome.
Using this information and a few other measurements is how we established the compression ratio.
I am certain we are correct.
The pistons are a 11.5:1 mahle Motorsport kit. So with the spacers under the cyls as we found it supports our conclusion.

[Mixed76]

Maybe show a pic of the combustion chamber and a side view of the piston? They sure look flat, but maybe it's the angle.

[Mixed76]

Sounds like a fun basis, short stroke 3.3 and 11:1.

[colingreene]

Ill post a picture of the pistons tomorrow.
the cyls are already out at EBS to get re finished.

[Trackrash]

Obviously you have it figured out. I just don't understand how you arrive at a 11:1 CR with a piston dome of 30ml. What am I missing?

[colingreene]

I mean I posted the math?

[Trackrash]

That is what I don't understand. How do you arrive at 55.726? Is that your combustion chamber and your deck volume? Your combustion chamber is 58? Then to that you should add the deck volume. So how do you get 55.726?

CR = swept volume +deck height volume + combustion chamber volume / deck height volume +combustion chamber volume.

Your swept volume is 552 and combustion chamber volume is 58 . So how do you arrive at 55.726? What is your deck volume? Looks like 2.274?

2.274 should be added to 58, not subtracted, right? Must have been a very small deck height BTW.

Should be something like 9.5 or 10-1 CR?

[colingreene]

https://www.kfz-tech.de/Biblio/Formelsammlung/Verdichtungsverhaeltnis.htm

Is what we used, the 55 came from the volume of the cyl with the piston at tdc and the combustion chamber combo filled.

anyway. Moving on from that.
I have since checked fit on the 964 pump we plan on adding.

We did discover the car had as i mentioned before 1965 Solex center oil cams
They do have some damage to them, we plan on not using them because for the compression/size of the motor its not optimal.
The new cam will be coming from Elgin
Id like to sell these off to someone but with the damage I dont know what they are worth.




I also have the nuts and parts needed to fasten them to the sprockets.

With that being said I do need a pair of 4 bearing large bearing cam towers.
If anyone has a pair they would like to part with that would be awesome.
Means I can sell my two pairs of small 3 bearing cam towers.
Did anyone ever mention the cost of the rebuild on these motors adds up?
Cause is currently clean.

[pampadori]

Not going to hurt my brain with the math for CR but those pistons do not look anything like 11:1 compression pistons. There isn't enough metal above the deck to be high compression. They look lower CR than standard 8.5:1 early 3.0 pistons.



Left is 8.5:1 and right is 9.3:1

Regarding your brakes - Did you have a vacuum source for your booster hooked up? With the carbs, i'd assume that you would have a large vacuum hose going to cyl #2 intake manifold for the booster. If you didn't, might explain why they feel so weak.

[colingreene]

Keep in mind the much larger bore means you need less dome to create the compression
Also note when we compression tested it it was in the 240 psi range supporting our assessment that it was in fact 10.9 to be exact.

Also as it being a 76 it was a pre boosted car so it has manual brakes.
Since I swapped the rear brakes and pads its gotten much better, I anticipate it being perfectly fine once i put the late S calipers on my car it will be fine.