There She Blows

[BrownStainRacing]

I’m not sure what kind of ring gap this engine has from the factory…

If I go with 0.0055” of gap per inch of bore…

2.835” x 0.0055 = 0.016”

According to this chart for less than 15lbs of boost a 70mm bore needs 0.016” ring gap on first and second ring.

I've taken a bunch of these NIB pred 212's apart for checking clearances.

Ring end gaps are all over the place, .010"-.022". Some have the 2nd ring tighter the the top ring.

Same with piston to cylinder. There's never 2 the same.

It might be best for you to pull it apart and check.
That way you can clean up the crank (smooth out the rough jagged edges), shim the crank and cam. Looks like you gonna need a "bullet proof " bottom end.

 

[65ShelbyClone]

You can also drill-out an 18mm spark plug anti-fouler and use that as a spacer. Amazingly, chain parts store often still carry them in the HELP! section.

19.5 degrees BTDC seems like an ok place to start?

I wouldn't want any more than that in the low and midrange. The blower is going to make full boost at any rpm and 11psi at say, 2000rpm, isn't going to need much advance. My non-intercooled turbo car runs about 200kPa of manifold pressure at my altitude and you can see how conservative the timing is. It has what amounts to a two-valve bathtub chamber and actually does have okay quench pads to help with knock sensitivity. The hemi Predator has none at all.

11psi at sea level would be about 180kPa.



That's just the base timing. It pulls timing out of that as the intake air temp goes up which happens rapidly under boost. Also keep in mind that everything above the line is a guesstimate; the current engine either can't handle or can't possibly create the conditions for those cells. 300kPa(29psi of boost) at 700rpm, for example.

 

[bob58o]

Good Stuff!

Maybe I’ll turn the key around so it takes away 5 degrees and starts me off around 15 BTDC.

Im aware that these types of ignition systems retard timing as RPMs increase. I believe it’s because of the limitations of the electronics. Perhaps a capacitor takes “x” amount of time to recharge/discharge.

It may not retard too much at 6500 RPM, but maybe 15 BTC at idle speed will be better.

 

[bob58o]

Ok. I did it for the fans! Lol
We will make this work (or blow up).
Just mocked up for now.

 

[bob58o]

Anybody ever notice that the Great Cornholio, when pretending to be the president, sounds like a turbo race car bouncing off the rev limiter and coughing out the BOV.
I can’t unhear it. I can’t stop laughing.

 

[Oilpan4]

If you blow a head gasket at least it will be easy to replace.

 

[bob58o]

If you blow a head gasket at least it will be easy to replace.

Oh ya. I normally liked to try to get the piston flush with the deck. I think the +0.020” rods put the Hemi flattop piston a few thousandths under. So I probably have 0.027” head gasket in there for piston to head clearance, which is 3 x 0.009” gaskets stacked. That might not be ideal. I think I remember seeing a thick 0.045” gasket, but don’t remember if it was for a 70mm bore.

 

[Oilpan4]

Anytime I see a "stock fiber head gasket" it's always 0.04 or 0.045". Doesn't matter if it's seventy something mm or or a 92mm bore.
Stock style heads have absolutely no squish area, hemi or not, the piston could come completely out of the hole and not hit anything. Maybe a valve with a really hot cam.

 

[bob58o]

Anytime I see a "stock fiber head gasket" it's always 0.04 or 0.045". Doesn't matter if it's seventy something mm or or a 92mm bore.
Stock style heads have absolutely no squish area, hemi or not, the piston could come completely out of the hole and not hit anything. Maybe a valve with a really hot cam.

Ya I did a Hemi engine once with a cam, maybe 285 lift 250 duration. I had to cut a relief in the piston. I don’t remember piston to valve clearance on this one. I usually aim for no less than 0.065”

And these Hemi heads usually get shaved 0.035 when I use them.

 

[bob58o]

Here is my DIY porting on this head. Honestly not sure if I did this before or after getting a valve seat for the 28.5mm intake and bowl blending?

 

[bob58o]

You can also drill-out an 18mm spark plug anti-fouler and use that as a spacer. Amazingly, chain parts store often still carry them in the HELP! section.

Is that what this is?
The sensor bottoms out so I assume this is it.
I cut one of these to make the bung. I forgot about it and just found it.

Its like treasure!

 

[bob58o]

So I guess I can start taking the engine apart. It’s only been run to break in. I probably ran it for a 1/2 hour or so a few times with no load while varying the rpm.

I’m no good at reading plugs and this hasn’t been really “run” but here’s the plug.

 

[BrownStainRacing]

So I guess I can start taking the engine apart. It’s only been run to break in. I probably ran it for a 1/2 hour or so a few times with no load while varying the rpm.

I’m no good at reading plugs and this hasn’t been really “run” but here’s the plug.

Plug looks good. But it'll change under load.

 

[Oilpan4]

If you use an unmodified spark plug non fowler it will make an oxygen sensor read leaner than what's really there.
Old trick for getting a vehicle to run richer or to hide a converter delete from the vehicle ecu.

 

[65ShelbyClone]

Good Stuff!

Maybe I’ll turn the key around so it takes away 5 degrees and starts me off around 15 BTDC.

Im aware that these types of ignition systems retard timing as RPMs increase. I believe it’s because of the limitations of the electronics. Perhaps a capacitor takes “x” amount of time to recharge/discharge.

It may not retard too much at 6500 RPM, but maybe 15 BTC at idle speed will be better.

Yeah, the ignition retards with RPM due to the latency of the magneto and having fixed timing. The same thing happens with modern digital ignitions, but latency is accounted for in the design and programming.

Is that what this is?
The sensor bottoms out so I assume this is it.
I cut one of these to make the bung. I forgot about it and just found it.

Its like treasure!

Yep, that's one of them.

 

[bob58o]

Well the RTV Gasket maker seemed like a good idea when putting it on. Taking the valve cover off after having used it is a struggle. I’m not sure what I used. Permatex Grey or something. Holds purrttyyy goooood.

 

[bob58o]

It’s possible I did that to the piston when installing it. I don’t remember.

It kind of looks like where the spark plug electrode might hit.

Plug doesn’t look like the piston had been hitting it.

I have no clue about the scoring on the top and bottom of the cylinder walls. Can still see cross hatching on the sides. Also no clue what the “gunk” buildup pattern says.

 

[65ShelbyClone]

How old was the fuel. What kind of oil is in it?

 

[bob58o]

It was last ran then put away in 2018.

I don’t remember what kind of oil I used. I probably did an initial cam break in using stock springs, then changed the oil. Then probably did another break in cycle with 26lb springs then emptied the oil again and put it away.

 

[BrownStainRacing]

It’s possible I did that to the piston when installing it. I don’t remember.

It kind of looks like where the spark plug electrode might hit.

Plug doesn’t look like the piston had been hitting it.

I have no clue about the scoring on the top and bottom of the cylinder walls. Can still see cross hatching on the sides. Also no clue what the “gunk” buildup pattern says.

Looks to me from the top of piston, there was some kinda fuel additive. That will cause a false plug reading.

I'm not sure about that gunk in the chamber, maybe fuel additive and oil mixing????

When you pull the piston, if you do??? Place it flat against the head. It will cover the whole chamber. Pred hemi head chambers are smaller then 70mm.
The ducar/tilly hemi head is jus a tad bit bigger and the 70mm piston will go down inside it (.015"- 020"), but when measured, it's about 2cc smaller then the pred hemi head.