I'm coming up with almost 11.3:1 Static C/R and 9.2 Dynamic C/R.

When planning things such as plug choice would you want to base your presumptions off the static or dynamic number?

 

Static is pretty meaningless in the grand scheme of things. However it is thrown around more often, so it's easier to compare.
Use dynamic, since it carries more info with it, but you can only compare it to other dynamic compression numbers... Not much to compare to.

Use cheap copper plugs. Pick a relatively cool plug, then read it, and choose your next set based on that. You'll probably dance around plug heat ranges until you find the "right one". Look for the heat line on the ground strap.

You're going to run E-85, or race fuel in that thing or something?

 

Both are important. Neither tells the whole story. Static doesn't take the cam into account and dynamic doesn't take into account that static compression is STILL the primary determining factor in peak running cylinder pressures (a big factor in detonation).

Both of those numbers look high for pump gas. 10.5/8.5 would seem a little safer.

I've heard of a lot of people who run high compression on pump gas. Some are successful, some aren't. It usually works great at first when the motor is fresh, but as the engine gets some miles on it you get some carbon in the chambers, maybe a little oil past the rings and you end up with a detonation monster.

I think you'll probably be happier in the long run not pushing the limits of compression with pump gas. It doesn't make much more power and the downside can be bad enough you'll wish you had never tried it.

 

Well, I'm kind of stuck with it. I didn't set out to build it this way, however, the shortblock was bought assembled and I happened to grab a set of (what I am told is) 62cc Trickflow heads when I first got the bug to build a motor without doing any math.

The piston is so close to zero deck but I cannot say for sure since my homemade tool didn't work too great (I used .001" for the value). .030" over bore, 6" rod, and 3.75" stroke, .039" head gasket with a 4.166" bore, finally 5.4cc valve relief flattops (I don't know if this is 5.4cc per valve relief or combined hmmmm...may have to look into that now).

I'm running a NGK BKR7E plug which I'm told is xref to Autolite 3922 (the coldest resistor plug Autolite carries) and will have to be conservative with my timing so hopefully it will work out.


I would love to run E85 but have not done my research to see how to do so.


BTW Sonix...I don't know what this is worth but the Autolite tech I spoke with said the ground strap had nothing to do with the heat range?

 

I'd trust the plug manufacturer first... How did he say was the best way to determine the correct heat range for your plugs then?
I've heard it's best to read after a good hot run, and try to get the heat line right in the curve....

That engine will rattle like it's full of pop bottles.... You could try and bring the heads to a competent porting shop, and get them to open up the chambers a tad...

the reliefs (5.4cc) is total.

didn't you try the ruler and feeler gauges?? that'll get you within .002" if you don't know how to use feeler gauges! .001" if you do! That's close enough for me.

 

I agree with running E85. If your numbers are correct that might be the easiest solution for you. I think all you have to do is put the E85 in your fuel tank and go.

 

He didn't really mention how to go about doing so, I had also always thought you look for the color right in the bend of the strap.

I also don't trust any rulers. They are just not flat enough, every ruler I have placed on a glass pane and tested with my feeler gauges was off too much to try to measure an engine with. I need a $70 machinest straightedge.

I might have to do E85...wasn't expecting such a huge C/R number since this isn't a crazy off the was motor combo. I think its more than adding the E85...the carb needs some heavy work; jets would have to be increased, fuel pump maybe increased (even though its a 255lph), fuel pressure increased, spark plug situation re-examined, timing re-evaluated etc. I think E85 pushes more fuel.

 

you just jet for 30% richer. The rest is tuning, you can't follow a chart, you just tune it for how the engine wants.
fuel pump should be fine. the rest should be fine.
Can you get E85 where you are? if so, would be worth a look. Try 94 octane first, you'll probably need to back off a schwack of timing, and just drive it in lower gears...

 

Everything I have read about E85 is that you need more fuel, but it is a higher octane. So it would be a better choice.
You might try calling a company that makes an E85 carb. Think summit or jegs would have one. See if you can get jet sizes and such from them.

 

Having run E85 since 2006, I can say without reservation that you can't just put it in and go, and it takes more than just jetting up (BTW, it's 47%, not 30%). Idle restrictors, power valve restrictors, and emulsion bleeds are all affected. If your Demon has screw-in capability for all of those, you can recalibrate it yourself - most likely. It would be best to get a hold of BG tech help and ask if they've been down that road.

You can search on the Carburetor forum for more details. If you go for a new carb, Quick Fuel Technologies makes a 750 DP E85 carb, $740 last time I checked. Wish I would have just gone that route instead of piecing it together like I did (but, the QFT unit wasn't available in 2006, as far as I know).

 

Why not just put a big *** head gasket in there?

 

Improper quench height will lead to detonation problems as much as too high CR.

 

I'd think he could still use a .060" thick gasket since he has basically zero deck instead of the .025" that stock uses unless stock also uses something like .015" thick gaskets too.

My motor used to run great on cheapo gas (87 octane here) 8.5:1 dcr with a .025" deck height and .041" thick gasket. Still was fine with 92 octane and 10psi of boost too.

 

With too much quench height you don't get proper mixing in the chambers, and you're as likely to get detonation as if your static compression is too high.

 

There are three stations I'm aware of that sell E85, two of which are about 25 miles away. The other is maybe 10...

A friend says he is running 11.8:1 with iron heads and 28* total timing which I do not know for sure but I will try to stick with the 93 octane for now. I have cold plugs and am going to be very conservative on the timing until I get things dialed in.


I did have the motor running (poorly at that) a couple of time these past couple years and I didn't notice any signs of serious detonation. I know this doesn't mean it isn't there or will not happen but hopefully it will work out.



Another note on E85. From what I have read the fuel lines in these cars may not be up to task. Hard lines and all. I cannot afford to totally equip this car for E85 at the moment.
http://www.e85fuel.com/e85101/faqs/conversion.php

 

Which cam and what's the installed ICL?

 

242/248 @ .050
.567/.600 after the 1.6RR's
106 ICL
110 LSA

 

That's CYA blather. Fuel system components have been ethanol-compatible since before 3rd gens. Guess what, other than the carb, I changed in the '57 for E85?

Yep, you guessed it, _________________________ .

Unless you need to maintain emissions-compatibility. But, you're way beyond that already anyway.