Racing Fuel + Pump gas

[msbaugh]

So I bumped up my timing to about 35* advanced and I heard a slight pinging under wot, I don't know the cr of this motor, but I've been running 93 Octane pump gas with out issues. I want to set it even higher and squeeze more power if I can. I've got a buddy with VP 110 race fuel from his kr900 mustang race car that he sold a few months ago... It's pretty much free to me if I want it. Would it be beneficial to mix some 110 with the 93 or a 89 octane punp gas and see if I can bump up timing with out pinging?

[Chryco Psycho]

Why not !!
 What RPM is it pinging at WOT at , if it is at low rpm the avnce curve may be too fast , heavier springs would solve that

[msbaugh]

Why not !!
 What RPM is it pinging at WOT at , if it is at low rpm the avnce curve may be too fast , heavier springs would solve that

I actually thought about that, but it's only around 4500-5000 rpm and it's only happened twice.. After I advanced it, I dialed it back down. I have about 20-22* total, it might be helpful to shorten that but I don't want to advance it any more than 32-35 if what I heard really was ping. That sure doesn't seem like much timing for that to be occuring

[Chryco Psycho]

at 4000 rpm your advance is in fully so changing springs will not help , if you are lean it could be making too much heat so up jetting 2 sizes or so may help , also the type of plug could be too hot causing detonation try a cooler plug

[msbaugh]

Good advice! A Colder plug might help. I left the jets in that came with the Holley im not sure what size they are probably 80 on front and back. maybe increasing them isn't such a bad idea, time to buy plugs and do wot reading.

[msbaugh]

I always get confused with heat ranges. I don't know how to compare them between different brands, it seems like everyone has a different number...  right now I have NGK iridiums in the car, I imagine they are probably on the hot side and they have that tiny little electrode, I can't find a number anywhere on the actual heat range of them, I have a set of autolight 85's in the garage somewhere but I don't know if those are colder or not. 

[Strawdawg]

My experience with my turbo cars has been bad when trying platinum or iridium plugs with small electrodes.  I get more detonation with them.  Others have had the same problems, but, whether that is a rule, or I am an exception, I cannot say.  I won't use them

If you take the numbers off the plug you should be able to cross reference them to other plugs and supposedly comparable heat ranges.  I believe NGK numbers tend to go up as heat ranges get colder.  They also seem to cover more heat ranges with one plug than some others do.

With anything that has high compression, in an older motor, I would be leery of running such plugs...

Don't be afraid of adding a little fuel as suggested

[MEK-Dangerfield]

What size engine do you have? I have the Autolite 85's in my 440.

Autolite numbers go up with the heat range, for what it's worth.

[msbaugh]

It's a 68 block 440, I don't know the compression because I bought the motor built with quite a few miles already on it.  I've put a lot of work into it myself in the past 2 years, I can tell you it runs well on 93 octane, it just pings when I advance the timing, so I'd imagine its around 10-10.5:1 or close to it...

I found a chart comparison and for what I understand the NGK iridiums heat range in there now is a 7 which is comparable to a 7/8 Champion heat range... I can't find a comparison with the Autolite 85's so I don't know if the Autolite ones I have are hotter or colder. 

My game plan is to add some race fuel on top of the pump gas, change plugs to a copper champion or autolite, bump up the timing to where I want it at about 36-38 and see what happens!

[HP2]

If you know cranking cylinder pressure and your cam specs you can back into the compression ratio.  Ultimatly cylinder pressure is all that matters since cam specs, cam timing,and altitude all consipre to alter the cylinder pressure.

[msbaugh]

The problem is that I do not know the cam specs, like I said earlier unfortunately I did not put together the internals and I don't have a build sheet, but I did do a compression test recently and the results were very pleasing
Cylinder
1: 180psi
3: 180psi
5: 180psi
7: 190psi
2: 190psi
4: 195psi
6: 180 psi
8: 185 psi

Generally higher cylinder pressure would reflect higher compression ratios, and those numbers are fairly high and all comfortably close to each other.  I would have to know when the intake valve closes to know true compression correct? Depending on how late it stays open my compression ratio could be more or less. With these numbers though and given the current situation my guess of 10.5:1 seems reasonable, It's just so hard not knowing all the specs...
I was an idiot for not getting all the paperwork I could when I bought this car, I was so excited I didn't care 

[Chryco Psycho]

great compression #s !!
 I have never had luck with expensive plugs , Champs or autolites seem to work best

[Strawdawg]

with those static numbers, I would guess you were right at the border line for 93 octane....Try some conventional plugs and/or maybe about four numbers in the secondary jets....If that does not help, then knock off a couple of degrees from total timing....I doubt it will make a significant difference in power...

There are so many factors such as quench, cam duration, weather, variation in fuel quality, etc., that sometimes you just need a little margin for error

[msbaugh]

Anyone want an update? I put champion rj10yc (a step colder than the equivalent 12 that I had in) copper plugs and put about 5 gallons worth of VP 109 race fuel, it's an unleaded oxigenated race fuel called motorsport 109 with out ethanol... I ran it with out doing anything else and it was awesome... I could definately feel a difference, maybe I'm crazy?   
Another thing to add is that the rpm kind of stutters now at idle.  Tonight I'm going to bump the timing up to say 37 and see where it takes me.

My buddy recommended to up the jets 2-4 sizes with the race fuel... any recommendations on what size to start with? I'm not sure what's in it now. I'm going to go get some float bowl gaskets and a few different jets at the auto parts store and do some more playing around after work tonight! 

[MEK-Dangerfield]

My buddy recommended to up the jets 2-4 sizes with the race fuel... any recommendations on what size to start with? I'm not sure what's in it now. I'm going to go get some float bowl gaskets and a few different jets at the auto parts store and do some more playing around after work tonight! 

What size carb do you have on there now? I assume it's a Holley, but I would look at the plugs before I started going up in jet sizes. Your idle problem could be that your idle mixture screws need re-adjusted. (A guess on my part).