engine and drivetrain Comp ratios, octane, timing and (avoiding) pinging - long

[ColinK]

Since this subject is being discussed in a couple of threads so I’d thought I offer my observations/experiences – YMMV. I’m not an engineer not do claim to be an expert on the M10 or the K/F.

Background on my car

When I rebuilt my ’72 tii back in ’90 I had it re-build to a 10:1 CR using an e12 head that had been decked. Engine measures about 195-197 across all pistons. Also had the K/F rebuilt, new injectors and installed an Isky 292 cam with everything else being stock (tii manifold, stock air cleaner).The spring on my 002 distributor broke back in 81(?) and it now has a 008 (still mechanical).

Since I’ve owned the car I always ran ethyl/super/premium since owner’s manual called for 98 octane IIRC. As an aside, I’m the 2nd owner of the car and have owned it since 12/77. I hate to admit it but I was the one responsible for its snorkel. It’s no longer a daily and has logged probably less than 5k since the rebuild (~154k total). I’ve added a petronix and an electric fan since then.

Couple of years ago I had it dyno’d on a Mustang dyno (Carb Connection in Kirkland, WA). As expected it started to lean out above 4k and I stopped the run at about 5.2k b/c of pinging. Put out about 105 hp. Went to Wes Ingram and he added an aux throttle linkage and the A/F ratio this year was good when I re-dynoed. On the first run it pinged above 5.5 again.

Octane, timing and purple gas

As I mentioned, the A/F ratio is solved but the car pinged a bit so I retarded the timing slightly and it pulled about 109 hp on the same dyno this year. Bought an adjustable timing gun and found out I was about 15 degrees BTDC (when it should be 25 degrees BTDC).

The car does not diesel and the plugs and injectors are clean so I don’t believe that carbon is building up in the head. Temp is in the normal range. Knowing that octane boosters are bogus and that the Union 76 94 octane gas has some ethanol, my only solution was to go w/ avgas or racing fuel.

For slightly less than $50 (tax included) I get 5 gallons of Sunoco racing fuel, 110 octane. Blending with another 5 gals of pump super gives me a non-scientific octane around 98. Bottom line, the car does not ping at 25 degrees, starts easier and seems quicker based upon the butt-dyno. I’ll re-dyno later and see what the results really mean.

So, my question is, does anyone else with a high compression engine run a blend, or does pump gas work for just fine? Thoughts and comments please.

[winstontj]

You just sealed the deal for me - there's NO FREAKING WAY I'm going over 9.5CR in my rebuild. This is a DD car that I put 20,000 miles a year on. I've got to be able to run pump gas - hopefully regular or mid grade at that.

Thanks! and best of luck with your dyno this year

[dapbmw]

i run 10:1 on a 121 ti head with a 304, sport valve springs, big valves, dual 45's and i do ping. i live close to an airport so i put gas there on a 50/50 mix too, and have not had pinging now even when revving to 7k. avgas is cheaper than race fuel. i jetted it a bit on the rich side so i won't run lean and hot and not fry my pistons. spark plugs are cheaper to replace than a $5k motor. my timing is right on and not retarded. the weather is getting colder now so i can get away with sunoco 94 now.

[bmw1602.com]

You just sealed the deal for me - there's NO FREAKING WAY I'm going over 9.5CR in my rebuild. This is a DD car that I put 20,000 miles a year on. I've got to be able to run pump gas - hopefully regular or mid grade at that.

Thanks! and best of luck with your dyno this year

relax.....

10.1 to me is not high comp.

13.5:1 is.

I built my race motor to run on pump gas for budget purposes.

it's a 10.5:1 comp. 121 head, ported, dual 45 dcoe's and a 304 cam. Not sure wear my timing is right now.

when I dyno'd it ran 115rwhp and during all 3 runs I had no pinging.

I always run my car on CA pump gas 91 octane! Never had any pingin problems and I drive to san diego for the auto-x 's.

So I'm not sure what your problem is but you should definatly be able to run that compression on 91 ocatane because I have for years. I do not know what's causing your pinging.

I run a pertronix, new plug wires, a crane ps92 coil and a crane hi-6 ignition box

[winstontj]

Harry and Dave and others:

I haven't bought pistons yet - heck I haven't even built the motor yet! One of my first posts here I got into it with Anthony and others about my want for 30mpg and 200hp - pipe dreams I've now learned better (sortof). I don't want to say that this is the same thing but maybe it's close. I'm building a ~200hp stroker motor to put in a caged auto-x car (far away at this point). I'm collecting parts, have bought pauter rods & billet rockers, etc. That car/motor can and will run on rocket fuel for all I care but for now, I want something that's a good blend. A compromise between both!

I want:

PUMP GAS!!! (87 preferred!!)

TORQUE

RELIABILITY, RELIABILITY, RELIABILITY!!!

MODERATE increase in HP

A Daily Driver with HP enough to run a 5-spd OD AND 3.45 diff.

All of these things I just mentioned make a tamed down stroker motor ideal - IMO. This will be Megasquirted and run distributorless ignition which is also a good thing in terms of getting away with running lower octane fuel and pinging. I feel that it's very easy to over-build a motor like this, with a purpose like this. I don't drive 50,000 miles a year but I do drive quite a bit and in the rain, snow, heat... you name it. This is my one and only means of transportation and I want to keep it reliable. Yes I want it to be fun, fast, etc. but with a fresh 2002 motor you have that - add 10-12% more displacement and it's going to be 10-12% more fun! I ask because as I said I feel that there is a tendancy to overbuild and because of that I want to learn as much as possible - things like at what compression ratio does 87 octane pump gas become a problem with pinging? 89? 91? I have no problem having a different MS-II progam for each fuel variant but I still want to know. I know for a fact that when I'm not driving the car, there's no way in hell my girlfriend is ever going to put in premium fuel, check the oil or do anything. I want to attempt to build a stroker M10 motor that is as rock solid and bullet-proof as possible. Make any more sense now? It's not that I'm freaking out - maybe I just haven't made my intentions clear enough yet.

Again, I thank everyone for their input and help and for all that you have taught me over the last few weeks. I feel like I've been hogging the board recently so I hope I'm not the only one learning!

One more time, Iv'e decided on:

9.5:1CR x 90mm bore

84mm S14 crank

Megasquirt-II

Ford EDIS dizzy-less ign.

Mild porting of the head

Stahl header

e30 318i EFI intake manifold

From this I'd like to pump out as much torque and HP as possible while running on 87-89 octane fuel. I'm quite certain that I'll be getting similar fuel milage but I'm not certain about the CR yet. Should I bump down to 9.1:1?

Thanks again,

TJW

[wickstad]

Colin.

I have nothing to help you with your octane question. I have filled my stock '74 2002 with premium only twice and it seems to run great (though I cannot get it started presently).

However, I had a maroon Tii blow past me and honk (air horns) on 405 at 124th a couple Sundays ago. My horn doesn't work or I would've honked back. My '74 is Verona.

[ColinK]

That wasn't me. There is another malaga '72 tii here it Seattle that i know the owner and a couple of others malaga tiis and '02s in and around. I'm on Cap Hill.

Hope to see you around. We should get a drive together while we have the El Nino window.

[peteinjp]

You just sealed the deal for me - there's NO FREAKING WAY I'm going over 9.5CR in my rebuild. This is a DD car that I put 20,000 miles a year on. I've got to be able to run pump gas - hopefully regular or mid grade at that.

Thanks! and best of luck with your dyno this year

relax.....

10.1 to me is not high comp.

13.5:1 is.

I built my race motor to run on pump gas for budget purposes.

it's a 10.5:1 comp. 121 head, ported, dual 45 dcoe's and a 304 cam. Not sure wear my timing is right now.

when I dyno'd it ran 115rwhp and during all 3 runs I had no pinging.

I always run my car on CA pump gas 91 octane! Never had any pingin problems and I drive to san diego for the auto-x 's.

So I'm not sure what your problem is but you should definatly be able to run that compression on 91 ocatane because I have for years. I do not know what's causing your pinging.

I run a pertronix, new plug wires, a crane ps92 coil and a crane hi-6 ignition box

Well those are good numbers. I'd like to know where your timing is at. I have 9.5/1 tii pistons and I know that my setup is probelm free- and it pings- however I have not idea what kind of gas I'm putting in. The people working at the gas stations don't know what the octane rating is. Like I said I think its about the equivilent of 90/91 or so- and it does not ping if I retard the timing from the stock setting (which was to be for old fashined high octane.) In the factory manual there are different timing curves for different gas. The States and German cars had different advance settings. So my car would run fine on regular gas too- if I retarded the timing enough.

[Beaner7102]

You are forgeting one important thing. My had book says 95 (RON) not 95 (MON), as measured in the USA. Check this site for a full rundown of the RON, MON and PON diferences:

http://www.btinternet.com/~madmole/Reference/RONMONPON.html

It states that 95 RON is the same as 87 MON and 100 RON = 91.5 MON. Another thing you need to remember is that Avgas has a higher % of tetra-ethyl lead - not so good for the environment, but better for planes so they dont fall out of the sky. Just something to keep in mind. Beaner7102

[Jaycen_PNW2002]

see the plugs mentioned in your post.

Your 008 is a tii dizzy, right? Not 008 vacumn dizzy w/o the vacumn cannister?

Your still using an early injection pump not a later one, right?

[ColinK]

No, that's something I've not tried and I'll look into this.

I would have thought that w/ the temp gauge being the normal range that this would not make a difference but I give it try. Thanks for the input.

Yes, the 008 is a mechanical unit. However, I've not had the advance curve checked to make sure the springs are still in spec.

Yes, the K/F is the same unit. Wes' work was able to get the A/F ratio was about 12.8 under WOT.

Correction: dyno figures from this year. max HP was 112.4 @5.8k and max torque of 109.1 @4.2k

[hpsenicka]

Stated pump octane ratings in Canada are based on the formula (R + M)/2.... presumably just meaning that they take the average of the RON and MON ratings.

94 Octane pump gas is available at Sunoco, but I have not seen higher octane fuel at other stations.

Regular gas is 87, and the premium gas at most pumps is 91 octane.