a couple things on seating my rings

[juanbenae]

after a complete split the case rebuild of my 3.0L spec911 motor last year i found out mid season that the carrillo euro copy pistons i installed were failing in other cars. prefer not to go into all that here & now, but suffice to say i have again taken the top end down installing a new set of euro mahle pistons & cylinders (ouch). for those not aware of the sp911 class rules i can do euro CIS pistons, stock CIS cams, and must run on 91 octane fuel. induction in the class is up to 46mm carbs which i run, or fuel injection systems that are beyond my budget and then some, or a stock 3.2 motor with the euro innards.

anyway, with the bearing and valve train already being friendly i am looking to just get the rings seated here. ive used the delo oil many suggested, will be doing the initial start up with a trusted wrench friend prior to taking it to a track test day for the seating run in. ive been picking KTL kevin's brain, researching here extensively and have the technique set for the ring seat effort.

what im wondering is will the back pressure of a two in single out stocker type muffler be better for what im looing to accomplish as opposed to the shorty burns cans i regularly run. will the back pressure the 2 in 1 out help my efforts? and lastly should i take the opportunity to go ahead and run some higher octane race fuel for the run in? it would be mixed 50/50 with some winter storage treated pump gas ive already got in tank. i will get all the higher octane fuel out prior to my 1st race weekend to stay class compliant...

thank you in advance for your thoughts on the matter.

t-23

[HawgRyder]

Because the bearings are already run-in...the power runs from about 30 - 50 MPH in 3rd gear would be what you are asking about.
The idea being to put pressure on the rings to get them to seat against the cylinder walls.
Method: Run gently up to 30 or so in the gears...get into 3rd...power on (not full throttle..but close) run up to about 50 MPH or so...let it slow down on compression to 30 .... repeat several times (I like to do it until the temps start to get close to max-normal).
You may have to do this exercise several times...letting the engine cool down for an hour in between.
If done correctly...the rings will seat nicely...and you will have a long life engine.
Bob

[Lapkritis]

You're going to get different answers here from folks with lots of experience. More than one way "works". I've done a lot of engines (outside 911) and I always seat rings by getting the engine to operating temperature (oil temp gauge) with non-synthetic correct weight and then running it hard in bursts for ~1hr. Then a full oil and filter flush and normal driving for another 1K another change and then BAU.

Load the rings while the bore can cut them. Otherwise you'll have an oil user.

[lindy 911]

Our road race engines (four cylinder, air cooled, two valve on two wheels) were always broken in WFO. Load hard, unload. Repeat.

[juanbenae]

so, was there any thoughts on it being an advantage to running some higher octane race fuel for the ring seating efforts?

[KTL]

The high octane fuel may have your AFR considerably richer than you want it to be, potentially "washing down" the cylinders with that rich air-fuel charge. I suspect your carbs were already tuned to run around 12 AFR pedal to the metal. So if you run higher octane you're going to richen that mix up even further, no?

[911pcars]

Originally Posted by KTL

The high octane fuel may have your AFR considerably richer than you want it to be, potentially "washing down" the cylinders with that rich air-fuel charge. I suspect your carbs were already tuned to run around 12 AFR pedal to the metal. So if you run higher octane you're going to richen that mix up even further, no?

Probably more of a waste of octane than anything. If the engine doesn't require higher-than-normal octane fuel, there's no advantage. In addition, unless there's an ECU involved, the fuel system doesn't know what fuel it's providing.

[304065]

Originally Posted by 911pcars

Probably more of a waste of octane than anything. If the engine doesn't require higher-than-normal octane fuel, there's no advantage. In addition, unless there's an ECU involved, the fuel system doesn't know what fuel it's providing.

I agree with Sherwood and octane rating does not determine mixture. Mixture can be used to delay (or worse, accelerate) onset of detonation, but going from 91 to 104 octane moose juice won't change your mixture if it's gasoline in both cases. OK, if you add 50% toluene or you add motor oil (which has an octane of Zero) different story but you get the idea.

We broke my engine in on 100, but that is because we were adjusting the timing on the dyno.

[juanbenae]

thanx for the input. here we go!




img]http://forums.pelicanparts.com/uploads22/DSCN18761392351051.jpg[/img]

[juanbenae]

thanx for the input. here we go!

[Eagledriver]

I don't think there is a problem with breaking in the new rings. I just warm it up then run it hard. Maybe limit the RPM to 6k or so for the first 20 min. If the fuel is old, you might want to through some 96 octane in or dial back your timing until you are sure you have a good load of fresh gas.

-Andy

[KTL]

I stand corrected.

W/out an ECU, true the fuel system doesn't "know" what fuel system it's being provided. But that doesn't mean the mixture won't change. I don't agree with saying 91 vs. 104 doesn't change anything. 104 is potentially harder to combust. Pump gas and race gas are not the same thing in terms of what additives they have & how those affect combustion. Pump gas is of lower quality for a multitude of reasons and that's not always friendly to carbs.

On a mild compression engine you're going to have less effective combustion should that high octane fuel not burn as effectively, which initially depresses the air-fuel ratio during the combustion process until complete, as that fuel takes slightly more time to burn across the chamber. If you're already on the rich side of the spectrum, you can see pseudo-richer effect of the higher octane isn't necessarily going to be of any benefit in terms of making good power.

Key to breaking in your rings is max cyl pressure w/out detonation. Well the higher octane is indeed going to help with its increased resistance to detonation. But it's also going to reduce your peak cyl pressure when that high octane mix is not being effectively burned.

It all depends on what that fuel is doing inside your engine. Unleaded or leaded, what's the specific gravity (which affects float level- literally), what's your timing, etc.

Sunoco Race Fuels | Beyond Octane
Sunoco Race Fuels | Specific Gravity - What Is It And Why Does It Matter?
Sunoco Race Fuels | Race Fuel 101: Lead and Leaded Racing Fuels

Not trying to overthink this (too late, already did) but there is some strong consideration for what fuel you choose. Carbs are funky and they need the jetting, fuel and timing to all play nice together since there's not an ECU with sensors to adjust on the fly.

So I wouldn't funk with the octane if you've already got it dialed in on whatever gas you've been using. In the end you'll be fine with pump gas & Andy certainly brings up a good point about getting some fresh stuff in there to boost old gas. But keep in mind old pump gas has a way better shelf life than at-the-track race gas.

[lindy 911]

Just a couple of observations;

Octane is a retardant; resists ignition. But once ignited, high octane fuel burns the same as low octane fuel.

Shelf life on race gas like VP is almost forever as long as it's sealed in a tight container where pump gas goes sour in about 90 days.

I said earlier to start it, warm it then pound on it. Story hasn't changed.

[Lapkritis]

Originally Posted by lindy 911

warm it then pound on it.

Such a romantic on valentines day...

[lindy 911]

Same thing can be said about shaping a piece of steel.

[Mahler9th]

Didja get 'em seated?

I am expecting the best year ever for Spec911 racing here in NorCal. And I hope to get back out there myself later in the year.

See you out there!

[juanbenae]

it all went very well. arrived a couple hours b4 the afternoon session so I took the opportunity to run a road that runs the west side of the facility that has a couple long uphills before entering the track. ran it about 5 or 6 runs hard on n up, and then achieved really good decal action running down hill. I then brought in iand cooled it for an hour before making the same run prior to going up to pay for my test session. this was done by design so had I been thrown out for racing around the facility's hills I was still not a paying customer....

got out and did a 2 laps out the box, came in and had my pops do a look over of the motor compartment and oil lines. with all being good went out for around 20 miles and came in, topped off the oil with the thermostat opened for the 1st time. while on track I was hard on throttle from 5k to 6.5+ as the day's five sessions went by. many opportunities at sears to get quality decal work done too. I was not fast all day while taking care of business and it actually was a great exercise for the driver too. worked on the qualifying line at a 85% speed and got rid of a bad habit or two at various corners.. did around 100 miles with some 1/2 hr cooling set in between during 5 sessions. got a new air/fuel gauge which was nice to have. instead of wondering about mixture issues I could look down and know even under the hardest throttle the mixture was good

as for the fuel, the tank had less than three gallons I had treated with seafoam after the October even, diluted that well with 13 gallons of fresh gas as I pulled out of town. been working with the motor reinstall so I purged the fuel lines as I worked at getting it going. that purge gas did not smell the least bit sour. I seafoam my tank at the close of every year and try to leave very little fuel on board.

thanks for the insight here guys. felt like I was in good hands all day..

yeah mike, it appears that 25 car grids will be common this year. both stomp & rix after having not raced at all last year are back, and a few others have committed to mare racing this year. will be fun.