Burn patterns on piston and chamber

[steve cowan]

“From memory we were 8% richer than stoich for MS109.”

“Engine came off dyno and went in my car showing 12.5 AFR @ WOT.
I have used 2 other carbs but worked on the 12.5:1 at the track 
950 hp (750) 850 annular. 
Idle afr is 12.5
Cruise on transfer slot is 15.0
WOT steady 12.5.”


Your cruise rpm would have to be low to be on the transfer slot alone.
A 950 HP and a 850 annular are completely different carbs when looking at fuel atomization. The 950 came in different sized venturi and throttle bores depending on which model.
These holley carbs never run 15:1 AFR at cruise rpm without work. They are always way to rich.

Fuel wash usually means fixing fuel atomization. Using the correct booster for the size of the venturi .
Mechanical Secondary could be opening too soon. Too much venturi area too soon.
More intake temperature for vaporizing of fuel.
Port shaping and sizing of the cylinder head and intake manifold. Manifold finish.

Both carbs have different emulsion set ups,both carbs have adjustable transfer slot jet in main body.
Spark plugs come out pretty clean with a thin WOT ring on base of porcelain,engine was dynoed for Max power at WOT at that time.
Timing mark on plugs was still conservative and never got after it as in running on edge as seen by photo's.
I think fuel wash is a common problem in a low port 23 deg head but that's my opinion.

[steve cowan]

That burn pattern or lack of tells me there is quite a bit left.A good running engine has a nice even burn across 90 percent of piston and chamber.It should have a light gray/tan light dusty texture if right.When you have a sludge look across 1/3 of your piston and no even heat or cover across the rest ,you are leaving pretty good power behind.Could be cyl prep or ring type issue but I see allot of room in the valve job in that pic that needs addressed also.It will taking going to a bigger valve to get all the cuts sharp and correct again,it don't look like it could be fixed any other way.jmo.No disrespect to anyone involved but I see allot could be improved on.I never put a engine together without roll radius the sharp edges and laying some texture on top of piston to help with a even burn.im no fan of flattops to get a nice mixture motion,if that's used your valve job and head and ring seal needs to 100 percent on point.

Appreciate everyone feedback and no my feelings are not hurt lol.i am here to learn and any constructive criticism is fine by me.
Just to clarify-
Heads 165cc ported to 186cc
2.10" avg csa
1.94" - 1.5" valves
89% throat on intake
Bowl 100% of intake valve.
I done valve job with stones as that's all I have.
40,50,60,70,82
I ported heads,intake and built engine.
The block was honed using profilometer by my machine shop I use,they honed to JE recommendations.
Cam is a comp roller
240 - 256 @ 0.050 "
406 lobes
1.7 - 1.5 rockers.
Ran best ET,mph at track 109 ICL,109 LSA.
Made 522 ft/ lbs @ 5300rpm
570hp @ 6600rpm
Down 5 hp @ 7000rpm.
3620 pound Streeter
1.46 in 60ft
6.71 @ 101mph
10.62 @ 124. 65mph.
So I have some work to do by the sounds of it, I wonder if the MS109 fuel is not suitable for 11.4 compression?
I used it because of the short cam worried about cylinder pressure.
This year it had 20 dyno pulls,30 passes at track and maybe 500 miles of street, so not alot of work.
I have plenty to think about.

When you say “bowl is 100% of intake valve” Are you saying the CSA of the bowl is 100% of the CSA of the outside diameter of your 1.94” valve?…2.95 square inches?

The bowl area up towards the throat is approximately 1.94" across, depending where you measure, I see some people taking measurements above the guide boss.my heads are smaller at the guide boss and tapers up towards the throat to the 1.94" ish size,then it is 1.72" diameter at the throat.
Area can be calculated from there.

[Orr89rocz]

Wow now you got me questioning my car. I only had the heads off once since i got it together few yrs back due to lifter failure. Not a ton of run time on it i guess, few short street pulls, mostly street driving and a few dyno hits. I dont if i ever made a track hit or not that yr. But my flat tops looks like a triangle pattern of small circles

Is this bad? Lol 555 big block ported dart 345’s with twin 80’mm turbos. Almost 10:1 on e85, made 1800+ at the tires. Runs fine to me but i wonder

[bob460]

Wow now you got me questioning my car. I only had the heads off once since i got it together few yrs back due to lifter failure. Not a ton of run time on it i guess, few short street pulls, mostly street driving and a few dyno hits. I dont if i ever made a track hit or not that yr. But my flat tops looks like a triangle pattern of small circles

Is this bad? Lol 555 big block ported dart 345’s with twin 80’mm turbos. Almost 10:1 on e85, made 1800+ at the tires. Runs fine to me but i wonder

I still can't believe you only run 135 seat pressure and making 1800hp at the rears..............faaaaaaaark....

[David Redszus]

20221203_182359.jpg20221203_180151.jpg
Curious on what to look for and which direction one should take when looking at burn patterns.
Spark plug wetting seems to be a issue for a lot of early OEM type cylinder heads.
The fuel used here was MS109
I am interested in opinions on what guys think is happening in the burn process.

MS109 is an excellent fuel with a wonderful distillation curve, good RVP, no lead and no alcohol.
It should burn very clean. What did you use for MS109 stoich value?

But fuel preparation is poor and/or partial throttle mixture is overly rich.
The burn deposits suggest liquid fuel instead of a vapor.

Timing most likely is a bit retarded, based on low chamber temperature and high
exhaust temps. Piston could use a bit more heat.

Loose valve guides might also be a contributing factor to oil deposits.

[steve cowan]

20221203_182359.jpg20221203_180151.jpg
Curious on what to look for and which direction one should take when looking at burn patterns.
Spark plug wetting seems to be a issue for a lot of early OEM type cylinder heads.
The fuel used here was MS109
I am interested in opinions on what guys think is happening in the burn process.

MS109 is an excellent fuel with a wonderful distillation curve, good RVP, no lead and no alcohol.
It should burn very clean. What did you use for MS109 stoich value?

But fuel preparation is poor and/or partial throttle mixture is overly rich.
The burn deposits suggest liquid fuel instead of a vapor.

Timing most likely is a bit retarded, based on low chamber temperature and high
exhaust temps. Piston could use a bit more heat.

Loose valve guides might also be a contributing factor to oil deposits.

We dynoed for max power at the time,pulled off dyno and in my car AFR show 12.5:1 if I remember I worked on 109 fuel had stoich of 13.5:1 so in theory it is 8% richer.
I have disassembled 1 cylinder head and the K - lines are worn,looks like there has been some valve floating on intakes.
The valve seat has gone to around 60 thou wide I set it up at 0.040".
Using a vacuum pump so it shows very little oil coming through guides.
Dave,
Do you think MS 109 works more efficiently with higher compression ratio compared to my Engine with a static of 11.45:1.
It's a fairly short intake lobe so I suspect cylinder pressure is way more than pumpgas can handle.
Thanks for looking

[jed]

Lloyd. Now when you are taking your engine apart for refreshing it would be interesting with some pictures of a perfect burn pattern.
And some tuition to how to get there would be great too.
But to get a true burn pattern, shouldn´t the engine be run at wot and turned off instantly?
I looked at all of my heads and they were all shiny so I think it has more to do with them running on idle than anything else.
But I would like to make it better if possible.

Erland

Erland used the phrase “perfect burn”. During the later years of my engine building career I became very interested in burn patterns. I took lots of pictures of combustion chambers and piston tops. This is one that I think is close to perfect as one can get. It was a street performance LS came in after dropping a valve.

[David Redszus]

Do you think MS 109 works more efficiently with higher compression ratio compared to my Engine with a static of 11.45:1.
It's a fairly short intake lobe so I suspect cylinder pressure is way more than pumpgas can handle.

A SCR of 11.5:1 will (DCR = 9.09) produce a compression temperature of 511F at 30 deg BTC, which is
below the auto ignition point of MS109. Pump gas, with its higher tail ends, will produce even more carbon deposits.

If chamber oiling is not present, I would address carb mixture preparation regarding idle and transition.
And add more timing.

[ClassAct]

20221203_182359.jpg20221203_180151.jpg
Curious on what to look for and which direction one should take when looking at burn patterns.
Spark plug wetting seems to be a issue for a lot of early OEM type cylinder heads.
The fuel used here was MS109
I am interested in opinions on what guys think is happening in the burn process.

MS109 is an excellent fuel with a wonderful distillation curve, good RVP, no lead and no alcohol.
It should burn very clean. What did you use for MS109 stoich value?

But fuel preparation is poor and/or partial throttle mixture is overly rich.
The burn deposits suggest liquid fuel instead of a vapor.

Timing most likely is a bit retarded, based on low chamber temperature and high
exhaust temps. Piston could use a bit more heat.

Loose valve guides might also be a contributing factor to oil deposits.

David, which pictures are you looking at that relates to these comments?

TIA

[Tom68]

Do you think MS 109 works more efficiently with higher compression ratio compared to my Engine with a static of 11.45:1.
It's a fairly short intake lobe so I suspect cylinder pressure is way more than pumpgas can handle.

A SCR of 11.5:1 will (DCR = 9.09) produce a compression temperature of 511F at 30 deg BTC, which is
below the auto ignition point of MS109. Pump gas, with its higher tail ends, will produce even more carbon deposits.

If chamber oiling is not present, I would address carb mixture preparation regarding idle and transition.
And add more timing.

That's not taking in the cooling from fuel evaporation is it ?

[David Redszus]

David, which pictures are you looking at that relates to these comments?TIA

Based on Steve's initial post photo.

That's not taking in the cooling from fuel evaporation is it ?

No, it's not. But that fuel does not have exceptional Heat of Evaporation. Nor does it have high temp tails.

[HQM383]

Lloyd. Now when you are taking your engine apart for refreshing it would be interesting with some pictures of a perfect burn pattern.
And some tuition to how to get there would be great too.
But to get a true burn pattern, shouldn´t the engine be run at wot and turned off instantly?
I looked at all of my heads and they were all shiny so I think it has more to do with them running on idle than anything else.
But I would like to make it better if possible.

Erland

Erland used the phrase “perfect burn”. During the later years of my engine building career I became very interested in burn patterns. I took lots of pictures of combustion chambers and piston tops. This is one that I think is close to perfect as one can get. It was a street performance LS came in after dropping a valve.

Would this be the result of an engine that sees a broad rpm range (lower than race stuff) and a lot of idle?

[HQM383]

But fuel preparation is poor and/or partial throttle mixture is overly rich.
The burn deposits suggest liquid fuel instead of a vapor.

Timing most likely is a bit retarded, based on low chamber temperature and high
exhaust temps. Piston could use a bit more heat.

Both carbs have different emulsion set ups,both carbs have adjustable transfer slot jet in main body.
Spark plugs come out pretty clean with a thin WOT ring on base of porcelain,engine was dynoed for Max power at WOT at that time.
Timing mark on plugs was still conservative and never got after it as in running on edge as seen by photo's.

Loose valve guides might also be a contributing factor to oil deposits.

Now we can see the combustion chamber with the head removed does that take precedence over spark plug reading?

Steve, I still think it would be easier to switch to lambda display when not using a fuel with 14.7 stoichiometric.

[In-Tech]

Yes, we Americans decided on AFR instead of Lambda... me included, until I understood. Then I was on the hunt for Lambda with different fuels, NitroMethane was fun The green color of the exhaust in a nitro engine explained a lot.

[mt-engines]

Decell fueling can cause lots of deposits on the chamber and piston.. road race stuff. Unleaded fuel generally looks crappier than leaded.

I wouldn't lose sleep over this.