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Topic Review (Newest First)
02-16-2013 02:21 PM
cobalt327
Quote:
Originally Posted by 64nailhead View Post
Cobalt & F-Bird,
Being a novice to engine building, Barry mentioned something that I've never heard of: polishing the head chamber in an effort to get a better/cleaner burn to eliminate detonation. I'm asking how effective this is and if there is a benefit for lower compression, say 9.5 - 10.5 compression when making tuning adjustments for a novice like myself. I ask because I'm going to be changing my head gaskets to get a more desirable quench distance and I could polish the chamber at the same time.
If you have covered all the other bases, and your time is available, sure- go ahead and polish away. Percentage-wise I believe it's a waste of time/effort on a street engine, but there are others who would have you believe it's a "must-do". Beyond knocking down any irregularities that could cause preignition (glowing hot spots), I just do not agree.

If you want to make a difference, do the things that will give a significant, measurable improvement- like keeping the quench tight, maintaining good ring seal by torque plate honing the cylinders, maintaining a good valve stem oil clearance which will also keep the seat concentric, a good valve job and cleaning the bowl up, etc.

Edit- Another avenue you might want to explore is the various coatings applied to the piston crowns and combustion chambers that are said to aid heat retention, etc. Not a cheap process, but there might be something to them that goes beyond polishing the chambers.
02-16-2013 11:50 AM
vinniekq2 I made the mistake of asking about fuels from Sonoco,they faxed me close to 100 pages
02-16-2013 10:55 AM
Landshark928
Quote:
Originally Posted by barry425 View Post
Landshark928, I'm sorry, but you are just plain wrong about the octane/burn rate. Also, this is a fact that was widely known before the internet was even conceived. Would you mind telling me how old you are? Just curious.

You need to do more research. The facts I mentioned were referenced from the head chemist at Sonoco, Jim Wurth. The guy who blends their fuels and even race gases. I would think he would know a thing or two about Octane ratings and burn rates.

I had 4 years of chemisty in college, I'm a nuclear physics major. First year students learn the difference between flash point and burn rate.

Here are a couple articles you may want to read to inform yourself and dispell the "Octane Myth". It is hydrocarbon content that determines burn rate once ignition takes place, Octane has nothing to do with it anymore.

Sunoco Race Fuels | Beyond Octane

From Sonoco's own site:
"Naturally aspirated race motors with large combustion chambers spinning at high RPMs really like high-octane, fast burning fuels. They need the octane to prevent uncontrolled combustion, and they need a fast-burning fuel so that the flame front can span the large bore of the combustion chamber quickly. If you’re not sure which fuel burns faster than others, one indicator is specific gravity. “Lighter” fuels – fuels with a lower specific gravity – tend to burn faster because fast burning hydrocarbons are themselves light. Look for a specific gravity close to 0.70 and you’ll likely find a fast burning fuel. Of course, consult with the fuel producer to verify your assumptions. You might be surprised to learn that some of the highest octane fuels may also be some of the fastest burning fuels!

You might also be surprised to know that fast burning fuels may not need as much timing as their slower burning counterparts. Many times we get calls from individuals who are dialing in new motors on a fast burning fuel but they’re using timing and jetting numbers from their old motor and fuel combo. “Retard the timing a couple degrees and see what happens” is not the suggestion they expect to hear! With high octane, fast burning fuels, it is easy to dial in too much timing. In such cases, the engine is not detonating, but it is past the point of optimum spark advance, so it’s just heating things up and making less power. A little less timing may really wake up the motor."


And another great read... but a little more technical.

Octane is not how fast a fuel burns

"Octane ratings are ONLY a measure of a gasoline's tendency to resist detonation. It has nothing to do with deflagration. Octane rating tells us NOTHING about the speed at which the flame front travels across the combustion chamber. AGAIN! Octane rating tells us nothing about flame speed. There are hydrocarbon fuels (gasoline is just a mixture of many hundreds of different hydrocarbon fuels) which burn at exactly the same speed yet have wildly different octane ratings. OK, one more time; octane rating does not correlate with burn speed.

Octane rating tells us one very specific thing----> how resistant the gasoline is to the free radical activity that causes detonation. Actually, if all else was equal, a faster burning (deflagrating) fuel would have a HIGHER octane rating than a slower one. Why? Because the faster deflagration takes place, the less time the gasoline mixture around the edges of the combustion chamber has to get "beat up" by the free radicals which cause detonation. There's a race of sorts going on between the advancing flame front and the free radical activity. The goal is to get all the a/f mixture consumed through deflagration before detonation has a chance to occur."



So please come back with empirical evidence that higher Octane fuels burn slower, and not just "It works for me" or "100 internet threads claim it", or "I heard it at the track".
02-16-2013 10:23 AM
1Gary If you look on the valve cover,the white tag you see is where you would find my name on some of the Cosworth's.



At a 185hp with only 140 c.i. and the first EFI with 12.5 c/r,would outrun any 4 cylinder engine of it's day.Now I'm not saying it wasn't without it's problems,but the factual truth was we fixed that in the later yrs.Had it not been for the car being priced only $600 less than a vett,EPA killing the performance,and a crappy body,the car would have been continued to be produced.These days I'm told the Cosworth's Vega's are a collector's wants.Aside from the dyno tests I ran on them,having driven one,they where far from a turd.At only on the high side only 2,500 lbs,that 185 hp mattered.


Now Barry.Although I am very pleased to see your involvement in Vega's,I got to say .010 is too tight.I'm basing that off all the yrs of building engines,and also building the Cosworth.All I can think of is maybe the measurement is off. That isn't to say you don't know what your doing either.Mistakes are made sometimes by the most experienced engine builders too.
02-16-2013 04:30 AM
thinwhiteduke
Quote:
Originally Posted by barry425 View Post
You said "9 years older then you". Did you mean "9 years older THAN you"? I'll cut you some slack, seeing as how you are 74. :-)
I'm confused here now, did I miss a post or two here somehow?

Duke
02-16-2013 03:40 AM
barry425 You said "9 years older then you". Did you mean "9 years older THAN you"? I'll cut you some slack, seeing as how you are 74. :-)
02-16-2013 12:44 AM
bygddy
Quote:
Originally Posted by barry425 View Post
Landshark928, I'm sorry, but you are just plain wrong about the octane/burn rate. Also, this is a fact that was widely known before the internet was even conceived. Would you mind telling me how old you are? Just curious.
Age is displayed on your right above posts
02-16-2013 12:21 AM
barry425 Landshark928, I'm sorry, but you are just plain wrong about the octane/burn rate. Also, this is a fact that was widely known before the internet was even conceived. Would you mind telling me how old you are? Just curious.
02-16-2013 12:17 AM
Landshark928
Quote:
Originally Posted by barry425 View Post
Higher octane gas burns slower than lower octane, so the timing can be set slightly more advanced, HOWEVER, unless the engine is in detonation there is no advantage in advancing the timing and running higher octane fuel.
That is an internet myth. Octane rating does not impact flame burn rate, it is based on the hydrocarbon content of the fuel mix. A perfect example is Sunoco Maximal, which is their fastest burning fuel, and coincidentally one of Sunoco's highest octane fuels at 116 (R+M) / 2. A lot of Pro Stock teams rely on Maximal for those sub-seven second runs. When they are turning 9,000 rpm or more, the fuel has to burn pretty quickly to achieve complete combustion.

The octane number of a gasoline has little to do with how fast it burns or how much power the engine will make. Octane number is the resistance to detonation (pre-ignition). If the octane number is high enough to prevent detonation, there is no need to use a higher octane gasoline since the engine will not make any additional power. Octane number is not related to flame (burn) speed either. Variations in octane quality are independent of flame speed. There are some high octane gasolines in the marketplace with fast flame speeds and some with slow flame speeds. It depends on how they are put together.
02-15-2013 11:25 PM
barry425 As far as timing goes, you simply don't get it. The close quench causes a higher turbulence in the combustion chamber. Instead of the flame starting at the plug and traveling across the chamber to the fuel, the fuel actually travels to the flame front. The reason that you set the timing advanced of top dead center is to allow for the lag in time of the fuel burning. You want the maximum cylinder pressure to occur just as the piston is starting down from TDC. Higher octane gas burns slower than lower octane, so the timing can be set slightly more advanced, HOWEVER, unless the engine is in detonation there is no advantage in advancing the timing and running higher octane fuel. It just costs more for gas that will waste itself out the exhaust valve (because of the slower burning). I've already made all these tests that you are recommending. My setup works the best. If you haven't tried it, don't knock it (pun intended).
02-15-2013 06:41 PM
64nailhead Cobalt & F-Bird,
Being a novice to engine building, Barry mentioned something that I've never heard of: polishing the head chamber in an effort to get a better/cleaner burn to eliminate detonation. I'm asking how effective this is and if there is a benefit for lower compression, say 9.5 - 10.5 compression when making tuning adjustments for a novice like myself. I ask because I'm going to be changing my head gaskets to get a more desirable quench distance and I could polish the chamber at the same time.

Barry,
IMHO I have to agree with others that .010 quench seems unrealistic for anything other than engine that is going to be torn down and rebuilt on a regular basis due to alot of factors such as, rod stretch - which is a number that is going to continue to increase as the rods get older and more heat stressed as the number of heat cylcles increase; as the rod bearings and wrist pins wear with normal use; as the valves and guides wear with normal use; carbon build on valve face and piston surface with normal use (especially with a carb setup.) I may be all wet with this, but I would never dare to try a such a low quench for fear of a catastrophic failure.
With that being said, from looking at your pictures how did you manage to get an electric fan on the engine side of the radiator. My son and I have put a sbc into a 77 Astre (Vega lookalike). We are running a swp with an aluminum radiator and we have 3/8" of clearacne between the water pump pulley bolts and the radiator. We mounted an electric fan on the front side of the radiator. The only time it has come close going over 220 is on the 4th run on a rolling dyno (not enough air flow.)

Cobalt, my 1st car was a 73 Vega that I paid $125 for in 1986. It needed a downhill grade to 70 mph and it melted down at 68K. Your right, it was piece of turd!

Trying to go fast without wrecking our engine - Jim
02-15-2013 04:16 PM
cobalt327 You might notice the poster said "my Vega had the original 90 hp 4 cylinder". Not a Cosworth. Iron coated pistons on an aluminum bore was a bad idea for that engine. One of the biggest turds GM ever made. I owned the only one that I know of that went the distance on the original engine- "the distance" being it ran until the body literally fell off the car during a Rochester winter, the fenders flapped like a drunken seagull whenever the duct tape ripped off at the hoodline.

It ran the whole time I owned it w/a broken head bolt, I could spin it by hand. Don't know why it never blew the HG...
02-15-2013 03:59 PM
1Gary Aaaaa,the Cosworth Vega was a pet project of mine while working at Chevy.You'll find a number of them with my signature on them.
The first yrs they where released before they got DE-tuned where outstanding performers for a 4 cylinders. We resolved the silicone mix so the two center cylinders didn't settle like the foundation of a house on the blocks and because of the Cosworth that problem was resolved totally for the whole Vega line of engines.

To rev the Cosworth engines to 7 grand and alittle beyond was no problem.I know because I built them!!. And we got to test drive one outside of the plant.Was told any tickets where on us!!.

F-Bird.................what do I say??. Well guess more of the same,huh.LOL.A dud??.Nawwww.........!!!.
02-15-2013 02:01 PM
cobalt327
A couple things...

For a street engine and 99% of competition engines, 0.010" quench is too tight. Besides the obvious problems of having the head and piston hit, there can be clearance problems between the valves and pistons, as well as top ring infringement depending on the piston design into the chamfer at the tops of the cylinders, unless things are closely inspected and corrected as needed.

The statement:
Quote:
All quench benefits are lost if the piston to head clearance is greater than .030 inch.
Is just not true, period. The majority of the benefits are seen at distances as wide as 0.040"-0.045" and benefits are still seen in a diminishing fashion out to as much as 0.055".

Running that hydraulic cam grind to 8000 rpm is well past the power peak, no reason to shift that late; the vehicle will ET better shifting considerably earlier.

Quote:
I run 91 octane (California) with timing set at 26 degrees...
Max power timing on the early small chamber SBC heads is ~36 degrees. If you take away 10-plus degrees of timing, you could probably run kerosene. But even running it on 91 octane pump gas, the engine will be significantly down on power.
02-15-2013 09:34 AM
Landshark928
Quote:
Originally Posted by barry425 View Post
I am so glad that you opened the door to talk about Doug Roe's experience. When my Vega had the original 90 hp 4 cylinder in it, I purchased a Doug Roe head. When my engine was stock, it got 21.4 mpg on a measured course strictly on the freeway. I had the block decked for the tight quench and bolted on the Doug Roe head, which had a heart shaped combustion chamber (instead of the stock open chamber). I took the car on the exact same course, filled at the same pump in the same gas station and got 43.0 mpg.
I then took the car to a chassis dyno and the specialist started tapping his gauges. I asked if something was wrong. He asked if I had done something to the engine. I felt about 1 inch tall, thinking that I had ruined something. I told him that I had modified it and asked why. He said that it was making 58 horsepower at the rear wheels. I said that it was a 90 horsepower engine, thinking that I had ruined the engine. He said that a GT engine (110 horsepower) only makes 35 hp at the rear wheels! So, I had doubled the gas mileage, almost doubled the horsepower, and the icing on the cake was that it was smoother than a V-8. That engine lasted 94,000 miles, which if you recall, was some kind of a record for that engine design. Most became boat anchors at 40,000.
I did the same thing to the first V-8 that I put in the Vega. It was a small journal 327 with the .010 quench, quadrajet carb, modified (to fit) cast iron manifolds and a 400 turbo hydro. This engine took me to work and back for 20 years, logging 300,000 miles, and still passed smog when I took it out in favor of the reworked LT-1.
You can theorize and bench race all you want, but I made it work for, let's see, 37 years now. If you can't believe the truth when it is told to you, look me up in Diamond Bar, CA, and I'll take you for the ride of your life.
B.A. Murphy (in the book)

Nice looking Vega!

Pistons hitting heads is not theory. Telling folks on an internet board that .010 quench is fine is irresponsible IMO. It have may worked for you. But without knowing the intended viewer's set up, it's dangerous to broadcast to all. I've seen forged pistons rock in the cylinder +0.005". That cuts your 0.010" in half. Then factor in up to a 0.02" rod bearing clearance. Now you're down to 0.03" clearance. Any rod stretch and BAM. Any carbon build up and BAM. Too close for comfort for the typical build. You have to factor in rod bearing clearance, manufactures tested rod stretch at what RPM. Pin clearance, floating or pressed, piston to wall clearance and piston rock. Piston material and any growth from heating.

Not to mention seldom do folks actually measure their clearance for quench. They use a calculator with manufacturer specs. Those specs could be a hair off due to manufacturing tolerances. A couple items off a hair and BAM. A static 0.010" clearance is not a Dynamic clearance of 0.010" once warmed up and running.
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