Maximum Streetable Compression Ratio?

BitchinBeezer said:

Would the "professional" engine builders please chime in & tell me if I'm doing this right & whether either of those combos would be streetable?

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I'm Sorry, Bitch.

Personally I have found the dynamic compression to only be somewhat helpful.

There are a lot of other things that go into "how much compression can I run"

Temperature, mixture swirl, exhaust sytem, how well the carb atomizes the fuel and how well the ports deliver the atomized fuel are only a few of them.

I would start with about 10-1 static and tune from there. Jim

comnoz said:

how well the ports deliver the atomized fuel are only a few of them.

I would start with about 10-1 static and tune from there. Jim

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Assuming the 10:1 CR Stage 1 combo, could you provide some input on a poor man's options as far as cylinder head work & whether 3mm ovesized intake valves W/port work would be a benefit.

While I understand the advantages of the "Fullauto" heads, they are out of the question due to the cost. What would be a less expensive alternative.

I had excellent results W/my 86 in Panhead when I installed 1/8" oversize intake valves (leaving the exhaust std) & opening up the bowls & doing some minor port work. An 1 7/8" S&S intake manifold was used ti feed the intake charge. I used the same combination on an otherwise stock 62 FLH W/likewise substantial power gain.

Perhaps the Stage 1 Maney cylinder head?

BitchinBeezer said:

comnoz said:

how well the ports deliver the atomized fuel are only a few of them.

I would start with about 10-1 static and tune from there. Jim

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Assuming the 10:1 CR Stage 1 combo, could you provide some input on a poor man's options as far as cylinder head work & whether 3mm ovesized intake valves W/port work would be a benefit.

While I understand the advantages of the "Fullauto" heads, they are out of the question due to the cost. What would be a less expensive alternative.

I had excellent results W/my 86 in Panhead when I installed 1/8" oversize intake valves (leaving the exhaust std) & opening up the bowls & doing some minor port work. An 1 7/8" S&S intake manifold was used ti feed the intake charge. I used the same combination on an otherwise stock 62 FLH W/likewise substantial power gain.

Perhaps the Stage 1 Maney cylinder head?

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A 3mm oversized intake valve along with some port work will make a good improvement in power. Particularly if you have a 30mm port head to start with. Jim

Maybe one of these would work...

In a 750 engine there just ain't much squish area to be very effective and some the most powerful Norton twins had no squish at all d/t opening bottom of head for bigger bore pistons to leave pure hemi chamber. Effective squish is said to disappear about .045" and above. A 750 head adapted to 920 jugs leaves a squish ring over 3/8" wide in places so definitely worth getting squish close with piston to help stifle detonation. Might even be enough to allow a Singh Groove or two to function.

Here's some data points but mostly for water cooled engines. 12 CR is about car engine tops on 93 octane if Al heads and fairly over lapped cam one would want in a street-able hot rod.

https://www.google.com/#q=octane%20comp ... io%20chart

I looked at that dynamic CR calculator and it appeared to be very empirical to me. Has someone evaluated combustion chamber pressure and worked backwards considering cam timing etc, to get the algorithm ? If not, where did the calculation method come from ?

hobot said:

Effective squish is said to disappear about .045" and above. A 750 head adapted to 920 jugs leaves a squish ring over 3/8" wide in places so definitely worth getting squish close with piston to help stifle detonation. Might even be enough to allow a Singh Groove or two to function.

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According to KB piston literature, quench is still present up to around .065". The pre-09 Gen III 5.7 hemi had a .065" quench height stock.

W/quench distance, less is more to a point.

W/O a rev limiter, .035" is said to be minimum when using steel rods W/an automatic transmission, .040 W/a manual.

One of the reasons I was considering the 10.5:1 high compression J&S pistons was the .050" quench distance. I'm still pondering using them & cutting a small dish into the center of the piston to reduce CR to 10:1 while still maintaining that .050" value.

Using the lower crown 8.5:1 piston (.140" quench distance) combined W/a .003" head gasket & .020" head deck reduction to get to 10:1 would result in .080” quench distance.

Even though the Norton 850 bore doesn’t result in a large quench pad, I think it would still be worthwhile to maintain the .050” quench value.

The main man on octane vs detonation is Richardo's work that also discovered water helps the burn make mo power. After that research on each particular engine type and set up is needed or just restricted to being conservative following general rule of thumbs in building. A fast burn hi compression chamber may need less octane than slower burn lower CR chamber, then throw in the craft's mass and its gearing and etc etc. I bet if I can find a way to detect ping before its human ear audible in Norton's we may be surprised on what a hot tuned and run Norton can tolerate.


http://www.autospeed.com/cms/A_110213/article.html

hobot said:

The main man on octane vs detonation is Richardo's work that also discovered water helps the burn make mo power. After that research on each particular engine type and set up is needed or just restricted to being conservative following general rule of thumbs in building. A fast burn hi compression chamber may need less octane than slower burn lower CR chamber, then throw in the craft's mass and its gearing and etc etc. I bet if I can find a way to detect ping before its human ear audible in Norton's we may be surprised on what a hot tuned and run Norton can tolerate.

http://www.autospeed.com/cms/A_110213/article.html

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Water/methanol injection was used in WW II in the Pratt & Whitney R2800 (among others) for "emergency power".

The methanol was an octane boost but it was primarily used to prevent freezing.

Water alone retards detonation but also turns the internal combustion engine to a form of steam engine as the water expands X 1700 when it flashes to steam.

The Germans, on the other hand, used N2O as "emergency power".

On the early versions of the Shorts 3-30, with the PT6-45B engines, they used water methanol injection for the emergency reserve power system.

NASTY stuff. Constantly changing out pumps and tanks would corrode quite quickly. Not to mention what it did inside the engines.

I guess it was better than crashing into a mountain.

I would think an injection system is a band aide fix.

Proper parts selection and design should yield better results.

Build up a Maney 1007cc with a Fullauto head Massaged by Comstock and JS Motorsports goodies and move on with life.

" The Germans, on the other hand, used N2O as "emergency power " .

quite spectacular , with a armour pierceing round , or cannon shell , into the tank .

The methanol is realy a anti detonant / anti knock . Used to increse output in conjunction with the H2O , and CONTAIN TEMPERATURES .

the old air cooled radials were driven on the cylinder head temperature guages .

Theoretical & actual , for a specific head type might vary , valve seat recession / re cutting . If the valves back a bit somes lost .

If oversize valves are installed out on the original seats , you might gain 0.25 ( higher ) .

So someones going to have to get the burette out , to ascertain the actual head volume ,

10CR is the most sensable static CR as there's 1000's of Combat with .040 over jugs rasing their CR a bit above 10, like mine, yet no problemo no matter what gas put in - as long as not lugging like snapping throttle off ~2000 rpm, 30 mph in 4th. Special fuel and anti-detonation fuels is always cheating but hey what they say about love and war...

I don't understand what this topic is about. Is the bike intended for some kind of illegal street racing ? If it is to be used for touring, you need to accomodate lower grade fuels, so must be conservative with comp. ratios. And why would you do the hot-up on a street bike anyway ? If you start fitting larger valves and porting the head, you could destroy mid-range power, and a race cam is unnecessary. If you are going to race the bike in AMA controlled competition, do the tuning with the rule book in your hand. I only ever use methanol fuel, the bike could never be used on public roads, it doesn't even have a kick starter or a generating circuit. I suggest you need to make a decision about what end purpose you intend for your bike. If you use a 10 to 1 comp. ratio, and an otherwise standard motor, you could still end up with a problem if you get the mixture too lean across the whole range of throttle openings, depending on the weather. I don't believe many road riders tune their carburetion, ignition advance and cam timings in the same way that most race guys must to remain competitive. Perhaps we need a good engine management system to retrofit to early commandos ? Or are they good enough already ?

acotrel said:

I don't understand what this topic is about. Is the bike intended for some kind of illegal street racing ? If it is to be used for touring, you need to accomodate lower grade fuels, so must be conservative with comp. ratios. And why would you do the hot-up on a street bike anyway ? If you start fitting larger valves and start porting the head, you could destroy mid-range power, and a race cam is unnecessary. If you are going to race the bike in AMA controlled competition, do the tuning with the rule book in your hand. I only ever use methanol fuel, the bike could never be used on public roads, it doesn't even have a kick starter or a generating circuit. I suggest you need to make a decision about what end purpose you intend for your bike,

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In your mind people that do any performance upgrades on a street bike enhine are foolish then?

If you don't have anything constructive to contribute, why are you wasting your time reading & posting?

FYI I know exactly what the purpose of this bike would be. It would be to make me happy when I twist the wick & that's all that matters.

I don't know how long you have been modifying & building engines, but I doubt if it's been any longer than I have been at it. This is just my 1st foray into Nortons so I'm gleaning information.

If you search my posts you might get some idea of what I'm looking for as far as a performance envelope.

I don't think doing a performance upgrade on a street bike is foolish, if there is a competition application for it involving similar bikes. Why are you doing this ?

BitchinBeezer said:

acotrel said:

I don't understand what this topic is about. Is the bike intended for some kind of illegal street racing ? If it is to be used for touring, you need to accomodate lower grade fuels, so must be conservative with comp. ratios. And why would you do the hot-up on a street bike anyway ? If you start fitting larger valves and start porting the head, you could destroy mid-range power, and a race cam is unnecessary. If you are going to race the bike in AMA controlled competition, do the tuning with the rule book in your hand. I only ever use methanol fuel, the bike could never be used on public roads, it doesn't even have a kick starter or a generating circuit. I suggest you need to make a decision about what end purpose you intend for your bike,

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In your mind people that do any performance upgrades on a sstreet bike are foolish then?

If you don't have anything constructive to contribute, why are you wasting your time reading & posting?

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I'm getting that old familiar feeling.

I think there has been enough good and solid info from professional and "nonprofessional" Norton engine builders for 10 people to make a decision. I think it's time you pull the trigger. Make sure you press it up against your temple

+1 Pete. Shit or get off the pot.

When I was a kid, we used to hot up 650cc Triumphs. My bike was on 11 to 1 comp with E3134 race cams, and ran on avgas. There was only one service station for miles around which sold it, so if you had to fill up, the bike ran like crap until you refilled with the 135 octane, leaded fuel. The bike was extremely fast for those days, however I got tired with the near misses and when I was 27 went racing for twelve years. It is a sublime obsession and I still love it, however cannot afford to do enough of it these days.

pete.v said:

I'm getting that old familiar feeling.

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Then perhaps you should look into having the dosage of your medication increased.

pete.v said:

I think it's time you pull the trigger. Make sure you press it up against your temple

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On second thought. perhaps you should consider a different therapist.