How much ignition retard per pound of boost?

[Orr89rocz]

This is neither a "I know a guy". or a with intercooler chart.. Do you have an example of a car tuned within this chart and 93 octane ,where the combo failed?

A 454 with flat top forged pistons and open chamber heads is under 8:1... A 496. same is less than 8.7:1.

I am saying that chart is relatively conservative. It underestimates what is really possible imo When considering small or big block chevy/fords most likely. Even ls cars. A 9:1 guy with a conventional head sbc sbf etc could Most likely go beyond the limits proposed by that chart in a drag/street appliction.

[F-BIRD'88]

110 octane unleaded race gas is readily available, blends great with good pump gas to get the performance octane level protection needed to PROTECT $$$$ your INVESTMENT $$$. The smart money does this when wanting to push the envelope..

[David Redszus]

This is neither a "I know a guy". or a with intercooler chart.. Do you have an example of a car tuned within this chart and 93 octane,where the combo failed?

A 454 with flat top forged pistons and open chamber heads is under 8:1... A 496. same is less than 8.7:1.

I am saying that chart is relatively conservative. It underestimates what is really possible imo When considering small or big block chevy/fords most likely. Even ls cars. A 9:1 guy with a conventional head sbc sbf etc could Most likely go beyond the limits proposed by that chart in a drag/street application.

The chart is not conservative...it is flat wrong.

Even if it were correct, it still would not provide useful information regarding knock control related to boost.
We need to know actual inlet air temperature; after the intercooler and including fuel evaporation (if any).
And even that information would apply only to a specific engine and maybe not even to other nearly identical engines.

[mt-engines]

The reason I haven't chimed in is becauseits not a question that can be answered. You need a good datalogger and drive it.

Some engines I have done don't need any timing pulled until 8-10 psi. Some have nothing pulled until 15. Too many variables.

You answer has been brought up enough. I don't see why this thread is still going.

[F-BIRD'88]

This is not a intercooled combo.
What part of that are you not reading?
The inlet temp and blower outlet temp is known within a real world range.. That includes HOT..
Not labratory.. not theoretical.

[plovett]

Well, I was looking for a rule of thumb. Rules of thumb are inexact by definition. And I would say charts with few inputs are intended for a situation within a limited range of parameters, that aren't input-ed on the chart. Plus, the combination I am talking about will be crude, with crude controls, compared to a lot of what you guys are talking about.

I am sure just retarding the ignition by 1 degree per 1 psi of boost will leave significant power on the table compared to a fully optimized and precisely controlled combination. That is okay for me.

I appreciate all the input. I don't really think anybody is actually wrong here, just looking at it from different angles and from vastly different intensities of perfection. Feel free to keep debating it. I am learning little bits here and there. I like the chart, but don't take it for more than it is.

Since we are meandering and octane is relevant and has been mentioned, how about octane boosters? The way I would use it would be another crude battle axe of a solution to a very precise and complicated problem.

I don't mean the goofy ones at the parts store that might add a few tenths. How about serious octane boosters?

I mentioned I don't plan to use an intercooler. I would consider adding a serious octane booster to each tank of gas. If it increased the cost/gallon by a dollar or a little more, that might be a good way for me to go. And If I didn't have any booster, I could just dial my BTM to 2 degrees of retard.

Any recommendations on octane booster I could buy by the case? Boostane? Octanium?

[F-BIRD'88]

IMHE Effective real world octane booster is a 5 gallon pail of 110 octane unleaded race gas.
Blends in and raises the octane of pump gas very effectively.
like this. www.proracingfuels.com
This is what I use.

[F-BIRD'88]

You also need to consider and research Water Methanol Injection. It is a Serious Octane Booster.

[David Redszus]

Any recommendations on octane booster I could buy by the case? Boostane? Octanium?

Boosting fuel octane will require a trip to the paint dept of your local hardware store.

Look for:
m, xylene, 115MON
p, xylene, 110MON
o, xylene, 100MON

Ethyl alcohol, good cooling and knock protection

MTBE, call a local chemical house, might need to buy a drum.

[plovett]

Any recommendations on octane booster I could buy by the case? Boostane? Octanium?

Boosting fuel octane will require a trip to the paint dept of your local hardware store.

Look for:
m, xylene, 115MON
p, xylene, 110MON
o, xylene, 100MON

Ethyl alcohol, good cooling and knock protection

MTBE, call a local chemical house, might need to buy a drum.

I had heard of using toluene, EtOH, and MTBE, but not xylene. Thanks!

[plovett]

You also need to consider and research Water Methanol Injection. It is a Serious Octane Booster.

Yes, that is a good idea. Plus, it's cool because it makes me think of late WWII piston engines as they often used it. Hmmmm. However it is another "system" to put on my engine, adding complexity and possible failure points. That's why I like the idea of boosting the octane. So simple.

Thanks!

[Stan Weiss]

The chart is just a somewhat guess of what may work. Octane needed is more a factor of cylinder pressure. So I guess what camshaft is in the engine has no effect on octane needed?

Stan

[plovett]

The chart is just a somewhat guess of what may work. Octane needed is more a factor of cylinder pressure. So I guess what camshaft is in the engine has no effect on octane needed?

Stan

Would the same chart, using DCR instead of SCR, be useful? It would still be just a chart that assumes a lot of variables are in a "typical range".

[BLSTIC]

Maybe try get all the stock-ecu dumps of turbo vehicles that you can get and compare the timing vs MAP values in those, pay particular attention to engines that require similar 'naturally aspirated' timing to what you expect yours to be happy with.

That said, I put 1 degree retard per psi of boost into my turbo 4v honda for test driving purposes and it didn't blow up and went much faster than it did N/A.

[David Redszus]

The chart is just a somewhat guess of what may work. Octane needed is more a factor of cylinder pressure. So I guess what camshaft is in the engine has no effect on octane needed?

Stan

Octane requirement is more sensitive to chamber TDC temperature than to pressure.
A change in IVC will affect DCR and therefore compression temperature (and pressure).

SCR = 10.0
IAT = 100F
IAP = 14.7 psi
IVC = deg BTC

IVC....psi.....temp.....DCR
107....226.....754......7.47
108....229.....758......7.54
109....232.....762......7.61
110....235.....767......7.68
111....237.....771......7.74
112....240.....775......7.81

Camshaft motion (lift) is dynamic and does not match the theoretical motion curve; it will often close later than expected causing variations in DCR, temp and pressure. It might be a contributor to cycle to cycle variations.