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Cool Cans/ Header Blankets/Ignition Systems


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With my background in import building, the cars we built and even ones straight from the factory were running Compression Ratios of 11,12,13.5ish all the way up to our drag cars at nearly 15:1 running on ethanol.

 

I'd like to boost mine CR up a little bit, however, I've learned that lower CR's are more adaptable with power adders.

 

without having to rebuild the motor, minimize the head chamber volume, maximize quench action and buy all new pistons and such im wondering if i can get that CR up using the following less intrusive methods.

 

1) cool cans, fuel coolers

2) intake port air as cool as possible

3) keep the heat down under the hood (header blankets?)

4) gross overkill ignition systems

5) open the spark plug gap as much as possible with a range zero spark plug.

 

EDIT EDIT_______________________________EDIT EDIT

for those who haven't read this thread, ive now learned WHY the smaller displacement motors run higher CRs and why ours shouldn't. I was not taking into account piston speed, rev speed and detonation but purlely looking at the issue from a TDC and BDC psi value. This thread has been turned into more of a knowledge base and would be more informative if you read it backwards, from the bottom to the top.

 

-Matt

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any input is appreciated, if it is indeed true that American cars run low compression ratios it explains a lot to me about why their STOCK power output efficiency is low.

 

 

I guess that I don't understand your point. These cars are meant to be used on the street, using commonly available gasoline. In the US, that is normally 93 Octane maximum (except in California, where the gasoline has been crippled down to 91). Mustangs don't run on Ethenol. How do you expect to be able to run such high compression on street gas?

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1) cool cans, fuel coolers - Great idea, IMO.

2) intake port air as cool as possible - Good idea. How?

3) keep the heat down under the hood (header blankets?) - Good and bad. Header wrap will keep ambient heat down, but condensation/rust/corrosion is always an issue when wrapping exhaust. Either buy coated headers or coat them yourself. Several coating products are available online.

4) gross overkill ignition systems - You could run the cam cover/distributor setup with an aftermarket ECU. However, these setups are typically very expensive.

5) open the spark plug gap as much as possible with a range zero spark plug. - Zero degree plug is a good idea when running boost anyway. Opening gap beyond spec isn't a good idea, IMO.

Most of your ideas may be worth pursuing, depending on serious you are. However, investing in a set of pistons will probably be the most effective solution. Good luck.

 

Ken

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My Corvette has 10.5 to 1, which is about as good as you are going to do with 91 Octane. Anything higher than that is getting into an area where knocking is going to occur pretty regularly without some additional modifications, such as cooling the intake charge, reverse head cooling (like on the LT1), etc. And if you do go too high a compression for the fuel octane, the knock sensor is going to retard your spark and your Horspower anyway, which sort of defeats the purpose.

 

If you want to go into the 11:1 + range, you may as well resign yourself to the fact that you will be adding some aftermarket octane boosters or AVGAS.

 

As for running ethenol. Again, this defeats the horsepower purpose. Ethanol has a much higher octane rating, but it also has a lot fewer BTUs. So, your horsepower is again reduced by the fuel energy content, even as your compression ratio goes up.

 

It's a catch 22. If you are going to invest time and money into the mods that you are talking about, I think it would be much better invested in simply getting a supercharger instead of changing out major engine parts (pistons, heads, etc)

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My Corvette has 10.5 to 1, which is about as good as you are going to do with 91 Octane. Anything higher than that is getting into an area where knocking is going to occur pretty regularly without some additional modifications, such as cooling the intake charge, reverse head cooling (like on the LT1), etc. And if you do go too high a compression for the fuel octane, the knock sensor is going to retard your spark and your Horspower anyway, which sort of defeats the purpose.

 

If you want to go into the 11:1 + range, you may as well resign yourself to the fact that you will be adding some aftermarket octane boosters or AVGAS.

 

As for running ethenol. Again, this defeats the horsepower purpose. Ethanol has a much higher octane rating, but it also has a lot fewer BTUs. So, your horsepower is again reduced by the fuel energy content, even as your compression ratio goes up.

 

It's a catch 22. If you are going to invest time and money into the mods that you are talking about, I think it would be much better invested in simply getting a supercharger instead of changing out major engine parts (pistons, heads, etc)

 

+1

 

These cars are designed to maximize efficiency on the crap (pump) gas that we are given. Trying to make horsepower simply from raising the compression ratio on a street car makes about as much sense as putting air shocks on the rear to clear your reverse-offset Cragar S/S mags.

 

Another thing, compression ratio is a fixed ratio. You cannot change the numerical ratio unless you physically change the heads or the rotating assembly. It can be argued that power adders (boost) increases the "effective" compression ratio, but numerically, it does not change.

 

Low efficiency? A stock naturally aspirated 281 cubic inch engine making more than 1 rwhp per cubic inch is definitely respectable. In fact, it makes EXACTLY the same bhp/cubic inch as a 2003 Z06 Corvette (1.17 hp).

 

Besides, a lower CR makes it "boost friendly".

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Besides, a lower CR makes it "boost friendly".

Agreed.

 

Assuming he really wants to up the CR, I'd start on the inside of the engine. If you're planning on dumping a ton of boost anyway, upgrading the internals isn't a bad idea.

That'll give you the option of selecting a higher ratio at the same time, probably cost about the same as any combination of external mods, and leave you with a much stronger setup.

 

Ken

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Ok

1. You have to modify the internals to get a higher actual CR. Period. It is a mechanical equation.

2. Detonation destroys pistons.

3. A blown engine boosts the effective CR. You are pressurizing the charge making it compress more AF mixture.

4. Rest assured the CR is optimized by Ford for pump gas and the computer controls.

5. If you are going to modify the bottom end for boost it would not be to increase the CR. You would want stronger internals.

6. A engine built specifically for operating with alot of boost has lower CR than a NA "built" engine.

 

Buy a S/C or a turbo bolt on system and get better results with less headache IMHO.

 

Cheers!

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6. A engine built specifically for operating with alot of boost has lower CR than a NA "built" engine.

 

Cheers!

 

your #6 actually brings up a good point that I had somewhat overlooked. Because back when I was working on Skylines, we would pump 20-25 psi boost into normally 8.6:1 CR motors. As well as 8.2:1 WRX STI's that were running 15-20psi boost.

 

so were the S197 Mustangs with 9.8:1 CR built with moderate boost in mind? 4-9ish psi?

 

I've already gone with the Paxton w/ Air to Air cooler, however im just trying to tidy up things like the Fuel Coolers, the overall heat under the hood etc. It's all thermal efficiency. Keeping heat down should to EFFECTIVELY raise CR. I'm much more experienced with smaller motors, and simply assumed the same rules basically apply.

 

however, the boost pressure thing i had COMPLETELY overlooked. Until you pointed that out.

 

Oh and before i forget, why do bikes run such a high CR? My "Busa' (1300cc) runs 12.5:1 and my Yamaha R6 (600cc) is at 13:1. Im just curious. Or is it a whole nother can of worms?

 

-Matt

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Oh and before i forget, why do bikes run such a high CR? My "Busa' (1300cc) runs 12.5:1 and my Yamaha R6 (600cc) is at 13:1. Im just curious. Or is it a whole nother can of worms?

 

-Matt

 

Yes, it's a whole 'nother can of worms. The problem with fuel detonation is directly related to how fast the fuel burns. And that is what knocking is all about. When the flame front exceeds the piston speed (lower octane), knocking occurs. That's why knocking is much worse at low RPM/high load applications.A motorcycle engine operates at much higher RPMs in the first place, so even a low octane fuel flame front can't exceed the piston speed. That is why a motorcycle can operate at higher compression on lower octane fuels. (Harleys operate at much higher loads and lower RPM on two cylinders and are much less tolerant of low octane, like cars)

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Yes, it's a whole 'nother can of worms. The problem with fuel detonation is directly related to how fast the fuel burns. And that is what knocking is all about. When the flame front exceeds the piston speed (lower octane), knocking occurs. That's why knocking is much worse at low RPM/high load applications.A motorcycle engine operates at much higher RPMs in the first place, so even a low octane fuel flame front can't exceed the piston speed. That is why a motorcycle can operate at higher compression on lower octane fuels. (Harleys operate at much higher loads and lower RPM on two cylinders and are much less tolerant of low octane, like cars)

Thread hijack:

Mark - You need a mod coach asap! :hysterical:

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I'm making fun of your sig :finger:

 

Upgrades:

Harley Davidson Sticker

Sheriff Department Sticker

Full tank of Premium gas

4 coats of wax

2 layers of Armorall.

New air in all four tires.

Can of Fix-a-Flat in the trunk.

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I'm making fun of your sig :finger:

 

Upgrades:

Harley Davidson Sticker

Sheriff Department Sticker

Full tank of Premium gas

4 coats of wax

2 layers of Armorall.

New air in all four tires.

Can of Fix-a-Flat in the trunk.

 

ohhhhhhh, gotcha. Well, after I paid for the Shelby, my wife put me on a mod-free diet.

I have added an oil change and now I also have a cell phone charger in the power port :happy feet:

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ohhhhhhh, gotcha. Well, after I paid for the Shelby, my wife put me on a mod-free diet.

I have added an oil change and now I also have a cell phone charger in the power port :happy feet:

:hysterical: Man, I'm glad my wife isn't as bright as yours!

Seriously though, the modding thing gets way out of hand way too quickly. You're a wise man.

 

Ken

 

p.s. I wasn't being a jerk, by the way. Just joshin' ya. ;)

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:hysterical: Man, I'm glad my wife isn't as bright as yours!

Seriously though, the modding thing gets way out of hand way too quickly. You're a wise man.

 

Ken

 

p.s. I wasn't being a jerk, by the way. Just joshin' ya. ;)

 

I understand. I kept rereading my post to see what "mod" I had missed. I couldn't figure out what a MOD COACH was. :headscratch:

 

My modding problem isn't just with the Shelby. If I do too much with my cars, my Harley gets jealous.

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Yes, it's a whole 'nother can of worms. The problem with fuel detonation is directly related to how fast the fuel burns. And that is what knocking is all about. When the flame front exceeds the piston speed (lower octane), knocking occurs. That's why knocking is much worse at low RPM/high load applications.A motorcycle engine operates at much higher RPMs in the first place, so even a low octane fuel flame front can't exceed the piston speed. That is why a motorcycle can operate at higher compression on lower octane fuels. (Harleys operate at much higher loads and lower RPM on two cylinders and are much less tolerant of low octane, like cars)

 

Now i understand why the Honda's, Nissans, and Subaras, low displacement 4 cycliders rev much faster, higher and can get away with lower octane (lets say 91ish) at high CR's. I never realized that rev's were the underlying factor here. Which is why an S2k with a 8500 redline out of the factory can get away with a 12.5:1 CR.

 

this actually makes a ton of sense now. I was simply thinking of TDC and BDC psi values and ignition systems not taking into account, displacement, rev speed and piston speed.

 

many thanks to everyone who helped me understand the differences and more importantly WHY, they are present. Now I've got to learn how to work with these big American motors.

 

Cheers!

-Matt

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Now i understand why the Honda's, Nissans, and Subaras, low displacement 4 cycliders rev much faster, higher and can get away with lower octane (lets say 91ish) at high CR's. I never realized that rev's were the underlying factor here. Which is why an S2k with a 8500 redline out of the factory can get away with a 12.5:1 CR.

 

this actually makes a ton of sense now. I was simply thinking of TDC and BDC psi values and ignition systems not taking into account, displacement, rev speed and piston speed.

 

many thanks to everyone who helped me understand the differences and more importantly WHY, they are present. Now I've got to learn how to work with these big American motors.

 

Cheers!

-Matt

You're welcome. And actually it gets even more complicated than that. My explanation was sort of a simple one. In reality, you can easily get multiple flame fronts and secondary hot spots, etc. It's a science unto itself. And before knock sensors, engines were a lot less efficient. The best place you can operate a gasoline engine it at the "critical" point, just before it wants to knock. It's all very interesting stuff. I had the benefit, when I was younger, of starting out working in an Army motor pool, where I met a hardcore weekend racer. I went from barely being able to change a spark plug, to swapping out engines and grinding cams. Too bad I had to grow up and get a desk job :( Cars were much more fun.

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