Cam design limitations

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StrokerScamp said:
I live by the K.I.S.S. rule myself. Turbos and blowers and such are cool but you can spend your whole life trying to figure it out when you couldda been cruisin.
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Well, I started "cruisin' in a normally-aspirated car in 1954, and spent a lifetime with natuarally aspirated stuff... and when this "turbo revolution" came on the scene via, mainly, the black Buicks, I decided it might be interesting to see what it was all about.

Just like building a natuarally-aspirated car, a basic setup can be simple and stilll pay some pretty big dividends (witness Tom Wolfe's 12.95 second e.t's on an almost completely stock, junkyard turbo'd /6 Dart Swinger) but, the realy good running cars that impress take a little more R & D.

If you don't want to set the world on fire, you can give that asthmatic /6 cylinder head a LOT of help for very little efffort with a 10-pound boost turbo setup for the street and not bother with an intercooler, blowoff valve, MSD boostmaster "dial-your-own-retard" or a header. Mid 13's for a /6 car like that should be a piece of cake.

That beats the heck out of buying and prepping a small block V8, and all that goes with it to accomplish an engine swap, for that kind of performance.

How much horsepower you need to satisy the seat of your pants will determine how deeply you have to dig to accomplish the e.t.'s you're after.

It's all good!!:cheers:
 
This is how I understand it... It's not about the exhaust gases expanding as they exit. Because it doesnt. As soon as that the flame front goes out, the gasses begin to cool, the more distance they travel, and more surface area they touch, the cooler they get. As an example... At the exh valve, they are around 1200°. At the port opening this drops to 900ish. After the first turn in the header, 800, at the collector, 400. As they cool, they slow down and contract. You wrap headers or coat them to keep that thermal drop to a minimum over the length of the pipe. If the energy that is lost by thermal dissipation is retained, that energy goes directly into the turbo and produces boost faster. My impression is, if that coated tubing is wrapped, it will result in fractures in the metal. I've seen that on motorhomes with stainless manifolding too, never mind plain steel.

Bill - If it was me, and a serious effort, I would not be using anything you are...lol. I've be making my own exh manifold/turbo mount, and having someone weld up a sheet metal intake with a large raised plenum and centered throttle body. It would not be carbureted. It's too easy to grab a junkyard EFI system and retrofit or by something like Megasquirt. I got spoiled when I ran a ProCharger dealer years ago. Carbureted boost is like replacing a 5.0L in a Fox body with a flathead V8 with Offy heads and intake, and Strombergs. Sure, it looks cool and does make some power. But you're leaving a lot on the table. Tunable EFI is the way to get intercooled turbo cars to run hard consistently.
 
So heat has nothing to do with it. Ok, that's enough for me. I'm out.
 
6pakattack said:
If what you say is true,how does this setup fit into the factors ?? Just wondering !

http://ststurbo.com/
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to tell you the truth i dont know... we did alot of research on those and it must have something to do with the turbo its self...

read below

StrokerScamp said:
All a turbo is, is a driven fan made to do work. It's about expanding and creating more of an INTAKE charge. A windmill is the same principle. It just does different work. It is a driven fan used to do work, same as a turbo. A turbo just happens to compress the intake charge, being driven off the outgoing exhaust gasses. There are certainly more exhaust gasses because of the added intake charge, but those gasses do not escape until they exit the tail pipe, so in theory, the turbo could be plumed at the tail pipe exit. As long as it has exhaust gasses to drive it, it will do its job. As to whether or not being close to the head makes a difference.....Certainly it would. Because hot gas molecules are bigger than cold ones. That means the hot gasses must flow faster to get through the exhaust since their molecules are expanded. That creates more boost. Since you are cramming more intake charge in, surely more exhaust has to come out. That's beneficial to a turbo since it is powered off of the exhaust. It's not the heat that drives the turbo fan. It's the FLOW. The added heat at the exhaust outlet makes the turbo much more efficient by high spool speeds due to the increased flow from the high heat. Much in the same manor a steam engine operates on the expanding steam from boiling water. A turbo away from the heat will still create boost, but much more poorly than one close to the combustion.

Not sure Bill wanted a turbo discussion. We should try to get it back on track.
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bingo SS... its nothing new... think about a header collector... you add an extension pipe until it becomes a restriction (the point it stops burning paint) and now you have a tuned collector...

once the gases cool its a restriction for the hotter expanding gases trying to escape...
 
Yes, and I just don't buy the "it's coolin off right after combustion" thing. The process is still takin place comin outta the manifold. That's why there's FIRE in da HOLE. LOL Because unburned exhaust gasses that didn't get burned in the cylinders are being burned in the exhaust. You caint tell me those exhaust gasses aint expandin. No way no how. It's grammar school science.
 
No expert here, but wouldn't longer exhaust headers simply cause a little more lag and slower spool up?

Certainly if the exhaust gas becomes cooler, the air will become more dense, and therefore will have less pressure to hit the turbine as quickly, so boost will come on more gradually?

Grant
 
Stroker - Take a basic infra-red temp gage and try your theory... I have. That was where the examples came from (ok, given, it was out of my memory). My middle school classes taught that heat expands, cold contracts just as your "hot molecule bigger" statement. Must be different schools...lol The basic hot larger is right. But the speed bit as a result of "bigger molecules thru the same size hole means faster" is dead wrong when referring to hot gas flow. As soon as the burn is done heat creation stops. Simple physics. Without a heat energy source, heat is dissipated. It's the same thing with areas of the chamber. If you have "fire" in the manifolding, you have a huge problem. You do realize what an EGR system does, and why, right? They are currently used in every production gasoline engine. It's called and Exhaust Gas Recirculation system. It uses exhaust gases, directly out of the exh port, to COOL the intake charge and chamber. It reduces the oxides of nitrogen and helps keep the engine out of detonation and ping.

On the collector, the collector length has to do with exh pulses and wave tuning, or series of exh valves opening and closing. Nothing to do with exh heat or creating a restriction. A tuned collector uses the frequency and inertia of exhaust pulses to help evacuate the cylinder better. Nothing to do with heat. The paint burning is what you do to find the best area for an X or H pipe connection.

But what do I know.
 
moper said:
You do realize what an EGR system does, and why, right? They are currently used in every production gasoline engine. It's called and Exhaust Gas Recirculation system. It uses exhaust gases, directly out of the exh port, to COOL the intake charge and chamber. It reduces the oxides of nitrogen and helps keep the engine out of detonation and ping.

QUOTE]

I am enjoying this discussion and learning a lot. Thanks for all the good information, everybody!

Every now and then, I see something that I take issue with though, and while I'm just a dilettante at this combustion theory business, I can add my 2-cents worth (and, that's what it's worth, literally) to the discussion, from time-to-time.

Here's how EGR was explained to me: Adding already-burned gasses to the intake charge is JUST like putting a brick in a toilet reservior. It takes up space, yes, but since there are no combustable products in it, it can add nothing to the combustion process. So, what is its value?

It takes up space in the combustion chamber in a benign manner, thereby reducing the amount of combustible gasses available to burn, and raise the temperature... and in doing this, reduces cylinder pressure. This reduced cylinder pressure allows more ignition timing (spark-advance) berfore detonation sets in, and also cools off the combustion process (and in the act of doing so, reduces oxides of nitrogen.)

It certainly does nothing to reduce the temperature of the intake charge ("It uses exhaust gases, directly out of the exh port, to COOL the intake charge.") before it gets into the combustion chamber. It is, after all, fresh (HOT) exhaust gas...

BTW, the inclusion of direct injection has made it possible to do away with EGR on some currently-produced automobile engines.

Having said that, I must reiterate that this ol' Valiant that we are building is a last gasp, hobby, project of two old geezers who should be in a couple of rocking chairs somewhere, reminiscing about their 1950s drag racing exploits in ther Olds 88's, out behind the airport (we had a quarter-mile marked off) and trying, in the process) to elude John Law... not breaking new (personal) ground with a bunch of unfamiliar (turbo) technology.

WEe have a LOT to learn, and not much time to get it done, so your many comments and information on this BB are much apppreciated by both of us!

Please keep the comments and input coming in as every one gets read, evaluated and if pertinent, acted up on.

Lookin' at a new header design as we speak... I'm about convinced that the long-tube design, attractive as it is, will cost us...

I ran an NHRA (Brand-X) Stocker for years, and was the Stocker class tech guy at 3 different drag strips; I know the value of a tenth... BUT, we are not building an NHRA "class" car here; just a test-n-tune play-toy, so we're not knee-jerk about flowing the head and buildding a sheet-metal intake. This is not a Comp Eliminator car...

Too darn old to learn the vagaries of EFI; besides, everything I read, says you can make just as much horsepower with a blow-thru Holley as you can with EFI... the EFI is just easier to get tuned correctly.

Besides, we already have the blow-thru carb and manifold...:blob:

Took a rocker arm to the heat treatment place; 16 on a Rockwell C scale... $50,00 to anneal 12 of them. The, $75.00 to re-heat treat them back to their original hardness (not very, it turns out.)

Pretty reasonable, I thought...

Now, I need to round up 12 to get treated to the 1.6:1 song-and-dance I have planned for them.=P~

Anybody got 12 to sell?
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OneOfMany said:
No expert here, but wouldn't longer exhaust headers simply cause a little more lag and slower spool up?

Certainly if the exhaust gas becomes cooler, the air will become more dense, and therefore will have less pressure to hit the turbine as quickly, so boost will come on more gradually?

Grant
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I am pretty sure you're right about this.

Our particular car will be a drag-only car with no need for responsive throttle RPM rev-capability. We intend to load the converter (and engine) heavily and build lots of boost before we release the brakes, so the value in a quick-spooling turbo would seem to be in a street car environment more-so than in a drag car, I would think.
 
"It certainly does nothing to reduce the temperature of the intake charge ("It uses exhaust gases, directly out of the exh port, to COOL the intake charge.") before it gets into the combustion chamber. It is, after all, fresh (HOT) exhaust gas..."

You're right Bill. If you note tho you cut off where I said "and chamber". My Neon's EGR port (and back in '73 the floor jets) are in the plenum of the intake, which was why i mentioned the intake charge. It is inaccurate and you're right. But the ultimate end goal is reducing the chamber temps. My point was to note that it was much cooler than the flame front and combustion temps inside the chamber. I mentioned it because Stroker was saying he believes exhaust gases are still increasing in temp (generating heat) when traveling out of the chamber and port and I believe that to be incorrect.
Another point of fact, perhaps a better example, are the thermal barrier coatings that can be applied to the piston, chamber, port, and interior of the manifolding/header are all designed to limit the heat dissipation from the exh gasses and retain that energy with the result of keeping gas velocity in the port higher. The tuner crowd uses these fairly regularly.

I understand your approach is have fun. You asked how I would do it... lol. For me, I'm at the point that it's more hassle to do things the way you are. I don't have the time, money, or patience to "do over". That's why my '65 has the 170 in it, when I have all the V8 stuff, plus engines sitting there too. I just want to get in, turn a key, and drive it. Maybe after I retire. If I can ever retire...lol.
 
moper said:
You do realize what an EGR system does, and why, right? They are currently used in every production gasoline engine. .............................But what do I know.
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It shows you don't know that EGR systems are NOT used in "every" production made. I have a 2004 Ford Ranger without an EGR system. There are many new vehicles made without them. I've worked on dealership lines since 1980 so I think I know about EGR systems. I've done diagnosis and repair on turbos while on the line and sat through some turbo repair and theory classes for Ford, GM and Chrysler, so I know a touch about how turbos work. I'm no expert....and I've said it many times. Me personally, I don't like turbos. I don't really give a rat's butt how you think they work, either. I think sometimes you'd argue about how to take a piss just for arguement's sake.
 
You're right. A simple exageration on my part on the "all" and "every". At least I accept you're right about EGRs...lol
A different opinion obviously gets you riled. I'm sorry about that. I might suggest showing where science backs up your ideas. Because if I see something I don't think is right, I'll speak on it. I would expect anyone who disagrees with me to do the same. Discussion that results only benefits everyone.
 
moper said:
You're right. A simple exageration on my part on the "all" and "every". At least I accept you're right about EGRs...lol
A different opinion obviously gets you riled. I'm sorry about that. I might suggest showing where science backs up your ideas. Because if I see something I don't think is right, I'll speak on it. I would expect anyone who disagrees with me to do the same. Discussion that results only benefits everyone.
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No problem, Moper. I agree that the purpose of the EGR is to lower temperatures in the combustion chamber, though I have NO scientific evidence to back that up. However, common sense would seem to indicate that when you introduce a non-combustible (already burned exhaust gasses) into the mix in the combustion chamber, (the "brick in the toilet reservoir" deal,) there's not as much combustible material to create heat; ergo, there's not going to be as much heat. Heat in egregious quantities in the combustion chamber, is bad to create oxides of nitrogen, one of the three main polutants the EPA tries to rein in, so the manufacturers used this ploy to control NOX emissions, starting about 1971 or '72, and still use it, today on a lot of vehicles.

But, you know all that...

Discussion is what this board is all about. If we all agreed on everything, there would be no need for discussion (and, little discussion.)


I learn something every day here, and am thankful for that, because at 72, I still have a LOT to learn...:study:
 
You're 72 Bill! I had no idea. That's so cool you're still playing with what you love.
 
moper said:
You're 72 Bill! I had no idea. That's so cool you're still playing with what you love.
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Been doin' it a long time (since I was 15)... gonna keep at it 'til I get it right... LOL!

Like, THAT's gonna happen.... :banghead:

The turbo thing is really outside my "frame of reference," but with a little (LOT!!!) of help from my friends (on FABO, mostly) I think it may be do-able...

We'll see.

Thanks for the kind words!O:)
 
Bill, it has to do with the ramp. Think of it as a pitched roof on a house. the lifter has to ride up one side and down the other as the valve opens and closes. If you want a high lift (lobe large) then if the duration is too short (does not look like /\ but ||) the lifter cannot ride up the ramp of the lobe correctly and you will lget cam and or lifter failure very quickly. You can go a little more lift and less duration with a roller setup but not much.

Larry
 
lhearold said:
Bill, it has to do with the ramp. Think of it as a pitched roof on a house. the lifter has to ride up one side and down the other as the valve opens and closes. If you want a high lift (lobe large) then if the duration is too short (does not look like /\ but ||) the lifter cannot ride up the ramp of the lobe correctly and you will lget cam and or lifter failure very quickly. You can go a little more lift and less duration with a roller setup but not much.

Larry
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Hey, Larry...

Thanks for the input!!!

I think I've got it, now....

I just never considered the physical relationship between the lifter and cam to be significant in this sort of situation.

Shame on ME!:violent1:

I appreciate the information and the graphic way it was described in your note.

Happy Holidays!
 
we run low 8 the 1/24 in mates 6 with 236/230 480 lift 170 mph
 
ian said:
we run low 8 the 1/24 in mates 6 with 236/230 480 lift 170 mph
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Ian,

I don't know what you mean when you say, "we run low 8 the 1/24..."

I'd like to hear a lot more about that engine, if you don't mind. Maybe you could post some pictures or a video???

Is the car that pale blue on in the video at the bottom of your sig line?
 
Bill Dedman said:
Ian,

I don't know what you mean when you say, "we run low 8 the 1/24..."

I'd like to hear a lot more about that engine, if you don't mind. Maybe you could post some pictures or a video???

Is the car that pale blue on in the video at the bottom of your sig line?
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no mate not the car in my profile thats a 408 has ran 143 the 1/4 , the engine in the dark blue car is a straight 6 265 cubes cast crank,h beams, forges runs a glide,has a girdle ,camshaft is a solid ft ,its still down 100 hp we are still sorting it
 
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