Head Cam Swap results

[96capriceMGR]

O2 bung plugs are readily available drill and tap one.

One of the resident computer nerds(by his own description) from the Impala forum calculated that 1psi was worth 12ft.lbs. at least with the gen1-2 350ci motors which matters because of piston surface that pressure is applied too.

[SMOKEmUP]

I'd be real interested to hear how that was calculated. Trying to run the numbers in my head. The small block chevy has a total of 100.5 sq in of piston surface area which would be 100.5 lbs of force pushing back against the pistons (1psi pushing against 100.5 sq in). How does he convert the pounds of force pushing back on the piston into ft lbs? I would think the reversion is where the power is lost. Because while both valves are open the pressure could blow back into the intake charge, heating it up causing all kinds of problems. Maybe big dave can school us on the practical application of the otto cycle.

I haven't seen the O2 bung plugs. But I googled it found a K&N part number and checked Summit. Sure enough Summit has them, that's expensive for a plug. I wonder if plumbing supply places would carry a metric plug 18x1.5mm.

[af2]

[Big Dave]

It is the same thread as a spark plug so the plug adapter used to inflate cylinders with air to change the springs will work.

The O-ring on the air chuck will melt with the heat unless you can isolate it, if you have a one piece male fitting. I have seen other styles of the same adapter idea that came with a female 1/4" NPT to thread on your own male air chuck or to run a short length of straight hose with the air fitting on the end of the hose. (this was about three times the price of the simple one piece air bung without the hose; but, after wrestling with trying to get the air chuck to clear headers I wish I had bought that style now).


Big Dave

[86GN]

Smoke, FAST uses these values for a 1 bar map sensor. 15 kpa = .71v, 60 kpa = 2.86 v, 90 kpa = 4.29 v. It's linear KPA to voltage.

[Paul P]

Just a quick calc using a 3.75" stroke with no losses counted. 100.5 pounds of force on a 3.75" arm would be 31.4 ft/lbs. I know frictional losses are pretty high so that would reduce that number significantly so 12ft/lbs might be close. Plus all the pistons are not pushing on it a the same time. It's complicated for sure....

[Big Dave]

Why you want headers but not a 3" exhaust.

Smoke your log style cast iron exhaust manifold is a great heat sink, and muffles under hood noise of the exhaust as it is released into the exhaust port of the head when the valve pops open; but for performance it blows. The reason it blows is because of the engine dumping exhaust into the log from adjacent cylinders. There isn't enough time for the plug of exhaust gas to move down the header pipe to equalize pressure in the log manifold between adjacent cylinders 8 & 4, and 5 & 7 (for those Ford guys reading this the firing order for all Chevy's is 1-8-4-3-6-5-7-2, but don't laugh at Chevy you have adjacent cylinder problems also and our firing order doesn't change with different cams).

When the intake valve opens on cylinder number eight the exhaust valve is still open (overlap due to cam duration) and the exhaust valve is also open on cylinder number four which is still dumping highly pressurized exhaust gasses into the log manifold. Now because we have already exhausted cylinder number eight (piston past TDC and going down) the pressure in that cylinder is low. So the pressurized exhaust log manifold acts just like an air distribution manifold on your shop air compressor feeding air to all the branches of pipe in your shop; as you open up that branch compressed gas (air) moves into the area of low pressure.

This in-rush of exhaust gas from cylinder number four enters cylinder number eight (on it's intake stroke) and dilutes the charge just like an EGR valve does. (good for limiting detonation due to high compression, but bad for optimizing your available cubic inches of fresh charge of air and fuel). If your cam shaft has a long enough overlap the in-rushing exhaust gasses will actually pressurize the cylinder and travel up the intake manifold diluting the vacuum signal to your MAP sensor (with the consequence of your engine running rich).

The same thing happens in cylinder number five; and to a lessor extent (because of the difference in the amount of time between pulses) in cylinders numbers one and six. If you were to lengthen the manifold feed to the to log enough to prevent the gasses from having time to flow back you would have a set of shortty headers that prevents exhaust gas reversion made of cast iron (Sanderson actually makes some). Steel tubes are lighter and we all know in racing lighter is better, so we all ask Doug and others to please make a set of steel tube headers that fit my car.

Time is the critical factor with headers. The longer the tube length the less chance there will be for a plug of exhaust gas to reverse direction at the juncture of the tubes and travel back up an adjacent tube due to reduced pressure. For some strange reason racers have observed a correlation between the length of the tube and torque; with longer tubes making more torque than short tubes. I suspect it is because racers run long duration cams and need a longer tube to avoid getting into a reversion issue.

So from a strictly plumbing point of view, thinking of exhaust gasses as nothing more than a flowing fluid, we have already found a way of increasing the air fuel charge in the cylinder of our car's engine by just adding long pipes to the exhaust port. This is what the big boys do with their zoomy headers. (They realized if you point them up you get to enjoy a down force on the car for no additional charge. How much down force? Enough to blow the pants off of a crew member at the crack of the throttle.)

I have addressed the fluid dynamics aspect of headers but there is a wave theory aspect as well because as we all know an UNCAPPED car is noisy. If we know that cars are noisy and we know that noise is the result of sound waves we can apply what we learned in physics class about standing waves in a pipe. In class the physics teacher bored all the guys talking about organ pipes instead of talking about tuning header pipes for our car. The same rules apply to the exhaust headers as apply to the church organ. An OPEN pipe will maintain a standing wave if it is tuned to the frequency of the wave's length.

We are attempting to capture the energy of the wave pulse (that energy that is able to rip off the crew man's blue jeans) and use it to create an area of low pressure at each end of the pipe (one end being inside the cylinder of our car). If we happen to find the right length of the wave, then any half, or quarter, or eighth (etc.) wave length will also yield an area of low pressure where we want it.

However this point seems to be lost on every one in the advertising world selling headers, if you close off the end of the pipe and slap on mufflers all bets are off. Adding a down pipe and tail pipe just lengthens the pipe so if it were a fraction of the tuned length (this time going one times or two times or four times the length of the standing wave) we indeed have an area of low pressure at both ends of the pipe (provide we leave the muffler off and have no bends in the pipe). But as soon as you bend the pipe the wave form crashes into the wall of the pipe and starts to reflect around destroying the standing wave.

So unless you intent to run uncapped around town, then we can forget about scavenging the exhaust by means of sound waves because it just isn't going to happen. Most header companies realized this in the mid seventies and stopped offering tuned length headers for street cars (you can tell street headers because they have a flange on the back of the collector to bolt up an exhaust system). Competition headers are still tuned equal length with adjustable length collectors (no flange to bolt up mufflers).

My last pet peeve is coffee can exhaust systems. We run mufflers to quiet down the noise off the combustion process. Why then would you want to amplify the noise with a megaphone? (chromed coffee can exhaust tip without a muffler) The same goes for a three inch exhaust.

Unless you are running over 500 cubic inches there isn't enough volume of exhaust gas to pressurize a free flowing exhaust system. It is essentially open to atmospheric pressure. The residual pressure that can be measured is due to fluid friction which you will have with any size exhaust pipe you choose.

Big diesel truck engines run at atmospheric pressure on the intake and exhaust side of the valves so they have no throttle plates restricting entrance and six inch exhaust pipes. You will also note that they are NOISY. Even with a five foot long chambered exhaust muffler, they are freaking noisy. That is why they have shinny chrome plated stacks that point straight up; so you do not get the full blast of noise they are producing. A three inch exhaust is also noisy, and a 2.5" is all an engine under 500 cubic inches needs to get the gasses out of the car (assumes true full dual exhaust with no CAT and Y-pipe).

I will now turn over my soap box to any member who disagrees.


Big Dave

[SMOKEmUP]

To be nit picky the LS1 firing order is 1-8-7-2-6-5-4-3.

If I understood what you wrote the difference between a shorty header and a long tube header (with the same primary and collector diameter piping) is the long tube header will prevent less reversion. Assuming we're talking about an exhaust system that has low back pressure (street system with mufflers and tail pipes) I've seen dyno tests where the long tube header will change the torque curve and make more power indicating wave tuning is changing the power output.

This brings up an interesting subject. How does mufflers, catalytic converters, and cross overs change the exhaust pressures, velocity, and wave tuning? How do you design a street tuned exhaust system to include cats, crossover, and mufflers?

[Big Dave]

Copy that 1-8-7-2-6-5-4-3. That's an improvement over the generation I & II firing order, now you only have immediate reversion associated with cylinder two by six, but much more back pressure on the passenger side bank as there are three cylinders dumping in close proximity.

It isn't wave tuning unless we are talking about an open exhaust. Even in the dyno cell they run mufflers, hanging them directly off the collectors. So any improvement in horse power (torque over time) is due to less exhaust gas reversion with longer tubes, not wave scavenging action which requires ether a totally closed tube (prevents all exhaust gasses from escaping) to reflect the wave or an open tube (atmospheric pressure) which causes an inverse wave to be reflected back up the pipe.

Theoretical ideal's for a street exhaust system dictates long small diameter tubes feeding into two low resistance cats (only if they check for them which they do not in many states) with three inch inlet and outlet (same as used on the Corvette) feeding into a three inch X pipe as close to the collectors as the Cats and tranny will allow. It then necks down to 2.5" diameter tail pipes going back to the mufflers which are of the turbo design (no perforated tubes with isolation chambers) but instead being large chambered open areas that rely upon echoing to cancel out the sound waves. This system is what is used on the ZL-1 427 Corvette, so I will have to agree with the GM engineers on this one. You may be able to buy all the parts (assuming they will fit the F-body chassis) and use them. The factory uses a cast iron to tube header combination on the 'vette instead of a straight tube header if I remember correctly.

The shorter the tail pipe and the closer the mufflers to the header the better; as all pipe, regardless of diameter, has fluid frictional losses (the bigger the diameter of the pipe the more surface area it has with more fluid friction, assuming equal pressure). The sooner the exhaust gasses exit the less need for restrictive bends and kinks in the plumbing. Unfortunately we all have to sit somewhere, and modern cars have the passenger compartment sitting inside the frame rails; necessitating the movement of the muffler to the rear of the vehicle.

Big Dave

[af2]

[Big Dave]

If you're just trying to plug the hole of an Oxygen sensor in the header pipe you can always do what I do and screw in a spark plug. I then put an old spark plug wire and run it back up into the controller box for my 4L80E transmission. You should here the speculation on what that computer controlled spark plug is doing in the exhaust pipe at car shows.


Big Dave

[af2]

[Big Dave]

A Champion spark plug is used to plug hole in my tail pipe that had an O2 sensor for the old TBI (broke it tring to get it out so I had to plug the hole and was too cheap to buy a new sensor for a carburated engine) and I needed something to fill the hole. Tried an old spark plug and it went right in.

Now that plug could have been out of my '47 John Deere or the '69 Gravely yard tractor, or even one of a half dozen Stilh 2 cycle motors I use to beat the yard into submission (or even a SBC or BBC, since I have couple of examples of those lying around; including the old style gasket plugs from the 60's, but since that has a 3/4" reach I don't think I used one of those. I keep all the old plugs in case I break one and need a fast replacement in a drawer under the work bench and it holds a bunch. (have I ever mentioned I'm loath to throw anything away)