Newbie Questions

[nvysion]

Hello,
I would like to understand the following mods :
- 3 or 5 angle valve job
- shot-peened rods
- beehive springs
- LSD (A413 trans)

What these terms mean, what are the benefits of these parts/mods ?

Also, when I drive at a constant speed, I can see that the intake pressure is below atmospheric pressure (vacuum), even though at this speed the turbo must provide a lot of air.
When I open the TB by accelerating, the pressure increases immediately and goes positive (at the same RPM).
That makes me think that the turbo is pushing some air but not enough for the RPM speed because the TB position limits the amount of air coming to the intake.

Is this correct ?

If I had the same engine w/o a turbo, I would have to open the TB more at this RPM to get the same amount of air (vacuum) to the engine at the same speed/RPM, right ?

If I have vacuum in the intake does that mean that the cylinders are not "fully filled" at atmospheric pressure, ie VE less than 1 even if the turbo is pushing some air ?

Sorry for these dumbs questions but there is a long time I wanted to know, I hope I'm understandable despite my poor english level.

Louis

[NAJ]

I can answer your question about airflow and LSD.
LSD is Limited Slip Differential.
None came from the factory but there were a couple of manufacturers that made LSD units for our FWD Transaxles(manual and auto)
FACTS
1)There is always vacuum in the cylinders.
(Disregarding race engines with valve overlap @ high rpm)
(My VNT has 0 valve overlap)
2)High pressure always moves to low pressure to equalize.
3)An internal combustion engine always uses up its air supply before its fuel supply.

When the intake valve starts to open the piston is at the top of its stroke and as it moves downward there is a void, low pressure area(vacuum), outside air rushes in to fill the void(equalize pressure).
The internal combustion engine is not efficient and you will never fill the cylinder 100% with air.
Technology has given us Intake Manifold design improvements and Multi-Valve engines with Variable Valve Timing that drastically increase airflow and efficiency increasing horsepower with smaller N/A engines.
That is why today Mom's grocery getter can blow me off the road.

As far a turbocharging.
For the turbo to increase airflow and air pressure in the Manifold it has to be turning fast.
Boost is totally dependent on RPM and exhaust flow past the turbine.
The turbo increases air pressure above atmospheric in the Intake Manifold so more air enters (also more quickly) the cylinder when the intake valve opens.

[nvysion]

Thanks NAJ
What are the LSD's benefits ?

I still not understand how there is vacuum in the intake despite the air that the turbo provides.
I can see that I have vacuum even if I'm at 100 or 130km/h, so there are a lot of gases that move the turbo which should pump a lot of air.

If there is vacuum in the intake, that means that this air can't enter enough due to the TB position, because if I accelerate the intake pressure increase immediately at the same engine speed.
Where does the air from the turbo go if it can't pass the TB ?

[NAJ]

When the piston is at the top of the exhaust stroke there is nothing left in the cylinder.
As the piston starts down on the intake stroke both valves are closed but there is no air in the cylinder(vacuum).
Pressure in the Intake Manifold is either Atmospheric or Above Atmospheric(Boost)
When the intake valve opens the air in the manifold rushes in to fill the void.
This happens over and over with each cylinder, piston coming down with both valves closed so there is always vacuum in the cylinder.
Pressure increases from boost take place in the Intake Manifold which is where you read vacuum/boost.
If there were no vacuum in the cylinder air would never enter the cylinder/engine.

[Dr. Johny Dodge]

a lsd is a limited slip differential
most cars are built with what is called an open diff - this is the classis one wheel spin or burn out diff as all power goes to one wheel

a posi trac type diff has clutches in it to cause power to go to both wheels

now a lsd is like an open diff until one wheel starts to spin then it transfers power to the other wheel with the idea that that wheel has traction

driveing in the snow would show the differences in these diff's

open diff spins one wheel helplessly when stuck

posi trac will cause the back end (rear wheel drive) to fish tail in the snow

an lsd might help you get un stuck as the other wheel has a chance to drive the car when one is slipping - but can also cause the rear end to fish tail as power shifts from one wheel to the other

K , when doing a valve job , they cut different angles on the valves and seats
- old school way is with 3 diff angles
this causes a pinch point where the valve and seat meat as the valve is closed - that makes a seal that won't leak cylinder pressure

a 5 angle job creates a different profile to the shape of the valve seat that helps improve airflow past the edge of the seat - however , not all shops are set up to be able to cut the 5 angles so if a shop says they can't do it , it dosen't mean it can't be done - they just don't have the equipment

diagrams would help but I don't have any handy - you could probably google then

[nvysion]

Thanks both for your help

[Dr. Johny Dodge]

shot peened rods - this refers to blasting the rods with small steel shot (balls)

kind of like blasting somthing with sand

but hitting the steel connecting rods with steel shot is a little like hammering on them - this makes the metal denser and (hopefully) stronger

beehive springs - are a coil spring that changes diameter as you move along the length of the spring
the coils will be a smaller diameter at one end that at the other end

[nvysion]

Thanks John,
Hope that will help other members too

[NAJ]

Here is an article I just found online explaining engine principal and theroy of operation.
I looked thru this article and it is very good.
Maybe this will help you understand Manifold Vacuum/Pressure and Cylinder Vacuum/Pressure

http://webtools.delmarlearning.com/s...882625_Ch2.pdf

[nvysion]

Thanks NAJ,
that seems well written, I will read it.

What are the beehive spring's benefits vs stock ones ?

[NAJ]

Quote:

Originally Posted by nvysion Thanks NAJ, that seems well written, I will read it. What are the beehive spring's benefits vs stock ones ?

You want to ask The Pope about that but my guess would be they are tighter than stock and prevent valve float at high rpm.

Valve float is when the valve does not completely close before the next valve opens.
This happens at high rpm. the beehive springs more than likely slam the valve shut when the cam lobe is no longer pushing on the rocker(follower)

[nvysion]

Thanks