Bone's Engine Pull - Part Deux

[blackviper]

By the way, the last 4 numbers of the metric part number is the length of the belt in millimeters.

 

[WOT]

A couple of points to ponder:

It is my experience that if you bend a rod on a nitrous hit it is due to too much timing. Nitrous speeds up combustion so much that you have an extreme pressure rise while the piston is still traveling up on the compression stroke. It acts like hydro-locking the motor. You compensate for this by retarding the timing when the nitrous comes on. Are you guys doing anthing to retard the timing when the nitrous hits?

The vacuum behind the TB is the normal result of starting to approach the flow limits of the TB. An easy answer is to get a larger TB. The other answer is to spin the SC faster to make up for loss of airflow. You won't run into the airflow limit 'wall' until you hit choke flow (sonic airspeed) in the TB.

If you are seeing 2" of vacuum (2" of Mercury (Hg)), then you are seeing about 1 psi of pressure drop on the intake side to the SC. You can always spin the SC faster to get that 1 psi back.

On the upside, that 1 psi pressure drop actually cools the air somewhat going to the SC, but I haven't calcualted how much....

By having some vacuum between the TB and SC rotors, you are leaving some HP on the table, but I'm not sure if it is really significant. Plus, larger TB's are harder to calibrate with the TPS and can create some driveability issues.

For example, when suddenly opening the TB to say 20% throttle from sitting at idle, the computer commands the injector cycle to compensate for the sudden rush of air inflow with an 'accelerator pump' injector cycle (basically, it adds additional fuel to eliminate an off-idle stumble just like the squirters did in a carbuerator). Once the airflow stablilzes, the computer commands the correct amount of fuel for that airflow, but it will be less than the initial shot that it does to prevent the stumble. If that 20% throttle opening happens to flow a bunch more air because the the TB is bigger, then that inital 'accclerator pump' injector cycle will be wrong and the engine could stumble or do a lean backfire (especially when cold outside). You would need to remap the computer to compensate for the increased flow at a given TPS reading.

This remapping is not in the full throttle portion of the tune and is not in the part throttle feedback loop portion either. It is in the TPS to airflow estimation portion and is typically not easily adjusted. It can be done, but it's just a bunch more work.

Anyway, that's just my thoughts for the moment.....

 

[Prof]

Interesting input WOT...Welcome...

As temps rise the pcm automatically starts to pull timing to avoid detonation...but I have no idea if/that it occurs as NOS hits...

Anyone else?

 

[Bone]

By the way, the last 4 numbers of the metric part number is the length of the belt in millimeters.

Last I was using a belt around 93.5 inches. So I am the middle of several sizes. I searched with David Weaver for months. Option was to take an 8-rib and cut a rib off.

 

[Bone]

A couple of points to ponder:

It is my experience that if you bend a rod on a nitrous hit it is due to too much timing. Nitrous speeds up combustion so much that you have an extreme pressure rise while the piston is still traveling up on the compression stroke. It acts like hydro-locking the motor. You compensate for this by retarding the timing when the nitrous comes on. Are you guys doing anthing to retard the timing when the nitrous hits?

My timing was very conservative.
I have a SC flash with a VEC 3 on top of it for timing control.
2 stages colder iridium plugs.
3 knock sensors (2 stock and 1 MSD).
Higher octane fuel and toluene mix was used.
Lower compression Diamond pistons were used.

I had stock rods using a SC and NOS. Way too much HP for stock rods.

 

[1sicponi]

Bone, I have been pulling engines apart since I was 14. First was a Briggs and straton for a go cart. Shaved the heads with a file to get more compression. What I saw in those picks scared the shit out of me. The plug wires go under the intake? I'd rather try and hide shit like Orange county ny choppers do. Thanks for the picks. Great sight.

Think I'll just look at how pretty and clean it looks under the hood. And to think I almost bought a ROE S/C and was going to install it myself. bobbymac

 

[belgiumbarry]

Bone, I have been pulling engines apart since I was 14. First was a Briggs and straton for a go cart. Shaved the heads with a file to get more compression. What I saw in those picks scared the shit out of me. The plug wires go under the intake? I'd rather try and hide shit like Orange county ny choppers do. Thanks for the picks. Great sight.

Think I'll just look at how pretty and clean it looks under the hood. And to think I almost bought a ROE S/C and was going to install it myself. bobbymac

now , what's wrong with that ? :dontknow: ..........

 

[blackviper]

Bone, if you're in between 2 sizes, try calling Napa Auto Parts. They have a larger idler pulley. I can get you the part number if you need it.

 

[WOT]

My timing was very conservative.
I have a SC flash with a VEC 3 on top of it for timing control.
2 stages colder iridium plugs.
3 knock sensors (2 stock and 1 MSD).
Higher octane fuel and toluene mix was used.
Lower compression Diamond pistons were used.

I had stock rods using a SC and NOS. Way too much HP for stock rods.

Sounds like you have your motor set up correctly, but you just need stronger parts!

Oh, and just to clarify, usually you retard the timing not only for detonation resistance, but to insure that peak cylinder pressure is actually occurring after top dead center. Since the nitrous speeds up the burn, you end up losing power with too much advance even though you might not have any detonation whatsoever. But the pressure spike can cause seriously ludicrous cylinder pressures and do things such as bend rods and blow out head gaskets, etc. Typically you would want to retard 1-1.5 degrees per 50 hp shot of nitrous. So, for a 250 shot you would want to retard up to 8 degrees more than you would for just the SC. So if you are retarding 5 degrees for the boost, then you retard another 8 degrees or so for the 250 shot of nitrous.

Either way, it sounds like stronger rods are in your future. Best of luck to you.

 

[Bone]

Bone, if you're in between 2 sizes, try calling Napa Auto Parts. They have a larger idler pulley. I can get you the part number if you need it.

Thanks. I haven't gotten that far yet. The larger crank pulley is being redone by David Weaver, offset is a little off-line. I already have fabricated another idle tensioner pulley (and bracket) from when I put the smaller SC pulley on, to keep a good grip, so my belt size is non-standard.

 

[Bone]

Sounds like you have your motor set up correctly, but you just need stronger parts!

Oh, and just to clarify, usually you retard the timing not only for detonation resistance, but to insure that peak cylinder pressure is actually occurring after top dead center. Since the nitrous speeds up the burn, you end up losing power with too much advance even though you might not have any detonation whatsoever. But the pressure spike can cause seriously ludicrous cylinder pressures and do things such as bend rods and blow out head gaskets, etc. Typically you would want to retard 1-1.5 degrees per 50 hp shot of nitrous. So, for a 250 shot you would want to retard up to 8 degrees more than you would for just the SC. So if you are retarding 5 degrees for the boost, then you retard another 8 degrees or so for the 250 shot of nitrous.

Either way, it sounds like stronger rods are in your future. Best of luck to you.

I used 2 degrees/50 shot and added 1 more for safety at the end. Already had a reduced SC timing from Sean.

 

[Bone]

Crower Billet Rods! Had to send them back for a modification to the floating wrist pin. Should be in the mail today back to me!
:rock:

Here is one next to a stocker.



Watch out Stinker, I am coming back! We are tied 1-1 at the Nats! :rock:

 

[Ram From Hell]

Thanks. I haven't gotten that far yet. The larger crank pulley is being redone by David Weaver, offset is a little off-line.

That's a slight understatement. They're off by a full rib-width.

 

[Bone]

Crower rods Round 2!
Had the pins (floating wrist pins) redone to fit our rods. Looks like Gen 2 rod wrist holes are a different length - 9.85 vs 9.45 approximately by my measurements.

Anyhow, here they are with Diamond Pistons.

 

[belgiumbarry]

you're serious about the rebuild he ? :dontknow:

 

[Bone]

you're serious about the rebuild he ? :dontknow:

LOL, I have no other choice! :nurse:

 

[belgiumbarry]

LOL, I have no other choice! :nurse:

haha ! :rock: good work... maybe i ever ask you to make me a copy ...

 

[Bone]

haha ! :rock: good work... maybe i ever ask you to make me a copy ...

Not a problem. Now shipping an engine would be interesting.

 

[Bone]

Crower Tag Specs

 

[belgiumbarry]

Not a problem. Now shipping an engine would be interesting.

don't they float :dontknow: :dontknow: :dontknow: