How would you describe engine bog?

[boostm3]

When you guys are writing about engine bog, how do you experience it? I mean, does the bog you experience feel like just a kind of mild flat spot when the spray intitially starts, or, does it really stumble and feel more like a misfire?

 

[salvageV6]

Really stumbles.

A good test is low rpm say 15mph and hit the test switch, car will bog and stumble when the alky. hits.

You don't want any of that feeling when it kicks in WOT.

 

[blackbuick87]

When you hit the gas a HUGE black cloud comes out the back and covers the whole road, and your buddy following you smells so much alcohol his eyes burn

 

[KWIKR 1]

I was at the track not to long ago and was getting a big miss and puffs of black smoke out the rear of the exhaust at mid track and off of the line . Could it of been from the alky ? It felt more of a ignition problem . It was a "dead miss" then a bog. If so is it from pump speed being up to high or the turn on point to low?

 

[DMan]

Hey Paul!

Good to see ya

Bogging that I've experienced is *real* bogging where the car bucks and spits when the alky turns on too soon or if I don't have enough airflow going. There have been a couple of times when I've gotten HUGE backfires out the exhaust, but it is rare.

Denis

 

[boostm3]

Hey Dennis....Oh man, Ive never experienced anything like that. What I feel is very subjective I think, ie, much subtler. I trigger at 4.5 psi. When I use my .7mm jet, at the point where it starts spraying, Im usually floored, and when it comes on, I feel no interruption in the increasing strong feel of the pull, as the centrifugal blower makes its way up to redline and max boost.

My .7mm jet delivers 275cc/min which I measured. My 1mm jet delivers 300cc/min which I also measured. When I was using it, I think I detected a momentary, and very slight flattening out of the power, which of course picked up again as the boost built. To accomplish that same smooth power delivery I do with the .7, I had to raise the trigger to 5.5 psi, which was higher than I wanted to go. See, with a 7mm redline, and with me hitting 5.5 psi over 5K rpms, that doesnt give me but about 1500 rpms in which to cool the intake tract. I prefer to start it lower. So my options were either to set up a 2 stage system, or to just live with a .7 or maybe .8mm jet. AS this delivers about 17% of my gasoline rate, I think its fine enough so I'll stay with it.

regards...

 

[blackbuick87]

Boostm3 @ what point do you start to experience knock? You want the turn on point to be about 2psi below that. I would think the same would apply to a supercharged application

 

[DMan]

Hey Paul,

If you're anywhere near Middlebury CT today, maybe we can hook up and talk it over. I'll be there from about noon to 2 pm. I'll have my GN with me.

A two stage system would be ideal, and its pretty easy to set up. I recently converted my single stage system to a two-stage, and performance and driveability is *MUCH* better. I can start injecting sooner with a lower flow, and as the boost gets high, I can supply the flow I need to control knock. Clearly the ultimate is to install Richard's MF2, but you will be surprised what a simple two stage can do.

I think I implemented the second stage for under a hundred bucks, and YES, we can make it look NICE ENOUGH for the BIMMER crowd!

Gimme a call.

Denis

 

[boostm3]

Boostm3 @ what point do you start to experience knock? You want the turn on point to be about 2psi below that. I would think the same would apply to a supercharged application

Bob, Im in a little different position than most of you guys. You can change your afr and your timing at will. But with an OBDII M3, the software that we get with the Dinan base supercharger kit is pretty much the software were stuck with. Its a minor miracle in its own right that this software is written so that it ran the car well when I was 8 psi out of the box, and now at 11 psi. In addition, there's a 5V HFM signal limit, beyond which it starts throwing lights and codes. I hit that at 6000 rpms. Redline is at 7000 rpms. Just shy of that 5v 'limit' Dinan has implemented an 'hfm clamp' which freezes the signal just shy of 5V. What this means is that while Im way rich at 10:1 at 5800 rpms, by the time I get to the 7K redline, Ive leaned out to 12.7:1, which is still ok, but I realize that anything which would add more airflow will cause be to be unacceptably lean. There are only a couple of tuners in the country that can tune this software, so Im going to take the fact that with a 10.5:1 static CR and no intercooler, being able to product 11 psi with no knock, and 350 rwhp as a blessing, and not push my luck.

In answer to your question, I dont hear any knock without the water injection. But I do see egts rise higher than Id want, and the intake air temp sensor as well, and I can feel the timing being pulled up high, but I cant tell whether thats in response to unheard knock, or to the high IAT values which will also cause timing retard in our cars. AS for turn on point, dont forget the shape of the curve delivered by a centrifugal blower, vs a roots style or a turbo. The latter two deliver a torque curve in the shape of a big hill right off the bat, and it declines the rest of the way. whereas on mine, it inclines to about 4K, and it stays at that level almost to redline. Its a very flat torque curve, but the biggest difference is the shape of the boost curve. Roots blowers and turbos make alot of boost way down low. But on a CF blower, we use roughly the forumla that as the rpms are doubled, the psi values are cubed. For instance, at half redline, 3500 rpms, I could be making just 2.25 lbs of boost. But at 7000 rpms, Im making 2.5 x 2.5 x 2.5 or 11 psi! So, its steadily increasing but ramps up quickly near the end. This means that I have to trigger a little differently than you turbo guys because the volume and turbulence of the air isnt there until higher up. If I were turboed, Id probably trigger around 3.5 psi. But Im finding that 4.5 to 5 psi is just about perfect for the .7mm jet.

 

[boostm3]

Hey Dennis. Id really enjoy hooking up with you and talking about this. Ive got so many things to discuss. But Middlebury is about 1.5 hrs from me, and today just doesnt seem to work out. But we really should do it. Richard walked me through a 2 stage system using his parts. Basically, you just take the base 1S system, and to it add a solenoid valve controlled by a second hobb switch for the higher stage. Thats it! But he says the better way is to also add an accumulator and his Manifold 806-201 to shut the pump off when the accumulator is filled.

My problem is I just dont have a decent work facility, but I do think this would be the preferred way to go if I were after 'perfection'. Maybe someday.

Dennis what do you think of the shureflo pumps relative to the Aquamist pumps? Ive read the specs for the SMC kit alot of the buick guys are using, and it seems to have a function to control pump speed! Is this a characteristic of shureflo pumps or something else? Also, I dont understand the ratings of those pumps. For instance, on teh Aquamist pumps, they are rated at diffferent flow rates, depending on what nozzle is used. For instance, the .7mm jet flows about 265cc at 100 psi. And the 1mm jet flows about 335cc at about 54 psi. But the shureflow pumps are rated in terms of like 2 gallons per minute! This is so much more, like hundreds of times more flow than the aquamist pump delivers if you look at the flow rate with the different nozzle sizes, that they must be using 2 different rating systems or something. Can you explaing the huge discrepancy?

Regards..

 

[salvageV6]

I'm using a NOS Alky. solenoid about $115 from Jegs.

Second stage triggered electronically but a manual Hobbs switch will work fine.

Middlebury is a nice town.

Work in Cheshire myself.