I had posted I would continue the argument by email because work has been hectic this week and when posting on the BBS I don't have enough time to formulate my thoughts very well. I end up just streaming words from my mind and hitting save.

I have access to a cycle simulation program with 100's of inputs and a model of the Lightning engine. It was for a medium-duty gasoline study (as a diesel replacement). When I get some free time I want to change the model by changing exhaust properties (and other things) and then I'll get a better understanding of exactly what is going on in-cylinder.

As for mods, there's plenty of other people with dyno experience that can tell you what mods are the best. The obvious chip, pulley, filter, and MAF (for 99-00) are the first to come to mind. The mods for the cobra are probably going to be the same. Mosty likely anything beyond that the $$$/hp goes way up.

Interestingly, I spoke with an emp. of Eaton yesterday you said blowers are only going smaller. They are coming out with an M30 for Brazil. He also mention the tip seals on the rotors (very important for blowers) are designed to wear. After 50K miles like I have, the seals are most likely gone, and a rebuild would net some power. He also said there is a factory fill on the blower gearbox that needs to be replentished at around the mark as well. It is "designed" to slowly leak away. And interestingly, he said several of the blowers have been spun to 20K rpm in house, obviously to the detriment of efficiency.

 

You just did. Who's the bonehead?

 

Thanks, but don't count me in. I'm real familiar with the SVO kit.

What you didn't/don't realize is that the combustion chambers are different between SVO and 96-98 heads. That's why the SVO-kitted Mustangs suffered, not the other reasons you misattribute.

You say you've worked on some SVO kitted Mustang so you should recall that the kit came with its own processor. Vortech kits don't. The SVO processor's spark curve was tailored for 96-98 heads, and the Vortech kit used stock timing. With the SVO processor's spark curve and SVO heads, they ran like crap. With a stock processor and a good chip, the SVO-kitted cars also picked up a lot more than 15 rwhp.

It has nothing to do with the "huge fundamental difference between a roots-style compressor (by nature a constant volume device) and a centrifugal supercharger"

And by the way, a centrifugal supercharger does NOT have
a volumetric flow closely related to the pressure differential across the blower," unless by "somewhat" you mean "sortakinda". Pressure tends to go up exponentially with a centrifugal supercharger's output, but not flow.

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Actually, he's correct. You just misunderstood what vehicle he was talking about.

No, we were talking about the Cobra compared to the Lightning. No hard feelings; he even says he just lets the words stream out of his head and hits Send.

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I don't think anecdotal reasoning involving a 380 hp Briggs and Stratton is going to prove your point.

It just did.

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What I believe Mr. White Lite was suggesting is that assuming the head design and port size is reasonable for your volumetric flow

You and I are on the same page. White Lite isn't. He has never once said that "assuming the head design and port size is reasonable for your volumetric flow", in fact, he said the opposite - that 380 hp out of a Briggs & Stratton is POSSIBLE with an M112!

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(ie, you're not needlessly backpressuring the blower and getting some outrageous discharge temperatures/hp consumption) then further bottleneck reductions at the head via larger ports or other head modifications is likely a waste of your time.

We also agree here. But White Lite doesn't. Read his posts! He even says, regarding the 1/4" hole inlet gasket restrictor,

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The mass of air through the constant volume device is a function of swept volume, inlet density, and rotational speed. If you force it through the smaller hole, or more restrictive engine, the outlet pressure (boost) will go up, raising the power consumed and heat generated by the blower. Will your measured HP be less? Sure. Will it be significant (if this is the same engine we are talking about)? No. Not on an egnine with a 380 HP rating.

Right there, restricting the engine's ports won't make a significant power difference.

Here it is again:

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Will 1/4" intake gaskets hurt power? Yes. Why? Bacuase the power consumed by the blower will go up. Will airflow go down? No.

Sorry, Charlie. You can only flow so much air through a 1/4" hole. You can believe what you want, though.

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The Eaton simply will not take advantage of the reduced downstream pressure in the same way a centrifugal supercharger will.

Wrong. But the Lightning community hasn't seen matched/"package deal" downstream mods yet. Once better and better headers and cat-backs come out, the gains will be there. There are already lots of modified Mustangs with Eaton blowers from Saleen, Roush, and Allen Engine, making huge gains from downstream mods.

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I'm not going to comment on the exhaust aspect of things since I don't have nearly the volume of experience relating to how exhaust mods correlate with the type of forced induction. To me, it seems less relevant since it is effectively isolated, internal EGR aside, from the compression source itself.

I do have the benefit of the experience with downstream mods, so even though you admit you don't, why are you and White Lite sticking to your guns instead of learning from somebody who's been there and done that? You're more concerned about trying to defend your point of view.

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Again, I think the extreme reasoning regarding B&S motors and completely plugged up exhausts is not likely to prove anything regarding how small changes will affect overall power output.

We agree here, but this line of thinking is not at all what White Lite has ever said. He's said the opposite. If he MEANS otherwise, that's fine, but I'm not a mindreader.

You guys are getting all bent out of shape. White Lite, you say you won't let your panties ride up, but yet you call this an "argument" and are being defensive. This isn't an argument, just a discussion. If you want to learn something, open your mind. If you want to be right, close it, and convince yourself you're right even when you're not. I said from day 1 that this wasn't an attack or a flame. You tried to talk about stuff you knew about, and I put in my .02 on what I know about. That's what it takes to get the big picture, exchange of information.

Like I said, people get all bent out of shape on here, so I went out of my way to state that I wasn't flaming White Lite. Both you guys seem pretty cool so I hope everyone can calm down a bit.

 

I'm the last guy to ever get offended or worked up over an internet discussion- I actually enjoy this kind of thing when I get some free time.

You are correct, and I do know that. Even on normally aspirated applications the SVO heads required significant spark advance over the factory heads precisely because of this combustion chamber difference. The SVO blower application was no exception.

I should have mentioned this, but my base assumption was that most people reading this forum wouldn't be very familiar with the workings of this particular kit- as soon as we made the swap to an aftermarket MAF on these cars (well before any head swaps) we went back to a modified factory ECU. In fact, there were better gains to be had from this change (and more risk as well) than we saw with the head swap, even after retuning. The reasons for this are the ones I explained in my first post.

I'd also like to clarify something here

When I say that, I'm referring to changes made downstream of the blower, but upstream of actual combustion. Specifically, heads and cams. You simply don't gain the additional volumetric flow by reducing downstream backpressure (of the blower, not the engine) that you do with a Vortec or other centrifugal. My entire discussion revolves around that base, and does not relate at all to exhaust mods.

Just reiterating that I'm not discussing exhaust mods. The nature of the exhaust separation from the source of compression suggests that exhaust mod effectiveness would not be linked to what type of blower you're running. Many Mustang guys have achieved substantial stains on supercharged vehicles by running long tubes and good mufflers.

This is a key point, and really the crux of the discussion in my opinion. I'll show two compressor diagrams here- the first from and S-Trim (Vortech), the 2nd from an M112.



Notice for a constant RPM line, say 40k RPM's, how much the flow (in this diagram corrected mass flow) changes for a relatively small change in delta-P, here expressed as P2/P1. If I were to put a set of ported heads with large lift cams on my S-Trim supercharged vehicle and the corresponding boost went down from 12.5 psi (P2/P1 = 27.2/14.7 = 1.85) to 10 psi (24.7/14.7 = 1.7), I could expect an 30-50% increase in corrected mass flow into my engine. This is the nature of any centrifugal compressor, whether its an S-Trim on a vehicle or a industrial scale centrifugal feeding a Refinery Alkylation plant.



Here's a curve for the M112. We won't be able to use the same numbers because of differences in the charts, but they do provide us with flow number for both a 5 psi delta-P and a 10 psi delta-P. So if you were running 10 psi nominal boost on your vehicle, swapped on a set of ported heads and regrind cams, and managed to drop your boost to 5 psi (a large and somewhat unrealistic decrease), how much additional airflow can you expect as a result of this? A scant 3-6% throughout the middle range of the blower's operation.

This is the difference in nature between a centrifugal and a positive displacement compressor, and is primarily the theme I was hoping to get across. It is important to understand how different types of compressors are going to react to changes both upstream and downstream (but still before the engine) of the unit itself.

 

I've never once got out of shape. And the definition of arugument doesn't imply beating each other up and screaming, yelling, and cussing. An arugument is each person stating his or her point of view, which is what I have done.

My resonses may have been hurriend and not well thought out (which doesn't imply my opinions are wrong, just that I didn't have time to sit down and take my time to state them in a manner that sounds professional).

My views as originally stated were for modifications to the lightning engine. I offered up the cobra engine and mustang engines as comparisons. You [truckn] were the only one to go to the extremes of such ludicrous ideas as an M112 on a B&S 5 horse or putting intrake gaskets with 1/4" openings. The basis of my arguments revolved around modifcations of a like engine.

Once, again, I challenge you to find blower curves that show large airflow changes with increased downstream pressures. If you look at the Eaton specs for this very supercharger, you can see that it has very little effect. Now you have shown the inclination to take that and extrapolate to any other recipricating engine reguardless of size or configuration, so I must be very careful is me response. (Luckily my work is over and I have some time!!!! Except when it comes to proof reading. That takes too much time!!!)

The airflow does in fact change with delta pressure. If you magnify the plot the size of a wall, you might even conclude that there is a 3% difference in airflow between the 5 psi DP and 10 psi DP lines. So IF you had a super duper head, exhaust, cam, port, muffler arrangement that increased airflow so much through the engine, that at the same exact engine speed and inlet density, the boost somehow went down by 5 psi, then you would pick up 3% in airflow. Would you see a power increase? Yes you would. You would get back 20 hp from the blower, and maybe 12 hp (3% X 400 hp) from increased airflow for a grand total of 32 hp. Now we all know that there is probably no way that you could even lower the boost by 1 psi, so maybe you will see 1/5th of that, or 6 hp.

For clarification, my argument, based solely on physics and published compressor data, shows that I can calculate airflow through the compressor. The published data says nothing of downstream components because it doesn't need too, they are NOT relavant to airflow. If you can look at the published data and agree with that, then the rest of my argument makes sense. If airflow is the same, but it is easier for the air to move from the blower to the cylinder, then there will be a decrease in the pressure drop between the manifold and cylinder, therfore a decrease in boost. For others that may not understand, a decrease in boost at the same airflow is not bad, it is good. Airflow is what you are after, the higher the boost has to be to get that airflow, the more losses you are going to suffer.

I will completely agree that downstream sources may net a SMALL difference it power. I have said plenty of times that I agree with this. I have also said that the magnitude of these changes are very insignificant compared to the large changes that are measured with upstream modifications. The are even less significant when you calculate $$$/hp.

If [truckn] would like to offer up a physics and combustion based argument for why the airflow goes up with downstream modifications (no equations necessary, just verbage for now), then my opinion can change.

To discuss the mustang GT blowers completely, I would have to be much more familiar than I am with that application. The part that I do know, however, was that the SVO supplied computer has very conservative calibrations for use on a car with a higher than ideal compression ratio, and no intercooler for a very inefficient compressor. While the eaton may be the most efficient of the roots style compressors, it is not very efficient compared to the Vortech, Paxston, etc. It is no wonder that . With a stock processor and a good chip, the stock headed cars also managed to pick up power. Do you think it had anything to do with the fact that the SVO computer had very little timing advance to try and eliminate the onset of knock???!!!!

I'm sure that there is emperical data out there to support just about any claim. Especially if you are one of the one's (and by YOU, I mean Tuners) that have something to gain by selling this equipment. It is hard to argue with physics though, and bold claims of experience and emperical data can only go so far. After all it has been proven on TV that motor up can make you car go forever and all you have to do is add one little bottle per 3000 miles!!!!

All in good fun and the search for good information...

 

I think this the best thread (discussion) ever on this site. Thanks to all who've participated! If you think you have more to add, please don't hesitate.

This is the kind of civil bench racing discussions that generate thought and understanding. Good thing we're not all sitting in a bar having this discussion - because its places like those, mixed with the knowledge of these fine people, where perpetual motion machines are believed to work.

THANK YOU!

 

alrighty, first post ever...here goes:

i'm 18, just graduted, and have taken the one available physics course at my high school thus my knowledge of the subject is somewhat limited. however, my interest and enthusiasm isnt. this is most likely, as stated, the best post i've ever been privaleged to read, yet a lil over my head at times. for my clarification white lite, is this what youre trying to say (in plain english): the power output of the engine is restricted by the blower (since the stock exhaust is adequate) and the efficiency of the stock blower is determined by the flow of the "upstream" MAF/tb/filter, etc...correct???

 

Thanks guys - I didn't know my contribution to this thread was appreciated this much! I'll try and keep the brain juices flowing...

Here's another phenomenon I have observed in my Lightning: when I go uphill, it seems like the truck doesn't want to go as fast as when it's on flat ground - so it must be making less horsepower. And when it's going downhill, it seems to want to run away and go even faster all by itself - thus more horsepower! I think it has something to do with the angle of the air flowing by the side-exit exhaust pipes, decreasing back pressure and cooling the blinker fluid reservoir.

 

I am no engineer and by no means an expert in thermodynamics, but I see something that needs to be address with your post.

From the above excerpt, you mentioned that exhaust temperature would decrease as downstream mods are employed. Wouldn't this be a benefit? This would indicate several issues that may be of value to having a full exhaust mod done.

1. With less temperature and boost, the overall long term health of the engine should increase.

2. Headers with a larger pulley may maintain the exhaust temperature, increase boost to prior levels and increase overall horsepower.

3. With less exhaust temperature the timing could be increased, less potential for detonation, thus, more power.

From what I have read on the forum, an exhaust mod by itself is of little power benefit; you must make adjustments to get more power.

What do you think?

 

Generally, yes, this would be the case. Is it enough to matter? Who knows? I doubt it, but there's always that potential. Its definately going the right way.

The pulley is going to increase boost way faster that any downstream mod can bring it back down. Until I run the cycle simulation, I don't even really know how exhaust temperature scales. I need to see if it is even significant.

There is definately an advantage to running with less boost and temperature at the inlet to the intake port. It will make the pressure and temperature just before ignition (and after) lower and cooler, and delay the onset of knock. Again, the cycle simulation should give me an idea how these things scale. It predicts knock, but the model is built from emperical data from a bunch of different engines who all behave a little differently. If it was me, I would be hesitant to be right on the edge of knock. I enjoy driving my vehicle a lot more than working on it. Knocking on forced induction applications is a recipe for disaster.

And this is for truckn:

The M166 blower I mentioned was stated purely in jest after all of the bickering that was going on on the board about the subject. Since I know someone at Eaton (a former emloyee from where I work), I knew there was no such product. Instead they are focusing on foreign markets who are taxed by displacement and are making supercharges for ~1.0 liter engines.

 

I'll tell you what, all this bench racing theory only goes so far. Take your Lightning truck to the track, then make mods, and take it to the track again. Then tell all of us in the Lightning community of your results, good or bad.

Now get out there and race!

 

I made my post because I was told that without a computer program to take advantage of headers you really don't see a power increase for reasons I stated above. With the computer programmed for it 35rwhp(I believe) could be seen. Now that's not to shabby.

 

I am proud to have you as a fellow 99 owner. Have you ever noticed how we seem to be a more well-rounded and logical thinking group?

 

Thanks for clarifying that. However, you're still wrong. But that's ok, we'll just line 'em up someday when I've got my "useless downstream mods"

right. but White Lite has posted that he disagrees, is all I'm saying.



Hate to sound like I'm tryin to rain on anyone's parade but I defy you to show me a 50% gain in mass flow from intake porting, intake valves, and cams. Or are you talking about something ludicrous like completely unstreetable cams? I'm saying intake valves and ports, and not full ported heads, because you did say "downstream mods upstream of combustion." This excludes the chambers, exhaust ports, and exhaust valves.

 

That statement means nothing. What pulley vs. what downstream mod? A 1mm larger lower pulley will make a lot less effect on boost than going to a mondo exhaust system.

That's my point - you don't know. Not only do you not know, you are relying on a simulation to tell you, a sim that you admit "predicts knock, but the model is built from emperical data from a bunch of different engines who all behave a little differently." Gee, sounds realistic to me!

You go on to state:
If I can ignore my experience and look only at the published data, then your argument makes sense. Just like a Motor-Up advertisement makes sense when you have no real world experience.

If/when you get the chance to get some hands-on experience rather than going only off physics and someone else's numbers, you'll agree with me.

This is the most cowardly method of challenging someone. You want me to start spewing technobabble or else I have no credibility? I could correct you up and down the boards here with polysyllabic mumbo jumbo, but I'm not here to tear you down, hurt feelings, prove myself, or dazzle baffle and confound those without a formal education. Why should I get in the mud with you?

From your perspective we should just whip out our johnsons and compare length while we're at it. Over time I've found that lots of people (especially with degrees) need to demonstrate their knowledge - mostly to themselves, because they have little to no real world experience, no harm in that, we all started somewhere - so they use big words and terminology. It takes a bigger man to be secure enough to translate into layman's terms so he can carry on a normal conversation.

Speaking of unethical methods of debate, you've gone back and changed the wording in your posts to defend yourself. How low is that?!

Amazingly you also have switched sides several times to defend your point rather than just saying "Good point, I agree." Oh that's right, you want evidence rather than "bold claims". Here ya go:

first side: re: 1/4" intake ports: Will your measured HP be less? Sure. Will it be significant? No.

flip flop side: You [truckn] were the only one to go to the extremes of such ludicrous ideas as an M112 on a B&S 5 horse or putting intrake gaskets with 1/4" openings. The basis of my arguments revolved around modifcations of a like engine.

First 1/4" intake openings won't decrease airflow. "Will airflow go down? No."
But now you say 1/4" intake openings are ludicrous.

First a Briggs&Stratton could "theroetically (a lot of assumptions here) make the same power", based on your physics calculations and your lack of experience.
But now you say it's a ludicrous idea.

First you were comparing 5.4 to 4.6, SOHC to DOHC, and 5,200 to 7,000 rpm. But now you're comparing "like" engines.

Ooooooook. So now that you've changed sides, I guess you agree with me! Does that mean we're friends again and I can buy you a round yet or are your panties in a bunch?

We can all resume watching out normal programming now on other theads.