is 21psi , 21psi ? blower vs turbo...
 

kinda got into a debate with my buddy last night . he wants me to put a big 88mm turbo (or something big like that) on my truck but i didnt see what the point was. i em very open minded about this so please dont think im bias im very open to make more power ! so debate went like this. im running 21 psi right now on my d1 . he thinks if i run 21 psi on a big turbo that i would see serious gains over the d1. so my question in theory IF IAT AND TORQUE/HP CURVE WAS IDENTICAL would the bigger turbo make more power over the d1? and im looking for good hard evidence why.

psi = pressure per square inch. a measurement of resistance. it's more of a relative term. cfm is the make or break point. i can run 30psi from a tvs 1320, or 30psi from a pt6262. pressure is the same, power difference is in favor of the turbo. the cfm difference is huge, hence the power differerence

Depends on where it is on the map. If that turbo isn't working as hard at 21psi, which it probably wouldn't be, then it will make more power. Also, its not good practice to judge turbos and blowers by CFM, since the pressure is not constant. Better to use lb/min or g/s :)

Why didn't the F1 go on your truck?

A turbo has close to 40psi of back pressure in the exhaust witch really holds power back vs a pro charger having big headers and open exhaust, but the procharger uses crank power to make power. Because of the back pressure of the turbo the pro charger makes more power on the same boost, but then you pull the power right back out of it having to turn the blower. I'm sure you know this but the difference will change according to boost level, what turbo, ect. At 21 psi I'm sure a turbo would make 1000hp on your engine

i understand that boost is just a measurement of restriction , but why would the turbo make more power if the turbo was pushing more air/cfm wouldn't that cause an increase in manifold pressure also? where does the power come from? i understand that boost is just manifold pressure so does the increase in hp come from more air flow through the valves when open but when closed the waste gate bleeds all the extra air after 21 psi?

cause i have my heart set on a vette , and tring to sell everything to get one lol :jest: plus i dont know if the f1r was going to be the right choice for my set up. that a big blower a requires allot of na power to get going.

I'm currently doing a write-up to explain just that... The short answer is the turbo requires less effort to make boost and flow air.

Well a na engine can make a lot of back pressure and still run fine, its just how an engine works. You could add more back pressure then boost pressure on a turbo when you turn it up and still gain power. Maybe someone will chime in that can explain it a little better.

i understand that a big 88mm turbo will flow more cfm , no doubt about that but im not buying the "less effort" thing not when big gains are involve like 150-200hp more.remember in post 1 we are assuming iat are the same . im talking peak power here too not hp curve or spooling off the line just peak power.

Its actually not an easy question...but since we are talking about prochargers and turbos, it simplifies it somewhat because the compressor sides are very very similar. Versus say a roots blower and a turbo which are worlds apart.

As Jake alluded to, its not really about pressure, but the mass of air you are moving. The more mass of oxygen in the cylinder the more mass of fuel you can put it and the more power you can make. Plain and simple. However, volumetric efficiency goes up with more boost. The engine becomes more efficient because the cylinders will be filled more readily with a higher pressure difference across the valve. So for max power you want max boost and max air mass..

That sounds great, but with a turbo the higher the boost pressure on the compressor side, the more pressure you have on the turbine side, which the engine produces on the exhaust stroke. This is why excessive backpressure costs a lot of power; you basically turned the exhaust side into a big air compressor for the turbo. However, high backpressure setups spool very well (think factory turbo cars), and the less backpressure the slower spool. To reduce backpressure you want a huge turbine on the turbo...most pure race setups have seemingly disproportionately large turbos. For instance, twin 80s on a 350ci engine. Great full race power, but forever lag, which is not of concern because this is a race-only setup. Obviously, most street vehicles compromise full race power for spool benefits. Also note that closer the boost to backpressure ratio is to 1:1 the more the engine behaves like a NA engine.

With a big procharger, you have a similar problem, the power needed to turn that big compressor comes directly from the crank. Instead of the engine powering the compressor through the exhaust stroke like a turbo, it powers it through the power stroke to do work on the procharger. You can see this graphically if you are familiar with engine cycle charts (otto cycle in this case), specifically the P-V diagram. With a turbo, the exhaust phases will be raised, and with a supercharger the power line will be lowered (keep in mind I mean from the ideal, with either it will be higher than the engine NA). The important thing is the difference between strokes. Basically, there is no free lunch to make extra power. The reason you get a boost is because the benefits outweigh the costs, ie, if a blower costs 100hp to turn and it nets you a 600hp increase, its a pretty good trade.

Then there is the subject of compressible fluids, which is why big compressors move a lot more mass of air for a given pressure. Lets assume the compressor isentropic efficencies are the same (say 70%) between two different size compressor. With the larger one, the output from that compressor is going to be the same temperature and pressure as the smaller one, however, the mass of air (and therefor oxygen) coming out of it is going to be greater than the smaller one. As you can imagine, the bigger compressor is going to require more power to turn, so the difference between out of boost and in boost will be quite dramatic with either super or turbo. Which is why big turbo cars, say a supra for instance, cant get traction until 4th gear at 120+ and are a dog out of boost.


As for your original question of would an 88mm turbo make more power than a D1, I would say almost certainly. An 88mm and an F1 would be fairly close I think.

It is absolutely because of less effort. Let me explain it this way. I'm sure you've heard the old saying, 1/3 of the fuel energy goes to turning the crankshaft, 1/3 goes out through the radiator, 1/3 out through the exhaust. Just some rough numbers. Turbos make use of the heat in the exhaust, which is wasted anyway... Superchargers draw off of the power on your crankshaft that you need. Where would you like to take the power hit? Pulling 10% off of the crank, or 10% out of the exhaust energy, only a fraction of which robs power via backpressure?

Are you calling "big gains" 150-200hp? If so, thats not big at all, for these engines anyway. In theory 15psi of boost will double NA power...turns out to be more like 70-80%, so if you engine makes 400rwhp NA it will make 720rwhp at 15psi.

i realize turbos are more efficient and draw less power then a supercharger but im not buying thats where and extra 200hp is coming from.maybe 50hp??

lol .no not just 150-200hp from a base but and additional 150-200 hp on top of what im making now. the debate was that by adding a 88mm turbo to my set up i would go from 700-750hp to 900+hp , and going from say 750hp to 900hp is a big gain.

Jarrett was showing 1100hp at the track with his 370 and PT88 on 20psi. That gain you spoke of is a big one...big not impossible in the least. Hell, foose04's latest track passes are showing at least 750hp, and that's a 4.8 on like 16psi...

Since procharger does not make or publish compressor maps, it will be impossible to bench race it, but I am pretty certain an 88 will make a lot more power than a D1.

There are so many variables you just can't put a number on it, just like a big wheel turbo makes less back pressure a huge head with 2in primary headers with open exhaust will do the same for a procharger setup, I don't dout you could make the same power with a f1, big heads/header, ect.. as a 88mm turbo with a nice ex wheel, but the average d1 stock head, average header setup won't compete with a 88.

To give you a little comparison to you truck, my truck is pretty much the same thing, xcab 4x4, a stock 10.25:1 comp short block (ly6 with GM flattops) with some hand ported 317 heads. Isky Triple 12 cam. I have my turbo kit with a billet 75/75mm BW turbo with race cover and meth injection with a M15 nozzle spraying 50/50 Meth and -20* WWF.

I ran it this weekend, on 14.5ish psi and 14.5* of timing with about 95oct fuel and made a half a dozen pass's at 11.03 to 11.3, 122-124mph. Pretty much the same HP showing as you only with about 5 or so less psi of boost. Yours needs to make 5lbs more psi of boost to make enough power to spin the blower and propel the truck at the same time.

that is a good comparison ,and so far this has been a good thread discussion .pm sent.

I really have nothing good to add here... but I find this stuff fascinating.:jest:

I wonder how these comparisons would look at lower boost levels where the supercharger is more efficient. At the same boost level with a good exhaust it seems that the blower actually pushes more air through the engine, its just the added drag on the belt is greater than the opportunity cost of moving less air through the engine with added back pressure from a turbo (and lets face it, the exhaust design itself looks like it wont flow well... stock manifold on the driver side and a log on the passenger?? My 1 7/8" ARH seem like they would outflow this by a ton).

At say 10 PSI where the average Joe tends to hang out, and where a blower can be much more efficient I wonder how that game changes. Take a 6.0 with ideal mods for both (cams spec'd correctly, best exhaust for both situations, free flowing intakes, and heads), which do you go with? For arguments sake lets set the ceiling at 10 PSI, then a simple increase in boost is out of the equation.

Blower pulls power from the crank regardless. If you want max power at 10psi.....still go turbo. The only thing a blower has to offer over a turbo is throttle response.....

you guys are missing the point here. the original question is will the turbo flow more air which equals more hp even thou its making the same boost, and pretty much from what ive been reading is it will.

I am going to try my best to make this make sense. Yes, a turbo will flow more air at any psi than a D1. Why? The reason is simple, the main advantage of a turbo is that the turbo's speed is independent of the engine's speed. This means your turbo can spool to your boost level and STAY there. A supercharger cant do that because the boost is a linear function of engine RPM, because the supercharger's speed is fixed to the crankshaft's. This means that at every RPM other than redline, the turbo'd motor has more boost than the supercharged engine. The turbo'd engine will be producing more torque and flowing MORE AIR from spool all the way to redline. At redline, both engines could theoretically be flowing the same but one rpm is very insignificant overall. Make sense?

Additionally, a larger turbo will flow more air than a smaller turbo at the same pressure level, because the exhaust housing on a larger turbo is less restrictive. On a turbocharged engine, lowering exhaust pressure has a similar effect to raising intake boost pressure.

but.... say we still run with the D1 for this example, what if you pulley down like crazy and run a wastegate to control boost? Then you can have your boost everywhere. or do the same with an F1. d1 @ 10 lbs=600hp ( hypothetical hp ) . Overdriven F1@ 10 lbs on wastegate makes over 600 hp?? yay or nay?

No. Your still making 10 psi. But with a overdriven f1 with a boost limiting valve at 10 psi will reach 10psi a lot sooner than a d1 without. So the result would be a big torque increase. But then the argument about overworking the supercharger and creating more heat.

This works vary well, if the sc is spinning full blast but makes 0psi it dont take much power at all to just spin it free, on a sc it only eats power from the crank according to the amount of boost it makes not how fast it spins.

at that point your just making more power to waste more power. Superchargers suck up a LOT of power to turn

But you still gaining a lot of power. And since your blessing off some of the boost there is less pressure against the turbine so it doesn't "use" as much power

Yes you are still using the power. Just because you vent it to atmosphere after you compress it doesn't make it free power. Just think about that. You are basically suggesting over driving supercharger and then wasting all of the work that it did bby bleeding off most of the boost. Do you not see what's wrong with this?

The fact remains that a supercharger will always be inferior do to the fact that it's speed is fixed to the cranks speed. The turbo will have a more consistent level of boost and will therefore flow more air through the rpm band.

Yes. But by overdriving it you will see max boost a lot sooner. Maybe even as low as 3k rpm depending on the setup

I did alot of research on this when I was thinking of going procharger, I know it seems like it would just be working against everything but it does work, most people see more peak power because it brings the power curve down a bit cause it makes more boost everywere below the peak rpm. Look into it works

East Coast Supercharging did this years ago on Vettes with their Novi 2000 kits. It worked. As I recall it boosted way better down low.

I think there are pluses and minuses to the blowoff with a Centri blower. I don't think anyone is trying to get TVS type low end by doing this. As 2plus2 said the blower is directly tied to the crank, and sometimes people with centri blowers see a spike in boost at redline... if you just bleed off a few pounds at or near redline its not going to be eating that much power and I would say it could work well.

I'd say we're a a little off topic here haha.

Also, if something like a TVS creates a certain amount of air with every revolution, I dont see how it matters that the turbo will be spinning faster... you will just bleed off all the 'extra boost' at the lower RPM's if the goal is to compare apples to apples, 21# to 21#.

I'd be curious to see how much more air a SC moves than the turbo due to the free flowing exhaust and difference in cam specs.