Guyz, I have been discussing this with my fellows, and everyone seems to have his own opinion on the matter, so I thought, why not ask for a professional reply on the matter.

In general, lower boost = safer engine, and vice versa. However, boost is not equal, running 6PSI of boost on a P1SC is not equivalent of running the same boost on an F1.

Take this for Comparison purposes only, numbers are not real.

P1sc 10PSI = 750 RWHP

F1 6.5PSI = 750 RWHP

Does this mean that running an F1 in this case is safer ( on the engine) than the P1SC because of lower boost? I mean at the end of the day, both are pushing the same amount of air at max revs.

I am asking this also because people always claim that because headers drop the boost by 1-1.5 PSI that its safer to bump the boost by using a smaller pulley. Well if "reading" lower boost is safer, why dont you throw a big *** head unit, which will give you same power if not MORE for less boost.

I am bad at explaining, however try to understand what I am saying. Is boost everything?

 

I understand what you are saying and was just going to ask this I hope you get a response. I am wondering because at altitude we generally get 1-3 PSI less off the same size pulley as someone at sea level. So I was wondering if running a smaller pully to up the boost is safe.

 

They are both moving the same amount of air, which is why they are making the same power - the P1 needs to spin faster to produce the volume of a slower moving F1. In the end, it is not the boost that damages the engine, typically it is a bad tune, bad gas (detonation) or a premature / worn part failure (over stressed).

 

Same thing here - you have thinner air, which is why you have less boost. The main area of concern is AFR, not boost. If you have a good tuner, you can turn the boost up and add fuel as long as you have a safe AFR.

 

All very good questions with several different answers. As far as the flow of the head units it goes back to the analogy of a straw and a garden hose, you can have the same amount of psi in both but the hose is going to flow more air even at the same psi.

"There are no free lunches" as one forum member put it to me in a similar thread, combustion is combustion and you are going to put a certain amount of stress on your engine at certain rpm and hp. However, a key component of understanding FI is knowing what Static compression ratio (SCR) is and how it effects a FI motor. The old saying with FI is that you have to go with a low compression motor if you want to make big hp... BS, the LS2 has not only proven that theory wrong but IMHO it has shown that high compression motors make great FI motors, they are the best of both worlds you keep your low end power when you are not boosting and have incredible power when you are. What SCR tells you is what the internal compression in the cylinder is when the piston is at TDC AND with the compressed air added to it. The formula is (psi / 14.7) +1) X Comp Ratio, what this means is a 9:1 motor at 16psi with make nearly the same SCR as a 11:1 motor at 10psi. So where is the difference... the 16psi motor is making more heat, 66 degrees more to be exact which is the main cause of detonation.

As you can see there are many answers to the question, as stated headers, cam, and air density can all play a factor too. For me the best and safest way to make power is the lowest boost possible to meet your goals with high compression, cam, headers, and don't forget the meth for added safety.

 

Hey John, what psi are you making with that F1 at 598rwhp? Did Jayson tune your car?

 

The straw / garden hose analogy works if you are blowing air into an open environment, but not if you are forcing the air into a positive displacement air pump like our V8s. Our engines can only pass a fixed amount of air per revolution, unless you pressurize the intake manifold. If you keep the charge air temp the same, it doesn't matter if your 6 psi comes from a 1200 cfm head unit or 3000 cfm head unit. It doesn't matter if you feed it air through a soda straw or a fire hose, provided both can maintain 6 psi over the whole range of engine rpm and load.

All centifugal compressors heat the air as they compress it. Less efficient compressors have a higher discharge temp than more efficient compressors. And the efficiency of any given compressor is not a constant across its map of pressure ratio versus flow rate. You want to pick a head unit that will operate efficiently given your planned boost and your engine's air flow capability.

 

I would argue that the LS2 platform CAN make good numbers with FI, but the compression ratio is less than ideal, especially with the octane quality of gas continuing to spiral downward. Even the LS9 utilizes a far lower compression ratio. If I were building a motor specifically for FI, I would want my compression ratio to be somewhere in the neighborhood of 9:1 or 10:1 max. Non-forged internals also contribute to a motor that is tempermental with FI, necessitating a solid tune. A batch of bad gas could be costly. Just my $0.02.

San

 

That could be measured by any data-log device, and is mainly effected by intercooling as well. However, by saying that its like you're saying brand X is 20 year old technology, and brand Y is the latest, thus can produce the same power as X with much less boost. Yet we are talking about two competitor products, and when I use the word competitor I mean, you have a hard time choosing between both, because none are the best, each has positives and negatives, if the PC had a significant advantage over the Vortech, you wont see Vortech in the market anymore.

A friend with a 10PSI P1 is doing 450 RWHP while the other with an F1 @ the same boost level is doing 700 RWHP (all else equal), if your theory holds true, then the F1 is generating MORE power than the P1 at the same boost level, because it has a cooler discharge air temp? Thats soo untrue btw.

 

There is no question that high octane is an important part, thats why I always recomend meth injection and or torco additive. But like I said about the 2 different motors SCR is still the same and you still have a great chance of detonation in the lower compression motor and high boost because you are making more heat. Every pound of boost equates to around 11 degrees. If you look at the new LS9 ZR1 motor they have forged dome piston that are at 9:1 CR and they are running 10.5 psi, (a lot for a root style blower) when in my opinion they should have run the motor at 10.5:1 CR and 7psi and made more down low power with less heat. That would keep your SCR around 15:1 (very safe).

 

Honestly I thought the same way too about the restriction of the valves and intake, but as stated earlier when you add headers the psi drops. The larger impeller blower that flows more CFM is going to feed more air to the motor. I admit it was hard for me to understand but I have seen many dynos that show there is a difference.

 

VertC6 thanks for the responses, but my head is really going to explode over this, whats your comment on my latest reply.

 

I hear ya, I have done years of research on FI and I still am learning of new techniques of engine building, cam designs and so on.

There are so many things that can influence this, such as the cam duration and lift. The higher and longer the valve stays open the more it will allow air to flow in, just like the added headers will allow gases to flow out easiler and droping the psi because there is less "left over air if you will" left in the combution chamber. There is know way to easily explain it, but just know that a bigger blower with less boost, more belt wrap because you are using a larger pulley which will eliminate belt slip, and high compression is the way to go IMHO. (Don't forget the meth)

 

I would agree that water/meth/whatever is cheap insurance and well worth the time and money.

San

 

There are many, many factors determining power of an FI motor besides boost. But if you pulled one head unit off of a particular engine that you just ran at 10 psi on the dyno, and replaced it with another, larger head unit pulleyed to give the same 10 psi, you'll get the same hp. Again, assuming the intake air temp is about the same. For a given engine, tune, and intake air temp, 10 psi is 10 psi.

Two similar size engines can have wildly different power outputs at the same 10 psi of boost. The low hp engine probably does not breathe very well, or maybe the cam was indexed wrong, and the high hp engine probably has the right cam, good flowing heads and optimized intake and exhaust systems.

Regarding technology, new versus 20 year old, the only thing that has changed is compressor efficiency. Increased efficiency means that the blower heats the air up less for the same boost level compared to an older, more inefficient blower.

You don't need to take this from me, check out any reputable book on forced induction. A classic, easy read that covers all the bases is "Maximum Boost" by Corky Bell, ISBN 0-8376-0160-6. I also have "Supercharged" by Corky Bell (ISBN 0-8376-0168-1) and "Turbochargers" by Hugh MacInnes, ISBN 0-89586-135-6. I'm honestly not trying to sound condescending or snotty or anything like that, but y'all need to read up on this stuff before posting what may be misleading info.

 

No I hear your saying but why then does a maggie at 8 psi perform different from a procharger at 8 psi, and a turbo performs even different from the 2 of those and yet they are all running at 8 psi? The torque is greater with the turbo and maggie, but the procharger has more hp than the maggie and less than the turbo.

It seems to me that there is more to it than just the boost pressure, if you look at a dyno graph of a D-1 procharger and then compare it to lets say an APS system at the same psi and same motor the torque is much higher with the turbo. Yet the turbo doesn't spool as quickly so you see the lag in the hp compared to the D1. I just think there is more to it than just psi when it comes to the way the air flows into the motor. I am definitely not an expert but I have seen so many dyno graphs over the years, specially between P1's and D1's and the D1's are always much higher even with the same boost levels. David at MTI said thats why they always recomend the D1. Anyways have a great Christmas.

 

Yes - Jayson did the tune. I am making 9-10psi.

 

I hope im not doing that, because my only purpose of this thread is to educate myself. Ok let me make myself even clearer, the two brands I am talking about are Vortech & Procharger, head to head comparison. Both are 2007 models, no 20 year old technology involved, yet the PC (according to PC's claim) makes ~584RWHP @ 4.5PSI, while the Vortech does ~575RWHP @6.5PSI (both on a Stock C6 Z06). As far as I know, BOTH were done on a similar model of dynamometer.

Even IFF the PC really did compress air and produced lower IAT, the difference could & should not be this huge, which is in simple terms running at 2PSI LESS and yet producing more.

Since the PC is a tuning kit, I am assuming that the car has a rather aggressive tune, while the Vortech had a mild tune, since it was offered as a "Kit" and those canned tunes are always EXTRA safe if you know what im saying.

 

No worries, my "read the books" comment applies to every one who posts here, including myself. As I mentioned, there is a huge number of variables affecting power output. One manufacturer might tune the AFR to (or a bit beyond!) the safe lean limit in order to generate maximum power for use in ads. Another manufacturer might keep the tune to an ultrasafe 11.5 AFR knowing that they are leaving maybe 50 hp on the table, but also knowing that their customers can hit that number with relative safety.

Then there is a large difference between chassis dynos. Dynojet models are widely believed to produce larger hp numbers than load dynos like the Mustang. A manufacturer wanting to publish attractive hp numbers would probably run their test car on a Dynojet, while another company might choose to test on a load dyno because they are believed to be more realistic.

It's nowhere near as simple as we all wish it was! Happy Holidays!!!

 

To simplify all of the above: A bigger head unit will push a larger volumn of air. Kinda like 500 cfpm @ 10 psi, or 1000 cfpm @ 10 psi. The larger volumn at the same pressure will make more horsepower. Of course, the tune, injector size, etc., must also consider the increase in volumn.