What makes boost #'s differant?

[98GREENGLOW]

Ive been reading up alot on boost lately and one thing puzzles me. Why is it that boost or psi will be dfferent from system to system. Example 6 psi on our car will get you an extra 75 Hp at the crank. 7 psi on a Humvee will give them an extra 180 hp at the crank. What gives? Even if its on the same vehicle. Example.. Batman's math showed that he was getting about 13 hp per 1 psi of boost( I think it was 13) so is it safe to assume that my powerdyne is also getting 13 hp at the crank per every 1 pound of boost? Or those it very from system to system even if it's applied to the same car. Anyone know how it works. When I do the math of 6 psi of boost times 13 hp at the crank I get 78 extra crank hp. Assuming that you lose 18 of that through the drivetrain you should have 60 rwhp going to the rear wheels. If you dynoed 160 stock then you should dyno 220 with the powerdyne assuming the numbers work the same. Please explain to me why it would or would not be the same. Ie been pondering this every since I read about that Humvee and a turboed 350Z that puts crank hp from 276 to 350 with just 5.6 pounds of boost.

[Jack]

I am not a volumetric expert, but think of it this way...the engine sizes are different. If a certain volume of air is pushed through a 4" pipe at 6lbs of boost, how much more boost will be required to get the same volume of air from a 2" pipe? It will take more boost, obviously to equalk the same volume of air. On a smaller engine you need more boost to equal the HP gains of a larger engine.

I hope I got that right, if not I am sure there will be 500 posts correcting it. [img]graemlins/rofl.gif[/img]

[speedy-v6-camaro]

A lot depends on if there is an intercooler present. I have seen a honda 1.4L drag engine with twin turbos and intercoolers make over 1000 hp (my bad). Intercoolers make it so you can get the best timing possible and produce quite a bit of hp.

[ July 15, 2003: Message edited by: speedy-v6-camaro ]</p>

[Darknight]

[img]graemlins/bs.gif[/img] So the boost was higher than the combustion pressure? [img]graemlins/rofl.gif[/img] I don't think so. 1,000lbs of air pressure alone, without combustion, is enough to make a very, very powerful engine, with max torque available from idle. Most engines developed specifically for high pressure air alone don't get up to 1,000 psi.

Maybe you meant 1,000hp?

That said, some engines are better designed to utilize the airflow than others. Given equal setups between two sizes of engine, the larger will have the larger absolute gain. If 10# of boost on a 3.8 makes the engine gain 40%, and also 40% on a 5.7, the 40% of the 5.7 will be larger. Assuming the 3.8 made 200hp, it will now make 280hp. If the 300hp 5.7 gains 40%, that comes to 420hp.

So then, also, some engines of the same size can better utilize the boost than others. If engine A has 80% volumetric efficiency under non-boost conditions, and engine B has 70%, engine A has a clear advantage. It will be able to make the same power with less boost, or more power with the same boost, assuming its fuel system is up to the challenge. Without belaboring the point, there you have it.

DK

[ July 15, 2003: Message edited by: Darknight ]</p>

[Arctc Wolf]

horsepower per psi boost depends on the efficiency of the compressor, any intercooling, engine efficiency, and parasitic losses.

least efficient compressors are roots type, then lysholm, then centrifugal sc's and turbo's. more efficient means thhey can create more boost w/o heating up the air as much. same psi and less heat means more power and possibly the potential of mroe boost being run.

intercooling reduces the psi of the air since it is cooled and becomes denser, as well as hits air restrictions inside the intercooler. some intercoolers allow for a more straight through design, but don't cool the air as much, others have a more restricted design, and cool off the air more.

each engine is different. 2 valve pushrod motors tend to be least efficient of all, then sohc 4 valve motors, then dohc 4 valve motors, then dohc 5 valve motors, and then all those new technologies such as Vtec, VVTi-L, VANOS, ect. camshaft profile, head design, and combustion chamber design all play roles in how efficient as engine is as well. This is why the 350Z w/ it's dohc 24 valve motor can make another 70-80 hp with just 5-6 psi., and u can make 50-60 rwhp with your 5-6 psi.

parasitic losses must aslo be taken into account. A SC draws off crank power while a turbo runs off the exhaust. also, if the turbo is too small for the engine, and produces too much backpressure, parasitic loss can occur.

[mattsv6]

it also has too do with the pound per hour airflow capabilities at a set pressure ratio. if you run a compressor out of its efficiency range, it wont prove all of its airflow due too it spinning faster then designed. for example:

single t3 on a 4cyl @ 15 psi will be fine because it will be in its efficiency range

same t3 and 15psi on a big block with alot more cubes will jsut spin it past it efficiency range and you will barely have any gain.

hope this helps

[Mighty Thor]

It's all about "air flow"

It doesn't matter if its from a SC or Turbo (Parasitic lost ofcourse from SC and probably Turbo from backpressure). The amount of HP depends on displacement and other factors. If you have mods in your car, it really makes it even harder to determine just how much you have gained. Because a blower will pretty much act synergistically with the mods.

When Vector Perf. was around, James Dynoed the Camaro bone stock and it was 156 rwhp. When he installed the blower he dynoed it again and it came out to 262 rwhp at 9.3lbs of boost (I think he could have gotten better results if he wasn't hitting the limiters). This is right before he shipped that car to Florida. He's not very big on mods. I suggested that he would have gotten better results if he had full exhaust set-up.

I was impress with that number on a bone stock Camaro. There is an article on this on our messageboard. I also have the second article from GM highperf. where he put blowers on both V6 and V8.

[98GREENGLOW]

You guys have been very helpful and I now feel that I have a somewhat understanding of it. Might Thor, do you also notice a significant powerloss during day driving with the powedyne? Here in Hawaii I sometimes feel like Ive loss 2 pounds of boost during the day. When youve only got 6-7 pounds of boost thats alot! Then when I drive at night it feels good again. Those the heat really do that much to us? Those an intercooler eliminate that problem?

[nocutt]

<blockquote>quote:</font><hr>Originally posted by 98GREENGLOW:
You guys have been very helpful and I now feel that I have a somewhat understanding of it. Might Thor, do you also notice a significant powerloss during day driving with the powedyne? Here in Hawaii I sometimes feel like Ive loss 2 pounds of boost during the day. When youve only got 6-7 pounds of boost thats alot! Then when I drive at night it feels good again. Those the heat really do that much to us? Those an intercooler eliminate that problem?<hr></blockquote>

Depends...sometimes the restriction or design might even make an

[Mighty Thor]

<blockquote>quote:</font><hr>Originally posted by 98GREENGLOW:
You guys have been very helpful and I now feel that I have a somewhat understanding of it. Might Thor, do you also notice a significant powerloss during day driving with the powedyne? Here in Hawaii I sometimes feel like Ive loss 2 pounds of boost during the day. When youve only got 6-7 pounds of boost thats alot! Then when I drive at night it feels good again. Those the heat really do that much to us? Those an intercooler eliminate that problem?<hr></blockquote>

Yes, I do. It's been 105 deg. this week and the car feels sluggish. At night is about 86-92 and it improves, not much though. When i pop the hood the blower does feel very hot to the touch.

Definately winter is best.