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Ddouglas: Good to hear from you.

Your information is somewhat outdated. It would have been 100% correct 20 years ago. At one time Roots blowers had adiabatic numbers down in the 40%-50% range. They are now a lot higher. You certainly don't need nitromethane, water/meth, and 7:1 compression to run 10psi with a modern Roots blower. On Magnason's site they have a Roots blown Chevy with 10.5:1 compression running 13psi on pump gas. That's really not unusual anymore.


Here is an excerpt from my book, it has current numbers:

Here is a list of various forced induction devices and their maximum adiabatic efficiency numbers.

Roots superchargers

1. Eaton 5th generation M45 67%
2. Eaton 5th generation M62 66%
3. Eaton 5th generation M90 62%
4. Eaton 5th generation M112 62%
5. Eaton TVS 900cc(55ci) 72%*
6. Eaton TVS 1900cc (116ci) 75%*
*At the time of this writing the Eaton TVS superchargers are so new I have never seen one.

Centrifugal superchargers

1. Vortech S-trim 72%
2. Vortech V-7 YS-trim 74%

Lysholm or “screw type” superchargers

1. Lysholm LYS 1200A (73ci) 64%
2. Lysholm LYS 1600 A (98ci) 66%

Turbochargers

1. Garret T3-60 74%
2. Garret T04E-46 76%
3. Garret T-61 76%

This list is far from complete, but it’s a good representation of what’s out there. A few things become immediately apparent. You may have noticed that numbers from a lot of the major supercharger manufacturers are missing. That’s because a lot of them are fairly secretive about their compressor maps. It’s somewhat ironic that the two companies that are the most vocal about how cool their compressor discharge temperatures are don’t post compressor maps on their web sites to back up their claims.
 

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To clear up just what those numbers mean, here is another section from my book. Please keep in mind, this section only deals with temperature, and does not take into account drive power requirements or other issues that are in another section of the book. I also left out the charts to keep the post smaller.


Lets talk a little more about adiabatic efficiency. A quick search of automotive forums on the Internet or magazine articles will turn up a lot of statements about how low the adiabatic efficiency numbers are for a Roots blower and how great they are for the other types. However very few people understand what these numbers mean in terms of discharge temperatures, air density and horsepower. It’s interesting to me that so many people want to base their forced induction decisions on the idea that they need a high adiabatic number, when they don’t even know what that translates into in terms of horsepower. Isn’t horsepower what we are after here? The differences are not nearly as big people think, certainly not on street cars below 400 horsepower. A typical 4th generation Eaton has a maximum adiabatic efficiency of 65% versus 75% for the better centrifugal superchargers and turbochargers. The realities of engine installation tend to put the numbers at about 60% and 70% throughout much of the operating range.

The following chart shows the effect of adiabatic efficiency on discharge air temperature increase (called Delta T). The bottom line represents 100% adiabatic efficiency and the top 60%.


As an example we will compare two fictional superchargers, one with an adiabatic efficiency of 60%, and one with 70%. At 7.5psi the differences are minimal. With an inlet temperature of about 77F the difference in discharge temperature will be only about 8F. This will translate into air about 3% less dense resulting about 3% less power for the less efficient unit. In real numbers that means a 200 horsepower engine will have 194 horsepower will the less efficient supercharger. That advantage of 6 peak horsepower is almost nothing when you consider all the dynamic factors on a real car. For example, you would not sacrifice 10% of your mid range power to gain 3% at the top end would you? Now lets factor in an intercooler. A good intercooler can remove about 80% of the heat increase, which means it will take more heat out of the air from the less efficient unit, thus closing the gap between the two. After the intercooler the difference in air temperature will be less than 2F and the difference in air density will be truly insignificant.

As we increase boost the more efficient supercharger will enjoy a greater advantage. Lets compare the same two superchargers at 14.7psi. The more efficient supercharger will enjoy a 16F advantage and 6% advantage in air density. That will translate into a horsepower advantage of about 6%. On a higher-powered engine this is starting to become meaningful. It’s the difference between 400 horsepower and 376. Of course with that much boost we will probably want an intercooler so lets factor that in. With a great intercooler taking out 80% of the temperature rise it knocks that 16F advantage down to less than 4 degrees and the horsepower advantage to less than 2%.

The Following chart shows the air density decrease associated with various adiabatic efficiencies. Notice that even at 14.7 pounds of the air density ratio only increases from 1.47 to 1.53 with a 10% improvement inefficiency.



I hope it’s clear that on a real world street car, the improvements offered by a slightly more efficient supercharger are pretty minimal. Your efforts are much better spent focusing on other areas. However I must point out that at very high boost and power levels a 10% advantage in adiabatic efficiency becomes important. For example when you are trying for 700 horsepower with 30 pounds of boost each percentage point of air density becomes a big factor.
 

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On Magnason's site they have a Roots blown Chevy with 10.5:1 compression running 13psi on pump gas. That's really not unusual anymore.
Not to argue with you or anything, believe me, I was not saying roots type were not effecient for the power they steal compared to what they add, the information I have is very up to date along those lines and as you'll see, the magnason's is exotic and not fully trusted either my thought was along the lines of the heat they generate being ineffecient-Geez, I do believe I have truly hijacked this thread now:
Corvette Forum - View Single Post - Has anyone done Magnason with H/C yet?
Same forum and thread about the ATI units:
Corvette Forum - View Single Post - Has anyone done Magnason with H/C yet?
 

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Discussion Starter #84
haha...yes. I dont think Im fully grasping this concept of "adibiatic efficiency" - - but I do appreciate your help and input Mr Gordon. You are very knowledgable on this subject and I respect that greatly. If I may ask you or anyone else who knows a question (and this is what Ive gathered from the 6 pages of discussion in this thread):

if everything in my spider is stock and I buy:

a programmable ECU
an Intercooler kit
rebuilt used turbine
free-flowing exhaust tailpipe
and custom built headers

then I should be good up to 7.5psi of boost? If not, what level boost would be safe for that 'stock' setup (considering the L-jet system)?
 

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The Magnuson supercharger is an Eaton supercharger in a slightly different case. All the internal parts are identical. I can't think of a more proven supercharger. Exotic? Not really, it's probably the most common supercharger. I would agree that the TVS is unproven, but it's brand new, give it time. If you want to see a 13psi 10:1 compression motor on a dyno run with a Magnuson MP122 (not a TVS) go to Magna Charger manufacturers intercooled supercharging systems for late model GM and Ford cars, trucks and SUVs utilizing OEM quality Eaton hybrid superchargers.

I read the posts from the Corvette forum. I think I covered that discharge temperature issue pretty well in the post above.
 

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I think I covered that discharge temperature issue pretty well in the post above.
Yes, I took 10 minutes to gather my thoughts, didn't realize you posted that till after I made my response to your ratings. Again, either turbo or supercharger, I'd not argue either of them are awesome upgrades and I've worked with all types before. MPTY!
 

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It's all good! I really love all types of forced induction, and I think any of them can make an Alfa Spider competitive with newer cars in the stop light grand prix. Which type to use is largely a matter of personal preference. I love a hot normally aspirated engine to, but it's really hard to get competitive horsepower numbers out of one while retaining good fuel economy and driveability, which I why most of my current efforts are focused on forced induction.

Greg,
hiperformancestore
 

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I really love all types of forced induction, and I think any of them can make an Alfa Spider competitive with newer cars in the stop light grand prix.
I can imagine Bigpapajoe is now really confused about where to go from where he is. I'd imagine if he wants that 400BHP and do it on a budget, he should "prepare" the engine first for boost and let the other stuff fall into place and then Greg, maybe you'll have an awesome kit designed by then that we all can put onto our spiders!?!
Bigpapajoe, I'm sticking to my original suggestions.
 

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haha...yes. I dont think Im fully grasping this concept of "adibiatic efficiency" - - but I do appreciate your help and input Mr Gordon. You are very knowledgable on this subject and I respect that greatly. If I may ask you or anyone else who knows a question (and this is what Ive gathered from the 6 pages of discussion in this thread):

if everything in my spider is stock and I buy:

a programmable ECU
an Intercooler kit
rebuilt used turbine
free-flowing exhaust tailpipe
and custom built headers

then I should be good up to 7.5psi of boost? If not, what level boost would be safe for that 'stock' setup (considering the L-jet system)?
No, maybe 6psi of boost for 2 reasons. #1: Turbo=hot air. Hot air and high compression do not mix very well, they will cause detonation, especially if the fuel supply can't keep up.
#2: As Enrique pointed out, the cork with high flow (which is what a turbo or supercharger will add to your engine) is the L-Jet can not keep up due to its type and design of fuel injection. You would surely run into detonation problems with your turbo/high compression engine and lack of fuel supply. Get the head, cams and full exhaust kit this year. Next year get the ECU, fuel pump, fuel rail, fuel injectors and fuel pressure regulator. The year after that decide wether or not you even want to boost your engine. If you do, you must commit to either supercharger or turbo and STUDY (come on you're in college, you know how to do this) both designs of them to decide which ones would be the best overall for YOU as far as form, fit and function. Next, you'll need to buy a 50lbs bag of rice and some super glue. For each import that tries to race you and fails, you must glue a grain of rice onto your windshield (I'm already upto 5 now-since yesterday). With your boosted engine, you may want to look into buying several replacement windshields as well:eek:
 

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Gordy, John, Murray and anyone else I may have inadvertently missed (this is a long thread!), thank you for the nice comments. I'm just trying to offer some thoughts and do my part like everyone else...

Joe,

When it comes to increasing power, nothing beats forced induction (supercharger or turbo), but you do need to know what you're doing. (People that go this route often go through several engines!) I know Greg really knows what he's doing and he's working on a Spider project that a lot of us are following with great interest. (Do go to his website and read up on it!) There's another Alfa guru who has been working on a "turbo kit" for a while, and he's close to getting it ready, but "close" can (and probably will) still take several months or even a year. These kits should make these set-ups relatively affordable, since they are designed to allow the owner to do most of the work and achieve a set-up that is safe. For me, experience with the specific application which equates to operational reliability is paramount, as I have seen way to many talented DIYers screw up their cars (not Alfas) after installing a turbo system that worked great at first, but then had a failure that only experience would have prevented. I second David's suggestion about studying forced induction. (By the way, David has knowledge and mechanical skills far beyond the average DIYer, so what is easy for him could easily turn into a nightmare for someone else.)

As far as the question regarding the electric fan and tail pipe, I wouldn't categorize either one as an upgrade that will yield more power on the street. There have been a lot of discussions about the fan, and it really only makes a difference at very high rpm (5k and >). Think about it this way: If you are driving around the streets and using only half of your engine's power, whatever power you are loosing from driving the fan, you can easily make-up by pressing the accelerator a little more. If you are on a race track however, and you are using your engine's full power, and there is no more to be had, and you remove the power draw caused by the fan, then you will see a power gain. Last, but also important, I can assure you that the electric fan will not cool better than the factory set-up, and it's also extremely difficult to install one on a '87 Spider and have it look other than "shade tree". I have one in my '74 Spider, but will not do it on the '84 or '87 cars.

As far as the tail pipe, it will make no difference in your car because that's not where the restriction is. Open your hood and look at the exhaust side (driver side) of your engine bay and note the very short pipes that conform the "manifold". These are much shorter than a set of headers, and designed to purposely restrict the volume of spent gases. They are also much shorter than the manifolds of the series 2 Spiders and the series 4 Spiders, because by 1990 there had been some progress with the emissions and Alfa was able to return to a less restrictive design. The Alfa design of the series 2 and 4 Spiders is actually excellent, and rivals some sets of headers. (To grasp how the design affects spent gases leaving the engine, think of it as an auditorium full of students, with only one exit that has double doors. Open only one of the double doors and watch people leave slowly, and then open up both doors and see the difference.) The second exhaust restriction is in the cat, followed by a relatively narrow exhaust pipe, so by the time you get to the tail pipe it doesn't make that much difference. Don't get me wrong, the IAP tail pipe sounds really good (Centerline also sells one) and people who have installed one (I haven't) really like it, but I doubt there will be any power increase, until you address the source of the restrictions. What I would do is check the diameter of the IAP pipe and see if it would fit my overall plan. That overall plan would include a larger diameter exhaust to be installed from the cat on back. The Magnaflow is 2.25 inches in diameter, and that's a pretty good size. If you go with a Magnaflow exhaust however, then you probably wouldn't need the straight pipe anyway. Of course, regardless of which way you go from the cat on back, you would benefit greatly from headers and a modern materials free flow cat.

You also need to be realistic as far as when you would be in a position to do upgrades. I would recommend that you start putting together a spread sheet with prices for parts (a different column for each supplier, so you can compare prices), specialized labor, etc. Then you can decide what to do and when. For example, if you aren't going to be replacing a restrictive, but perfectly good exhaust, with headers, cat, etc., which is going to cost you a pretty penny, then why not install the stinger pipe, and enjoy the sound for a few years? There really is a lot to consider, but it's actually a fun process. Years ago I decided to go the conventional route with my '84 because I wanted to keep it within the performance parameters of the period, and also because I could execute my "master plan" a little at time. Both routes, conventional or forced induction, are anything but inexpensive. A good plan that doesn't waist $$ however, will make either route affordable.

I also cannot emphasize enough how beneficial it would be for you to see other Spiders, and perhaps drive them. Try to get in touch with the AROC chapter closest to you and see if you can join them from time to time. Alfisti are very friendly and I'll guarantee you that it will be fun!

Best regards,
 

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(By the way, David has knowledge and mechanical skills far beyond the average DIYer, so what is easy for him could easily turn into a nightmare for someone else.)

Best regards,
You made me blush Enrique!! Points I'd like to add to that though: I came here to learn more about this mysterious car I traded a motorcycle for. Waterpump, radiator, oil pressure guage sending unit, 1rst AND 2nd gear didn't work, motor mounts shot, transmission mount shot and gobs of oil leaks. I've seen many threads on "Removing water pump" which helped me realize, it does not matter who you are, where you are, these cars have lots of built in tricks. I've found my solution was to remove the crank pulley, then water pump, then get ahold of those bottom studs with stud removers and install SS allan bolts. Problem solved-for any future R/R of the water pump. Of all the problems I've had with my car, none still remain, thanks for the information this site provided and the help and support (JohnM sold me a new/used radiator for my car) from the members here. Since then I added performance parts left and right trying to get the car "up to speed" if you will. Again, Joe could easily start this project on his own, my warning would be, if he ever, ever even thought he was doing something wrong, just ask the BB to be sure. I offered to install all the parts on his spider for free, if he chosen to do so-with free room and board while the work was being done, as I love this type of work or I'm just a cheap wh*re-either or...It is not who you know, who says what, it is always the end result that speaks for itself. I've asked opinionated questions here and have learned from a friend (spider21-WE ARE NOT ONE IN THE SAME), I don't need any one to tell me what looks best, because beauty is in the eye of the beholder, so I'll stick with that lesson. Turbo, roots type or centrifugal chargers are all great, it does become a matter of personal preference. Again, thank you Enrique!
 
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