[Blazin72]

I got to thinking today about putting a supercharger on the 350 in my Blazer today and wanted to gather some opinions. I would guess the engine is making somewhere in the neighborhood of 400 hp right now and actually dont even know if running a supercharger is really that great of an idea. It has a cast crank so I was thinking that I may want to limit the rpm to about 5500 with the boost. The engine has Sportsman II heads on it now with a Comp 282 solid lifter cam (236@.050) and just under .500 lift. The biggest hangup is that it has 9.8:1 compression with hypereutectic pistons. How much boost could I really get away with and would any more than just a couple PSI really be worth the cost of the blower?

It's just a wild idea I come up with today and if I have to I'll spend the extra money to buy some heads with larger chambers to bring the compression down some. Sure it's expensive but my last pay check had 134 hours of overtime (two weeks) and Ive got money burning a hole in my pocket

[THADD]

A B&M/Weiand would work well. I would recommend a cam with an LSA of 114º, a limit the boost to around 4-4.5 pounds. The pulleys that come with the mini blowers are usually 4 pound. If you do put heads with larger chambers, you can kick the boost up.
B&M claims that a 144 on a stock 350 will increase power by about a hundred horses. Go to www.holley.com and look under superchargers. There is a ton of good info there.
I see these blowers on Ebay all of the time. Very often, they go for under a grand.

[scot]

Use a centrifugal vortech type!
More efficient than a roots--less heat generated.
This is 2005 afterall.

[jimdavis]

In the Holley catalog, and probably on their web site is a chart titled "Effective Compression Ratio." As a side note, I developed that chart and wrote 95% of the copy in the Weiand Supercharger Technical Information when I was at B&M before the whole B&M blower program was sold to Holley.

Anyway, to avoid detonation, you need to maintain what is known as an "effective compression ratio" of 12:1. If you look at the chart, you will see that by interpolating between the numbers, a 9.8 c.r. means you can only run about 3 pounds of boost to stay close to the 12:1 figure.

One solution would be to run two head gaskets. I have done this on blown engines before and gotten away with it. You would have to calculate how much this would lower your c.r. I am taking a wild guess at maybe a half a point. That would get you to where you could run 4 to maybe 5 pounds of boost. This is enough to give your engine a substantial kick in the pants.

In any event, I would definitely install an MSD boost retard device which retards your timing when the engine goes into boost to avoid detonation. The device is adjustable so you can dial in whatever amount of retardation you need to avoid pinging.

As covered in another post in here, you should have no trouble with a cast crank and eutectic pistons if you limit your rpm to 5,500. The small blowers do their best work at lower rpm ranges anyway. When I was at B&M I know of a number of vehicles running the small blowers on cast cranks with as much as 7 or 8 pounds of boost and no problems.

Another post to your question recommends a cam with 114-degree lobe centers. That is good advice. We also got our best dyno results with RV-style cams which have more lift and duration on the exhaust than on the intake. Because the blower is cramming air into the intake side, you don't need the big lift, big duration that you need on an unblown engine. Yet, because the blower crams more air and fuel into the cylinder, you do make a larger amount of burned gases to exhaust hence the need for bigger lift and duration on the exhaust side.

The biggest advantage you will get with a blower is more bottom end and mid range torque. It will dramatically improve the seat-of-the-pants feel in the speed ranges where you drive 90% of the time.

Here is an interesting thing we learned after literally hundreds and hundreds of dyno tests. An engine with stock heads, stock valves and a stock cam would make just as much power (and sometimes more) than an engine with big valves, big ports and a big cam up to about 4,500 rpm. Below 4,500 the blower can pack enough extra fuel and air to more than overcome the small ports, valves and cam timing. But at 4,500 the modified engine with the big heads, valves and cam would blow right by the stock stuff and at 6,000 would be making significantly more power.

What this says, if you have a daily driver that you want a lot more low and mid range oomph out of, you can stick one of these small blowers on a totally stock engine and usually pick up about 100 more hp at 4,500 without spending a lot of dough on anything other than the blower.

[jimdavis]

Originally Posted by scrot

Use a centrifugal vortech type!
More efficient than a roots--less heat generated.
This is 2005 afterall.

While it is true that a centrifugal blower will out perform a roots type in the upper rpm ranges, they rarely match the low and mid range of a roots. For a daily driver that will rarely see more than 5,500 rpm, I would be much happier with a roots blower myself. That is probably why all the O.E. factory blown vehicles use a roots instead of a centrifugal because they want bottom end performance, not max power at 6,500.

[camaroman7d]

Jim, I understand the point you are making, but I think some of it is confusing to those that might not know better. While I agree the small blowers are much more happy at lower RPM's, and I agree a roots blower makes a lot more bottom end than a centrif..

What I don't agree on is that a blown engine will make the same power with stock heads, cam, etc... as one with better flowing parts. While with a blower you can cover up poor flowing parts and still make decent power. Let me try to explain, with a small blower it doesn't move enough air to take advantage of the larger ports, valves etc... This is why they are a good choice for stockish engines. I will take the challenge any day to see a small blower make anywhere close to the low end power my larger blower makes with the aftermarket heads, cam, large port manifold, etc... It's not going to happen at any RPM.

The advice of running two head gaskets, I don't agree with either. You will be even more likely to detonate that way. By keeping a tight quench, you can actually run more boost than having a wide quench and lower compression. This is how I can run 12lbs of boost on 8.47:1 compression. According to your chart that isn't possible on 91 octane. That chart is a good starting point and will keep people out of trouble, but there are far too many variables for that chart to apply to all engines (cams, timing, cylinder head material, combustion chamber design, piston design, quench, fuel, etc...)

Without hijacking this thread I would love to discuss some of these things with you via PM. Maybe we will both learn something. Don't take it as an arguement, it is not meant that way at all. I saw some similar info in another thread and I just didn't say anything. I am not saying you are wrong or that I am right, but it would be interesting to discuss it.

EDIT: no disrespect meant by this.
Royce

[jimdavis]

Royce....no disrespect taken.

I guess I needed to go into a little more detail. However, when at B&M we did participate in a blower comparison staged by Hot Rod magazine. I believe all the tests were run on Air Research's dyno. We ran our little 162 blower against BDS, Weiand, and I think Hampton's 6-71's. The limiting factor was we all had to run a maximum of 12 pounds of boost. I don't think we could quite get to 12 psi on that engine with our blower. I believe we got to about 10 psi where the big guys were at 12. All ran on the same engine. We made more power than any of the big blowers up to about 4,500 rpm.

Now, that Hot Rod engine had big valves, big cam and big ports so this is not really representative of what I said earlier and that is where I need to qualify my statement.

Another contributing factor to the small blower outperforming the big ones at lower rpms is the small blower is turning faster which means less air leakage around the rotors. The bigger blowers also have a greater leakage path due to their larger size. At lower blower speeds this air leakage with the bigger blowers means less air is being pumped into the engine compared to the smaller faster turning blowers. We have seen this in dyno test after dyno test. When we were doing all our blower development we literally ran hundreds of dyno tests in every conceivable combination and also ran many back to back tests against other 6-71 blowers. We always could make more power in speed ranges under 4,500 rpm.

In arriving at data that showed the small blower making more bottom end power with stock valves, ports, and cam, we ran several tests with that configuration. Then pulled the stock heads and stock cam and put in a big cam and heads then put the same small blower on it. We didn't make any more power at all until the engine ran past 4,500.

Interestingly enough, with the same blower drive ratio, we got much higher boost readings at 6,000 rpm with the stock stuff. That's because the boost gauge is reading pressure in the manifold and when you go to bigger valves and a bigger cam, boost goes into the engine and doesn't build up in the manifold.

Going back to the Hot Rod test, Magnacharger attempted to participate in the test with their blower, which if memory serves was only 112 cubic inches. They made 12 psi of boost on the boost gauge but made zero increase in power. That's because in order to make 12 PSI they turned the thing so fast that it was heating the air up to a very high temperature which expands it, creating a higher boost reading but no more power because the actual amount of air going into the engine is the same as with no boost.

I only recommended the two head gasket solution as a quick low-buck solution to too much c.r. I don't mean to imply this is a perfect solution. I have done it on some of the dyno engines we flogged and was able to achieve the results I was looking for.

I am not setup to PM and am on my way out of the office now. I will check back in this forum when I get home but then I am out of town for a week.

[Blazin72]

Centrifugal is out of the question. I dont want/need anything fancy like that and I think a roots type blower would look a lot better under the hood of an old 4x4 than a centrifugal unit. Im not looking for maximum power gains either, the truck doesnt need it. I just get bored with what I have after a while and have an itch to change something and I think this time around it's time for a blower. The two blowers I was looking at were the 144 and 177 ci units because they are relatively small and should work well for I want. When I looked last night the parts list for them listed adapter plates for either 2x4bbls or a single Dominator. I want to continue using the 750 DP I already have, are there any blowers that come with a plate for a single 4150 style carb? How much of a power increase could I expect from 3-4 psi?

[NXS]

Originally Posted by camaroman7d

Without hijacking this thread I would love to discuss some of these things with you via PM.

This is one of the best threads I've seen in a long time with much knowledge, please leave it here for us all to read and learn. {insert Einstein accent here} verdy verdy enter-resting

[NXS]

3-4 psi?

it works like this:
atmosphere is 14.7 psi so at 14.7 psi twice as much air is going into the engine and a 350 hp engine will make 700 hp.

3 psi is 1/5 of 15 psi so 400 hp x 6/5= 480 hp....but a small blower may only be 50% efficient so the 80 HP boost will be 40 hp. 440hp @ 3psi

[Blazin72]

Well, I bought the Weiand 142. Now I need to know what modifications I need to do to my 750 DP so it will work properly with the blower. Any tips?

[camaroman7d]

First let me say, the little blowers are great for applications such as yours. Your carb will bolt on to either one. As far as prep'n your carb for blower use, if you do a search on the web there is info out there. I bought blower carbs for my engine and have used the same type on other blown engines I have tuned. A lot of the boat guys run blowers and it was on one of those forumns that I saw the details on how to boost reference your carb. Do a search on "boost reference" or "boost referencing". You may also want to look into a little larger carb, with a blower you can probably use it. See if you can find a blower carb already set up in the 800+CFM range.

NXS, I agree there is a lot of useful info, but I don't want to hijack this guys thread to discuss differences in theory and/or opinon on blowers.

Jim, I was not at your dyno session so I can't argue your results. I know of another blower builder that has done dyno testing on the same engine with different size blowers, the results are not the same as what you came up with.

I think the results you saw were due to the restrictive heads during the test. Don't get me wrong small blowers are fine and are great for certain situations. The way I see it is this flow is power, boost it not necessarily power. As you said yourself boost is a measurement of back pressure in the manifold, this is one reason I do not like that chart/formula to tell you how much boost can be run on XX compression. Once again I will use my engine as an example. I have 215cc Dart Pro 1 heads, fully ported, large valves, etc.. My engine makes 12lbs of boost, now if I put on a set of stock heads with 165cc runners, I would make more boost. I would not make nearly as much power or be able to move as much air. Engines air nothing, but air pumps the more air you move the more power you can make.

Now with small runners, small cam, mild engine, you do not need to use a big blower and it would be a waste to do so. I am assuming this is the kind of engine you did your dyno testing on. This would give the type of results you found. Now put that small blower on my engine and it would be able to compete. It wouldn't be able to make much boost, I would have to spin it real fast and we both know that is not the way to make the best power.

During your test did you use a single carb on all the blowers? Did the larger blowers get the benefit of two carbs? This will make a difference as well, if you can get the air in you can't make power. Larger blowers need to get the air in and not be choked off. Though in your tests I bet a single carb on a larger blower would have faired pretty well.

Blower leakage will vary depending on the tolerances the blower is set up with.

I guess my point is, that on a stock engine a small blower is a great fit and will probably hang with a big blower to a point, also smaller engines will like them. If you make the engine free flowing, the larger blower will out perform the small one accross the board.

Maybe back when you did your testing (How long ago was that?), the larger blowers weren't as efficient as they are now.

Basically a larger blower moves more air, the more air you move the more power you make. Boost isn't all that matters. A smaller blower can not move the same amount of air as a larger one, with that in mind it can't make the same power. So a larger blower only making 8lbs of "cooler" boost will make more power than a smaller blower making 10lbs of "overheated boost" this is another reason boost is not an accurate way to judge.

If the engine is free flowing you will have less leakage passed the rotors, in your case with the restrictive engine it is possible that had something to do with the results.

I am not sure how else to express my thoughts on this. We may just not be looking at things the same way or with the same goals in mind. I will not buy that a smaller blower will out perform a larger one in any RPM range. Sure if you handicap the larger one by spinning it too slow or restricting flow, you can scew the numbers. we haven't even talked about what happens when a real world load is put on the engine. What if you spin the larger blower faster and limit the RPM's and not the boost? As you can see it can be made to look whichever way you want. I am sure as with many magazine articles, they were trying to prove a point or push a product. I am not a hater of the smaller blowers, they are great for mild aplications, they are a lot cheaper to set up (single carb saves a lot of money on fuel lines, linkages and air cleaner/s) and in most cases are more than enough.