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Old 08-23-2004, 08:00 PM
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Blower Question?

I dont plan on getting a blower or anything but im just curious why do you need low compression to run a blower??

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Old 08-23-2004, 08:28 PM
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You need lower compression to run a blower because shoving more air/fuel mixture than the atmospheric pressure is like having higher compression. If your compression is too high, you will detonate. High octane fuels have more resistance to detonation than do low octane fuels, but even high octane fuel has its limits, usually around 12:1 to 13:1, depending on head design. What I mean by this is that if you have a 10:1 engine running normally aspirated, the air/fuel is being compressed to a pressure of 10 times that of atmospheric pressure, which is about 14.7 psi, giving you 147 psi. If you were to run 10 pounds of boost with a supercharger, the pressure of your air/fuel mixture is at 24.7 psi. When you fill the cylinder and compress it into the chamber, you are getting 10 times that amount, 247 psi, which is like having 16.8:1 if it were normally aspirated, and would easily detonate. If you are going to run 10 pounds of boost, aim for 7.5:1 or lower, or you will need race fuel.
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Old 08-23-2004, 08:40 PM
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There are variables in the boost/compression/fuel equation. It's never set in stone.

I had a Buick GN with a TA49 turbo, Kenne-Belle front mount IC, and SMC alky injection. I had no problems running 18psi of boost with 93 octane pump gas and 8.5-1 compression.

I made an alky injection kit for a blown 351 in an old Mustang, I forget the year. He had no problems with 8.8-1 compression and 9psi of manifold pressure. A manifold pressure switch and a knock sensor, via relay, was used to switch the washer pump on and off. It worked very well for a home engineered kit.

A strictly hotair setup with no alky or water injection will not be able to run elevated boost levels on pump gas.

Larry
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Old 08-23-2004, 08:47 PM
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hey thanks for the insight Larry, I am starting a blower motor project and I would appreciate some pointers from a guy who obviously has experience with blowers like yourself. I want to run a sbc 400 stroked to 427 with 15 to 20 intercooled psi of boost from an ATI ProCharger. I'm expecting 1000 HP with AFR 215 raised runner heads and all forged/billeted internals. I need to know what is my estimated max CR with polished aluminum chambers with dished pistons and a tight quench. I also would like to know if a production 400 small block with 4 bolt mains will hold up to that kind of power
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Old 08-23-2004, 09:07 PM
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haha i get it ima genius not really tho lol
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Old 08-23-2004, 10:17 PM
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My advice is to find an experienced builder that you can visit personally and have a sit down chat. Don't waste his time with bench racing. Set a goal and stick to it. You can't go throwing in stuff after plans have been laid already.

No, a production block will not live very long at all at that level. Do not polish the combustion chambers. The compression ratio used is dependent upon the intercooler efficiency, combustion efficiency, and the intended use of the vehicle. If you want a streetable engine keep it between 7.5-1&8-1.

Have a peek at the available pistons and discuss it with your experienced buddy. A 427" SBC is kinda pushing it with off the shelf pistons available. A 24cc dish, 76cc chambers, a 0.050" head gasket and the pistons 0.020" in the hole will be 8.79-1. Custome pistons can be had and I'm sure that someone may have pistons with larger dish volumes but you may have to stick to a short rod to make it work.

Like I said, set a goal, make plans and stick to them. Engines like you're describing require planning. Lots of it.

Larry
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Old 08-23-2004, 10:40 PM
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I plan on making an 8 second dragster with this motor, using race fuel only and trailoring it to the track. I have the engine planned out almost completely, and I'm not going to cheap out on anything. My block not going to live long is sad news, I'm afraid New aftermarket blocks will cost me both nuts

Just curious, why is not polishing the chambers a good idea? I was always under the impression that the more smoothly the chambers are polished, the less chance for a hot spot to develop as well as there being less obstruction to tumbling and swirling.

I am going to use an ATI ProCharger with the biggest bugger of an intercooler I can get for it, I may have to dream up an unconventional way of mounting it, but I know I'm going to need it.

I plan on using custom pistons, preferably ones where the top ring land is strong enough not to frag with the kinds of forces I will be flogging on it. I'm aiming for 8:1 or less, so I will need a big dish and short rods. Which sounds better, 5.7" or 6"? I've heard advantages to using both shorter and longer rods, each has it's own tradeoff I guess...

As for a goal, 1000 HP will be my goal, anything less and I've done something wrong in my opinion.

I know I need an NHRA license for 8.90 ET or faster, and I know it's going to cost a fortune, but I am committed to it. I just want to do it once and do it right.
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Old 08-23-2004, 11:01 PM
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1000 hp out of a 427? Not without nitrous, my old el camino had a blown 472 (stroked small block) with a 10-71 blower and i was barely pushing 900.... good luck

it did have torque though
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Old 08-23-2004, 11:17 PM
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Quote:
Originally posted by elcrusch1
1000 hp out of a 427? Not without nitrous, my old el camino had a blown 472 (stroked small block) with a 10-71 blower and i was barely pushing 900.... good luck

it did have torque though
You're full of it kid. Don't post that crap here. Be honest, listen and learn.


Mad Maggot,

Polished surfaces can cause fuel to form droplets, tiny ones, but it's not the kind of thing you want for good combustion. The fuel must stay atomized and suspended in the air to burn properly.

Do this, Take a water hose and spray the car after you wax it. See the water form droplets on the surface? Then dump some on a piece of sandpaper, see how it lays down even and smooth.

Tha sandpaper will dry faster than the car because the water is spread out thinner. Droplets are thicker so they take longer to evaporate. Same goes for gasoline in a combustion chamber.

Larry

Last edited by coldknock; 08-23-2004 at 11:23 PM.
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Old 08-24-2004, 01:29 PM
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lol

dont hold back Larry tell us how you really feel...

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Old 08-24-2004, 04:27 PM
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I can bench race with the best. The difference is that everbody listening knows that it's just bs. It's for a laugh.

I have no tolerance for outright lies.

Larry
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Old 08-24-2004, 07:51 PM
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oh elcrusch1, you need to go to Airflow REasearch's website and click on the "dyno tests" section at the top, there's a 434 small block that makes 1001 HP with 14 pounds of boost from an ATI procharger and AFR 210cc heads. This motor was built by Vrbancic brothers racing in Ontario, California, and actually dyno tested. I plan on using better heads with the AFR 215 raised runners, as well as more boost, so I think I can attain 1000 HP just fine.

Larry, thank you for the information on chambers, I was just about to polish the chambers on my dad's 440 heads I ported, but I can see now that is not a good idea. Just curious though, what can be done about the hot spots that may form at the tips of the rough bumps of metal if it is not smooth? I heard these get hot enough to act as second spark plugs in iron heads, regardless of cooling.

and elcrusch1, the reason you did not attain as much horsepower is that you are using a roots blower, without an intercooler, so you are not making as much effective boost. roots blowers are good for 30-80% increase, as a ballpark estimate, while intercooled centrifugal superchargers can make upwards of 150% increase in some cases.
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Old 08-24-2004, 08:03 PM
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Use a 60 grit cartridge roll to get rid of the casting flash and round off all the sharp edges. Don't use anything finer as it will be too "slick".

Look close at the area around the valve seats. Unless a chamber sweep was performed during the valve job there might be a ridge there. Be sure not to nick the seats if you decide to smooth out the ridge, if it has one.

Larry
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Old 08-24-2004, 08:59 PM
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alright, I will definitely do that, and thanks again Larry. I'm sure when my dad's charger is detonation free he will thank you also
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Old 08-24-2004, 10:08 PM
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you guys hijacked my thread i dont care tho i already got the infromation i wanted

Thanks..
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