Oct 14th, 00, 11:29 AM
Thanx to all the help I've been getting, but I've got a question for the Einsteins.
IF you supercharge an engine, does the flow characteristics of your heads stay relevant or is the supercharger capable of overcoming the heads shortcomings?
350,350 new paint
Oct 14th, 00, 04:43 PM
Supercharging does in a WAY overcome the shortcomings of the heads flow characteristics in that more fuel mixture is still going to be forced into the combustion area regardless of the path it takes to get there compared to a normally aspirated motor.
Step on a water hose and turn the facet on half way and then all the way and you will still see more water shoot out when you have it on full blast, right??? (even though you are resticting the flow with your foot)
You are not going too change the FLOW CHARACTERISTICS of your heads BUT you are definitely going to change the FLOW VOLUME through the heads when you supercharge or JUICE for that matter.
Oct 20th, 00, 07:51 AM
Put it this way my buddies 69 had a 6-71 blower on a 355 motor. He changed from Sportsman II heads to the AFR 220cc heads and picked up 1/2 sec in the quarter. Heads still make a difference with a blower, but the blower will push the air through a smaller port. Better flowing ports still make more power.
Galen W. Rouse
Oct 20th, 00, 05:35 PM
Hey there Crash. Bob and SR are correct on the cylinder head thing. In fact as the boost increases, the shorcomings of an exhaust port will become relavent in a hurry. The cam of a blown motor is profiled differently also. Just as the object is make Horspower by building as much cylinder pressure as is feasable wether it be mechanicly or chemicly, The cam needs wider lobe centers to reduce overlap and retain the extra "compresion" in the cylinder longer. Usually something on the 113 1/2 to 114 is good. A blower or nitrous motor make excellent street engines when a high powered street car is desired. The converter is tighter, the cams allow a much smoother idle, nice things to have on the street. The boost builds torque down lower so the motor doesn't need to buzz up the RPM range. The downside is deeling with the pressure. The block should be o-ringed, a very high quality piston from a high end co., normally stay away fro the 2618 high silicon material. The ring land should be lower on the piston and ring tension, bearings and other little factors are to be taken into consideration. As long as shortcuts are not taken and the wallet doesn't get to tight, it will be a fun combination. And they look ok poping out of the hood. Just my nichols worth on this one and I hope some light is shed Galen
S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
Oct 20th, 00, 09:58 PM
Does a blower create a positive boost in the intake system or just boost the atmospheric pressure above the pistons?? What I mean is: when the piston travels down the cylinder in a normally asperated motor, atmospheric pressure "pushes" the air and fuel into the low presure area created by the piston traveling down the cylinder. But when a blower is used does it create a higher (ie.false) atmospheric pressure in the intake system?This would make it easier for the piston to such air in ( In this case heads would make a difference in performance). But if the blower creates positive boost in the intake system one would think heads wouldn't make a differece, as long as the port was at least big enough to allow the cyliders to fill.
I hope this makes sense, its the theory ive sort of come up with but I could be way off base.
Oct 21st, 00, 04:56 AM
A supercharger does create positive pressure in the intake manifold when under boost. I have my boost gauge plumbed into the manifold.
Since the engine is a big air pump the heads are still critical even with a supercharger; you need to be able to get the air in and out. On a supercharged engine with stock or low performance heads you will see higher boost in the engine than if you have a good flowing set of heads on the exact same engine with no other changes; however, even though the stock-headed engine made 10 lbs of boost and the engine with some AFR's or Dart heads only made 7 lbs., the engine with the better heads will make a bunch more power! Just remember the engine as an air pump and you'll realize how important the heads, cam, intake/carb, headers, etc. are to determining how well the engine runs.
Oct 21st, 00, 09:16 AM
So if you were to run heads with an intake port generally too big for for an engine (ex:220 cc heads on a 302 that does't see lots of revs), you probably wouldn't see the drop in torque at lower rpms. due to the boost with a supercharger.(??)
Oct 21st, 00, 01:26 PM
Basically yes, at least where a fair amount of boost is concerned. I'll give you an example. The guy who helped me with tuning my EFI car does a lot of dyno work. He owns a Dyno Jet chassis dyno. He was tuning an 88 Camaro with a 406 Chevrolet and a Vortech blower. This is an expensive piece and has the BIGGEST head that Brodix offers for a small block. With a normally aspirated engine that stays under 7000 rpm the bottom end torque and throttle response would be soggy to say the least. This car made 764 h.p. to the ground at 6500 rpm; it would have made well over 800 to the ground but the dyno does not allow the tire speed to get above 165 mph and shut the dyno down. This is 1000 h.p. or more at the crank. The torque at 2800 rpm (where the run was started) was about 520 ft. lbs. to the ground; probably 650 at the crank. It peaked at almost 650 ft. lbs. at about 6000 rpm (about 800 at the crank). So even though the heads would have been way too big for anything less than a big inch sprint car on alcohol, they still made a ton of torque even at the lowest rpm tested due to the blower and it's 15 lbs. of boost.
Oct 21st, 00, 01:41 PM
CAMCOJB brings up an excellent point in that for example on a NITROUS motor you will see a power SPIKE on a dyno graph when the juice comes on. Sometimes the spike is so severe it is difficult for some dynos to measure it accurately. But what you also see is a fairly flat torque curve from the time the juice comes on until you stop.
With this type of power spike, it can overcome some flat spots in your power curve that you might normally see if you were normally aspirated EXACTLY as CAMCO described above.
Oct 22nd, 00, 07:16 PM
SR and CAMCO- what you guys have said makes sense! Using nitrous to overcome a flat spot on a motor is an interesting option ( assuming its tuned as well as it can be). That '88 sounds nuts!! must be something else to drive.
Oct 23rd, 00, 03:57 AM
There are several different blowers to consider. Roots type (GMC,B&M,Weiand), Screw type (Whipple, Norm Drazy's one), centrifugal type (Paxton, Vortec, Procharger) and Turbo (exhaust driven).
Each has its place in the quest for more power.
Cost, ease of installation, size and OA weight, and Thermal Efficiency---in other words how good does one to the other compress air??
The screw blowers are true compressors because they phyically change the compression ratio of the compressed air (doesn't make sense, does it), kinda like a shop air compressor. The rest just create boost by pushing more air into the heads and intake manifold then the engine can flow for a given rpm. Its this backed up air that creates boost whereas the screw blower's air is under pressure as it comes out the blower impellers.
Blowers beat the air to death so that is why it gets warmer and less dense which means less power production even though more air is going through the engine under pressure.
To get more power out of a blown engine intercooling is sometimes used. Especially for turbo's.
Another way to increase power is to aid the engine injesting the pressurized air by using heads with bigger valves and ports. Also as stated earlier, use a blower cam, one with wide lobe centers and more exhaust timing and lift.
You can't use just manifold boost pressure to gage blower efficiency because one engine can have alota boost but small heads and average cam and create a higher indication of air pressure on the air gage. Another engine can be set up closer to "right on" and not build manifold pressure but produce a heck of alota power when compared to the other engine. This is because the air is going through the engine more efficiently and creatingt more power and not just backing up and creating pressure in the intake track.
I read alot and want a blower very bad to be able to get into the 700/800 hp range with my big engine and so I've researched the subject extensively. This is why I'm so long winded. (If I could just get my mouth over my carb???) pdq67
Oct 23rd, 00, 02:35 PM
Great answers guys and I just ran across one more.$$$$$$$$$.
I see that although some chargers are a lot more efficient, they are a lot more money.Guess you have to decide how much you want.
350,350 new paint
Oct 25th, 00, 08:17 PM
You made it all come together pdq, Thanks for the info.