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Intake manifold test

260Alpine

Silver Level Sponsor
It does and drops a bit. Max of 180HP at the 14" length. 170HP at 12" and 160HP at 21". HP and TQ always crossover at 5250RPM. When I get new printer cartridges I can print a graph and scan it to here. Pick the length you want Bill.
 

260Alpine

Silver Level Sponsor
Bill, The HP is for stock cams. Add 30HP for peak and 20HP for lows with HP cams. Around 5000RPM for stock, 5500 for HP cams.
 
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Bill Blue

Platinum Level Sponsor
Jim, could you do three rpm's?
16" - the shortest overall length I can accommodate
20" - what I now have
21" - about the longest I can do

I'm especially interested in the impact of runner length on power outside of the power bands. Example would be the expected torque of the different runner lengths at 2,000.

Bill
 

Charles Johns

Donation Time
Bill, my 2.3 is a carb engine that could use the stock intake, but it places the carb with the barrels sideways. I opted for the Esslinger intake due to the carb being placed with the 2 barrels running lengthwise with the head, which should help the starving of the #1 - #4 cylinders. Much different than yours with FI, but the problem is similar. If I can make 110 honest HP and get 30 plus MPG highway with a carb and no computers, I'll be very happy. Engineering formulas say the 2.3 should be at about 2900 RPM doing 75 MPH with 25.3" rear tires, 3.89 gears, a .75 Overdrive and hauling a fat 76 year old Dude with his lovely riding shotgun. The way I built the engine TORQUE was my goal at 2500 to 3500 RPM. Automotive formulas are not trustworthy unless we punch-in conservative numbers...which I did. With about 2450 pounds as car weight, frontal area of 19 ft., drag of 40, 400# passengers (me 250/her 150), and other factors entered conservatively, 32 MPG at 75 was what I got. Anyone have GOOD numbers for frontal area and drag? I just guessed, checking the phases of the moon, air temp, time of day, humidity, and factored in the color of the car. I think I'm close.
 

260Alpine

Silver Level Sponsor
003 (3).jpg 004 (2).jpg Bill, Here you go! 20" and 21" were very close so I printed 20" and 16". I did the charts with open header and no accessories so the numbers moved a little. Looks like you have about the right length. Took a while to resize the graphs without cutting anything off to let it upload.
 
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Bill Blue

Platinum Level Sponsor
Jim, I'm not home, so I can't study the graphs like I want, I should get home sometime Saturday.

In the meantime, I see that the 20" runner produces more hp at 6,000 rpm than the 16". I saw a runner length calculator that showed a first order harmonic giving a 10% boost at 6,000 to 6,500 rpm. So I have to ask, did the 21" length show more hp at 6,000 than the 20" runner?

Bill
 

260Alpine

Silver Level Sponsor
Bill, The 20" made peak HP at 5000RPM. The 16" made peak HP at 6000RPM. The 21" lost 2Hp but the curve was almost identical to the 20". I think you reached the point of diminishing returns.
 

Bill Blue

Platinum Level Sponsor
I decided to see the real life impact of runner length, so put the car back together with a total runner length of 22". Resulted in a 20-80 time of 13.3 seconds with two people aboard. 22" is a maximum max, it made the air intake runner want to prop the hood open. So I shortened the runners to 21 1/2", a comfortable max. 20-80 time, unchanged. I then went for broke, shortened the runners to 19", the minimum they will go without cutting. 20-80 time, 13.4 sec. So the runners have been shortened 3" with no impact on performance. They are now at 20", but not tested. I fully expect no change, but I will do it so there is ho hole in the data. At that point, I will cut the runners so that the maximum length they will accommodate is 19" and see what happens as the runner length gets down into the 15" to 16" range. Right now I am pretty much dumbfounded that there is no difference between 19" and 22". How can that be?

Comments, especially explanations, welcomed.

Bill
 

RootesRacer

Donation Time
Bill,

Torque peak may have changed but the area under the curve was about the same?
You have a lot of interactive physics going on and are only changing harmonics by 15%.

1/4 miles times are about area, not peak points.

With your testing, you are using a single gear and measuring the aggregate torque across the range of your engine. If you were making a HP monster and had a close ratio gearbox, you might see an advantage running over a narrower RPM range, but for how you are testing (wide RPM range), the resonant point will be less impactful on results.
 
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Charles Johns

Donation Time
Back when Moses was discussing camel racing, I studied motorcycle intakes because they must be very specific length, diameter, and sometimes tapered for best power. If memory serves, sometimes length makes little or no difference because the fuel-air mixture is dispersed/vaporized equally in both lengths. If the intake squeezes the mixture just before it enters the chamber it may vaporize droplets that were not already gaseous. The physics of fuel/air mixture are a mystery to me but I understand the basics...change liquid to droplets, then to vapor (gas), then ignite at just the right moment for the biggest BANG. Sounds simple but it AIN'T! FI solved many problems but seems to have injected (pun intended) others. With much higher pressures at the injectors, timing becomes more critical, and I am guessing due to the instant filling of the chamber with vapor...but I am often wrong.
 

Bill Blue

Platinum Level Sponsor
These are not 1/4 mile times, but the time to accelerate from 1600 rpm to 6500 rpm while in third gear, which equates to 20 mph to 80 mph. A fellow can present the argument that the area under the curve is the same, the times will be the same. The problem comes when you look at the times within the total, i.e., the time required to go from 20 mph to 30 mph. These times are amazingly consistent, not a full tenth of a second difference in any of them when comparing 19" runners to 22" runners.

Charles, imagine your surprise you discover that length seems to make no difference when you measure the output of you intake manifold that can be adjusted to various lengths.
Bill
 

RootesRacer

Donation Time
These are not 1/4 mile times, but the time to accelerate from 1600 rpm to 6500 rpm while in third gear, which equates to 20 mph to 80 mph. A fellow can present the argument that the area under the curve is the same, the times will be the same. The problem comes when you look at the times within the total, i.e., the time required to go from 20 mph to 30 mph. These times are amazingly consistent, not a full tenth of a second difference in any of them when comparing 19" runners to 22" runners.

Charles, imagine your surprise you discover that length seems to make no difference when you measure the output of you intake manifold that can be adjusted to various lengths.
Bill

I wasnt insinuating that you are testing 1/4 miles times, but rather you are looking at average area under the curve in the operating range of the engine.
1/4 mile times also follow this rule, but under a a narrower operating range becuase you have to shift at reasonable points. In your case you are just running a single gear across a wide op range.

If you had accelerometer data overlayed with RPM (and speed) you could more easily see the effect of your intake harmonic changes.
 

Barry

Diamond Level Sponsor
I decided to see the real life impact of runner length, so put the car back together with a total runner length of 22". Resulted in a 20-80 time of 13.3 seconds with two people aboard. 22" is a maximum max, it made the air intake runner want to prop the hood open. So I shortened the runners to 21 1/2", a comfortable max. 20-80 time, unchanged. I then went for broke, shortened the runners to 19", the minimum they will go without cutting. 20-80 time, 13.4 sec. So the runners have been shortened 3" with no impact on performance. They are now at 20", but not tested. I fully expect no change, but I will do it so there is ho hole in the data. At that point, I will cut the runners so that the maximum length they will accommodate is 19" and see what happens as the runner length gets down into the 15" to 16" range. Right now I am pretty much dumbfounded that there is no difference between 19" and 22". How can that be?

Comments, especially explanations, welcomed.

Bill


Bill,

Acceleration is a function of HP. As Jarrid noted, the time interval in your 20-80 MPH (1600-6500 RPM) acceleration test is a function of the average HP in that RPM range (aka, the area under the curve).

Regarding your question about why there is no time difference with 19" and 22" runners, I suspect that both of those runner lengths are considerably too long for your engine. The OEM car makers invest a LOT of time / effort / money to determine the best intake manifold parameters and there are probably good reasons why the runners on the factory manifold are about 13". Understood that under hood room may limit the factory runner lengths, but I would be very surprised if the factory intake manifold is not biased toward torque rather than HP.

Note that the intake runners are "dry" in port or direct injection engines, so pretty tightly curved can be just as good as straight.

Just my SWAG.
 

Charles Johns

Donation Time
Imagine my surprise when an engineer told me those intake noises from a race bike were actually sound waves coming back through the exhaust when both valves were momentarily open. Me and my non-engineer buddy looked at each other as if to say...SAY WHAT? I began a search for exhaust noise feeding back thru the intake, and found it to be TRUE. Back then biker guys were really into "tech" because the Japanese and Germans were making 2-wheelers go really fast. Who Knew? Apparently engineers did and that got me to looking at other NON-OBVIOUS power robbers, gremlins, and doo-hickies, that can hurt performance. That search was when I learned points make a much longer spark than electronics, and below about 5500 rpm the old mechanical devices work fine...but must be kept tuned. However, I never figured out how to keep muffler bearings from leaking...so I keep a pan under them now.
 
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