Manifold air speed

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hdsadey
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Manifold air speed

Post by hdsadey »

So as with most things, I can't seem to leave well enough alone! I got to thinking about manifold air speed in relation to rpm. The equation for determining cfm requirements of an engine are as follows: displacement × rpm × volumetric efficiency ÷ 3456 = carb cfm. So I plugged in my numbers. 408 × 3000 × .85 ÷ 3456 = 301 cfm. The .85 represents 85% efficiency due to engines are not 100% efficient. 85 seems to be universal as to a performance efficiency number.

Now through my research and falling down rabbit holes, I discovered that 540 straight valve aircraft engines have 550 cfm carburetors. The standard 260 hp engine makes peak power at 2800 or so they are rated. This further got me thinking about my 408 setup running direct. I was currently running a FiTech Go-EFI 4 with 400 hp capacity. These 4 barrel setups flow a maximum of 1000 cfms. Since manifold air speed is of utmost importance I wondered if the 4 barrel was slowing the air down to the point of lost power.

Curiosity got the best of me. I ordered a FiTech 2 barrel kit that has 500 cfm flow. It too has 400 hp capability. I used a Moroso 2 hole adapter to bolt it to the same Performer manifold. Now I've only done a static test on the trailer but WOW what a difference! Starts easier, the tip in throttle response is a whole lot snappier, idles smoother, and the rpm limit went up 300. I had it choked up at 2700 on the trailer, this afternoon I recorded a 3000 rpm run up. Tomorrow I will be going to test it to see how much of an improvement it made. Plan to bring the angle finder and torque wrench to readjust the prop. I'm excited!!!!!
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02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

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Slidin Gator
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Re: Manifold air speed

Post by Slidin Gator »

Now your using the old noodle, why would you put a 1000 CFM induction system on a 500 CFM application?

After you run it, tell the crowd about the difference in throttle response.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

hdsadey
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Joined: Sun Jul 01, 2012 7:42 pm
Location: venice fl.

Re: Manifold air speed

Post by hdsadey »

Cause at the time I got it for the 302 they didn't have a 2 barrel option. Since working at the engine machine shop and getting experience with the new dyno, I've come to realize alot of things! Carb size is often oversized on engines too many times.
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

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keys2pines
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Re: Manifold air speed

Post by keys2pines »

Damn man! I had the same idea after seeing the 2 barrel fitech. Now you have me thinking about changing mine!
12x6'8" Frank Barnes deckover, 383 DD, 72" Sensenich JM
Our keys house for rent, 10% off for SA members https://rentalsfloridakeys.com/view-uni ... /#image-10 :usa:

hdsadey
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Re: Manifold air speed

Post by hdsadey »

So here are the results of my water test on Sunday. Throttle response from 4 barrel to 2 barrel was more crisp and clean, 4 barrel had a lag, 2 barrel has virtually none. I left the pitch alone until we made our first stop, wanted to see how many rpms I gained. With the 4 barrel, wide open was 2800-2900, 2 barrel raised it up to 3100. I was able to put another full degree of pitch to bring it back to 2800. My cruise in deep water dropped another 200 rpm. Everything was going great until it wasn't. I developed a throttle issue due to what I assume was RPM noise, as that's what the fault code was coming up on the handheld unit. I had routed the tach signal wire too close to the spark plug wires and apparently getting interference to the ecu. Tried moving them but working on a hot engine isn't fun on the water. Was able to wipe the program and start over, but it again returned. Other than the issues, I would call the swap to the 2 barrel a great success. It woke up an already powerful setup even more. Manifold air speed on a direct drive is damn important!!!!
20190623_140536.jpg
This is parked up on a 3 foot high embankment, couldn't do that before! It's also got polymer.
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

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keys2pines
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Re: Manifold air speed

Post by keys2pines »

That's awesome! You're using a performer air-gap right? I ran my tach wire through the center of the intake manifold, under the runners, keeping it away from the spark plug wires. I think you should send me your 2bbl for testing, see if the results are repeatable on a chevy :D
12x6'8" Frank Barnes deckover, 383 DD, 72" Sensenich JM
Our keys house for rent, 10% off for SA members https://rentalsfloridakeys.com/view-uni ... /#image-10 :usa:

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kwanjangnihm
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Re: Manifold air speed

Post by kwanjangnihm »

hdsadey where is this spot? nice!!

Image
He'll cut your throat, baby, stick you in the back, drive off in your Cadillac.
He's more trouble than you think, he'll kill your sugar, leave you in the drink.

hdsadey
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Re: Manifold air speed

Post by hdsadey »

Peace River.
Screenshot_2019-06-26-10-07-25.png
No sir just a regular Performer. Idle-5500 power range. Not sure it would act right after being on a Ford motor! Lol :shock:
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

Heavy
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Re: Manifold air speed

Post by Heavy »

hdsadey Like you i have chosen to run a ford motor but have chosen the big block and gear box route. i just got back from picking the new motor up and running it on the dyno. i still feel there could be some fine tuning to be done and would like to verify the true numbers of the build as i no there can be alot of variables put into a engine dyno to tweak the numbers. do yall do dyno test on the weekends or just through the week?
14' Jimmy White /557BB Ford Motor :florida: :rebel:

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digginfool
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Re: Manifold air speed

Post by digginfool »

hdsadey wrote:Peace River. Screenshot_2019-06-26-10-07-25.png

No sir just a regular Performer. Idle-5500 power range. Not sure it would act right after being on a Ford motor! Lol :shock:

Looks like a great place to ride. How far up the river are you allowed to ride?
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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keys2pines
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Re: Manifold air speed

Post by keys2pines »

hdsadey wrote: Not sure it would act right after being on a Ford motor! Lol :shock:
Lol! I'm contemplating running a velocity stack, saw some good dyno results with them. Or possibly a restrictor plate, just curious if it would help any. I really don't want to throw $800 around just yet.
12x6'8" Frank Barnes deckover, 383 DD, 72" Sensenich JM
Our keys house for rent, 10% off for SA members https://rentalsfloridakeys.com/view-uni ... /#image-10 :usa:

hdsadey
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Re: Manifold air speed

Post by hdsadey »

Heavy, we only generally work Mon. thru Fri. I can talk to the boss and see if there's exceptions to the rule. What size is the engine? Maybe some specs on it?

Diggin, we can ride all the way up to Wauchula and beyond. Down to the Gulf of Mexico through Charlotte Harbor. Don't believe there's a limit to run. Most stay south of State Road 70 and north of Punta Gorda. There had to be at least 30 boats out on Sunday.
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

hdsadey
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Posts: 283
Joined: Sun Jul 01, 2012 7:42 pm
Location: venice fl.

Re: Manifold air speed

Post by hdsadey »

I thought about a restrictor plate, but didn't want it skew the results. Thought it would disturb the airflow to much and not give a smooth fuel charge. TRUST ME I DIDN'T WANT TO SPEND THE 800 EITHER BUT I COULDN'T STOP THINKING ABOUT IT!!!!!
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

Heavy
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Location: Kathleen Fl

Re: Manifold air speed

Post by Heavy »

Hdsadey- Thanks for the reply it is a 557ci BB motor. i was told by the builder that they had built the motor before and got 750hp and 754 tq , with the tq number at 4800rpm. We built mine took a little more off the deck and turned 697hp at 5800rpm and 680tq at 4800. between the 2 builds they had the dyno brake rebuilt and they told me they thought truth was somewhere between the 2 sets of numbers. i guess numbers are only for bragging as long as your happy with performance. just curious to what the actual numbers are, verses what i paid thinking i was going to get.
14' Jimmy White /557BB Ford Motor :florida: :rebel:

hdsadey
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Re: Manifold air speed

Post by hdsadey »

Heavy, so we currently do not have the adapter brackets for BBF. Stuska has them in stock and would probably a week or better to get them.

That being said, we would like to see the print outs of your engine's dyno session to see if the values look correct for afr's, egt's and bsfc (brake specific fuel consumption). This could help us determine if the engine is properly tuned and whether or not it needs to go back on a dyno for more. Dynos are tools that CAN be manipulated to show certain desired hp and tq numbers, not saying the shop that built your engine practices that. Correction factors can be adjusted to show larger numbers. We use the accepted standard SAE formula as to not deceive! We do however cool the room to the mid 80s before a pull. This does help to make horsepower, as much as 20 hp over pulls made 10 degrees hotter so we have witnessed. We feel while 85 degrees is not the dead of summer, it does represent spring and fall on the average. If you would like PM me and I will forward you an email address where you can send me whatever dyno paperwork you received and build sheet so we can review it. Thanks Daniel.
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

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kwanjangnihm
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Re: Manifold air speed

Post by kwanjangnihm »

hdsadey wrote: Peace River
Image

Will try to meet up with you guys once I get my junk running.
Not sure what is worse, hanging out with CM guys or hanging out with FORD CM guys?? :stirpot: :slap: :toothy7:
He'll cut your throat, baby, stick you in the back, drive off in your Cadillac.
He's more trouble than you think, he'll kill your sugar, leave you in the drink.

Heavy
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Re: Manifold air speed

Post by Heavy »

Welcome to a better class of CM guys.
14' Jimmy White /557BB Ford Motor :florida: :rebel:

hdsadey
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Joined: Sun Jul 01, 2012 7:42 pm
Location: venice fl.

Re: Manifold air speed

Post by hdsadey »

Or in my case a CM DD Ford guy, THE TRIPLE WHAMMY!!! LOL

Most importantly an LS engine is just a Windsor wearing a Bowtie!
02 Predator 12' 0320 Lycoming
2019 Circle H 408 Windsor DD Sig Series 74"
99 Donzi 16 Classic 350 Vortec

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