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 Post subject: Intake Manifold Design
PostPosted: August 18, 2017, 9:31 am 
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Location: Connersville, Indiana
Kicking around the idea of making a new intake manifold. Essentially recreating the intake that was used on the 2.3 Ranger Duratec and using it on the 2.5 Fusion. The Ranger used a small port head (Focus 2.0) while the Fusion has a large port head. Larger even than the 2.3 Fusion.

The old manifold had small diameter (1 1/2"), long (16") runners. Flow was fairly consistent across the rpm range, loosing 3.6 kPa from 3000 to 7100 rpm. The new manifold has large (1 7/8") diameter, short (13") runners. It drops off 3 kPa from 3000 to 6500 rpm. Other than runner design, the two intakes are the same. Same plenum size, throttle body and air intake.

The problem is I cannot forget the low (mid 2000's) power of the 2.3. Its problem was it signed off at about 5500. The new manifold looses some low end but is better on top end. Overall performance is about the same. Stock cams, of which I know nothing.

Does it seem reasonable to assume the small diameter, long runners will be able to support the 2.5 at high rpm? In short, can it punch up the low end and not sacrifice top end?

Any and all input will be welcomed.

Bill


Last edited by BBlue on September 8, 2017, 9:19 am, edited 1 time in total.

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PostPosted: August 18, 2017, 3:57 pm 
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A custom intake manifold is not a typical way to increase power. Have you thought about going the ITB route? That is what all the race style Duratec engines go with. Other easier options to gain more power with off the shelf parts such as Cams, E85, aftermarket ECU, lighter parts etc.

My understanding is that changing the length of the intake or exhaust runners is all about improving the power at a certain RMP range. I think it is going to be a bit guessing game and you'll really need lots of dyno time to see any improvement. The problem with a manifold is you cannot make adjustments to test the results.

If you want to do it though you could certainly make it lighter, run cooler, custom parts are always really cool and there is a reasonable chance you could make some more power.

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PostPosted: August 18, 2017, 4:45 pm 
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The car is a full street Sunbeam Alpine, complete with cruise, heater and A/C. There is absolutely no room for ITB's or fancy exhaust. This is a very tight environment. My ECU is MS3. Cams are about the only after market items I could use. I can try to optimize the intake for the engine as it currently exists.

My question is: Given the rudimentary flow data, what will the small diameter, long runner manifold do to top end (6500 rpm) power? I can vary the intake manifold. The layout is such that, using a "trombone" design, I can vary runner length from 13" to 16".

Bill


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PostPosted: August 20, 2017, 11:59 pm 
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Longer is probably better, but I don't remember the resonance lengths off the top of my head. For a street car with street ratios in the transmission, you don't want to trade away anything to get a top HP number. How far down do the revs drop when you shift at 6000 RPM? You want it to land in a place with plenty of power there.

You could take a look at some engines in a sporty Focus or something for more ideas, but as long as possible is probably what you find...
Good luck!

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PostPosted: August 21, 2017, 3:02 pm 
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BBlue wrote:
Does it seem reasonable to assume the small diameter, long runners will be able to support the 2.5 at high rpm? In short, can it punch up the low end and not sacrifice top end?
It sounds like the large ports in the 2.5L head are what conventional wisdom would say are 'too large' and would normally be expected to actually hurt performance somewhat relative to the 2.3L head. But Ford must have had some reason for doing so, even if it's not obvious to the casual observer. What this means to me though, is that nothing can be assumed. We can speculate all we want, but the only way to know for sure is to try each of the 4 length/diameter combinations.

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PostPosted: August 21, 2017, 9:11 pm 
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Hmmmm. Seems my "data" does not mean any more to you guys than it does to me. Guess I'm going to have to build it and find out.

Bill


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PostPosted: August 21, 2017, 11:09 pm 
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Bill- sounds like you need Pipemax from Larry Meaux.

It's a fairly basic software designed for domestic pushrod race engine builders- an empirical knowledge lot- to troubleshoot and home in on, their combo's.


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PostPosted: September 5, 2017, 8:20 am 
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Okay, it seems a little explanation is in order.

The 2.5 engine pulls okay from bottom to top. Is knock limited up to 2000. Really comes on at about 3500 and power increase all the way to redline, 6500. Having max power at redline is not good in this type of application. Probably okay when coupled with a computer controlled auto or maybe a race car with a many speed trans. I want power to flatten at 6000 but still pull to 6500 and increase power in the 2500-3500 range.

The 2.3 engine did not seem to be so drastically knock limited. In fact, it pulled incredibly hard down low. One driver commented he expected to hear the turbo (non- existent) to blow off when he let off the gas. The problem, while it would rev to 7000, it signed off at 5500. The 2.5 has a longer stroke, so the 6500 rev limit is a fact of life.

The purpose of the thread was to gain some insight into the flow capability of the smaller runner. The "data" that I posted seems to tell me the smaller tube was moving as much air at 7100 rpm in the 2.3 as the big tube at 6500 in the 2.5. But if that is true, why was power down?

Bill


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PostPosted: September 19, 2017, 6:44 am 
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Location: Connersville, Indiana
The intake ports on the 2.5 head keep bothering me. They are much larger than the ones on the Ranger engine. So large that I will probably be able to insert 1 1/2" I.D. runners into the port without modification of the runner or the port. What would be the best way to address that issue? Try to stretch the runner to improve the match? Just terminate the runner with no shaping? Insert the runner into the port? Just a deal killer?

I'm thinking the reasonable (who wants to be reasonable?) solution would be to go to 1 5/8" I.D. runners. The currant runners are 1 7/8". It seems logical the 1 5/8" runners would have better low end performance than the currant runner and better top end performance than the old runner. Maybe not the best performer, but less opportunity to be really wrong.

Bill


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PostPosted: September 19, 2017, 8:26 am 
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The general rule for intake length is 1.3" per 1,000 RPM. l think the better approach is to just increase the runner length. Have you consider advancing the cam? Dave W


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PostPosted: September 19, 2017, 6:23 pm 
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A few guys have attempted to tune the Duratec vvt, but none have had any success getting hp out of the exercise. So I'll probably not go there.

It seems there are three items that impact where max torque occurs. Runner length, runner diameter in relation to cylinder volume and plenum size.
1. Runner length, I think that 20" overly large runners are not a good idea. Can't say why, just does not seem right. I suppose I could say throttle response would be impacted.
2. On a 150 cid engine, the 1 7/8" runners produce max torque at 6468 rpm. Redline is 6500. Not much to be gotten there. The 1 1/2" diameter puts max torque at 4233 rpm. 1 5/8" at 4704 rpm.
3. Plenum. Small, 50-60-% of engine capacity, plenum for low end, large plenum for top end. My existing plenum size, 60%, is marginal for low end. So my current manifold gives me very little to work with.

The 1 1/2" runners seem ideal, I'm really hung up on how to handle the huge ports.

Bill


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