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Old 02-27-2008, 02:24 AM   #1
Back Road Runner
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Default ? Stock + common Delta cam open degrees & Stock intake runner length & Plenum volume?

Just curious if people know any of this data off the top of their heads.

I've sort of been wrapping my head around the intake setup and its relation to TQ => rpm and runner length, runner diameter, and plenum size. This of course correlates to the header, collector, and remaining exhaust on the other side plus cam setup(something I have yet to look into).

I've got some basics down, found a runner area calculator, have a rough idea on runner length based off the number of wave bounces, a generic Chrysler one apparently using a 6 bounce setup, and a generic relation of plenum volume in relation to the runner volume.

I am quite curious what stock is, and because runner length will vary depending on cam open/closed degrees, I'm curious how the common Delta cams fit into the equation on a stock intake.

I'll probably post a few spreadsheet pics when I get the numbers organized. I'd be curious how some of these settings relate to real world dyno runs for those who have done intake modification(cams, port/polish, spacers).
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Old 02-27-2008, 05:56 PM   #2
Back Road Runner
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Well, from what little info I've stumbled across..
Stock cam = 181 degrees open
Delta has a 264 degree open and a 272 degree open apparently.

It would be useful if folks can verify this.

The plenum is small, whatever it is. It's probably not bad given the short intake runners which are probably in the neighborhood of a foot. I'd like to have numbers if anybody has any.

Working off theory...
Both intake runner and exhaust primary are focused to a rpm by diameter
Example, a 3500rpm focus, the intake runner should be 1.4" in diameter and the exhaust primary should be 1.5" according to calculators and info I've come across.
The length is a bit tricky. It seems one is working off the bounces, 1st bounce, 2nd bounce, 3rd bounce, etc. and attempting to time one or several of them to a specific rpm(time when the valve's open. Earlier bounces carry a stronger wave, and the wave energy dissipates after each successive bounce. The main issue seems to be size constraint. We can't exactly fit 5 foot long intake runners to make use of the first bounce, so we used the 4th, 5th, 6th, etc.

I don't really understand the limitations behind this, but it seems that one would prefer as long a runner and economically and spatially feasible. If long enough(think 4-5 feet, it can actually make use of the 2nd bounce at a really high rpm(redline), or the 3rd bounce at 4500 rpm, or the 4th bounce at 3500rpm, or the 5th bounce at 2500rpm, etc. You get a lot of wave tuning use over the entire rev band. If we shorten the runner length to say a foot, we are severely limited in which bounces we can use. We are now stuck with only the 7th bounce at redline and higher bounces beyond that. Bounce 1 through 6 isn't even used because the intake is closed throughout the entire revband during these.

Info on the plenum seem to indicate that it should be 1.5 times the volume of one of the runners. For a 12" long runner of say 1.5" diameter, this would make it in the neighborhood of 32 sq.in. or around a 3" x 3" x 3" volume(if cubic). With a longer runner, the size would bump up a bit, towards the range of 75 sq.in. or a little over 4" x 4" x 4" in relative size.

The wave tune approach is symetrical to the exhaust header primary diameter, length, and secondary collector diameter and length. The secondary collect is sort of like the plenum and the primaries like the runners. The difference comes along with the relative change in air flow rates and wave speed(going from 1125fps to 1800fps).

One thing I don't get is flow velocity between the cold intake side and the hot exhaust side. On the exhaust side, one shoots for 240fps. On the intake side, the "suggested" runner diameters don't correlate to the same velocity goal. Air volume is 2.5 times as much when heated and coming out the exhaust side. However, suggested intake runner and exhaust primary sizes don't correlate to this. In fact, the exhaust side is only about 15% larger meaning the intake flow is quite low by comparison. To get something like the same flow rate as a 1.5" diameter exhaust primary, one would have to use a 0.5" diameter intake runner. The intake is only seeing 1/8 the flow velocities of the exhaust side using the suggested values. Why? I don't know.
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Old 02-27-2008, 08:01 PM   #3
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Interesting...
http://www.wallaceracing.com/intake-runner-length.php

One think I'll not is that there seems to be quite a few formulas for runner length. This one actually shows them all and seems to be the most comprehensive calculator I've found so far, even tells plenum volume.

It just doesn't mention which bounce it tunes for.

Last edited by Back Road Runner; 02-27-2008 at 08:13 PM.
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Old 02-13-2011, 12:07 AM   #4
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Bump this old thread real quick.

I'm looking to port out a stock manifold to gain extra flow to compliment my upgraded cams and ported heads.

I'm having trouble finding what diameter intake runners would be best without changing the length of the stock runners.

Engine I'm speaking of is EJ251 SOHC.
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Old 02-13-2011, 10:30 PM   #5
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The diameter is basically 1.5" and 12" long, plus more through the head to the actual valves. You end up with around 16" total length which along with the 1.5" diameter is entirely appropriate for the engine's power band. There isn't much of a need to go bigger even with cams since the size is well fitting for anything less than a racier build. If you were tossing on Delta's 3000 grind, I might look into fitting a turbo manafold on, something that comes stock with a larger diameter runner, although you also have extra work you need to do to fit stuff which is probably beyond where you want to go with this.

I don't think it really needs to be upgraded, although you can port it some to reduce pressure loss. Grimmspeed offers a porting service for the stock manifold, but they really just taper it a little bit and gasket match the thing. There just isn't a lot you can do with it physically. People do like the 2005+ newer manifolds as they do flow better than the older ones, but there's a bit of custom work with those too to get up and running.

I think you'll be pretty content just with the P&P work on the heads because they do in fact need the work to just even out the flow across all cylinders. The cams will get you the rest.

If you haven't already, I would look at an exhaust and a good ECU tune to really bring the car to life. You didn't mention what else you've done yet, but if you're on the stock exhaust and stock ECU, you've left a lot still on the table for gains. A set of TWE headers, 2.5" piping from there on back, and add an I-Speed SRS-30 tune, and you'll likely be up another 20 ft-lbs/20hp.
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Old 02-13-2011, 11:27 PM   #6
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Yeah, I've already got a full EL header/catback. I do not have an ECU tune. I was looking at the SRS-30, but I wasn't sure if the gains were worth the price. I have a spare manifold, and I'm just looking to bump the peak torque up just a tad more higher in the powerband.
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Old 02-14-2011, 02:43 AM   #7
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Cams will get you higher in the power band. I don't really want to go against what you've already got, but if it's not high enough, it could indicate that you might benefit from a more aggressive cam yet. They are what is mostly controlling that factor. Then it's the valves and head porting. After that comes the exhaust and intake manifolds, mainly the diameters of these which control flow velocity and scavenging efficiency. The choice in sizing also depends on the heads. Often it is beneficial to match the head porting average diameter with the average diameter of the manifolds. Toying with some engine modeling software indicates one can quite readily create losses in power when these are increasingly mismatched. In essence, you want synergy throughout the system and have to look at building up the engine in that manner. The engine modeling software also indicated much of the issue with the intake manifold restricting top end performance has more to do with runner length than runner diameter. I've often wanted to build a short runner intake manifold for these cars, and the plenum could be bigger too which can simply be widened to both increase the plenum and reduce the runner length. While the intake manifold is excellent for the stock cam and heads, it does start to become less fitting once we modify those parts.

The ECU tune will be a big deal. Expect something in the neighborhood of 15 to 20 ft-lbs gains across pretty much all of the power band. The tune is doing two things. One it is stepping you up in octane which allows for more aggressive timing. Two it tailors the setup more to the specific hardware so the timing and fueling will be much more appropriate. Simply it is much more refined as well as appropriate for the hardware run.

I've used the SRS-10 and SRS-20 tunes personally. I don't have upgraded cams on my car, so the SRS-30 isn't an option yet. The SRS-10 was a 5-10 ft-lb gain across the board. I never dynoed my car completely stock, but the gains were noticeable and comprehensive. I did a full exhaust and modified my intake to pull in colder air. With the same setup, I ran the already good SRS-10 tune and then the SRS-20 tune. The SRS-20 tune yielded another 5-10 ft-lbs across the board due to the step to higher octane and allowable timing gains from that. I don't really expect peak torque to get better with the SRS-30 tune, but I do expect that the timing profile is better suited to the cams so there's less loss versus say the SRS-20. My guess is that you'll grab a solid 15-20 ft-lbs across most of the rev range simply from the tune and the higher octane fuel (not more powerful but allows more timing which then makes more power).
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Old 02-14-2011, 03:45 AM   #8
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I've been toying around with some of these intake runner calculators. Right now I'm running Cobb Spicy cams, so the next step up would be race cams (delta 3000) and I'm not willing to take that step as this is a DD. My peak torque is currently hitting at 4114 rpms. I'd like to get that a bit higher, say 4750 and with these runner calculators, it seems that optimum would be runners of 18 inches length and runner area of about 2 inches (roughly 1.65 inches in diameter). Since I cannot change the length I was looking to change (port) the diameter of the runners. Am I wrong in assuming this would help my peak HP, even ever so slightly? Sorry If I come off as newb-ish, I'm pretty well seasoned as far as N/A mods, I'm just trying to squeeze as much power out of my 2.5 without high compression pistons, and as far as direction-wise at this point, I'm lost.
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