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#1
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high rpm power mod
This will be a trial an error mod similar to those intake manifold spacers.I was looking at an old engine and decided that the lower intake manifold can be installed between the normal manifold setup with the stock hardware.I contacted a local machine shop that will fill in or remove the extra injector bosses.The shop owner asked about installing nos injector nozzles or extra injectors,but I really plan on just getting the bosses cut off and filled in.In thoery I should get a better breathing engine along with a better powerband.I see one issue in relocating the egr system or just get rid of it all together.This mod is better suited for a supercharged engine for bigger gains,I feel about a 15whp gain is doable and is very inexpensive since I already have the parts.Any thoughts
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#2
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Looking forward to seeing the results. Sounds like a good project. Are you going to cut out the hood for clearance?
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Matt Locker Link 2015 BRZ Limited 6MT 92 Ebony LS-L ECUtune Stage2av1, Z32 MAF, 370cc injectors, TomsSVX intake, BontragerWorks 22mm RSB #003, HID Hi and Lo beams, OT endlink and bushing mods, PWR Aluminum radiator, Harvey's QC shift kit, 2.5" flowmaster 80 exhaust, 17" Michelin Pilot Sport A/S, Poly sway bar bushings, Slotted Bradi rotors, AFBeefcake powdercoated calipers, 97 grill, and a huge set of air horns. 300,000 miles and counting 92 Ebony LS-L. ecutune stage1v4, motorsport 1pc pulley. Garage Queen - sold to Dad in upstate NY 155,000 miles 19 Subaru Ascent Premium - -Hers !. 89 DL 4x4 little red wagon - a.k.a. The immortal suby. 275k R.I.P. |
#3
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Theory indicates that longer intake runners should provide more Hp "up top". It will be interesting to see the impact on the low end.
-Bill
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Retired NASA Rocket Scientist Most famous NASA "Child" - OSIRIS-REx delivered samples from asteroid BENNU to Earth in Sept. 2023 Center Network Member #989 '92 Fully caged, 5 speed, waiting for its fully built EG33 '92 "Test Mule", 4:44 Auto, JDM 4:44 Rear Diff with Mech LSD, Tuned headers, Full one-off suspension '92(?) Laguna, 6 spd and other stuff (still at OT's place) My Locker |
#4
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This seems backwards to me.
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Disclaimer: The above post is on the internet. |
#5
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Longer runners increase intake velocity for the upper end.
Shorter runners increase charge density for low end.
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[SIGPIC]http://www.subaru-svx.net/forum/image.php?type=sigpic&userid=5569&dateline=1207440 507[/SIGPIC] Naught but by the grace of God "42" Current Stable By Age:'89 Subaru XT6 Silver "Audrey" as in Hepburn '96 SVX LSi #767Brilliant Red "Lil Red" Now on the front burner. Looking for a totalled, but running parts car. |
#6
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That was noticed this morning about hood clearance,but maybe a sti scoop will cover things,also I can leave the egr in place.I will drop off the lower manifolds friday.About bottom end torque,my car is fwd and losing some torque will help with traction.Just tapping the gas spins the tires so I feel that by making our runners longer we can get more power.Stock runners on the svx is somewhat short to give good torque and long enough to make a little power up top.Now I may be going down a dead end road but it won't cost much and should spark a few new ideas on the forum.If this works like I feel it should,any stock sc svx should easy see another 20-30 whp in the upper rpm where power seem to fall off.My little idea came from reading about honda civic skunk racing manifold making 15-25hp over a stock manifold.
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#7
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Agreed. Commonly, longer runners are for torque and short runners for high rpm use.
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#8
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Yes wrong way around.
You shorten the inlet tract to raise the speed that the torque is produced.
Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#9
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After reading more about intake manifold design,I think we have room to play with since overall runner length won't exceed 7 or 8 inches.One site tested a 18inch runner vs a 12,an a 6inch but 18 produced some killer torque,also the svx has a very large plenum so I think some gains are there to be made.Correct me if I am wrong but by adding the lower manifolds to the existing setup I will increase the overall intake plenum volume as well.I should have the machine work done by next week so cross your fingers.
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#10
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I also agree that this seems bit backwards.
I was always under the impression that a longer runner provided more torque and a shorter one provided more hp. in the high end. That's why when people put in something like an outlaw spacer they notice an increase in tq. but not much else. That's what happened on my probe anyway, and a few other cars that I've noticed. There are a few OEM manifolds that have the best of both worlds. One off hand is BMW. I forget what engine it is, but it has a variable length intake tract. Long runners for good low end torque and then it opens or spins or something and the runners become shorter for great high revving power. That's what I always thought, anyway... If you really wanted, couldn't you just mill down some of the manifold, or something like that, and then do some porting? That seems like it would help on the top end.
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Jesus is the remedy 2015 Expedition EL Ecoboost Ebony Pearl '95 Subaru SVX LSi Home of the Bontrager Works 22mm rear sway bar!! |
#11
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A slight correction -- my earlier comment had to do with the "ram air" approach that MOPAR applied back in the 70s
There's a good write up on intake manifold design here: http://www.team-integra.net/sections...?ArticleID=466 -Bill
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Retired NASA Rocket Scientist Most famous NASA "Child" - OSIRIS-REx delivered samples from asteroid BENNU to Earth in Sept. 2023 Center Network Member #989 '92 Fully caged, 5 speed, waiting for its fully built EG33 '92 "Test Mule", 4:44 Auto, JDM 4:44 Rear Diff with Mech LSD, Tuned headers, Full one-off suspension '92(?) Laguna, 6 spd and other stuff (still at OT's place) My Locker |
#12
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Quote:
I think we have established that the original comment seems backwards. -- edit: Ah yeh beat meh. I'm not sure why it took 7 minutes to post this.
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"That which can be asserted without evidence can be dismissed without evidence." '92 Dark Teal SVX LS-L, >146,000m 3 pedals, 5 speeds., restoration underway. 2012 Honda Insight, slow but cute. |
#13
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"Ram air" (beyond a cool sticker for your Pontiac) goes way beyond the inlet to the air filter. The effect itself happens in the intake runners, as the charge pressure bounces up and down the intake runners between the intake valves and the plenum and throttle body. There is plenty of good reading available on it. Overlook the bits about inlet scoops being stuck on cars, and you'll find some pretty wild pressure wave science. The link SVXRide posted is very good.
Intake runners are tuned! I don't think they're often designed primarily out of convenience or aesthetics. It would be spectacular to see some math behind a manifold modification, and the border of insane to see a reprogramming of the IRIS valve to accommodate it! There are plenty of cars running variable manifolds now; the original Catera had a 3-stage manifold. It worked a lot like our two-stage one.
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Disclaimer: The above post is on the internet. Last edited by LetItSnow; 04-29-2008 at 07:22 AM. |
#14
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Another thing that would come into play regarding resonant frequencies is when the cams open. If you make the runners shorter or fatter, or change the velocity of the air coming in at a given rpm, you're going to have the frequencies bouncing around at different speeds than they were before, and this changes things as well.
Getting the IRIS valve to accomodate these changes would actually be one of the easiest things. You would just have to do dyno runs with and without it, before and after, blah blah blah, and just match the plots up and decide at what RPM to have it move. Then all you'd need is like an MSD window switch to activate it. This kind of thing was popular with the Mazda KL series motors for a while. Since it also has a variable resonance intake system (VRIS) people were always swapping on J-spec manifolds, or porting their own, and then just playing with the activation of the window switchs to make the most of their new power. Worked really well, actually. The only problem is that we don't have another manifold that we can just slap on. It's either a custom one-off piece, or just alot of porting on the stock one. But, I don't think that the IM is a restriction for MOST people anyway, so it's not like much of this will be done anyway.
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Jesus is the remedy 2015 Expedition EL Ecoboost Ebony Pearl '95 Subaru SVX LSi Home of the Bontrager Works 22mm rear sway bar!! |
#15
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It looks externally rather large, but in fact is pretty darn small inside. Most of the space is taken up via the IRIS crossover and by the thick cross-sectional aluminum casting. The true plenum volume is less than 1/3rd the size it needs to be for a true performance engine, IMO.
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