intake manifold beginning

[thespeedfactory]

Just so you know...everything in my build was done in the back yard. I have no access to good macnine shops, large CNC mills, flow benches, dyno, or a good fab shop. On top of that i don't speak the language nor does anyone on this island care or know to care anyting if it is not Nissan.

This is a home build. Sure I could have made a plenum with a larger volume. I didn't want to pay $40 each for velocity stacks. So I used what the Nissan engineers made for their high revving 2.8 liter...it cost $40.

Cheap and it should give me the range and power I want. I don't need a shitton of top end power as there is ABSOLUTELY no where on this tiny island to use that.

Please understand that if I was in a place where there were real tracks and machine shops, I would have done things much different.

This car and everything on it was designed for the 150M. Why else would I raised the compression, have a 4.27 LSD, smallish plenum, and soon to be nitrous, all with a HX55. Not exactly run of the mill m30 build.

While I appreciate the pretty builds, I am quite satisfied in the fact that I personnaly assembled this engine and did 96% of the work by myself with literally zero tech support or shop assistance.

It is VERY easy to make a phone call to a reputable shop and say hey can you build me a car...how much? Write the check and be done.

Thank you for the volume and flow discussion in the thread. I appreciate the information and differing viewpoints.

Meanwile I will be re-assembling my entire engine myself on Wednesday and smoking the 27X10 Hoosier asphault slicks off. I will post pics on Thurday of everything put back together.

[5mall5nail5]

speedfactory - do realize I am not trying to bash your project, its definitely different and i know its low budget and such. your racing rules/class/track are definitely unique so your window of operation is that much smaller. we just got off on what constitutes a good intake and have arrived at this conversation.

keep us posted with the results and how it works out.

PS how much cutting was needed to get a 27" tire under the E34?

[e34m535t]

Id be interested to see any pics of the assembly if you take some. I cant wait to see what your m30 can do. I'm all about bang for the buck, and it seems like your really getting things done.

Take some videos of smoking tires too.

[Keaton]

cool build,sorry to see it get filled with some useless banter. would love to see some back to back dynos

THE PLENUM

The main purpose of the plenum is to equalize the air flow to the various cylinders, but its volume and shape, as well as the shape of the bell mouths, which are the opening to the runners, are also important. Generally, a plenum volume of approximately 80% of engine capacity for naturally aspirated engines to 150% of engine capacity for turbocharged engines works best.
In terms of function, the best plenum design would have the air duct feed the center of the plenum. Unfortunately, due to space limitations and production costs, manufacturers tend to build plenums that are fed from one end, with the plenum blocked off at the other end. This results in air rushing to the far end of the plenum and creates a slight imbalance of air flow to the individual cylinders are the air will tend to flow past the first cylinder and collect at the far end of the cylinder, which is usually at the last cylinder. Consequently, the first cylinder will run slightly lean while the last cylinder will run slightly rich.
The easiest solution to this problem is to fit a second throttle body to the far end of the plenum and fit a double air filter, intake system. But this only works on naturally aspirated engines that have sufficient space for a second intake system. On supercharged and turbocharged engines this solution is not feasible and you would need to modify the plenum or fit an aftermarket intake manifold with a more efficient air flow and air distribution design. There are three things you must consider when modifying the plenum or selecting an aftermarket intake manifold.

• First, the plenum should increase in size rapidly well before the first cylinder.
• Second, the plenum can taper towards the end from after the first cylinder but it should not taper to less than 1½ times the diameter of the intake runners.
• Third, the plenum should extend well beyond the last cylinder.

INTAKE RUNNERS

As is the case with the primary exhaust pipes, the diameter and length of the intake manifold runners influence the power curve of the engine. The intake runner diameter influences the point at which peak power is reached while the intake runner length will influence the amount of power available at high and low RPM.
A larger diameter intake runner will result in improved engine breathing at high RPM and will take peak engine power to a higher RPM but will have little low RPM power. This may be good for a modified race car or a drag car, but will not be good for a turbocharged car with a large turbocharger. For a good responsive modified street car or a rally car you would want an intake manifold runner diameter that is approximately 80% the size of the intake valve diameter on a two-valve cylinder, or the same size as the intake valve diameter on a four-valve cylinder. For a high performance modified race car or a drag race car you would want an intake manifold runner diameter that is approximately 90% the size of the intake valve diameter on a two-valve cylinder, or approximately 110% the size of the intake valve diameter on a four-valve cylinder.
In terms of intake manifold runner length, a longer intake runner produces better power at high RPM, while a shorter intake runner produces better power at low PRM. Generally, an intake manifold runner that is in the region of 300-400 mm long will sustain power at high RPM but little power at low RPM while an intake manifold runner that is in the region of 200-300 mm long will start building power from low RPM but will run out of power soon after peak power is reached. But note that the intake port on the cylinder head forms part of the intake runner. Thus the intake runner length is measured from the intake valve seat to the intake runner bell mouth, and not from the end of the intake manifold.

[5mall5nail5]

yay!

[creeves328]

SpeedFactory --- Not sure if it was mentioned yet, apologies if so...Did that 6th cyl have a longer runner than the rest? Mind if I suggest, extending the plenum so that runner has the same/similar length?

Cool stuff on this topic....

Notice on 5mail5nail5's manifold, the short runners and large plenum w/TB connected to the plenum entry. In this design, the runners HAD to be shortened substantially in order to maintain vacuum off-boost. This is one of the reasons you can use such a large plenum on ITB setups, cause the vacuum chamber is NOT part of the plenum. Besides an ITB setup, you could increase engine displacement, idle speeds, or MAYBE a vacuum chamber would help. The V8 drag racers have the same problems when using a Tunnel Ram.

Already pointed out, shorter runners will change the engine's power characteristics, from an inertial tuning perspective and port velocity is slower. Snails turbo will bring port velocity back in line, inertial tuning (runners being proper length, equal length) is less of a concern with turbo-ed cars (like Snails said).

Snails, was this Tom's design?

[5mall5nail5]

Creeves - correct this is Tom's design

[e30polak]

Snails, how much did that beauty run u?

[lughed]

Originally Posted by DTRguy

But with respect to manifold volume the theory is that 100% and smaller will provide a peakier power band. Exactly why I can not exactly tell you. Closer to 125% and you get more midrange and driveability characteristics.

Thats actually backwards. 100% and larger provides more peak power and less driveability and midrange. The theory for manifold design is the larger the plenum, and shorter, larger diameter runners, the peakier the power will be. To be more definitive, a larger plenum provides higher max power while shorter, fatter runners move the power band up the rev range. But they do have adverse affects on each other as well.

[thespeedfactory]

Bit more progress. Just have to button up the throttle cable, vacuum ports, and brackets for the fuelrail.

Clean it up, grind down all the mess, and start it up.

[DTRguy]

Originally Posted by lughed

Thats actually backwards. 100% and larger provides more peak power and less driveability and midrange. The theory for manifold design is the larger the plenum, and shorter, larger diameter runners, the peakier the power will be. To be more definitive, a larger plenum provides higher max power while shorter, fatter runners move the power band up the rev range. But they do have adverse affects on each other as well.

Actually I believe you are right... I do many of my changes to stock manifold runner setups and replace the plenums. So that led me to believe what I was told to be true. In the specific applications where I have done this on VW's 1.8t engine between a stock intake plenum/runners and a modified plenum on big turbo setups. In those instances, the cars' seemed to lack power but most noticeably in low to mid power. After I would modify the intake, power would not be sacrificed in the lower RPMs (noticeably) and much more had in the midrange. Most times though the intake would be done in conjuction with new IC piping too. So again this was what I was really going for. This led me to reaffirm what I was again originally told by another tuner (that I trusted). He did however stress to me 125% so I think this what I was mislead by. Which now as I think about it makes sense. I missed something in the translations... 100% for lower end power then, 125% for fuller spectrum (mid range) and upwards to 150% for top end at the expense of the bottom end. Does this sound correct? All of my plenums manage to be almost dead on 125% of total engine volume. Probably why I never noticed any loss of bottom end (turbo helps out my systems in those ranges)... my personal Golf project made 120lb/ft of torque at 2250 rpm (the NA 16v makes that at peak!).

Thank you for the correction. I am open to (re) learn new things!

[thespeedfactory]

Manifold done.

Bolting it up Saturday night. Hopefully the increased airflow doesn't brick the tune too much. I would really like to drive it next week.

Once it is verified to work adn I tweak the tune, I will get it painted. Probably some disgusting color.

[good & tight]

Originally Posted by thespeedfactory

Manifold done.

Bolting it up Saturday night. Hopefully the increased airflow doesn't brick the tune too much. I would really like to drive it next week.

Once it is verified to work adn I tweak the tune, I will get it painted. Probably some disgusting color.

That looks really good, interested to hear how it performs. When I switched from a B34 to B35 intake and larger cam the tune was way off, it needed a lot more fuel from the increased air flow.

[s52e368]

Originally Posted by thespeedfactory

Manifold done.

Bolting it up Saturday night. Hopefully the increased airflow doesn't brick the tune too much. I would really like to drive it next week.

Once it is verified to work adn I tweak the tune, I will get it painted. Probably some disgusting color.

i commend you on your efforts, especially considering your location and lack of resources.

i mean anyone ever seen karate kid part II, nuff said.

[DrivenInnov]

Im sorry if im coming in here little late, but what is the goal with this intake?

[creeves328]

SpeedFactory, would you like a technical assessment (not opinions)? I think it may be valuable for manifold #2, which I can say you'll wanna make.

[thespeedfactory]

Sure I am always eager to gather information.

My runners are 0 deg as opposed to 9-10 deg as recommended. The runners are 9" long as opposed to a 3-4" runner on a standard short runner intake. The runners are 2.25 OD with a .25 wall thickness. The injectors are at the factory angle.

The plenum volume is about 80-85% as opposed to 100-150% displacement and supports 2 bar and 800 HP on a 2.8 twin cam revving to 9000 rpm (with about 4 inches of runner before the ITB's); I have 3.5 liter single cam and rev to 6000. The throttle body is a 90mm Q45.

The car is running a hx55 and is tuned for 1.5 bar (map) with the old manifold. Once installed the tune will be tweaked for 2.2 bar (map).I am running progressive meth injection from 17 psi to full flow at 25 psi and up. The boost comes on about 3800 and with my 4.27 LSD I am in 4th gear crossing the 150M mark. From 3800 to 5800 I make full boost. I am installing single port nitrous to activate off boost and meth is installed for the top end.

The manifold was an outside the box experiment designed based on the uniques needs of this track. How many non oem FI intake manifolds have anyone seen for the SOHC 3.5 m30? I have seen pics of one (666 fab stock photo)

I understand the norm (and Hemholtz) but I am just trying something different. If it doesnt work out, I am out $400 I save it for my m20 turbo project and I put on my other short runner intake with OEM flanges, 4-5" runners and 150% plenum volume. It is a similar setup to what Pat has installed on his S38. (he made it)

OEM manifold has 16.5 inch runners 1.55 ish OD and less than 1.5 liter of plenum. I love the low end power with the OEM manifold and I don't want to loose all of it with a short runner and huge plenum intake. If the runner length screw me I can always cut out a few inches and stitch it back up.

I know it is outside the norm. I need to make max torque and power from 4800-5800. The manifold was built to accomodate the 150M drag strip.

Everything on this car is designed for this stupid short track. If you want to see what I am talking about click here.
http://forums.bimmerforums.com/forum....php?t=1348026

[creeves328]

Good info, thank you!

I wanna stress this is only to lead a hand and not to scorn. I'd never put someone down when they dream, design or create, and you sir did all this. The next phase is of design/development is learning/understanding how to improve, which is all part of the fun.

This is what I'd suggest from your pics (from your sig link):

The runner length is probably not a problem since you're forced induction, but do make sure all runners are equal length (inertial tuned). If not, the wave could result in 1 cyl canceling another since they share a common plenum. Judging from the photos, it looks like that 6th cyl has a longer runner than the others?

The runner diameter, is that .25 wall thickness on each end meaning inner diameter is around 1.75"? Or is that .25 gauge? If ID is around 1.75", thats probably a little small for your power. But if thats .25 gauge steel, the runner ID is probably a little on the large size. Port velocity is the thing here, but since you're turbo, that may not be a real problem. Make sure the runners dimensions are similar to the head port dimensions. Also the runners should transition in shape (from round to head port) over the distance of at least a few inches.

How's smooth are the welds of your runners to the plenum runners? Is this linear or does size change at all? Make sure the size is linear and there are no bumps from the welds inside.

Where the TB mounts to the plenum, make sure there are no bumps here on the inside of the plenum. This area should also be larger than the TB butterfly itself, make sure the TB is NOT larger than the plenum's entry.

In general, making sure there are no bumps in the flow are important. They would create dimension changes, and disrupt flow (affecting velocity, increasing pressure before the bump, lowering pressure aft, creating turbulence).

The injector angle, thats good you followed the stock angle. From the pics, it looks like the injectors are not in the actual airflow? If thats right, you may not have atomization problems, as fuel would form as droplets in the opposite side of the bung. Make sure the injectors are in the direct flow.

As for the track, man thats short. With your power, please be safe!!