Lower Intake Design

David R.

Registered User
I want to modify a stock manifold to have a larger manifold volume, and internal tuned-length intake runners.

I've done a lot of research on other manifolds people have done and I see a lot of modification to the plenum and plenum flange on the manifold, but I've yet to see pictures of modification to the rest of it other than careful porting. Per suggestion I researched Randy Baker manifolds, and that's all I was seeing (that and dividers put in the plenum). Many of the older threads the pictures would not show up or they were removed altogether. I serached all the pages of "randy baker intake" and that's all I found. I did come across a manifold someone made from scratch for a whipple (I dont remember his name, but I'm sure many of you know him) that was quite impressive, but not really what I'm after or even remotely capable of.

I also read talk of moving to split port heads, which makes sense if you're already hacking up the manifold and have minimal money invested into single port heads (in my case $0.00). This obviously changes the runner cross section, which I understands puts peak torque at a higher rpm which may not be ideal with the roots style m90? (just a wild guess there).

I have also done a good bit of research on the whole ram-air effect thing. I see a lot of conflict about whether or not it applies in a forced-induction environment. As near as I can figure, and from what I've found, the concept is entirely valid on our cars. The main difference being at boost the speed of sound is faster, therefore the ideal runner length must be shorter (hey, that's exactly what we want).

Points of Inquiry:

1. If anyone has pictures of their modified manifolds, I would very much like to see what people have tried. I'm sure it's been done, but I can't find pictures anywhere. I saved a lot of links to prior discussions on the subject and general information on the concept of runner-length tuning.

2. Also, forgive me but I'm not well versed on split port heads. Are they steel? Are they economical? For a mild street build that I'm going for, it sounds like they already flow better then my back-yard porting job could offer on single-ports. I'll look into them more, but if you have ground-breaking information in favor or against them please weigh in.

3. Really any other information you think I'm missing here. I'm learning all of this online and sometimes I have no idea what else I should be considering.


Basically I'm going to build an intake, and am weighing the major factors before starting(general design, major stock problems, head choice, etc.).
 
David,

The person who made the intake manifold for the Whipple mounted in a bottom discharge configuration was Mike Tuck. The manifold was a work of art, but during testing it was found to have uneven distribution of air to cylinders. It was hoped that adding a liquid IC core into the intake would smooth out the air distribution issue, but I never heard if that worked or was even attempted. Mike still owns the car, but is currently involved with road racing his Cobra replica. Mike's SCCoA user ID Super XR7 and you can search using that name for more info about the manifold he made. This is a link to Mike's garage page that has several pictures of his car. http://www.sccoa.com/forums/garage_vehicle.php?do=view_vehicle&id=33

The biggest obstacle to building an intake manifold is the mounting location of the supercharger. I'm curious about what you are planning to do in that regard. Are you going to another type of blower ? Will discharge continue to be on top and use an air to air IC or will it be bottom discharge like the Cobra & GT500 ?

David
 
Thanks, I remember that name now. Yes, that manifold is impressive to say the least.

The biggest obstacle to building an intake manifold is the mounting location of the supercharger. I'm curious about what you are planning to do in that regard. Are you going to another type of blower ? Will discharge continue to be on top and use an air to air IC or will it be bottom discharge like the Cobra & GT500 ?

David

I'm keeping my m90. In fact, I'll be running my esm s-port-style case, just to really get the whole town talking. The reason being cost. It might not seem worth it, but everything I read points to the stock manifold being what keeps these cars from making the power one might expect. I would argue that it's a worthwhile endeavor at any power level.

My original intent was to keep the rear-entry style. I did see the inverted design you're talking about kicked around a lot in threads. I'm not opposed to the concept, as I really think it'd be a great route. The only potential hang-ups for me would be the cost of the air to water inter coolers (something I haven't researched yet, but heard talk of large dollar sums) and the over-all added complexity of that system. Either way, I will be running a ram-air hood and will have an added 1 1/2" inch to raise the blower. Obviously if inverted, the elimination of the high top will yield considerable height. If using the inverted setup, I would hack-up a gtp case, and just use it. If you look inside them, their intake port is already that of an MPX, only the outlet side lacks slightly. The other advantage I have is the fact that I have no money invested in a nice front mount IC. I know this was a deciding factor for many folks.

Another concern would be the belt geometry. With a significantly higher blower, the tensioner would have far more leverage than stock. The problem I could see happening is the tensioner "running out of range" due to the stretch of the longer belt over a greater distance from pulley to pulley. Obviously belt length is crucial, but doable. Have any of you guys running twin screws run into similar problems?

In summary, and to answer your question more directly, I'm tossing the idea around as I look into what either direction requires vs. potential results. The main restriction here is my college budget. Though game-changer that may be, I don't feel that's going to stop me, just force me to get more creative:p
 
Casey also had one of those intakes and whipples but I dont remember any ody ever using it? Who bought it?
 
nah its not the intake. the m90 and erything on the SC inlet side and the cam are the major obsticles in obtaining HP. The M90 being the ultimate anchor. Look at max hp numbers of any car running even v8's running an m90 modified or otherwise WITHOUT Nitrous and youll see.

Money and or time is best spent elswhere
 
nah its not the intake. the m90 and erything on the SC inlet side and the cam are the major obsticles in obtaining HP. The M90 being the ultimate anchor. Look at max hp numbers of any car running even v8's running an m90 modified or otherwise WITHOUT Nitrous and youll see.

Money and or time is best spent elswhere

Didn't Phil Dalke's car break 400 rwhp on an MPX? Throwing a ton of boost at a motor seems like kind-of a fool proof way to go, and twin screws and turbos alike are the way to do it. I just see a lot of people suggesting they make far less power than projected and many claim the intake is to blame. I see a lot of information that agrees with this claim (the concept of ram air through runners, and calculated plenum size), but I don't see a lot of design principles where air is dumped into a small, clunky volume of space and sucked out at random points to be called anything more than "it'll do." When I look at our intake, I just see what looks like one giant compromise of engineering neglect. I'll admit I am new to the world of motor-sports, but I just don't see any real intent behind airflow in this part.

I'll buy my valve-train after I know what my heads and intake do, everything else has pretty much been decided on.

I'm not smart enough for the funny gas, so that's out for sure. :rolleyes:
 
Casey also had one of those intakes and whipples but I dont remember any ody ever using it? Who bought it?

Interesting, was that the same exact thing, or a similar design?



Also anybody that might know this, how much room the available in the intake valley? Is there any reason I shouldn't venture slightly downward as well?
 
Thanks, I remember that name now. Yes, that manifold is impressive to say the least.



I'm keeping my m90. In fact, I'll be running my esm s-port-style case, just to really get the whole town talking. The reason being cost. It might not seem worth it, but everything I read points to the stock manifold being what keeps these cars from making the power one might expect. I would argue that it's a worthwhile endeavor at any power level.

My original intent was to keep the rear-entry style. I did see the inverted design you're talking about kicked around a lot in threads. I'm not opposed to the concept, as I really think it'd be a great route. The only potential hang-ups for me would be the cost of the air to water inter coolers (something I haven't researched yet, but heard talk of large dollar sums) and the over-all added complexity of that system. Either way, I will be running a ram-air hood and will have an added 1 1/2" inch to raise the blower. Obviously if inverted, the elimination of the high top will yield considerable height. If using the inverted setup, I would hack-up a gtp case, and just use it. If you look inside them, their intake port is already that of an MPX, only the outlet side lacks slightly. The other advantage I have is the fact that I have no money invested in a nice front mount IC. I know this was a deciding factor for many folks.

Another concern would be the belt geometry. With a significantly higher blower, the tensioner would have far more leverage than stock. The problem I could see happening is the tensioner "running out of range" due to the stretch of the longer belt over a greater distance from pulley to pulley. Obviously belt length is crucial, but doable. Have any of you guys running twin screws run into similar problems?

In summary, and to answer your question more directly, I'm tossing the idea around as I look into what either direction requires vs. potential results. The main restriction here is my college budget. Though game-changer that may be, I don't feel that's going to stop me, just force me to get more creative:p

David,

Like you, I once assumed that the pancake style intake manifold was likely a big restriction and was going to make it difficult to make decent power (over 400 rwhp). In an effort to get the most flow possible the first set of aftermarket heads I bought (made by ESM) had intake runners that were more than 1/8" wider and taller than stock and the intake manifold was modified to match. The runners were enough bigger that I couldn't use stock intake manifold gaskets and had to use hand made gaskets every time the manifold was removed. The return plenum and the portion of the intake it attaches to was also heavily modded to flow more air and to direct the air a certain way. With these heads and intake manifold I made about 360 rwhp using an MP3 blower and MP FMIC. Made another 100 rwhp with a wet nitrous kit. After adding a 1.7 AR it made 425 rwhp using the same heads, intake manifold and FMIC and another 100 rwhp when using nitrous.

After going lean one night at the track and torching the heads it was decided to build a new 4.2 motor, with new CNC large valve heads and a ported stock intake manifold that uses stock intake manifold gaskets. I was really concerned that this intake manifold and matching heads with noticeably smaller intake ports was going to be a restriction...especially now that the displacement was increased from 3.8 to 4.2. Long story made short, I was wrong because the new intake manifold and heads flowed all the extra air needed for the 4.2 motor because at the same drive ratio my boost dropped from about 21 psi to 17.5 psi and car felt weaker. I swapped to a smaller blower pulley 3.00" diameter vs. 3.25" I was using to get boost back up to about 21 psi. So that told me the stock intake manifold wasn't a restriction at 425 rwhp, but now I was spinning the blower way too fast to keep up with the increased displacement. I also ditched the nitrous system because I was tired of breaking stuff or having the system malfunction half of the times I used it.

So shortly afterward I upgraded to a 2.3 Whipple and continued to use a ported stock manifold, but with a little trick machine work done to the rear opening to tilt the return plenum towards the firewall to allow for a larger inlet plenum to feed the larger Whipple supercharger. Once again I was concerned that this pancake style squished intake manifold that was only designed to support about 230 HP was going to be an obstacle to making more power. I was wrong again, because right off the bat it made 485 rwhp at slightly less boost than the 1.7 was at to make 425. After adding a larger intake pipe (4.0") with slotted MAF and upgrading from an 85mm TB to a 95mm TB, I was making too much boost and had to slow the blower down to get it to a more reasonable 22 PSI and made 499.6 rwhp in average conditions. That's where it's at right now, and the ported stock intake manifold is still not what is holding me back from making more power...it's actually the MP FMIC not being big enough to cool the intake charge. With a larger core on the FMIC I'm confident it will make 550 rwhp using the same ported stock intake manifold.

So if you are planning to stay with any of the superchargers based on the eaton M90 or a top discharge AR, TVS, KB or Whipple....I would not be too concerned about the stock intake manifold.

David
 
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David,

That’s really helpful. So is that about the ideal power level for your displacement and power adder, or is that far too loaded a question to even consider? I really don’t have near the experience to answer that myself, all I know is ~500 wheel horse is a ton of power. :D

How even is your tune from cylinder to cylinder? I assume great lengths have been taken to ensure your heads and intake flow all relatively close to one another. Ideally then, air distribution among the cylinders would be as even as your flow numbers, but obviously things change in practice. My question is do your spark plugs agree with your flow numbers, and if not, how much do they disagree? Are you able to achieve a fairly even AFR in each cylinder, thereby maximizing the use of the air consumed? Basically is the problem of uneven air distribution in the stock unit solved with proper porting, or is it a fundamental problem with the manifold.

From what you’re saying, big power is absolutely possible on a stock-style, slightly modified manifold. And furthermore, the intake keeps up at all power levels in-between. That clears things up for me. However I am still curious if there is anything to be gained from inducing ram-air by creating runner tubes. I am not saying the stock manifold is inadequate (I thought it was, but clearly it isn’t based on your results), but I still think there is possibly something to be gained here. Difficult? Absolutely. Negligible at best? Most likely. My understanding of the whole theory could quite possibly be entirely wrong, so that’s a main point of inquiry.

I really appreciate the input, you’re probably talking me out of a major waste of time.
 
David,

That’s really helpful. So is that about the ideal power level for your displacement and power adder, or is that far too loaded a question to even consider? I really don’t have near the experience to answer that myself, all I know is ~500 wheel horse is a ton of power. :D

How even is your tune from cylinder to cylinder? I assume great lengths have been taken to ensure your heads and intake flow all relatively close to one another. Ideally then, air distribution among the cylinders would be as even as your flow numbers, but obviously things change in practice. My question is do your spark plugs agree with your flow numbers, and if not, how much do they disagree? Are you able to achieve a fairly even AFR in each cylinder, thereby maximizing the use of the air consumed? Basically is the problem of uneven air distribution in the stock unit solved with proper porting, or is it a fundamental problem with the manifold.

From what you’re saying, big power is absolutely possible on a stock-style, slightly modified manifold. And furthermore, the intake keeps up at all power levels in-between. That clears things up for me. However I am still curious if there is anything to be gained from inducing ram-air by creating runner tubes. I am not saying the stock manifold is inadequate (I thought it was, but clearly it isn’t based on your results), but I still think there is possibly something to be gained here. Difficult? Absolutely. Negligible at best? Most likely. My understanding of the whole theory could quite possibly be entirely wrong, so that’s a main point of inquiry.

I really appreciate the input, you’re probably talking me out of a major waste of time.

David,

When I made the blower swap from 1.7 AR to 2.3 Whipple the goal was 450 rwhp and be able to run 11.5s without nitrous, so I'm pretty happy with it being right at 500 rwhp and running high 10s. I could squeeze more power from the combo if I had a bigger intercooler but not really concerned about it enough to make a custom MP front mount with 4" thick core vs. the 3" standard core. My transmission isn't the most efficient either. With a lock up converter I could add about 5% more rwhp or with a manual trans (plus 10% rwhp).

My street tune is fairly conservative, and my race tune is the same except for 3 more degrees of WOT timing and lower temps for cooling fans to come on. I use a dual nozzle methanol injection system full time to assist with intake charge cooling and to increase air fuel ratio. When using the race tune I also add about 3 gallons of C16 race gas to a half tank of 93 octane, just for added protection from detonation.

I don't have the ability to tell exactly what each cylinder is doing, just right bank and left bank, and tune is based on the leanest bank. One bank is about .2 -.3 leaner than the other. Since we don't have the ability to independently adjust fuel to each cylinder, one bank ends up running richer than ideal by about .2-.3 . So you end up with around 11.6:1 on one bank and 11.4:1 on the other. Plugs all look about the same, and I only change them if one gets fouled like at the 2014 Shootout.

I have no idea how you would even do ram air tubes inside of the pancake style manifold, so I can't really comment on how that might work. My guess, is not very well and possibly worse than stock. In the past people have cut open the stock manifolds and removed the triangle shaped wedge in the center and raised the top of the manifold and then welded it back together for more volume and greater flow. Not saying that it doesn't work, but I have yet to see any measurable results that would make me believe it was worth doing. I think some people assumed that the triangle wedge inside the manifold was for support and could be removed for more plenum volume, without creating any issues. I believe the wedge was actually put there to distribute air to all cylinders more evenly.

If you want to build a more efficient intake manifold, take a look at what Corey (aka Neverfastenough) has built. It can't be used with the stock style supercharger and that is why I asked about your plans up front.

David

PS: I'm not an expert on this topic, just a guy who has been around a while and seen a lot of stuff tried over the years.
 
That is excellent info! I was thinking about modifying a lower intake manifold, but had thought against it. I had, however, just finished off a ported and polished return plenum where i'd opened up the port to the manifold so that it matched the manifold opening, based on the dirt/ crud area where it is mismatched. There's some pretty rough casting in the return plenum (far worse than in the intake plenum), and based on the relatively smaller, oval shaped area where it funnels down into the intake manifold, i'd say that it looks to be very restrictive, but if the casting is removed and the area massaged, it should be improved somewhat. It also gets pretty dirty in there, too, because it looks as though some of the oil/ blowby that goes through the PCV (and the intercooler) gets a bit baked onto the metal, almost. When I was grinding away the casting layer, there was definetely the smell of oil happening. Before I put any of my modified stuff back on my SC, i'm putting an air/ oil separator on the car.

Stock used:

stockusedreturnplenumportintolowerintakemanifold.JPG

My ported/ polished version:

returnplenumportintomanifoldportedandpolished.JPG
 
Hate to be the bearer of bad news, but you guys are wasting your time and can very easily cause more harm than good. Intake manifold engineering is way over your heads and you should stick to things that you understand. :) I don't mean that to be arrogant, its just a fact.

If you follow the leads you will find on this website about porting the stock intake manifold you will end up over feeding the rear cylinders and starving the front ones. I have flowed the manifold both as a unit and by individual ports. There are weak ones and there are strong ones but it's not what you might probably think so without a flow bench you are again, wasting your time. Porting the manifold will make it worse, not better. Ford made sure that the stock manifold flowed evenly, if not massively, and even is more important than massive. The only porting that should be done to the manifold is to port match the individual cylinders, but even that if done wrong (99% of the home ported examples I've seen are wrong and I've seen a bunch) is worse than nothing at all.

Most people lack the basic understanding of how the air moves and behaves in a pressurized system and even more so when pressurized by a positive displacement blower. I'm not going to teach everything I know here in a simple post - and hell I don't know everything! - but I will say that making any meaningful improvements requires that you first understand the fluid dynamics of the system and how that impacts combustion. For example, by far the biggest restriction in the system is the intercooler, not the stock SC top or the return plenum or anything else. That's right, the intercooler is the weakest link, yet at 380rwhp going from a double IC to a MPFMIC netted exactly -0- HP on a dyno. Ponder that for awhile.....
 
That's right, the intercooler is the weakest link, yet at 380rwhp going from a double IC to a MPFMIC netted exactly -0- HP on a dyno. Ponder that for awhile.....

If the air passes too fast through the intercooler, it does not allow for heat transfer.
 
well I will be putting a stock intake back on the motor while it's getting redone. take the ported one off that I bought on here.
thanks for the info dave.
 
David, I looked up neverfastenough's profile. There isnt a great picture there to be referenced but I can see what youre talking about. If I planned on going turbo, I would just start from scratch like he looks to have done, and would probably use spit port heads (I hear those can flow way better then our stock ones would, doesn't matter here though).

My main goal is not to improve flow in the manifold, but rather to introduce the effect of ram air. As Dave said evenness is crutial so, so that will be the focus of my design after determining necessary dimensions for desired output (i.e. runner cross-section, runner length, plenum volume, anything else I don't know about yet).

I just asked about the balance from cylinder to cylinder because I was reading a lot of complaints on that, but it sounds like yours is pretty dang close to even. I thought maybe the pancake style of the manifold would create more imbalance than could be overcome by proper porting, but that's all but debunked by your afr numbers and the fact that your plugs all match. Good info, thanks for the input!


Dave, I completely agree, without a flow-bench almost any porting anywhere is useless. I read your thread about porting the stock manifold, and quickly realized how easily well-intended porting can have dramatic negative effects on flow. I'm going to be building my own flow-bench for this purpose. It is in early planning stage, but there is quite a bit of information out there on the subject. It certainly wont be professional, nor will it be calibrated very well but all I need is a consistent tool in a recreate-able environment. I'm still researching what measurements are relevant in a flow-bench system so I can have the proper sensors and model data on my oscilloscope or something.

I'm not going to teach everything I know here in a simple post - and hell I don't know everything! - but I will say that making any meaningful improvements requires that you first understand the fluid dynamics of the system and how that impacts combustion.

I'm learning a lot through research and sitting in the back of classes I'm not enrolled in at school.:cool: I started this thread to learn what else I need to go and learn, so do you have any suggestions on what or where I might look (major concepts to study, literature, reputable websites, etc.)? Don't get me wrong, I know I'm not gonna do a bunch of internet research be able and whip out this holy grail of an intake manifold. I'm actually just making the most complicated door stop of all time. :rolleyes: I'm not interested in making my car faster nearly as much as I am in learning everything I can about how the motor works; I'm having fun here playing speedshop with my other projects.

While I have your attention, do you know off-hand the stock duration for the intake valve (92 5-speed if that matters)?


1fstbrd, are you sure that line of dirt wasn't just from the gasket, and that the manifold doesn't already match? If not, I'll be port-matching the return plenum as well. Yours looks really nice--great job!
 
1fstbrd, are you sure that line of dirt wasn't just from the gasket, and that the manifold doesn't already match? If not, I'll be port-matching the return plenum as well. Yours looks really nice--great job!

Thanks! I couldn't honestly tell you if that line of dirt was blowby/ oil/ dirt through the system or whether it was the gasket......others would have to match it up to see, but when I get my car out of storage and do the modifications, i'll use some prussian blue dye to see where it contacts. Probably would have been a better idea to have done that in the first place, but I wanted to have the things done before I did the modifications and had the car in the infirmary for a little bit.
 
Awesome information on the manifolds, Dave. You've saved me a ton of work, because I was really thinking about doing a ported manifold. The time you've spent on these cars has helped people out here, immensely.

For example, by far the biggest restriction in the system is the intercooler, not the stock SC top or the return plenum or anything else. That's right, the intercooler is the weakest link, yet at 380rwhp going from a double IC to a MPFMIC netted exactly -0- HP on a dyno. Ponder that for awhile.....

That's interesting. Roadhawg's idea that if air flows too freely through the intercooler system, that it doesn't properly heat transfer the air, sounds like it's correct. Would a parallel to a high flow water pump or high flow oil pump be correct, in that things are flowing too quickly for those systems to really do their job?

On a dyno, i'm also wondering if because airflow isn't the same (unless fans are being used?) as having a moving car, would that also negate some of the intercooler's effectiveness for a dyno reading? I mention this because even something like the A/C condenser being in front of the intercooler seems to reduce the intercooler's effectiveness. After removing my condenser, i'd noticed that the temp gauge seemed to read a little on the cooler side, so it seemed to help the radiator out, too.
 
I'm not suggesting that porting the intake manifold is not useful, just that most people don't know how to do it right and end up screwing things up.

As for the return plenum not matching the manifold, that is by design. All intake components are done that way and port matching it does nothing when going from a smaller part to a larger one. I've flowed all the components of the entire intake system individually and they all flow enough for the power to be supported in this discussion.

I think you missed my meaning with regards to the intercooler. I did not suggest that a double intercooler is as efficient or as desirable as a front mount, I just pointed out that from a flow standpoint there is nothing to be gained by dramatically increasing the flow capacity by going to a larger intercooler. I left it to you to make the connection that increasing the flow of one part of the intake system (say a return plenum) by possibly a few cfm (maybe) compared to increasing the flow through the intercooler (by like 100cfm) resulted in no measurable power gain. Think about that for awhile.

Like I said, understanding some fluid dynamics is key to making an improvement to these systems. I have a flow bench and at least a small bit of understanding regarding the dynamics I mentioned, and I have decided that the best place for me to invest my time and money is in a better supercharger. It's all about gain vs. dollar, and even at $4000+, the supercharger is the best place (on the external part of the motor) to pick up hp in a value for your dollar aspect.

Inside the engine is a whole different topic. ;)
 
I
I think you missed my meaning with regards to the intercooler. I did not suggest that a double intercooler is as efficient or as desirable as a front mount, I just pointed out that from a flow standpoint there is nothing to be gained by dramatically increasing the flow capacity by going to a larger intercooler. I left it to you to make the connection that increasing the flow of one part of the intake system (say a return plenum) by possibly a few cfm (maybe) compared to increasing the flow through the intercooler (by like 100cfm) resulted in no measurable power gain. Think about that for awhile.

I'm digging the Socratic method you're using.

So you're saying that making one part of the intake system outflow the rest makes no difference and that the weakest link is the part to be modified first? And furthermore, that since the stock intake already flows very well that it should be of the last to be modified and that it would be useless to do so until most all the other parts of the intake system are first upgraded?

I'm not really talking about flow. Well, at first that was a main point of discussion but I realize now that the stock manifold is plenty sufficient for my purposes, and with only minor modification (flow pun, get 'em while they last :D) the manifold is sufficient to support quite large power levels. I got that now, and thank you guys for helping me understand that. What I am still talking about however, and what provoked my interest in the first place is the ram-air or wave theory part of an intake. There are several names for it, but I mean to refer to the pressure waves associated with the closing and opening of the intake valve, and the volumetric efficiency to be gained by this at specific rpms. I'm still researching (as we speak) but I've yet to find information related to the subject on anything but natural aspiration.

Are you even further suggesting that under boost, this phenomenon becomes irrelevant?
 
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