When does the UIM, LIM & TB become a restriction?
 

Just as the title says, at what point does the UIM, LIM, or TB become a restriction in making power? I have been reading the thread about the GroundZero LIM and was wondering about this.

Is it a matter of "port matching" or is it much more than that? My car will soon be running 20 psi occasionally, and I was curious if having something done to either the UIM, LIM, or TB would be beneficial at those boost levels.

Thanks.

bump

I dunno about the LIM, but I'm fairly certain that the UIM causes flow restriction at higher rpms, around 6250 - 6500 rpm. And since hp = torque * rpm / 5252, getting restriction at this higher rpm is not only gonna hurt your torque curve, it's gonna rob ya of max hp. Thus, the drop in our torque curves. Demetrious, on the other hand, uses a different UIM, which I believe plays an important part in his nice torque curve...

Umm...how exactly are you "fairly certain that the UIM causes flow restriction at around 6250-6500 rpm"?

Cuz I'm a super genius :p: No, really, cuz I've talked to some "big dawgs" who have told me this, including Demetrious himself. Ask Stephen (SPOautos). He'll confirm it for ya too. A couple of us have been going in a circle discussing exactly what is limiting the hp potential of the FD w/ stock twins (other than simply reliability lol)

Because they're guessing and not one of them has the sense to take their intake manifold to a shop with a flow bench to find out what it'll actually flow.

Seriously if you're that concerned with it, just take it some place with a flow bench, and have it tested. If you don't think it's flowing enough, port, polish, extrude hone it and your all set. You could get the new Ground Zero LIM, and a J-Tech UIM, or switch to an RE manifold if you feel like spending more money and want to get creative. Might as well upgrade the throttle body while you're at it.

Generally speaking - a forced induction rotary engine is not going to have to worry about 'flow' all that much. Sure, one could increase the sizes of all the aforementioned componenents but...what good does that do? It is not like the turbos can't ram enough air into the damned thing already.

Yes, I agree that theoretically there has to be some point where size would make a difference (keep your thoughts clean now...) but I don't even a widely modified rotary is going to start losing much performance....unless you were trying to get like 1000 hp out of one or something.

there is no dobut that a custom, goal specific manifold upper and lower would be better. how much? dont know. the stocker will have some compromises due to the fact it was for the street and had 255hp in mind.

I know of a couple of shops that routinely port/extrude hone the UIM when installing a ported engine and a single, etc. But like you and Jimlab have said, I don't think I've ever seen actual flow bench testing results. But I personally give ppl like Dee the benefit of the doubt that they know what they're doing...

Bump for more discussion. Anyone have numbers from either porting or replacing?

I measured 30" h20 (1 psi drop) from the elbo before the TB, to the bottom of the uim where the pressure nipples are. This was at 7500 rpm and 9-10 psi boost, with the secondary valves in place.

Interesting, however CFM through the intake runners is what would tell you whether there's a restriction or not at a given pressure level. Is the pressure drop still 1 psi at 15 psi? 20 psi? 25 psi? Measuring the volume of air getting through tells you when peak flow has been reached.

If you calculate the volume of air that the turbo(s) are capable of producing at a given boost level and compare it to the maximum flow of the intake after being tested on a flow bench, you'll find out whether or not the intake represents a restriction or not.

Note how flow pressure rises as the port becomes a restriction in the chart below. Also, note how flow (Corr CFM) tapers off as the port becomes a restriction. This is what we're looking for here.

http://home.gci.net/~jimlab/images/E.../Head_flow.jpg

It will benefit you when your making over 550rwhp with a large single turbo, but mainly for drag racing purposes. Your powerband will extend quite a bit. Demetrios carries his power through 9500rpms with just a street port.

I'll be dynoing my CYM in the next couple weeks. At first Demetrios and I will tune it for 15psi on pump. Gonna wait till spring for the race gas and 33psi. But in any case I'll post my results as I have the J-Tech upper and lower intake manifold and 80mm accufab throttle body.

The Ground Zero LIM is probably designed to fix the flow imbalance between the front and rear 2ndary runners in the 3rd gen manifold.

I have been told it has been measured at up to 12% difference.

Does the front or the rear rotor usually let go on a 3rd gen that detonated...

Jim,

For a simple orifice, 2x the flow means 4x the pressure drop.

Yes, it would be best to flow-bench test the manifolds and TB at true cfms. But with some correction for gross changes in flow area, installing nipples and measuring drops in the intake path on a mustang dyno would allow you to quickly find restrictions. 2 psi less drop in the intake system is 2 psi less at the turbo, and 3+ less at the exh manifold.

Your data shows flow at a constant 1 psi drop, as I understand it. I guess you know if it's port or valve diameter limited ... can't tell from just this data sheet. Either way, it doesn't really tell how much the ports will flow, since the max flow achieved will be proportional to the sq-rt of the pressure drop used in the test. It will clearly show how one head does compared to another tested at 28".

The "flow pressure" does not rise as the port becomes restrictive. As I see it, it is directly proportional to flow, and is likely a pitot type press meas't in the flow stream.

You know, it's funny that Mazda produced an intake manifold with a significant flow imbalance for nearly 10 years and the first I heard about it was when someone made a replacement... :p:

I've yet to see figures that back their claims.

The first I "heard" of it was a forum member whining about his ports not matching as delivered from a prominent builder. I had enough respect for the builder that the first thing that popped into my head was perhaps it was done for a reason.

I'm following you there. But has anyone ever calculated just what volume of air the stock twins are capable of producing? AFAIK, it's dead true that the stock exhaust manifold is a restriction for the stock twins (which I believe limits it to right about 420hp), but I haven't ever read of someone improving this and finding out the true max volume capability of the stock twins, not their related plumbing... (Word on the street is that Brian is working on a high-flow exhaust manifold, so who knows, maybe someone will finally able to max out the stock twins!)

This goes along w/ what I wrote above. Not to say that the aftermarket scene hasn't made great products for the FD, but to me it seems that some crucial main steps were never taken in the past DECADE (which is a LONG time), and we're just now starting to address these issues (like the stock manifold, UIM & LIM restriction, etc)

Ditto...

Maybe it's because the car hasn't really been sold in any real numbers for over a DECADE, so no aftermarket manufacturer would be willing to spend the money to develop a product that would have LITTLE RETURN on their investment relative to something for any number of other more popular cars...

Getting a max cfm rating doesnt tell you about pressure wave tuning and what rpm range the manifold is tuned for or most efficient at.

Um, OK. Thanks for showing up Stephen, next time bring some relevant information with you.

It is relevant, you just want to make light of it since you didnt think of it....pretty common with you.

Next you'll be telling us that manifolds arent pressure wave tuned and more efficient at certain rpms....and that it doesnt matter for turbo car...or something to that effect I'm sure

No, it's not relevant. Would you like to explain pressure wave tuning and how it applies to an intake manifold with FIXED runner lengths? There's nothing you can do to change the wave tuning of an intake manifold without increasing or decreasing runner length, and that's not what we're talking about here anyway.

Kento, explain that for me plz? Are you saying that initially it sold well, but it just hasn't been selling well ever since? Cuz in that case, I'd think there woulda been a monster of an aftermarket market for the FD when it just sold, and these issues woulda been addressed, no?

If that's not what you're saying, and you're saying that it's just now starting to sell a lot, you think the FD aftermarket product market is at it's height right now? I find that interesting...I couldn't tell you myself, since I've only owned the car for 2 years.

If your point was neither of these, well, my bad lol. Explain :p: