RX-Heven

iTrader: (1)

Has anyone done this? I thought I remembered someone doing this so I tried searching and but came up empty.

Anyways, I'm thinking about cutting the plenum in half lengthwise, gutting the dividers/diverters in the plenum and then stitching it back together. Then send it out to get Extrude Honed.

What are peoples educated guesses of any benefits or drawbacks to doing this (minus the Extrude Hone)?
My guess is that it would definately flow more in the top end but suffer down low, especially in drivability.

mcfly

is the stock manifold not good enough?

I have been reading 800 hp is possible with the stock.


regardless i am still interested in this.

onefastrx7turbo

iTrader: (5)

I have a manifold like this.

RX-Heven

iTrader: (1)

Well, what are your thoughts on this?

Do you have any before and after results to compare to?

How is drivability at low rpm and your top end?

Any pics?

TT_Rex_7

There's a thread about this by Dragon over on nopistons.

-Alex

rarson

IMO it's not. Partly because they added an extra rotor and kept the TB/intake side the same. If you look at the gains some of the N/A 20B's have shown by going to a custom intake setup, just imagine the difference on top of that some boost would make.

It's like back in the old days of turbocharging, head work was considered unnecessary. Why spend time on the head when you can just up the boost? Well, hopefully the error in that logic is by now supremely apparent.

onefastrx7turbo

iTrader: (5)

Finally snapped a few pics...Its a work in progress but you get the idea.

heres another view

another

stock for reference

mcfly

wow, i just realized how ugly the upper manifold is inside:P

will be gutting that now

RX-Heven

iTrader: (1)

Thanks for the pics.


Why did you cut up the tb inlet? Is that for a larger single plate tb?
Wouldn't it have been easier and better to just weld on a whole new flange instead?

onefastrx7turbo

iTrader: (5)

Dave, yea im gonna be welding the flange adaptor onto that. Im using the Q45 single plate TB....

RX-Heven

iTrader: (1)

How big is the Q45 tb?

onefastrx7turbo

iTrader: (5)

if i remember, its 90mm

mcfly

yes 90mm 100%

RX-Heven

iTrader: (1)

90mm (3.5") seems awfully big.
I can't imagine tuning or driving under part throttle would be much fun.

I'm going to go with a big bore fd tb. The overall areas are just about the same plus you have the nice and small primary for part throttle applications and ease of installation onto the uim. The GReddy tb elbow can easily be modified to accomodate 3.5" ic tubing without becoming a choke point.

90mm tb Area ~ 9.861 square inches
Stock fd tb Area ~ 8.520 square inches

iirc, the big bore fd tb adds just over 1.25 square inches to the overall area. Forgot exactly what Brian at Rotorsports told me it was. Not the cheapest route though at ~$500.

t-von

iTrader: (8)

Depends on how fast your turbo spools! If your turbo is laggy to the point that it isn't going to build boost till the mid rpm ranges, you will notice weaker lower rpm throttle response. Gutting the manifold will lower the intake velocity in the lower rpm's which will in fact slow the amount of air that is drawn into the combustion chambers. The less fuel/air you have drawn in, the less bang you will have and in turn the less torque output you will get. This happens because you will now have air being drawn into the combustion chamber from both primary and secondary ports at the same time all the time. In the really low rpm ranges, a turbo charged engine is just a suction vacuum. So basically your just lowering the engines ability to effectively draw in air efficiently in the lower rpm range. You will however get an increase in the upper ranges due to less restriction the the intake path.

Now since this is on a 20b, you may not notice a huge difference with the extra rotor and the engines already improved air pumping ability but, a 13b will lose a significant noticable amount of low end power having 50% smaller displacement.

TT_Rex_7

If you guys would take a moment out and head over to nopistons.com, you'll find a thread posted by Dragon. You'll notice he gutted his UIM, and is running a 90mm TB as well. FWIW, he's having low RPM surging/bucking with such a large TB. IIRC, it's something along the lines of 3-5% throttle at 55mph.

-Alex

mcfly

that sounds like an identical problem i had with my gtr when the tps was mis alligned:P

but thats a pos nissan

CMonakar

Keep in mind that Dragon aka Chris made two changes. First, he gutted the inside of the plenum so that all six runners were connected to a single chamber. Second, he switched the throttle body. Based on the conversations I have had with him I got the sense that he believes the TB is what hurt the driveability.

TT_Rex_7

And as we discussed, how the UIM is gutted probably plays a roll as well. To know for sure, you'd have to try a custom plenum. The volume of the gutted UIM, plus how the air flows directly into the two center runners is probably to blame as well.

Either way, I'd say 90mm is to large.

-Alex

mcfly

would it be benificial to weld in a spliter or would that just be going back on all the work you did to gut it?

t-von

iTrader: (8)

The single throttle body hurt some but not as much as the modified manifold. There is a reason the stock 3 butterfly throttle body has a delayed opening of the secondary ports. At partial throttle only the primary ports are open keeping the intake velocity high. The stock throttle body and UIM are designed to work together. You will have a similar problem even if you modify the UIM and leave the TB stock. Regardless of what TB is used, you will have to engineer the runners to stay separate at low rpm's to have better drivability.

Guys you need to understand the design elements of the stock manifolds. 13b and 20b are all designed with the same principles in mind. I could go out to my Fd or Fc right now and adjust the stock TB so that the primary & secondary throttle plates open at the same time (eliminating the delay) and experience similar low rpm buckling.

onefastrx7turbo

iTrader: (5)

you are right. However, Im not building the car for low rpm driveability or streetability. It will be used mostly for racing. Im hoping the bucking isnt real bad...

TT_Rex_7

I've gone through some extensive conversations with him, and we are both aware of the primary butter fly valve opening first at low throttle positions. However, your belief of keeping the primarys separate from the secondarys is incorrect. However, your are 100% correct on the fact that the UIM and TB were designed together, and that the modified UIM is hurting things as well.

For starters, does anyone know the volume of the new gutted "plenum?" If that isn't sized properly, you'll run into problems from the start.

Aside from that, does everyone notice how the TB directs air right into the center runners? I'm willing to bet at low throttle, the air isn't even close to distributed evenly! I would say this is a common problem with TB's directed straight into the center runners. Most people apply an angle like this \_/, which helps, but is far from the best designed plenum, IMO. By gutting the UIM, it's not helping to direct the air one damn bit! So, IMO, don't gut the UIM. If you want to try and solve the UIM problem, either build a custom one, or cut the gutted part of the UIM off, and weld on a custom plenum. My personal preference of a proper plenum is something along the lines of this:

[img]https://www.rx7club.com/attachment.p...hmentid=189285[/img]

Very true, however, a large part of this issue is TB size. A 90mm TB is TO LARGE! PERIOD! If you go adjust the stock TB so they all open at the same time, how much air do you think is flowing? It's darn well enough to compare to a large single TB. The primary butter fly valve is 45mm, and I *think* the two secondary butter fly valves are 55mm or 65mm each! That's quite a bit of air flow!

Between converstations I've had with Rich (Auto Illusions), CMonakar, and Guru Motorsports, we've all came to the same conclusion...go with a 70-80mm single TB. And for the best results, a ITB setup. Then, if you want to take it a step further, open the primary TB's before the secondarys on a ITB setup.

FWIW, Rich is going with a 90mm TB, but he has a totally diffrent beast from everyone else. Another reason he's using it is for the drive-by-wire feature on the TB. So, unless you plan on running 1000+ hp, and have a stand alone that can support drive-by-wire, go with a smaller TB.

Besides all of that, the TB isn't what's hurting the performance. It's simply the design of the UIM. (As well as the LIM) If you don't have the money to purchase a new TB, or an ITB setup, do what t-von suggested, make a custom UIM, and keep the runners seperate, and use the stock TB. Porting the TB would help as well. However, you'll need to get some larger butter fly valves. Another thing you could do while your at it, is smooth out the "bridge" that seperates the 3 butter fly valves. Just make sure that when your done, the bridge doesn't come to a point, and has a small radius on it!

-Alex

CCarlisi

You might be able to improve air flow by adding the hardtop

TT_Rex_7

A large TB isn't going to help you a damn bit! The stock TB will flow more than a 90mm TB, and without low RPM issues! A large TB, and gutted UIM is HURTING your performance!! I'm almost willing to bet the volume of the gutted area (plenum) isn't the proper volume. Nor does the gutted area direct airflow properly!

Remember, the stock UIM does a horrible job of directing air flow to the ports, and by gutting it, you still have the SAME issue!

-Alex