Exhaust design

[shnazzle]

Been thinking a lot about exhaust design for the '2 the past while, and spurred on even further by a chat with another member last night and a topic on here on stg2 cams.

I know there is no direct answer for this due to the number of parameters but...

Is the stock exhaust manifold design aimed at a combination of high-end power with a low torque peak?
Being a 4-cyl, is there any benefit to be had from an equal-length manifold, 4 to 1 collector? Doesn't seem so.

Currently the pipe lengths are similar across the two "banks" Toyota has designed (cyl 1/4 and 2/3), but the pipes in each bank are not equal.
Cyl 1 primary is very short, but cyl 4 has to go all the way from one side to the other. This can't be the best solution can it?! THis almost requires the valve timing to be slightly off between cylinders 1/4 and 2/3 doesn't it?

This pretty much excludes the stock manifold, Toyosport, CHE or any of the like that copy the design, from being efficient in pulling exhaust out and sucking air in.

So that leaves the designs of the Zero manifold and PPE;
Zero: equal length, better-flowing pipes into two collectors, one for each bank, with o2 sensors in each bank. Obviously without the obstruction of the pre-cats or chambers.
PPE: longer, thinner equal length pipes into one collector. Complete free flow. No resistance until it hits the main cat. Faster flowing, but more resistance lower down, and it seems to be aimed at high-rpm increases. Basically..2zz or 1zz+cams. And would 1zz+cam+ppe would run predictably bad for flow and o2-reading reasons. IT's just not in keeping with the design of the engine.

Zero is in keeping with the stock fueling/o2 readings. But, the flow in each cylinder should be much more equal and smoother.
PPE: Seems to be pretty unsuitable for the 1zz MR2 running on stock ECU as its o2 sensor positioning (once bodged in) can  never match that of stock ECU readings.

Am I right in thinking that for tuning a stock 1zz with perhaps a piggyback, the best you can do is get a Zero manifold and improve flow further down the line by a 200 cell cat and free flowing exhaust?

It seems that this way, you're beefing up the mid-range torque while allowing for higher rpm power to build.


Now to add a further complication; if you have this setup and then add a turbo.
You now have a much much shorter manifold (basically just a collector with little stubs   s:D s:D  ). So the whole manifold point is moot, but you need to increase  your downstream exhaust pipe size and flow. That's easy.

But what about supercharger? Now we need a manifold that's in keeping with the engine characteristics of the '2, but with a much higher flow at all revs.

[jvanzyl]

Somebody has been at the Red Bull early haven't they!

[lamcote]

I would agree with your post entirely. I believe that the Zero manifold with an upgraded cat and cat back exhaust is the best option for both natural aspiration and supercharged options. The standard cat seems to include a serious restriction in the inlet pipe so if I was going with a Zero manifold I would definitely be looking to change the cat.
You could argue that the standard manifold, having two pairs of different length pipes,  is actually good because of the variable cam timing on the 1zz ie one pair will match the cam timing at one point and the other pair will benefit at different cam timing, but the overall design doesn't look particularly marvellous especially with the pre cat chambers and the pipes are probably too short.
I agree the PPE seems to be for a very racy tune and not great for the road.
My vote is Zero manifold, sports cat and decent exhaust (maybe Flowmaster or Vortex?), my guess is that would give a standard car an extra 10-12bhp as the 1zz seems to be mainly exhaust limited, and there seems very little to be gained on the inlet side.

[cptspaulding]

How about a decat pipe for [strike:1cghda6k]between MOTs, er,[/strike:1cghda6k] track days

[shnazzle]

Somebody has been at the Red Bull early haven't they!

11am is not early!  s:) s:)  And besides these thoughts have been brewing for ages. Since my cat is knacked, I've wondered for a while whether it's worth putting a 200 cell in. Or whether I'd be hurting low-end torque with the stock manifold.

I would agree with your post entirely. I believe that the Zero manifold with an upgraded cat and cat back exhaust is the best option for both natural aspiration and supercharged options. The standard cat seems to include a serious restriction in the inlet pipe so if I was going with a Zero manifold I would definitely be looking to change the cat.  

Sweet. Can you elaborate on why you think it's best for the SC as well? That's where I have big question marks

You could argue that the standard manifold, having two pairs of different length pipes,  is actually good because of the variable cam timing on the 1zz

Very good point but still a bit inefficient it seems. I'm curious if Toyota has a reasoning behind this other than space/cost and cylinder firing order.

My vote is Zero manifold, sports cat and decent exhaust (maybe Flowmaster or Vortex?), my guess is that would give a standard car an extra 10-12bhp as the 1zz seems to be mainly exhaust limited, and there seems very little to be gained on the inlet side.

Agree. I guess I know what I'll be replacing my de-pre-cat stock mani with then  s:) s:) . I'll not bother putting a stock cat in. Might as well put a 200 in for now. Might suffer a bit in the short term until I get the zero mani or something of similar design.

[lamcote]

Regarding the supercharger, I've never seen anything to suggest that a supercharged engine needs anything different to a naturally aspirated engine, other than the pipe diameter if it is really high boost. The pipe length is related to cam spec as you say so low boost supercharging should have little impact compared to the naturally aspirated requirements.
I would think the standard manifold is very much designed down to a cost/ease of manufacture.
I am very interested in the comments elsewhere about losing mid range power with decats etc. There seems no logical reason for this unless they are installing drainpipe sized replacement pipes?
(NB if you look the decat issue up and you see anyone saying engines need back pressure, completely disregard everything they say, that's complete rubbish.)

[shnazzle]

Regarding the supercharger, I've never seen anything to suggest that a supercharged engine needs anything different to a naturally aspirated engine, other than the pipe diameter if it is really high boost. The pipe length is related to cam spec as you say so low boost supercharging should have little impact compared to the naturally aspirated requirements.
I would think the standard manifold is very much designed down to a cost/ease of manufacture.
I am very interested in the comments elsewhere about losing mid range power with decats etc. There seems no logical reason for this unless they are installing drainpipe sized replacement pipes?
(NB if you look the decat issue up and you see anyone saying engines need back pressure, completely disregard everything they say, that's complete rubbish.)

Ha yes the whole backpressure thing is rather funny. Not sure what that's based on. You want stuff to be sucked out and through, not back. Stupid.

I guess the decat thing is neither here nor there actually. It would only matter if you upped the pipe diameter of the entire system from manifold down. That would slow the flow on N/A (incl 2zz).
But with the zero manifold, decat and flowing exhaust, as long as the pipe diameter, header length, collector position etc are the same...just improves the flow for more top end I guess. Keeps the gasses moving, promotes scavenging and prevents back pressure other than those caused by pipe bends and bad welds etc.

[ChrisGB]

I've run the PPE setup. It is optimised for top end power and I had dyno runs before and after with it. Stock setup gave me 138bhp, a free flowing exhaust added 6bhp and slightly improved torque, adding the PPE yielded 157bhp with no loss in low end, small gains in the mid range and biggest gains in the top 1500rpm where a sports car should be being used. A piggyback and map increased this to 161bhp and boosted midrange a little too. Mostly as a result of leaning out the mixture to around 12.5:1. The PPE O2 sensor issue is not an issue if you wire it properly. Those that have had issues have bodged it or fitted a second sensor bung in the same gas stream and wonder why the fuelling is fubar. The two downsides to the PPE are noise (it can drone if paired with something incompatible) and corrosion. It is mild steel ceramic coated and can rust. I also tried stage 1 cams with the PPE and lost significant power (down to 134bhp). I put this down to the PPE being optimised to the stock cams and being sensitive to cam timing and duration.

[lamcote]

Thanks, that's very interesting, did your PPE exhaust system include their cat/midpipe as well or was it just the manifold?

[ChrisGB]

Thanks, that's very interesting, did your PPE exhaust system include their cat/midpipe as well or was it just the manifold?

I had both the car and the decat pipes, power almost the same for both. The PPE won't join up with the stock cat, it's a completely different layout.

[shnazzle]

That's interesting indeed. Particularly as the design is such a departure from stock, which is (hopefully) designed to the stock timing.

I wonder if someone has done similar "tests" on the Zero

[lamcote]

Presumably the PPE manifold pipes are a lot longer than the standard layout? Do you still have access to it to measure it up?
Can you get a stainless PPE manifold now, I thought I had seen reference to one on the MWR website?

[lamcote]

Have a look at the pictures on the MWR website for MR2 exhausts. You can see where all the benefits and drawbacks are:
 m https://monkeywrenchracing.com/product/ ... -flow-cat/ m
 m https://monkeywrenchracing.com/product/ ... -with-cat/ m
PPE manifold has long pipes that go right under the sub frame and then into a nicely designed collector and a high flow cat. Clearly an excellent design but it is not clear if the cat pipe is stainless.
PPE midpipe with cat that fits onto standard manifold has a nicely designed collector and high flow cat. This is limited by the standard manifold, but might work well with the Zero? But isn't stainless steel.
Standard cat pipe fits onto standard manifold, this uses the short manifold pipes, has poor collector design and restrictive cat, ie worst of all worlds.
The question is; would fitting a decent collector and cat onto the Zero manifold turn it into a 4:2:1 version of the PPE 4:1? If so, where do we get a stainless steel one from? The CHE version does not look much better than standard in terms of the collector design?

[loadswine]

As far as I know, the engineers at ppe, designed their sytem originally, as mild steel, with a ceramic coating, which actually works pretty well with stock cams. I had a similar situation to Chris, with a drop off in power at the top end, with stage 1 cams and the ppe, though I actually had two O2 sensors running , one on both banks, to allow for long term fuel trims. I had additional bungs welded in for that.  Measuring max maf readings at WOT in 3rd, the readings increased, when the ppe was substituted for a Che type manifold and decat pipe. The arrangement that would work best would be something like the Tubular exhaust and manifold that they do for the Lotus Elise 1zz. It is 4 into 2, equal length, with the 2 longer than we would have normally on the Roadster.
Manifold design, from what I have read, is a balancing act of narrower pipes for higher flow rate and larger diameter to remove restrictions, on NA engines anyway.

[shnazzle]

From the sounds of that, Nigel, the che-type actually sounds better.
And from what you say about the Elise, the Zero + good high-flow cat still sounds like the best option if the "1" part of the 4:2:1 is lengthened a bit to remove the aggressive bend.

[lamcote]

But which high flow cat? I reckon the design of the collector is vitally important, the PPE one looks the best design but it's very expensive for a non stainless steel pipe.

[shnazzle]

Yeah sorry but PPE prices are just mental. I'd sooner go to my local exhaust place and have them make one up for what I'm guessing would be about 200 quid less.

[ChrisGB]

For stock camshaft, PPE gives best bolt on power gains, no losses anywhere. For stage 1 camshaft, probably best to go for the Zero. For forced induction, custom larger bore manifold may be needed if significant power gains are required.

It's partly about diameters and flow, partly about scavenging pulse timings.

[jvanzyl]

So with costs of mapping and assuming a piggy back ECU, would I be correct in thinking that PPE is the cheapest first port of call giving you 23bhp. Then followed by zero manifold plus stage 1 cams? What power you looking at then?

EDIT: would the stg 1 cames plus zero be like Bernie setup so something around the 170bhp mark? Can't find the post.. but that would give you 33bhp extra...

[lamcote]

I'd be absolutely amazed if you got 33bhp from exhaust and cams, even if you include the high flow cat and midpipe which you haven't mentioned in your post.
I know it's dangerous to quote anticipated power but my GUESS is:
Zero c.4-5bhp, sports cat/midpipe c.5bhp, good cat back exhaust c.5bhp, stage 1 cam c.5-7bhp ASSUMING the cam actually works with the Zero! But all of that is well over £2,000 plus fitting!
Anyone else prepared to have a stab?

[shnazzle]

So confused now.

For the PPE, do you have one o2 sensor on the collector at the end spliced into both sensor connectors?

Where do you reckon Stg2 cams fit in?

[lamcote]

Yes I think you're right about the O2 sensor.

I think the stage 1 only works with a standard engine. If you have other mods, especially a remap, the stage 2 would be recommended but it must still be a risk.

The more I read, the more I think the 1zz is really sensitive to mods which is why people often don't get good results. It does make me wonder whether finding the right combination might just release a decent result though because I think the basic design is pretty good. There seems no reason why you shouldn't be getting up to c.95bhp/litre out of it with a driveable setup if you compare the spec to other engines.

[lamcote]

 l viewtopic.php?t=31122 l

Interesting thread, it seems to be someone else complaining of low power when using stage 1 cams with PPE manifold?

The good news is that it seems the stage 1 cam does work with non PPE manifolds?

[Bernie]

I'd be absolutely amazed if you got 33bhp from exhaust and cams, even if you include the high flow cat and midpipe which you haven't mentioned in your post.
I know it's dangerous to quote anticipated power but my GUESS is:
Zero c.4-5bhp, sports cat/midpipe c.5bhp, good cat back exhaust c.5bhp, stage 1 cam c.5-7bhp ASSUMING the cam actually works with the Zero! But all of that is well over £2,000 plus fitting!
Anyone else prepared to have a stab?

To get to 171 Robs spec

Crower Stage 1 Cams (Monkey Wrench USA)
Zero - 4 into 2 Equal Length, tuned collector, Manifold SS.
Silverstone Performance De-cat pipe, fitted with 200 CEL Sports Cat.
Blueflame Custom Twin Exhaust.
PPE Cold Air Induction system
Apexi Power FC (ECU)
Mapping / Dyno by Noble Motorsport.




Sent from my iPhone using Tapatalk

[shnazzle]

The interesting part here is "tuned collector". Got any pics or details Bernie?