racerboy8

Do many people run a external waste gate with many twin setups?

Mahjik

iTrader: (1)

There is no magical formula which says you either will or will not have boost creep. Some people have been known to run full exhaust without creep, some people get creep.

As for as how to control it *IF* you get it, check this thread:
https://www.rx7club.com/3rd-gen-archives-73/boost-creep-control-26389/

racerboy8

I found a thread finally after searching thank you though. My search finally worked. I have another questions. Does anyone use a external wastegate with stock twins.

HDP

iTrader: (2)

I don't see how you can without a redesigned exhaust manifold/turbo housing...

Mahjik

iTrader: (1)

Take a look at where the wastegate is located:

http://www.autosportracetech.com/RX-...BigPicture.htm

99gst_racer

What size in milimeters is the flapper door on the stock internal gate? Cant you just upgrade the flapper door to a larger size and then port the wastegate passages to allow more airflow, to counteract against the free-flowing 3" turboback exhaust?

Adding restriction to a free-flowing exhaust is hardly a fix - more of a crusty bandaid IMO.

Wouldnt it be possible to flange the stock cast manifold for a 40 mm TIAL? The manifold is cast iron right?

Mahjik

iTrader: (1)

IMO, it's not really worth all that trouble.

Creep generally happens when trying to control boost to a certain level. Ex. trying to keep the boost at 13 PSI, it creeps to 15 PSI. However, tuning the car to 15 PSI there is no creep as that was where it wanted to creep in the first place.

It generally happens to people setting their boost to 12-14 PSI. There are some people who have ported their upper and lower manifolds and creep much higher (up to 17 PSI). In those cases, something more extreme like replacing the wastegate door might be a viable option to try. Exhaust restriction is the easist to do. Since you would already be limiting your performance as reducing your boost from say 15PSI down to 12PSI (to eliminate the cree) is going to produce less the power; the added exhaust restriction is nominal.

racerboy8

Paul,
I don't think that you can weld to the stock manifold, as it is too thin. Limited space too. ac

99gst_racer

Therein lyes the problem. Do FD's usually only creep a few PSI above the preset level? In that case, yes, I agree with you when you say just tune the car to that level. If my boost was set at 13 psi and I was creeping to 15 psi, I wouldn't even consider that a problem. I'm used to the creeping problems associated with the DSM cars - which in many cases the boost creeps past double the value of the preset level.

Yes, that was the point I was trying to make. Many people's engines and supporting modifications will not support the the boost level that it is creeping to; regaurdless of tune.

I stand strong against exhaust restriction. IMO, it defeats the purpose of a free-flowing exhaust. It is very obvious that it is easier, but if adding a restriction is considered a fix, then why not just retain the stock (allready restrictive) exhaust components to battle the creeping issue?

I assume from your previous post, that the flapper door modifications are not a very popular upgrade in the world of FD's. So is it even possible for logical to flange the stock manifold for an external gate?

Mahjik

iTrader: (1)

There was a thread (not too long ago) where someone said that it was done, however, there were no pictures or proof to say it was actually accomplished:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/good-way-control-boost-non-seq-turbos-look-here-301949/

A slight restriction in the exhaust (i.e. a gasket width restriction) is really not going to be a big deal on these cars aside from helping you control creep (if it's a problem).

A free flowing exhaust does NOT always equal boost creep. Porting the wastegate is typically enough to take care of the problem. However, there are some people who run into the situation where they can only port so much and it still doesn't fix it.

99gst_racer

I honestly dont know the thickness of the OEM cast manifold, but if it is at least 2.25", then it seems like it would be possible to weld on a 1.5" diameter tube and route approximately 6" away from the manifold and then have a flange for a 38 mm Tial wastegate. And assuming that the stock manifold is cast iron, it is entirely possible to weld a stainless tube and/or flange to the manifold. And we all know that an external wastegate is the perfect solution to boost creep; and w/o any kind of performance sacrafice.

99gst_racer

hmm.... Interesting..... I'd love to obtain a spare manifold to at least give this a try.

rebuild FD

boost on my car creeps well past 15 with the boost controller set to 11 (full open), which is what killed my last engine

needless to say, I'm getting the wastegate ported this time

myexlex

there was this kid who welded a WG on the stock manifold(fc). Supposedly it worked and everything, but I feel like if you have outstanding creep then the problem lies somewhere else. I never seen it creep more than a few lbs, and it usually drops off by redline. SOme people have creep because they use an MBC.

rebuild FD

I didn't have significant creep with my MBC until David Garfinkle made a new flanged and ported y-pipe and crossover tube for me....the thing flows so well the creep immediately jumped to several pounds with a wide open exhaust (resonated MP only)....I thought about the exhaust restrictor but that basically defeats the purpose

Mahjik

iTrader: (1)

Defeats what purpose? Saving your engine?

racerboy8

Well I am going from an all stock FD to Air intake/3" turbo back all by pettit and I will let everyone know by sunday if I get creep. I am sure I will but maybe by some lucky chance I won't. Also I don't see how any mbc can have anything to do with creep? Maybe someone can tell me how a mbc directly would effect creep?

DaveW

Boost spikes, etc., are related to the type of boost controller. Creep is not. You can get creep with ANY boost controller! It is caused by too much turbo output for the WG to handle. As stated above, porting the WG or similar solutions are needed to prevent creep.

99gst_racer

Defeats the purpose of the exhaust. The purpose of upgrade the factory exhaust is to remove that restriction. Why on Earth would you then add a restriction? Many people (including myself), with many different set-ups on many different cars have conquered boost creep correctly. Exhaust restriction on a forced induction car is considered a problem. Restricting the exhaust path flow to fix creep is simply exchanging one problem for another.

I agree.

Mahjik

iTrader: (1)

This is not a DSM. These cars don't take to lean conditions like piston motors. Taking EVERY precaution to control boost is the goal with a rotary engine.

A 1/4" restrictor isn't really going to drop off any noticeable power. From the turbo back, you talking about several feet with just MAYBE a 1/4" which wouldn't be the same diameter. Honestly, that's going to mean jack when it comes down to the amount of power being put out.

Having said that, on the stock ECU, boost creep is not as much of a problem as spikes. With creep, the overboosting will kick in fuel cut. While that sucks, it will at least save the engine. The problem with spikes is that the ECU will not react fast enough (especially if it's a large spike) to control the wastegate.

Sometimes (some amount of) backpressure is a good thing. There is more to backpressure and exhaust flow than just "larger is better".

While that quote is geared more towards NA and pistons, it's just to illustrate that there is more to exhaust than just "larger is better".

99gst_racer

Well, I'll take your word for it, if you say 1/4" will not make a difference. I always read in articles about press-bent VS. mandrel bent.... Pressbent looses shape and diameter in the bends whereas mandrel doesnt. Even though the difference in the bends is only sometimes 1/4" or 1/2", there is known to be a measurable difference in flow. And for that reason, you, I and everyone else has mandrel bends underneath out cars.

The wastegate opperates of of a positive pressure source created by the turbocharger itself, correct? Please explain how the ECU reaction speed falls into play.

And that is very correct.... for a NA vehicle. For a forced induction piston engine, the turbochargers itself creates more than enough backpressure for the engine to opperate smoothly. I would assume that also applys to the twin-charged rotary, correct?

That was completely gears towards naturally aspirated piston motors......

I understand that Apex seals are much less forgiving than piston rings are, but both will fail from detonation and extreme lean conditions. Trust, my piston motor is not superman against pre-ignition. I agree that something needs to be done for the sake of motor longevity; I just feel there are better ways to controlling boost creep and spike than restricting exhaust flow.

Mahjik

iTrader: (1)

You are comparing apples to oranges. We are not talking about changing the "direction" of the flow. When changing the direction of the flow, that absolutely makes a difference. A restrictor plate is not changing the direction of the exhaust flow.

That should have read "solenoid", not ECU.