fd3s400438

Hello there just a quick one. I have about 470 bhp to the engine running a single HKS unit close to 22psi . The car has an aggressive port , HKS single TO4E turbo kit that came with the cast iron HKS manifold , HKS downpipe with the External Wastegate gas being dumped back in the exhaust downpipe and from there its a 3inch all the way to the back to the HKS CARBON-Ti back box

I am not sure if it is 3 inch outside or 3 inch inside diameter because a 3 inch pipe may be 70-72mm internally depending on manufacture

Anyway although I hava an profec b and an HKS external wastegate and 15psi spring I get alot of boost spikes and was wondering if my exhaust setup is a bit small for my engine. All pipes and connection have been checked and double checked and the profec B has been profesionally setup. My only comment is that hame friends running much bigger units ( GT4088 and bigger ) said than the profec tends to control larger turbos alot better than smaller like mine.

Small turbo with quick spool up + small exhaust = alot backpressure = boost spike

I may be wrong of course. Forget the boost spike... For you out there running 500bhp engine motors what internal diameter exhausts do you use

The next step I think is a 88mm pipe which is about 85mm internally ( 3.5 inch outer diameter )

Thanks and any help is welcome

rxspeed7

iTrader: (5)

I ran a to4s for many years with the FC cast Hks manifold hks 40mm wg and a profec b and never once had any boost control issues. What version of the cast manifold you have? The fd or FC? The fd one is somewhat notorious for bad wastegate flow.

fd3s400438

Its and Fd but lets focus on which exhaust diameter is better suited to much the engine power for now...

rxspeed7

iTrader: (5)

Well in that case then, with that setup I ran a racing beat rev1 dual exh. The engine was prob making 525bhp. I was running 23psi on a to4s with the 67mm comp wheel.

seandizzie

iTrader: (1)

If you had too much restriction in the exhaust it wouldn't spike, boost would taper off.

Is boost consistent with the EBC is turned off??

What are the setting on your profec?
Set-??
Gain??
Start boost??

I leave the gain 5 and start boost at 0 and only adjust the set. I find gain and start boost just make the boost inconsistent and the set works just fine by its self.

fd3s400438

With my EBC completely off i have steady boost of 0.9-0.8 bar... My setting in order to get about 20 psi gain = 15% , start boost 0.8 bar and set 65%

Any comment on the exhaust size diameter...What is a good diameter for 500bhp engine???

XLR8

iTrader: (52)

500whp is best done with a 4" exhaust. A 3" will do it depending on the turbo but you want everything to flow as much as possible to keep your total pressure and EGT's down.

seandizzie

iTrader: (1)

If the gate controls it fine with the ebc off the spikes are coming from the EBC

Leave the gain at 15% and set at 65%. Turn the start boost to zero and see how it goes. I find Start boost sucks, it will work out alright some times and others it spikes. I keep mine on zero because of the inconsistency it seems to have. You could always add more spring to the WG.

I have a different setup, 46mm tial, 35r, .8-9bar spring. I use set 40% gain 5% and start boost(setgain) at 0. That gets me around 1.3 bar and is very consistent. I run an open gate so i can really hear the gate working. Any time I start to play with set boost, its a crap shoot. Some times the gate never opens, especially at high rpm from vacum to fully boost, so I just leave it at 0.

Bigger pipe would allow more flow, but given your turbo I don't think it would make that big of a difference.

fd3s400438

The plan looks like this. Modify the HKS down pipe and dump the WG gas to the ground. Also tighten up the external wastegate spring to give me a boost control ''off'' pressure close to 15psi

The rest will be done with setting the start boost to 0 , gain between 10 and 15% max and set at what ever value it needs to give me close to 22 psi without any creaps

Lets hope for the best

seandizzie

iTrader: (1)

An open wastegate is very loud...

If you do this, do it in a way that is easy to go back if you don't like the noise.

fd3s400438

We have several cars running open wastegates so I know the sound. As if the Fd is not loud enough. LOL

My main problem is that I have maxed my 3inch exhaust and want to improve the exhaust gas flow a bit

seandizzie

iTrader: (1)

here is a formula for calculating(estimating) exhaust gas flow.

(Exhaust Temp °F + 460/540) x CFM intake flow= Exhaust flow

As the gas cools it will loss velocity so I would think a expanding exhaust would be best. Example. DP 3'' to 3.5 inch, midpipe 3.5 to 4", "cat back" 4" to 4.5. This is just a theroy of mine and I have no proof, but it makes sense on paper. Many race cars( F1, NASCAR) have pipes that get incressingly larger. Check out pic of the upside down Nascar.

Hope turning down the set gain gets you boost under control. Open gated rotarys sound great, I love mine...

fd3s400438

Ok so far I have re raouted the exhaust gas grom the external WG from the downpipe to the road as an open WG

I did notice that the boost is more manageble BUT the boost control does not respond on the SET setting

What I mean is this...

I have set the HKS WG to 1.2 bar from the adjustable screw...So with the boost control OFF I have in 3rd gear 1.25 - 1.2 bar which is about 18psi

I tried setting the gain between 5 and 10% , my start boost between 11 and 13psi and no mater what I dial in the SET value I will not get a decent rise in boost

My target is between 20 and 22 psi . I have to raise the SET all the way up to 70% and still I only get about 17psi in 2nd gear , 19 in 3rd gear and 20 psi in 4rth gear

And this is with 70% SET when with the boost control OFF I have 18psi in 3rg gear

All boost line fron the WG , selenoid , manifold etc have been changed , checked and rechecked

If there a case that my small HKS T04E cannot handle more boost and no matter what I dial in it cannot give me more

From my understanding if the boost control OFF give me 18psi I should be able to achieve 22psi with only 25% SET and I have reached 70% and still it doesnt feel strong...

C. Ludwig

iTrader: (27)

What trim is the compressor? Very good chance it can't supply the volume. Also a possiblity that damage to the compressor or turbine is contributing. Any number of possibilities. Wastegate hung open?

fd3s400438

its a 52 or 56 trim...I cannot remember since it was installed round 2005 or 2006...

What I have noticed is this...With SET 65% , gain 5% and Start Boost 0% if I do a quarter mile flat out i get about 19psi in 2nd and 3rd gear and maybe a 22psi on 4rth

BUT!!! if I am just crusing around and decide to floor it ( in 3rd or 4rth gear again ) from low rpm I get a huge boost spike close to 26psi and thank got the PFC boost limiter kicks in round 25psi preventing the worse...

Boost control off I saw a very nice 18psi in all gears ( even 20 ) no matter what revs I have in when I decide to floor it

When you ( I mean all the rest running Greddy profec B ) set a desired boost is it constant no matter what revs you decide to floor it or do you have similar issues???

seandizzie

iTrader: (1)

I am suprised it still spikes with the Start boost 0 and gain 5%.

As far as the different gears, I find pressure slightly increases from 2nd to 3rd,4th and 5th are generally similar, but second is generally a little lower... and tires are normally spinning.

Do you have the pressure sources for the waste gate on the turbo compressor housing or on the manifold(after the throttle plates)?? If its after the throttle plates try to route both sources from the compressor housing. Ie, after the turbo but before the intercooler.

When it spiked did you hear the waste gate open?

What are your warning/max boost setting, you can also set up the boost controller to to tackle spikes.

Maybe toss the EBC in the trash and add more wg spring??

fd3s400438

This is a clip from last night. Standing start , quarter mile run but could not see properly so I let the gas at 350m

Running track day semi slicks not suitable for a good lauch. I managed to see 1.55 over boost with 1.4 connstant boost only in 4th gear ( 22.7psi over dropping to 21 psi )

I think its the best bet to remove the EBC or sell it on Ebay and crank up the WG spring to 22 psi

RX7 Aronis 0-350m - YouTube
Mazda Rx7 0-350m with 18psi of boost - YouTube

mannykiller

iTrader: (93)

careful man^..... your approaching "Kaboom" PSI

0110-M-P

iTrader: (10)

My theory is the exact opposite of yours. In a turbo car you want the biggest pressure differential you can get between the inlet and outlet of the turbine. So expanding directly to a 4" downpipe increases turbo response significantly. Then because exhaust velocity slows as it cools (like you said), you taper the exhaust to a smaller size to help maintain the egt and exhaust velocity.

Right now, I have a full 4" exhaust, but am thinking of building a new custom one with a 4" downpipe and 3.5" dp-back because the 4" is just too damn loud.

seandizzie

iTrader: (1)

0110- then y on stock WG Fd's do people run 3 inch dp and a 2.5 inch mide pipe to avoid boost creep???Because the smaller pipe restricts flow, adds back pressure, incresses velocity. Just because the air is moving fast thru a smaller pipe doesn't mean its flowing more. Just means you added more back pressure.

Now, I don't know that incressing the size gradually(3" to 4") would benifit over running 3 the hole way as the smallest size is still the restriction, Ie 3, 3.5,4... even though the 4" is there it still had to go through the 3inch pipe originally. I said it was just a thought, no proof.

My thinking on this was pluming the WG back into the(3.5/4") mide pipe thats larger than the (3")Down pipe. So the added exhaust flow from the wastegate isn't as much of a restriction as 3" the whole way.

O and fds400438, can't see anything in the video but it sounds like your running throught the gears pretty fast.

dznutzuk

iTrader: (1)

Aroni, did you open the wastegate to see if the diaphram isn't leaking and/or torn? I'd like to see exactly how you hooked up the vacuum lines for the ebc. Αν θες να κανονισω να ερθω να το δω-Σπυρος Ηγουμενιτσα.

fd3s400438

Spiro I havent opened the wastegate because I have a track day in one month and if we brake something and cant find HKS parts in time I will miss the track day

Mechanical pressure from my WG spring is 19.8 psi dropping to 19.1 psi . This is with the boost control OFF.

The pipes are installed correctly exactly like the Greddy profec B spec 2 manual...

My problem is not only that the boost does not rise but the car behaves funny on the high setting. Its faster than OFF but it sounds like the WG is NOT working correctly...

fd3s400438

If I had a diaphram leak would the car still produce a healthy 18psi only with the WG spring BUT behave funny with the boost control on???

Last night I dialed in SET @ 75% , gain 5% and start boost 0.5 bar and I only got 20 psi in 4rth gear... So only a 2psi raise with 75% dialed in

Something is not right...