i am having a custom downpipe made and want to know which would be better for my set-up - i will be running a thermal 3" exhaust and 3"test pipe on stock internals

i plan on running 10psi on my 18g turbo

 

bump

 

btw - i dont think it can fit a full 3" DP due to the small mounting for the flange

 

if you don't upgrade the flapper on the internal wastegate of get an external wastegate then it will boost spike to atleast 15psi.

I recently had a guy i tune, from the stock downpipe to right under the motor to a 3in, then 3in thermal.

i set the boost spike to 15psi and it instantly hits it at anything over 60% trottle. even with no boost controller, it goes straight to 15psi form where it used to hold 7psi on stock spring.

just an FYI.

 

so what should i do?

 

I have a 2.5 DP on mine and I get no spiking. I did port out the wastegate hole to about as large as I could get it and I ported the entire cast iron elbow out to help with flow. I got the end of the elbow ported out to ~2.35 inches or so, any thinner and the walls of the elbow would be way thin IMO. Then its 2.5 inches after that. Porting the wastegate hole helped control boost much better than it did before though, you should try that first, there is a lot of room left there to enlarge the hole without doing the larger flapper thing. FWIW, a 3 inch DP is a waste IMO, especially considering how small the elbow outlet is.

I am going to be building a custom downpipe to bolt directly to the turbo pretty soon. I want to do a divided wastegate with a seperate dumptube. Pix to come!

 

are you running a 3in exhaust with the 2.5in DP?

 

No all 2.5 inch, IMO its pointless as a 2.5 inch will support 400whp. Mandrel bent with Magnaflow muffler and resonator.

 

or should i just keep the stock 2.25in DP that come stock on the greddy kit?


OR.... i am already having a custom DP made,... could i also do...
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nfn15037 &raquo;</TD></TR><TR><TD CLASS="quote">I am going to be building a custom downpipe to bolt directly to the turbo pretty soon. I want to do a divided wastegate with a seperate dumptube. Pix to come! </TD></TR></TABLE>

???????????????

btw this is a DAILY DRIVER and MUST be reliable

 

bump need some answers!! i already have a thermal system coming

 

If you are going to have someone fab a DP for you, spend the buck and have it done right. Get rid of that cast iron elbow and have someone built you a downpipe that flanges right up to the turbo. With good fabrication, there is no reason why it wouldn't be 100% reliable.

 

if i also got rid of the cast iron elbow would that eliminate the spiking??

does anyone know of a write up/ or picture i can take to the fabricator so he knows exactly what to do?

 

You would also need to port the wastegate hole. I have no experience with actually using a DP without the cast elbow, but I know someone on H-T has done it. Search around the FI forum, it is in here somewhere under archived posts.

 

if anyone knows - any info would be greatly approciated

 

help!!!

 

I've got a 2.5 to 3" flared downpipe...I don't get any spiking at all. Full 3" exhaust, no cat. I haven't touched the flapper or the cast elbow. I set my MBC to 13psi and it holds strong without any spiking or creeping of any sorts.

 

which kit do you have?

could it just be the greddy 18g kit that has spiking cause of the cast elbow?

 

Are you mentally challeneged? You have a 3 inch cat back, 3 inch test pipe and you're actually CONSIDERING a 2.5" DOWNPIPE? Jesus man.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Blazin Civic &raquo;</TD></TR><TR><TD CLASS="quote"> Are you mentally challeneged? You have a 3 inch cat back, 3 inch test pipe and you're actually CONSIDERING a 2.5" DOWNPIPE? Jesus man.</TD></TR></TABLE>

yes - since the cast elbow will not allow a full 3" flange and its rumored to spike with a 3" DP

need help

 

heres alittle info to help. I have the greddy kit on my 98 gsr and last weekend my friend and I made a 3" dp and put my 3" exhaust on. I just used a 3" 3 bolt header flande and used a dremel and made the wholes alittle biggger and it bolted up. Its alittle hard to get the bolts tight though so we had to take alittle ballpin hammer and make indents so the bolts could turn. I put the downpipe on and 3" kteller piping and a 3" n1 muffler with a 3" carsound cat and it made a huge diff. going from the little 2" downpipe and stock cat and greddy evo. Hope this helps...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Integra21 &raquo;</TD></TR><TR><TD CLASS="quote">

yes - since the cast elbow will not allow a full 3" flange and its rumored to spike with a 3" DP

need help</TD></TR></TABLE>

where teh hell is the rumor to spike? i know it spikes, try tuning a car and it instantly hitting boost cutoff.

 

I was getting spikes past 20psi, on my itr with 3''. The only way to solve it is to port the wastegate hole which is like 19mm or something retarded like that or weld on an external like me. Pics soon

 

I have a profec B spec 1 with the controller on it holds boost rock solid. that is with a 2.5" DP and stock cast elbow and flapper. I run a 3" exhaust.

the idea behind steping the DP and exhaust size is to increase exhaust velocity.

ps- if I run without the controller on it spikes like crazy

 

bump - not really looking to upgrade wastegate or anything right now - i do have Blitz SBC-ID - will i have a problem with a 2.5" DP to a 3" test pipe/exhaust?

 

it must stay very reliable for me (would a 2.5" DP cause these problems with spiking etc....)

i would still see gains if i just put on a bigger test pipe and 3" exhaust correct?