3.5" Downpipe or stick with 3"?

[jdpolzin]

Ok guys, I'm debating whether or not to tackle a 3.5" downpipe or not. I'm running a 252 c.i. Stage 2 GN1 headed motor. Everything is not together yet so I cant tell you what I'll be getting out of the motor. The car will be set up for E85 with 160lb injectors and will be running a FAST XFI management system once the money comes in. When the motor is in, I'll be putting the 60# inj. back in and running my TT chip for now. I have a Precision 70BB turbo. I'm also running TA headers and AC. I have an internally gated 3" downpipe right now. I'm having a hard time deciding which route I want to go with the down pipe though. I'd like to run an external gate to try to eliminate creep the best I can. I'm having a hard time finding a down pipe in 3.5" and I know it will be a nightmare trying to fit it with the AC. Should I keep this downpipe and use it? Or should I try to build my own 3.5" and use the gate port in the header for external gates? What would you do? thanks for the opinions! -----Jeremy

 

[turbofabricator]

"I" would go with a 3.5" round or even a 4" oval down pipe. It is a PAIN to work with, but it really makes a nice install. It will help around the A/C, for sure. Here's what a 3.5" oval stainless down pipe looks like: http://www.turbobuick.com/forums/ge...h/228325-tta-3-5-oval-down-pipe-finished.html If there is a 3.5" round pipe available for your turbo, it would be MUCH easier to buy it. I "like" doing this kind of stuff, though. The more challenging, the more I like it. Good luck.

 

[RobsIron]

I think we all know who Red Armstrong is. He's done big #'s with 'smart' mods on overall stock TRs.

I remember reading years ago that he had a high 10 sec car and all he did was change from a 3" dp to a 3.5" and got into the mid 10s.

Wish we could all say that, but maybe it just worked with his mods. Still makes a statement.

With your Stage II and a 70mm I'd definetly go with a 3.5' or larger.

Do more research. Maybe ask this in the Stage tech section.

 

[jdpolzin]

"I" would go with a 3.5" round or even a 4" oval down pipe. It is a PAIN to work with, but it really makes a nice install. It will help around the A/C, for sure. Here's what a 3.5" oval stainless down pipe looks like: http://www.turbobuick.com/forums/ge...h/228325-tta-3-5-oval-down-pipe-finished.html If there is a 3.5" round pipe available for your turbo, it would be MUCH easier to buy it. I "like" doing this kind of stuff, though. The more challenging, the more I like it. Good luck.

How about taking the challenge to make a few 3.5" DPs for us guys!!! I have talked with a few people that have suggested making my own and I do have the resources of a few different guys that weld stainless for a living. My problem is that I honestly dont want to go through the hassle. I know the TA headers hug the block so there is more clearence available there but why is there no-one making these? I have seen a few iternally gated 3.5" DPs but no external ones. I would like a nice looking DP so I'm afraid of a DP thats has many welded bends. It would be nice if some could bend these up similar to the THDP's. Do you think the internal gate would be sufficient? I have a Greddy ProfecB SpecII boost controller also, is this usable for an external gate, or is it simply controlled by the spring?


BTW, nice work on that oval TTA pipe!! If you could do that, I think there is much more room in a Gn to fit a 3.5!

 

[turbofabricator]

Well.....I don't do this for a living, and my time is too scarce these days. I occasionally do projects for guys that can't get what ever they need elsewhere. If I built up a 3.5" or larger DP, it would be made from mandrel bends and welded together. I really don't think that there is enough interest to have it digitized and pre-bent. I could be wrong, though. It would be kinda fun to fab up a 4" oval down pipe, though. It would be almost bigger than the whole engine. PM me if there isn't anything available. I would need your drivers side header and turbine housing, and any specific motor mount that you may have. (and some patience) It isn't easy making stuff like that.
Anything over 550 horsepower I wouldn't trust a internal wastegate puck. Good luck.

 

[Boost231]

thats what im talking about. one day i still need to hit you up Ken about that extra large HOTAIR DP

 

[jdpolzin]

I'll keep that in mind for sure! I would actually think there would be quite a bit of interest in a 3.5" dp. I started a thread a while back in the product request section and quite a few people responded. Might be suprised, you could be the next Terry Houston!!!

 

[turbofabricator]

Might be suprised, you could be the next Terry Houston!!!

It would take ALOT of orders to keep me from going to work. I have a pretty good job. (but I don't JUMP up out of bed to get to work, either.) If I did this for a living, I would probably begin to hate it. There is a local exhaust shop with a CNC bender, that I might be able to get involved. One other issue is that with 3.5" of tubing, there is very little room for clearance, and every car is just a skosh different, and fitment would be a HUGE concern. (motor mounts, frame welding, roll cage tweaking, accident damage, head milling, block machining, header mods, Chinese headers........ The last thing I want is a couple of guys P.O.'d at me cause their big down pipe hits somewhere, even though their car had been in a wreck, I am still the JERK! I have had to deal with STUPID Buick guys in the past. (MOST are stand up people, though) (I once did a set of heads for a guy and they had valve seal "issues", even though he adjusted the roller rockers so the valves were .100" off their seats-crushng the valve seals at .625" lift total, and his block was assembled in a gravel driveway and it mysteriously ended up with a piece of gravel in the main oil feed hole. I was STILL a &$$ hole) If a vendor wanted to handle all the marketing/shipping, I might consider it. I just don't have the time to spend dealing with the public. My time will cease very soon to. As soon the the new 787 makes it to Flight Testing status, I will be living at work. We already have over 860 787's on order, and we haven't even finshed airplane #1 yet. Cool airplane check it out: Boeing: Multimedia - Image Gallery - 787 Dreamliner

 

[jdpolzin]

When I was trying to figure out what I wanted to do for a career, my dad gave me some good advice:

"Write the top ten things you like to do in order from 1-10. Keep your most favorite as a hobby, make your second a career!"

I always thought this was a good piece of advice. I can understand your frustration. This is why I'm wondering if a 3" DP would be sufficient for my set up. I know there are a bunch of cars running 10's with a 3". The difficulty of the 3.5" fitting almost makes me say screw it. Although, I just have a feeling this may be my "weakest link." My set up is a little tricky, I'll have the stage motor, HRParts stage motor mounts, 70MMBB turbo, AC, TA Headers. Not sure how difficult it would be but others are telling me to fab it up myself. Where do you start? I suppose I'd have to use my buddies welder to tack the bends into place them take them in to work and have them finished up. It would be sweet if they were as basic as the 3" to make fit manderally bent!!!

By the way, do the TA headers stick out more than stockers? i know the ATRs dont hug the block as much as the stockers but I never heard of a difference in the TA's.

 

[steve hughes]

I made 2 runs at my local trac year before last with 3" dp on 3500# gn stage II 260 cube , 76 GTQ turbo .9.45 at 143 . Then changed to a 3.5" dp and made 2 more runs 9.40 at 143.5 mph. This was with no exhaust just open dp. If you have AC and aren't running faster than mid 9's i think you are wasting money on anything bigger than a 3"dp. If it's mainly a street car you won't see any difference.

 

[jdpolzin]

Steve, thank you for your info! Just out of curiousity, are you running an external gate? With those times, I imagine you are!

 

[boostingbuick]

I agree that a 3 inch should be enough flow. I have no test data but have read a tread about this a while back. But I am still wondering way my new Turbonectics 72 s-trim comes with a 4 inch v band outlet? When I called them they said because it needs it. Then I told them I was going to run a 3.5 dp and they said if I want to cork it up then go ahead. I was like

 

[steve hughes]

Yes i am running an external gate.

 

[turbofabricator]

You could always just use a 3.5" for the first 2.5 feet then neck it down to 3" as it hits the "clearance area". A 3.5" oval will give you LOTS of room, too. A 4" oval will be a good choice, too. If you plan on running faster than 10.00, then a 3.5" would be a good idea. Bigger IS better. (but ONLY for down pipes ) You can run real fast with a 3", but I think at 650+hp you will be leaving something on the table. Below 600, it will be fine to stay with 3". At 650 hp, I'm not so sure you would see a big gain either. But if you wick it up more, it should be measurable. If you have a chop saw and a MIG welder, you can do the cutting and tack welding. Just be sure to use stainless wire and Argon to tack it together. If you use mild steel wire, it will work, but you will have to grind off the tack welds or they WILL rust and look bad. Take your time and visualize how you want it to go. Cutting too much off of a bend before you fit it in place gets expensive. After you do a few of them, you will get better. It takes quite a bit of experience to prevent wasting bends, An in SS they are very expensive. One option would be to use mild steel and have it thermal coated. It would be a better idea for a biginner. You will screw up a few bends (OK...ALOT of bends ) It is a time consuming operation, but is very rewarding to look at what you have made and be proud of it. It will fit better in the long run, due to the fact that it was built to your cars dimensions.

 

[GNVYUS 1]

I think there are two vendors who are going to drop us new 3.5" DP's this Spring/Summer so keep an eye open.

Steve Hughes before and after time slips speak volumes about the real restriction in our setups, the catback. A 3" with a test/dump open seems to be the ticket. But I would like to see a 3" vs. 3.5" through the system to see if that helps any.

Ken, as much as we would all like to see you get on DP's for us, you seem to invent newly needed items every season and your inventing time is priceless IMO. Keep plugging away so one day we can buy your DOHC and quad turbo setups!!

 

[deezdad]

When I was trying to figure out what I wanted to do for a career, my dad gave me some good advice:

"Write the top ten things you like to do in order from 1-10. Keep your most favorite as a hobby, make your second a career!"

I always thought this was a good piece of advice. I can understand your frustration. This is why I'm wondering if a 3" DP would be sufficient for my set up. I know there are a bunch of cars running 10's with a 3". The difficulty of the 3.5" fitting almost makes me say screw it. Although, I just have a feeling this may be my "weakest link." My set up is a little tricky, I'll have the stage motor, HRParts stage motor mounts, 70MMBB turbo, AC, TA Headers. Not sure how difficult it would be but others are telling me to fab it up myself. Where do you start? I suppose I'd have to use my buddies welder to tack the bends into place them take them in to work and have them finished up. It would be sweet if they were as basic as the 3" to make fit manderally bent!!!

By the way, do the TA headers stick out more than stockers? i know the ATRs dont hug the block as much as the stockers but I never heard of a difference in the TA's.

And ya picked electrician?

 

[Ktbregal]

Interested also.

 

[TT/Ameasap]

Jermey,
I did it for sound and the fact I had the room to do a 3.5" system on my car. I have internal gate stock setup with sd2 and been 25 psi with no creep.
I custom built this one to exactly how I wanted it. probably 400 and time.