Budget Build Turbo Opinions - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 17 Old 03-02-2016, 12:07 PM Thread Starter
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Budget Build Turbo Opinions

Hey Y'all,

I looking to turbo my 04 cobra engine. It is in front of a 4r70w w/ 2800rpm stall and in a 4400lb car. I am on a very tight budget for the turbo itself as I had a trade deal on twin 35r's go south. The goal is approx. 750-800rwhp.

I have an ebay special 45r sitting in the garage, but I fear the exhaust side is to small. The exhaust side is twin scroll and is 76mm with .68 A/R and has a 4" outlet. I'm considering opening up the exhaust housing a bit to prevent excess back pressure. I'm a machinist/welder fabricator by trade so the machining wont be super difficult.

The other option I've been considering is the newer On3 7875. It will flow the air on the compressor side, but it has a .96 on the exhaust side and according to their site it is supposed to good for larger cubic in engines.

this is a street car so street spoolability is of great value. I don't want to have to wait until second gear for the boost to start rolling in. If I had the budget I would go with either the twin 35r's or twin 61's from On3, but that doesn't look like an option at this time.

Your opinions please. Thanks

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post #2 of 17 Old 03-02-2016, 01:05 PM
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This might not be what you want to hear, but tight budget build and turbo aren't really that compatible...I started my project as a so called budget build, and it's still a budget build but with about another $12k added on to the original budget haha! I haven't seen any direct examples of the On3 7875 reaching 750-800hp to the tire. The most I've seen documented is right at 700 on E85. That's not to say that no one has hit 800 with that unit, I just haven't been able to find any direct evidence of it. If you're happy with no more than 700 then that turbo should work out fine. From what I've read, it spools quickly. I have one BNIB on the shelf right now but never bolted it up because it's too small on the turbine side for my build. In my opinion either of those turbos would get you to about 650ish without much thought but anything above that you're going to have to step up to a better unit. Wait the extra time, save some more money and build what you really want if the goal is 750rwhp and up. That's alot of power and hard to get on an inexpensive budget AND keep it alive for any length of time.


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post #3 of 17 Old 03-02-2016, 02:00 PM Thread Starter
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This might not be what you want to hear, but tight budget build and turbo aren't really that compatible...I started my project as a so called budget build, and it's still a budget build but with about another $12k added on to the original budget haha! I haven't seen any direct examples of the On3 7875 reaching 750-800hp to the tire. The most I've seen documented is right at 700 on E85. That's not to say that no one has hit 800 with that unit, I just haven't been able to find any direct evidence of it. If you're happy with no more than 700 then that turbo should work out fine. From what I've read, it spools quickly. I have one BNIB on the shelf right now but never bolted it up because it's too small on the turbine side for my build. In my opinion either of those turbos would get you to about 650ish without much thought but anything above that you're going to have to step up to a better unit. Wait the extra time, save some more money and build what you really want if the goal is 750rwhp and up. That's alot of power and hard to get on an inexpensive budget AND keep it alive for any length of time.
Unfortunately it isn't my budget. The car is owned by my father. It used to have a Kenne Bell 2.6 on it and he wanted more power. So I sold the blower stuff and have been using the funds from that to buy the pieces to do the build. I thought that I had turbos lined up, but that didn't work out. Now I have to figure out a way to complete the build as best I can. I have a smidge over $1800 left for turbo(s) injectors, piping, couplers, etc. Fuel system is complete, just needs to be installed. Intercooler has been purchased. I'm fabricating the headers myself with tubing I have laying around and am water jetting the flanges at work with scrap we have in the dumpster. My "ebay special" is supposed to be good to 1,000hp, but I'm worried if I thin the walls out on the turbine side bad things may happen. lol. Having that BNIB unit would you happen to be interested in any partial trades for some parts, if you don't have plans to use it?
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post #4 of 17 Old 03-02-2016, 04:38 PM
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I hear ya, this is a legit cost fixed build! Which ebay unit do you have? You can search the turbo forums for folks that have used something similar and see what they made with the turbo. Is it a T6 or T4 flange unit? Your best bet, might be to go ahead and use that turbo and use the money you have left over to get what you already have right. If it's the Chinese GT45 turbo that's very popular then I'd just stick with that due to the budget constraints.

I'm not sure about opening up the housing, my first instinct would be to not touch it. If you're talking about opening up the area around the turbine without increasing the turbine size then I'd expect that to hurt performance. If you're talking about opening up the A/R then there you have to be careful as well once you start removing material from the throat of the turbine housing you can disrupt flow to the turbine. I personally wouldn't mess with machining the housing unless you want to put a larger turbine wheel in it. But then you'd have to get the new wheel, send the new CHRA off to be balanced with the new wheel, and then you're eating into your fixed budget.

I'd be willing to let mine go I guess. I did have plans for it eventually but that's not set in stone and is year's down the road. I painted the turbine housing with VHT coating, and tapped the compressor cover for a boost reference port but otherwise it's a new turbo. I honestly would feel bad selling it to you...I'd rather see you work with what you have and at least get it running and driveable before spending more money on another head unit given your budget constraints and what sounds like considerable personal time invested. Beggars can't be choosers.

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post #5 of 17 Old 03-02-2016, 11:00 PM Thread Starter
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Originally Posted by DreadFox View Post
I hear ya, this is a legit cost fixed build! Which ebay unit do you have? You can search the turbo forums for folks that have used something similar and see what they made with the turbo. Is it a T6 or T4 flange unit? Your best bet, might be to go ahead and use that turbo and use the money you have left over to get what you already have right. If it's the Chinese GT45 turbo that's very popular then I'd just stick with that due to the budget constraints.

I'm not sure about opening up the housing, my first instinct would be to not touch it. If you're talking about opening up the area around the turbine without increasing the turbine size then I'd expect that to hurt performance. If you're talking about opening up the A/R then there you have to be careful as well once you start removing material from the throat of the turbine housing you can disrupt flow to the turbine. I personally wouldn't mess with machining the housing unless you want to put a larger turbine wheel in it. But then you'd have to get the new wheel, send the new CHRA off to be balanced with the new wheel, and then you're eating into your fixed budget.

I'd be willing to let mine go I guess. I did have plans for it eventually but that's not set in stone and is year's down the road. I painted the turbine housing with VHT coating, and tapped the compressor cover for a boost reference port but otherwise it's a new turbo. I honestly would feel bad selling it to you...I'd rather see you work with what you have and at least get it running and driveable before spending more money on another head unit given your budget constraints and what sounds like considerable personal time invested. Beggars can't be choosers.

It is the Y2004K GT45. It is a divided T4 housing. I have searched around a bit, but mostly LS guys are running them with the larger housing that was available. I guess I could build the kit around it and see how it goes. Would def need to keep an eye on backpressure with is my biggest concern. It is supposed to be for anything up to a 3.0L engine with the housing it has on it, hence why I want to open it up a smidge.
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post #6 of 17 Old 03-03-2016, 04:30 PM
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Originally Posted by Quickstang92 View Post
It is the Y2004K GT45. It is a divided T4 housing. I have searched around a bit, but mostly LS guys are running them with the larger housing that was available. I guess I could build the kit around it and see how it goes. Would def need to keep an eye on backpressure with is my biggest concern. It is supposed to be for anything up to a 3.0L engine with the housing it has on it, hence why I want to open it up a smidge.
That is a pretty tight A/R but from what I understand, the Garrett housings will fit that turbo. I'd stick with that turbo for now, and see if you can find a 1.05 A/R housing to put on it if backpressure does turn up to be an issue.

Also, I think that goal might be a tad lofty for either turbo through a 4 speed auto trans.

MFT
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post #7 of 17 Old 03-04-2016, 09:23 AM Thread Starter
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That is a pretty tight A/R but from what I understand, the Garrett housings will fit that turbo. I'd stick with that turbo for now, and see if you can find a 1.05 A/R housing to put on it if backpressure does turn up to be an issue.

Also, I think that goal might be a tad lofty for either turbo through a 4 speed auto trans.

Car made 620hp to the tires with the converter locked at 17psi with the Kenne Bell. For max power I was wanting to push around 21-22lbs with the turbo. Combine that with less parasitic drag from the blower and that ballpark should be achievable. Will just have to wait and see. That number was also at sea level and with a low density altitude. Will just have to build it and see. I'm trying to get the car into the 10's for him. I'll have to definitely look into the Garret housings for sure. If this turbo ends up not being able to work out how much would you be looking to get out of yours? You can PM me the price if you want.

Here's the car:



When it had the blower on it:

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post #8 of 17 Old 03-04-2016, 10:04 AM
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How fast is it now at this level ? 1/8-1/4
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post #9 of 17 Old 03-04-2016, 10:39 AM Thread Starter
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I looked up some housing for the 45r. They cost more than what was paid for the turbo and more than the brand new 7875. lol. So I'm going to say that is out of the picture.
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post #10 of 17 Old 03-04-2016, 11:21 AM
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Nice sleeper! PM sent.


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post #11 of 17 Old 03-04-2016, 04:21 PM Thread Starter
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How fast is it now at this level ? 1/8-1/4
Fastest it has been in the 1/4 is a 11.51 @118. That was on a hotter day with around 1800-2000ft DA.
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post #12 of 17 Old 03-05-2016, 05:56 AM
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The 45r should make some big power for ya. With that housing, it'll spool like a mother, but probably limit it up top. Trying to figure out a compressor for my build as well.
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post #13 of 17 Old 03-05-2016, 12:57 PM Thread Starter
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The 45r should make some big power for ya. With that housing, it'll spool like a mother, but probably limit it up top. Trying to figure out a compressor for my build as well.
Will definitly have to wait and see on this one. Backpressure is gonna be the biggest concern and believe me, there will be two gauges right next to each other during testing and tuning. Backpressure and boost. anything more than 1:1 for an extended period and that turbo is going bubye and going to a bigger turbine housing.
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post #14 of 17 Old 03-09-2016, 06:37 PM
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buy the on3 88mm..it's a copy of the Precision PT88 and works quite well.

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post #15 of 17 Old 03-15-2016, 09:46 AM Thread Starter
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buy the on3 88mm..it's a copy of the Precision PT88 and works quite well.
That thing is massive. LOL. Thanks for the input, but I don't think it will work well for my application. In fact my 45r mentioned above isn't going to work either. I finally got the car back in the garage and started taking some measurements. There is absolutely zero room for a 4" downpipe to fit anywhere next to that engine in there. So, it's back to twins. Even then I'll have to fab up two 3" round to 90 degree oval to 3" round again just to fit 3" under the engine and crossmember. Should be a very fun time fitting everything around that engine bay. there's not even room for forward facing headers. I'm going to have to come down, under, and back up the front of the motor with the up-pipes just to make it work. Picture a 04 cobra Hellion twin system and you will get the idea. Joyous day.
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post #16 of 17 Old 03-16-2016, 08:09 AM
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Back pressure is a concern but if it is mainly a street car , the short bursts aren't going to hurt it. I ran a Turbonetics 7668 with a 3" dp on my 383 in my lightning and on the street it was awesome. Spooled instantly and just kept pulling. I ran [email protected] almost 124 at 4410 also. I just sold it and the turbo is on another truck and still working perfect. Before that is was on my brothers car and ran hundreds of times. I do agree though, back pressure will kill a turbo eventually but will not be something that happens in a short period of time. I never had my truck on a dyno but we figure it was making around 630-650 at 14.5 psi and that was probably about all it would make given the smaller exhaust side. I could hear the bp so to speak when I would let off at the track.

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post #17 of 17 Old 03-18-2016, 09:21 AM Thread Starter
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Back pressure is a concern but if it is mainly a street car , the short bursts aren't going to hurt it. I ran a Turbonetics 7668 with a 3" dp on my 383 in my lightning and on the street it was awesome. Spooled instantly and just kept pulling. I ran [email protected] almost 124 at 4410 also. I just sold it and the turbo is on another truck and still working perfect. Before that is was on my brothers car and ran hundreds of times. I do agree though, back pressure will kill a turbo eventually but will not be something that happens in a short period of time. I never had my truck on a dyno but we figure it was making around 630-650 at 14.5 psi and that was probably about all it would make given the smaller exhaust side. I could hear the bp so to speak when I would let off at the track.
Definitely sounds like the combination of smaller downpipe and smaller turbine side were hurting the top end. I want to try to avoid that for sure. I'm just going to have to find some more money and do the twins. A single would simplify the build, but for the power I want to reach, I don't have the room for a big enough down pipe. And no, I'm not going to run the dp out the fender or dump it in the front. This is a street car and will retain a full exhaust.
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