Precision 76mm too small for a h/c/i 408?? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 46 Old 05-06-2009, 04:15 AM Thread Starter
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Arrow Precision 76mm too small for a h/c/i 408??

Building up a mild h/c/i forged 408 with 8.8 to 1 compression...and already have a brand new quicktime turbo kit with a precision 76mm. Does this seem too small for the big cubes? I know a bigger better turbo setup will bring out more in the motor but I dont feel like getting rid of it and looking and spending for bigger...especially since its just a daily driver fun car.Anybody have the same turbo on their big cid motor?


87 GT 306 machined/built by me..Windsor Jr heads, E cam, GT40, lt's, Tremec 3550 etc....Tweecer R/T tuned PLX wideband

Bunch of parts for sale..306, fully forged 347, 0 mile 357, Fully Forged 408, tremec trans, clutch, and more....
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post #2 of 46 Old 05-06-2009, 04:41 AM
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With a properly sized back housing it should be fine. What are your goals?


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post #3 of 46 Old 05-06-2009, 08:11 AM
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my good friend had a 76gts on his built 410w. at 3500lbs, he ran [email protected] (dynoed 800rwhp). although a 76 is small for that engine, he still got good results.

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post #4 of 46 Old 05-06-2009, 08:19 PM
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I am also curious about that set-up........I have a 76gtsh/.96ar with a 408w in the works
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post #5 of 46 Old 05-06-2009, 09:00 PM
 
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76mm will be fine,thats what im getting for my 408.I have a quicktime kit as well.Call precision and ask for Mike Bacon or Joe.They can help you alot.
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post #6 of 46 Old 05-06-2009, 11:07 PM
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Yes, it is not properly sized for that motor...

The exhaust side cant flow enough to get that motor to its potential..

People run 2 88s on motors that big.

Before I get flamed...

Will the turbo work? Yea..

May it go 8s? probably

It is better suited for a 302... Yes

Im just saying that a bigger turbo like a G trim pt88 or 91 is a better match for that motor. Any 76 will choke it.
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post #7 of 46 Old 05-07-2009, 12:01 AM Thread Starter
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No specific goal...I'm just going with what I find for a good deal. I barely buy anything new hah....

The turbo has a .68 hot side which I was told will spool pretty quick. But with such a big cubed motor I don't need it to spool quick. so the smaller area will be a waste? Im not up on the a/r sizing, smaller number spools quicker? but not as good for high rpm boost?

87 GT 306 machined/built by me..Windsor Jr heads, E cam, GT40, lt's, Tremec 3550 etc....Tweecer R/T tuned PLX wideband

Bunch of parts for sale..306, fully forged 347, 0 mile 357, Fully Forged 408, tremec trans, clutch, and more....
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post #8 of 46 Old 05-07-2009, 12:20 AM
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Originally Posted by 357poweredstang View Post
No specific goal...I'm just going with what I find for a good deal. I barely buy anything new hah....

The turbo has a .68 hot side which I was told will spool pretty quick. But with such a big cubed motor I don't need it to spool quick. so the smaller area will be a waste? Im not up on the a/r sizing, smaller number spools quicker? but not as good for high rpm boost?
basically..

That thing is absolutely wrong for your motor..You will have back pressure issues and risk burning valves.
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post #9 of 46 Old 05-07-2009, 12:49 AM
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basically..

That thing is absolutely wrong for your motor..You will have back pressure issues and risk burning valves.


couldn't have said it better. you need to measure your pre-turbine pressure and compare to the downpipe. it will be high and you will kill the motor. you NEED a t6 turbo

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post #10 of 46 Old 05-07-2009, 01:23 AM Thread Starter
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I had plans on using this setup on a 302 stang I have but I want to take advantage of the motor being built with low compression and ring gaps gapped for boost, and I'm not going blower. I dont have the money to go all out on a nice setup just trying to use what I got.

I will be going with a Jay Allen custom grind which will be helpful in working with my setup...What's the biggest turbo I can go with while still using my stock T4? flange?...a turbo that would work best with my setup that will fit my hotside.


87 GT 306 machined/built by me..Windsor Jr heads, E cam, GT40, lt's, Tremec 3550 etc....Tweecer R/T tuned PLX wideband

Bunch of parts for sale..306, fully forged 347, 0 mile 357, Fully Forged 408, tremec trans, clutch, and more....
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post #11 of 46 Old 05-07-2009, 08:14 AM
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What's the biggest turbo I can go with while still using my stock T4? flange?..
pt88, bw s380. the turbine housing is alot bigger on a pt88 and s380 compared to a 76. the pt88 uses a 4" dp, so you would have to change that on your setup.
my friend swapped his 76 out for a pt88. he ran [email protected], and the car was 50lbs heavier. i like the pt88. for it's size, it packs a big punch.

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post #12 of 46 Old 05-07-2009, 08:46 AM
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pt88, bw s380. the turbine housing is alot bigger on a pt88 and s380 compared to a 76.
agreed...
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post #13 of 46 Old 05-07-2009, 11:53 AM
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Did any of you experts read the "mild" part in his first question? Is this a stock block? Just because it is a 408 doesn't mean it will take some abuse.

The proper way to pick a turbo has little to do with the engine. A 300 inch motor and a 400 inch motor will make about the same peak power with any given turbo. If a 76 mm will flow enough air to make 800 hp then it will make 800 on both engines. (at different rpms no less)
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post #14 of 46 Old 05-07-2009, 12:23 PM
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oh boy.....
it's the turbine side that is the problem.

edit: and to add- no, two different size engines will not make the same power with the same turbo (because of the back pressure caused my the turbine).

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Last edited by twofast; 05-07-2009 at 12:25 PM.
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post #15 of 46 Old 05-07-2009, 12:36 PM
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OK.....Then you are telling me that if we had a meter to measure the amount of "exhaust" air coming out of the pipes, a 400 will make more than a 300 with the EXACT same air going in the inlet of the turbo? Where does the extra air come from??????
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post #16 of 46 Old 05-07-2009, 01:02 PM
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OK.....Then you are telling me that if we had a meter to measure the amount of "exhaust" air coming out of the pipes, a 400 will make more than a 300 with the EXACT same air going in the inlet of the turbo? Where does the extra air come from??????

Yes, hotter air takes up more room than cool air creating more pressure on the exhaust side. The problem comes when there is say 10lbs in the compressor side and 20 on the exhaust side.

You can have exhaust backing up into the motor hurting ve and possibly parts.

Also, when the turbo sees more pressure on 1 side than the other, it loads the bearing system unevenly leading to failure.

And yes, we have meters for these things.
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post #17 of 46 Old 05-07-2009, 03:31 PM
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So now the bigger motor is hotter? Interesting....
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post #18 of 46 Old 05-07-2009, 03:33 PM
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So now the bigger motor is hotter? Interesting....
I don't have the patience for this nonsense.
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post #19 of 46 Old 05-07-2009, 03:53 PM
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Maybe you should call Job and ask him if debating with me is useless?
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post #20 of 46 Old 05-07-2009, 03:59 PM
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renfro,
if you think a 76 will make the same power on a 302ci as it will on a 577ci, then you have no business being in this forum.
but i will take some time and try to explain it better.
say to make 900hp with a 76mm on a 302 will take 25psi. the backpressure may be 50psi (as measured at the merge collector). the bp ratio is 2:1.
now, take a 500ci with a 76. it will only take 10psi to make 900hp. if the bp is still 50psi, then the ratio is 5:1.
having a 5:1 ratio will obviously cause reversion problems and the pumping losses will be much greater.
the morale of the story is- bigger engines need bigger turbine housings.

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post #21 of 46 Old 05-07-2009, 04:00 PM
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Maybe you should call Job and ask him if debating with me is useless?
I wouldn't waste his time with this.

Plus he won't be out of work for another half hour.
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post #22 of 46 Old 05-07-2009, 04:21 PM
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renfro,
if you think a 76 will make the same power on a 302ci as it will on a 577ci, then you have no business being in this forum.
but i will take some time and try to explain it better.
say to make 900hp with a 76mm on a 302 will take 25psi. the backpressure may be 50psi (as measured at the merge collector). the bp ratio is 2:1.
now, take a 500ci with a 76. it will only take 10psi to make 900hp. if the bp is still 50psi, then the ratio is 5:1.
having a 5:1 ratio will obviously cause reversion problems and the pumping losses will be much greater.
the morale of the story is- bigger engines need bigger turbine housings.
Interesting reading.... So if I call up xyz turbo company and tell them I need to make 1000 hp they are going to tell me that a turbo on a 300 inch motor making 1000hp with an 88mm turbo will not make 1000hp on a 408. I guess that all the turbo co. should change their compressor maps to include the cubic inch of the motor. You guy's are alot of fun.
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post #23 of 46 Old 05-07-2009, 04:25 PM
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Interesting reading.... So if I call up xyz turbo company and tell them I need to make 1000 hp they are going to tell me that a turbo on a 300 inch motor making 1000hp with an 88mm turbo will not make 1000hp on a 408. I guess that all the turbo co. should change their compressor maps to include the cubic inch of the motor. You guy's are alot of fun.
None of us mentioned a difference in power potential.

If you read my first post in here, I clearly stated it would still go 8s.
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post #24 of 46 Old 05-07-2009, 04:29 PM
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Interesting reading.... So if I call up xyz turbo company and tell them I need to make 1000 hp they are going to tell me that a turbo on a 300 inch motor making 1000hp with an 88mm turbo will not make 1000hp on a 408.
correct. they will recommend a different turbo for the two engine sizes. you're learning.

edit- i never said an 88 wouldn't make 1000hp on a 408. but the max hp will be different.

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post #25 of 46 Old 05-07-2009, 04:30 PM
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The "morale of the story" is that bigger engines can power bigger turbos thus making more power. The point is that if this guy is wanting to make x power at x boost he can expect a certain size turbo to do that job. He never said what power he wanted. If he is looking for 600 hp an 88 is useless. Hell I ran everything from a single 106 to two 88's on my 408. Comparing that motor to what this guy has is like comparing apples to potatoes. Bigger motors do need bigger exhaust housings but the compresser will only flow x amount of power. Period.


Where in the heck is MILLHOUSE we need an expert.
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post #26 of 46 Old 05-07-2009, 04:33 PM
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None of us mentioned a difference in power potential.

If you read my first post in here, I clearly stated it would still go 8s.
It is you guy's that are telling him to get the 88 for his near stock combo. Although he has not posted otherwise. I assume if he is trying to set records he would not be here. lol
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post #27 of 46 Old 05-07-2009, 04:39 PM
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correct. they will recommend a different turbo for the two engine sizes. you're learning.

edit- i never said an 88 wouldn't make 1000hp on a 408. but the max hp will be different.
They will not recommend a different turbo, they will recommend a different EH or trim. The fact are simple guy's a certain size compresser will make that HP on any config. engine.
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post #28 of 46 Old 05-07-2009, 05:01 PM
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You guys need a referee!!!!!!!!!!!!!!!!!

Ding Ding round 6!!!!!!!!!!!!

I luv a good clean fight.......LOL

Good info fellas!!!!!!!!!!!
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post #29 of 46 Old 05-07-2009, 05:46 PM
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It is you guy's that are telling him to get the 88 for his near stock combo. Although he has not posted otherwise. I assume if he is trying to set records he would not be here. lol
Damn, I never considered that a 408 with a set of heads, camshaft and intake is "near stock".

I just got rid of my gt4788 to put gt55 on my bone stock hci Dart 327.

Last edited by Will Evers; 05-07-2009 at 05:48 PM.
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post #30 of 46 Old 05-07-2009, 05:48 PM
 
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Like I said in my previous post,call precision turbo and ask to speak to Joe or Mike.I have the same setup and yes it will work,but I will be going bigger later.5s in the 1/8 arent a problem.
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post #31 of 46 Old 05-07-2009, 06:27 PM
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Damn, I never considered that a 408 with a set of heads, camshaft and intake is "near stock".

I just got rid of my gt4788 to put gt55 on my bone stock hci Dart 327.
Not much different than a 93 Lightening motor with a stroker crank. Still not more than about 600 or so HP before the block splits. That motor could break with a 62mm turbo much less an 88. Maybe he should put the 88 on so he can run it at 2lbs of boost before it breaks. Then he can brag to all his peeps that he can make 600 hp at 3lbs of boost.....
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post #32 of 46 Old 05-07-2009, 06:30 PM
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Like I said in my previous post,call precision turbo and ask to speak to Joe or Mike.I have the same setup and yes it will work,but I will be going bigger later.5s in the 1/8 arent a problem.
Hey I am just starting to have fun with these guys, don't run them off. Let them continue to argue that we should run an 88mm on a "mildly modified engine."
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Sorry Renfro,LOL!I'm not tryin to run anybody off,just tryin to give some alternatives.I think Brent Davis @ turbo forums is running an 88mm on his A4 block?I think hes running like 30lbs of boost to,and makin a 1000hp.Unbelievable,thats gotta feel like a monster.We're this subject to death!
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post #34 of 46 Old 05-07-2009, 08:51 PM
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lol @ the guys saying a 76mm is too small for the 408. It all depends on what the guy wants to do with it. 76mm will make good power on a 408 and will be plenty happy doing so. The issue is not the compressor side, which the 76mm refers to. The issue is the turbine side, which could have been anything going by what was given in the first post. Everyone making ASSumptions and automatically saying it was too small. On top of that the original poster has made no mention of what type of turbine wheel the turbo has. That makes a big difference as well.

One thing is for sure, now that he has informed us of the turbine housing size, he definitely needs a larger turbine housing. There are quite a few options available (as high as 1.71 A/R) to him depending on what the turbine wheel is and that will significantly reduce the backpressure in the exhaust manifold. The turbine housing and wheel will be the key to making this turbo work.

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post #35 of 46 Old 05-07-2009, 09:58 PM
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Now look, you guy's have gone and left me nobody to play with.
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