Fuel's Winter Project: Build It Before It Blows

[JeremyH]

A guide only, as my kit had to be odd man out with that rule of thumb.

Actually it fits you perfect. You created backpressure initially imho. You had a 3" downpipe (75mm) and a 65mm turbine wheel. There are lots of guys in the 700rwhp+ range with 65mm turbines and 3" downpipes.
Your new garrett turbo has a 76mm turbine wheel. That's a wheel bigger than the downpipe. So that larger wheel surface area was then having to condense back down in that downpipe, so the larger wheel was kind of diminishing returns with the 3" downpipe. A smaller turbine would have in fact had less back pressure at the same pressure ratio. That's why you saw good gains when you increased your downpipe size, it allowed that 76mm turbine to breath.

 

[JeremyH]

I would also need to redo the up pipe just a little to move the turbo forward in the engine bay so it didn't hit the can cover. A forward facing kit will help keep my spool down when going to the larger turbo. That is great info Jeremy thank you for sharing that. I really wanna try a CT43-8079

I would go no bigger than the 7675 thats a good step up from the 6765.

We are going to run a CT43-8079 on our coyote kit standard with a T4/4" vband turbine housing. 4" downpipe for two feet or so, then a 3" cutout, followed by a 3" y to the over axle pipes.

 

[weather man]

Actually it fits you perfect. You created backpressure initially imho. You had a 3" downpipe (75mm) and a 65mm turbine wheel. There are lots of guys in the 700rwhp+ range with 65mm turbines and 3" downpipes.
Your new garrett turbo has a 76mm turbine wheel. That's a wheel bigger than the downpipe. So that larger wheel surface area was then having to condense back down in that downpipe, so the larger wheel was kind of diminishing returns with the 3" downpipe. A smaller turbine would have in fact had less back pressure at the same pressure ratio. That's why you saw good gains when you increased your downpipe size, it allowed that 76mm turbine to breath.

The back pressure decreased when I went to the garrett. But it was a bigger a/r, so not apples to apples. Believe me, I wish I hadn't had issues with 3" when everyone else didn't!

 

[JoshK]

I need a turbo big enough for when I go big bore stroker Jeremy!

 

[weather man]

I need a turbo big enough for when I go big bore stroker Jeremy!

Did you look at the garretts Josh?

 

[JoshK]

I sent Dustin a pm earlier today, just haven't heard back yet

 

[JeremyH]

The back pressure decreased when I went to the garrett. But it was a bigger a/r, so not apples to apples. Believe me, I wish I hadn't had issues with 3" when everyone else didn't!

Yes it did, but that's what I ment by diminishing returns. That larger turbine helped initialy but on the big end in the upper rpms the 3" down pipe was hurting you because of the larger turbine size. Hence why when you went to the larger down pipe you saw a lot better gains on that turbine. AR size has a smaller effect on power 5-10 peak rwhp difference on a ar size change.

These were my numbers with the different ar's I did on my old setup at the same boost levels off the top of my head. All 3" downpipe. Note how torque goes up though. Even though the .68ar made less peak power that torque was a blast on the street.

.96ar 655rwhp 580rwtq
.81ar 650rwhp 601rwtq
.68ar 639rwhp 704rwtq

 

[JeremyH]

Dustin does the downpipe mod on his coyote kit as well he runs a 5" downpipe for 2-3ft then shrinks it back down.

 

[JeremyH]

And this is how JPC makes 1200rwhp with their 3" downpipe on their coyote kit on a 7675. I will use the 3v kit Josh posted as an example. They put a cutout right here.

 

[JeremyH]

I need a turbo big enough for when I go big bore stroker Jeremy!

You will have no problem spooling the bigger turbine with one of the those motors lol

 

[Bobby]

The easiest thing to go is just get our single kit and put it on. You can use some parts you have now.

 

[JeremyH]

Here is a look at their downpipe mod with the cutout on the coyote kit which allows them to use a 3" downpipe and still make ridiculous power. So no need to go stuffing a big downpipe in if you don't want to, this method works well also.

 

[gray1622]

If it was me I would just throw a 7675 precision and go from there. You already have nice kit on there. When you change your turbo you can get some back pressure data and If you have problem throw a cutout on there and go from there. I bet that 7675 will give that stock crank a run for money. If you go race car I would got s500 with JPC kit with a 5in down pipe out the passenger side front bumper....

 

[JoshK]

Why all the peer pressure on the 7675. For some reason I really want that 8079.

 

[ethic1]

Don't go with the masses or else you'll only be as fast as everyone else

 

[JoshK]

Haha, noted

 

[Department Of Boost]

Don't go with the masses or else you'll only be as fast as everyone else

That is sig worthy.

 

[jodadejss06gt]

If I'm not mistaken the 7675 has almost a very similar exhaust side as the 67 that you had. The difference is the Cold Side. If you move to that other turbo its a larger frame. I am very very close on one of my pullies with the 76. With the 11:1 and no timing in my car now, I can't feel much of a difference in spool. That turbo is capable of 1000+ why get a larger one?

 

[JeremyH]

If I'm not mistaken the 7675 has almost a very similar exhaust side as the 67 that you had. The difference is the Cold Side. If you move to that other turbo its a larger frame. I am very very close on one of my pullies with the 76. With the 11:1 and no timing in my car now, I can't feel much of a difference in spool. That turbo is capable of 1000+ why get a larger one?

Josh was already running the larger H cover on his 67, where as most run the S cover. You can get different size compresor covers or turbine housing on any size wheels.

 

[gray1622]

Anything bigger than 7675 you need a 4 in down pipe. That's going be a lot of work. Sure you could get a 3in to fit but I figure that precision knows what it's doing when they come with 4-3/8 v band flange. The cutout ideal is very interesting.