What turbo for 9:1 compression, GTX28/30?
 

Trying to decide which turbo to go with to get 400whp with 93 gas and meth BUT with 9:1 compression.
Let's not make this a discussion about why my compression is so low!

400whp on 93 is my ultimate goal, but of course I want the best possible dyno curve and response. I'm upgrading from a Precision that has some lag to it.
I do not plan on getting any more power out of it so I could care less about room for upgrading. I'm also trying to do this without E85.
All I know is that my turbo creates a lot of heat at 20psi and I'm trying to get something more efficient. So I want a GTX series turbo.

I've been doing a little research and the GTX2867R and GTX3071R seem like the better of the options. I've been told that the 3071R is the golden boy of the GTX30 series.
I'm just afraid that the 2867R won't be able to produce 400whp at 93octane/meth with 9:1 compression. And even if it did, would it be able to do it efficiently?

Thanks!

@Dipstik-sportech

@diss7

Banned

GTX3076 or go home

BW 7163

GTX55 or go home.

Lol.

A gtx2867r will do 400whp on pump on 11.0:1 comp.

It will easily do it at 9.0:1 on a 20 year old motor, sr,RB,3S,4A,fj. Etc.

You don't need to drop anywhere near that far on a fa.

But to answer your question, yes it will work.

If it's a track car I'd go gtx3071r as the comp would be in better efficiency zones in the high rev range.

If street car with light track, I'd stick to the gtx2867.

Lol...

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theres no reason for meth at that compression. It wont do anything and you wont get response from this motor regardless with a comp that low. That comp is extremely low for this motor. A gtx2867 will produce good torque but the top end is going to fall on its face after 6k because of that compression ratio. You'll need a gtx3076 or bigger. I wish I could remember who it was on here but he was struggling to hit 400whp with that low a compression on a gtx2867r. It will be blowing a lot of hot air.
Im on the gtx2867r and ran it out of its efficiency on the top end with stock compression at 460whp on e85 at 19psi. You'll be running MUCH higher psi on 93 at that comp. Fullblown had a car on their facebook page that was 10:1 on the 2867 on 91 that made somewhere around 400 at my psi I made 460 at, and I made 40foot pounds more torque everwhere compared to that motor.
Save your money, raise the compression back up and go e85. Or you wont the have torque or throttle response youre looking for

Not to be thread jacking, but are there hypereutetic pistons for the FA20? Are the stock ones just randomly cast or do they have bits of silicon in them?

if I remember right dipstick sportech maxxed out at 360whp at 16psi on 91 and 450 at 19 psi on e85 at 9.5:1 with a pte 5858 which should be comparable to a gtx3076.

I think you're overlooking his compression ratio.

I think its not worth buying another turbo when he can just put pistons in it and achieve his result at a lower psi and will make more usable torque. High cr with low boost will be so much better than low cr and HIGH boost. As far as usable torque and throttle response. But OP said he doesn't want to do that. I think he'll end up unhappy since he'll be running too big a turbo to make the hp number he wants.

The pistons aren't the problem. The rods are.

Clearly he just wants to buy a built block. One that comes in at 9.0:1 . What I am saying is that a 2L at that static comp using a gtx2867r is a great combination; because the motor running at that comp means the turbo will be boosting harder; and it's more efficient when boosting harder. So that comp and a gtx2867r end up being a great combo.

Run high static comp, the motor is more efficient. Because the motor is more efficient it means it's less of a restriction. Because it's less of a restriction it can ingest more air. This means to make the same power the turbo is operating at a lower boost level. This isn't necessarily a good thing.

Look at any modern turbo and note where the choke line is at given pressure ratios. Where the choke line extends it's furtherst to the right should be the target pressure ratio. This means that running lower static comp so that the turbo is operating at its ideal pressure ratio will result in optimum power.

That's why people running a gtx28 at 7psi will say the turbo will choke in the top end. Look where the choke line and therefore the efficentcy zones at that pressure ratio on the comp map and you'll see why. Now if they ran lower static comp, then the turbo can operate at a more ideal pressure ratio; and the setup will make more power with the same turbo.

Also, your comment about lower static comp will result in more usable torque is incorrect. Because he is knock governed by pump fuel.

Lowering the static comp would allow him to ramp up a small turbo very aggressively. Something you can't do at 12.5:1 on pump fuel.

Thanks for all of the replies guys. Lots of good info here. @Manji do you believe I can achieve 400whp with the GTX2867R on my compression efficiently?

I've already got the 9:1 compression :)

Yes easily. You'll get there at 1.0 - 1.1bar, assuming it can rev. I have a very similar setup myself.

If its a stock head it'll probably need 1.2 bar.

Either way, 1.0 - 1.2 bar are ideal operating pressures for a gtx2867r. That where the efficency islands are at their widest.

That's about 15psi, are you serious? That's crazy.

I'll also add that one thing I have noticed about forums is there seems to be this obsession with "High comp low boost for the win"

Probably because one person said it once, and the rest are just jumping on the bandwagon.

In the real world, with real world limitations like pump fuel, you'll find the opposite is true.

I'm not saying that high comp is bad. I'm saying too many people are looking at their turbo builds through NA-knowledge-tinted sunglasses.

Lets take a practical example. Using this motor and a gtx2867r (yes I love this turbo)
On 7psi making 300whp at 12.5:1, that pretty much all your going to get. Knock limited. Which in part is caused by the turbo operating at this level inefficeintly, but mostly because of the static comp. (This is why a bigger turbo at this level achieves marginally more power, as it's landing in a better efficency zone at that point.
But if you run the same motor at LOWER static comp, meaning the gtx28 has to BOOST harder (that doesn't mean is working harder, work should be judged by effiency zones) it will make 400whp at 14psi and end up at the same efficency zone. (So IMO similar work load on the turbo) You also wont be governed by knock as you could spike the mid range up higher if you wanted to.

A 2 litre motor, running a gtx28 frame turbo at 400whp, at 9.0:1 static comp will NOT have poor throttle response.

Because you're no longer near the knock threshold, you can get more aggressive with the tune, which is where a lot of throttle response really comes from.

You can't get that aggressive on pump fuel & 300whp & 12.5:1 c/r.

Fantastic, thanks man. I'll have to ask my tuner to get more aggressive because I'm at 350whp at 20psi right now on my Precision 5431.

I'd recommend swapping the cams out. That's whats holding you back.

I can't really divulge too much about it.

But its the head causing the restriction that is governing that boost level.

NA cams are often not very good FI cams.

I'm not familar with precision turbos at all, but even a tiny gtx2860r will hit 350whp at 20psi. But I'm point to the head, not the turbo.

Well I'll see what we can get from the current setup with a retune, just with an added water line because the GTX is oil/water, and v-band.

If I'm not getting close to 400whp then I'll cam it out.

Edit: I take that back. Cams are barely out, if at all, for this car. Not to mention they wouldn't be cheap since we need 4. And you have to pull the motor to install. Sounds like a ~$3000 job to me.

Pte5858 and I've hit higher than that on lesser quality fuel

You don't have to pull the motor to put cams in.

All the main camshaft manufacturers are putting their efforts into developing FI cams at the moment; due to the disappointed results from NA cams.

Early next year there will be some good options coming to market.

Honestly I'll probably never go back to Precision.

Were your results on 9:1 compression?

Mixed flow FTW

9.5

For what it's worth, I'm personally a huge fan of the gtx28 series as well.

nice saying:clap:

Unfortunately the masses of enthusiasts understand static compression whereas dynamic compression isn't as well known, or as well understood.

Yea you'll see a lot of PSI the lower the comp for pump gas. Technically you could run more than that if you wanted, but you'd be going past 400whp. Since the GTX28 is a relatively small turbo, I wanna say boost will be there at 2900-3000 rpm. Most people think that low comp will be bad response, but the response is offset from the amount of boost pushed. To make it better I would reccomend a twin scroll manny if they have one for the 28

I mean that's crazy low! I've been running 20psi so far! Although I can't really tell but it might be on a conservative tune. I'd be very happy with 15psi.

I'm not sure about 15 psi though... @woode made 412 whp on 93 on stock CR (I think) with 21 psi

You still remembering your drive of my car? Remember that was only a lowly GT2871R. :lol:

Sure did. Although, I think the OP's goals are quite a bit different. I wouldn't take my current setup to a track - I think heat would kill it.

I like to think of him as being an outlier.

So 12.5:1 CR with 21 psi on 93 pump gas only made 412 whp...yeah you'll need more than 15 psi

Could be a conservative tune. I've seen people with about the same psi making over 500whp.

Andddd now it's time for a GTX2867R!

How much did you sell yours for again?