Supra Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
62 Posts
Discussion Starter #1
Has anyone ever gone with a 74 or 76mm GT42 or PTE setup and found the lag was too much for them?

The turbos I'm looking at right now are the GT4294 (71mm) GT4202 (74mm) and the custom PT GT4276 (76mm).

I'd love to have the extra power of the bigger turbos, but I would think 800whp is PLENTY for mostly street use.

Looking for 10's in the 1/4, but being able to hit high 9's would be nice as well.

I like the linearity of the 71mm power band and how you can get 400hp at 4000 rpms or so.

I've also heard the on/off of the 74mm+ turbos is bad, but the power hit is just insane.

I have AEM + all the supporting mods (cams, heads, valvetrain, forged internals), so I'll be able to handle the power. It's just do I want the extra power for the lag?

I know a LOT of people on here will go for power no matter what, but it would be nice to hvae an extra 1000rpms of a powerband if it's mostly street use.

Let me know what you think if you've had/ridden in the different type of cars.

Thanks!
 

·
Bench Racer of the Year
Joined
·
692 Posts
You asked some very good questions - actually some of the same questions I have. I'll be dumping money into a turbo soon enough and actually want to hear these oppinions. I've herd so many people talking about the GT42s that I am almost possative we wont be disappointed.

Brian
 

·
Administrator
Joined
·
17,247 Posts
There are almost always pros/cons to discuss with turbo sizing. I see the GT42 class as being the "must have" if <10 second quarter mile passes are your goal, and obviously killer top end/dyno potential. Naturally, it doesn't take a GT42 to hit a 9, but you can see that nearly all who are doing it with regularity do indeed have "that much" turbo on-board.

I would never be able to give specific comments about turbos that large, but would tell you to make sure that you know what you're building for in terms of your own goals and plan accordingly. In some ways, these turbos can be somewhat of a "be careful what you wish for..." scenario. :)
 

·
Registered
Joined
·
1,303 Posts
I noticed you didn't mention a built bottom end. Most of the reputable builders/shops/tuners I've spoken to have told me that 800rwhp is already pushing it on stock bottom end components.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #5
The whole engine is built, sorry didn't mention it.

I've heard of stock supra engines going for 1000+ hp as well.

I know of a member personally that has ~850+ on a full stock engine, with just some cams etc, heads have never been removed.

This isn't on a supra, but 3L 3000GT, all of our cars are similar, but you guys seem to know more on single turbos than we do. :)

Engine has:

Custom ross racing pistons, pauter rods, stock balanced/polished/lightened crank, ARP studs all around, cams, valves, springs, stg III ported/polished heads.

It's ready for anything you can throw at it...I'm just trying to find a good turbo.

The nice thing is that you can just switch between them all if one isn't enough/ or too much power.

I definitely want spool no later than ~5000 rpms. I can deal with 5200 for full boost (~30psi), but I don't want 5500+. I've heard from one guy that the 76mm spools at 5600, but then others tell me that full boost is had at almost the exact same time as a 74.

From what I have seen in dynos and riding in my buds cars and from searching around....

71mm starts spooling a bit beneath 4000, and you can have + boost before 4000 or around 4000 and it just ramps up. 400hp by 4000 rpm is fully possible.

74mm starts spooling at 4500, and you MAY get 1-2 psi beneath that. Once 4700rpms hits, all hell breaks loose and youre in for a hell of a ride. Traction becomes a BIG problem, and it's VERY hard to drive on a roadcourse.

The thing is, for street only use, the 71mm has more power beneath the curve, and the 74mm really only takes over at 30+ psi. I do plan on running 35-40psi (if I get the bigger turbos) at the track....but around the streets probably 30-35psi max.

But, here's the kicker too. The 71mm can throw down ~800hp at 30psi or so, while the 76mm will throw down 900+ rwhp at 30psi, so obviously the 76mm is more efficient around that area.

But still 800rwhp isn't something to laugh at, I just like the 900 and 1000 hp marks from a bragging standpoint.

I guess the place where the 74 and 76 really shine is the highway where you can really open them up. On the street I've read it's hard to get into boost because you gotta get all the way up to 5k.

v8 linear power feels great, but so does a 200hp - 900hp hit in < 2 seconds at 4700rpms.

I'd just like to get some feelings from those who have had 2 similar turbo setups or ridden in them.
 
1 - 5 of 5 Posts
Top