StatoJase

I have recently changed the turbo on my 408 single set up. I originally had a gt4294 running 13 or 14psi boost made 560rwhp with heaps of pre turbine backpressure. Swapped to a diesel gt4708 with a 76mm comp inducer because it was bigger, free and fit without cutting much. Dynoed 627rwhp with 15psi boost and 780ftlb torque at 3200rpm. Pretty stoked with the results now got to wait for some track time. How does this dyno sheet look in comparison to other 408 with similar turbos and boost?

josepy121380

iTrader: (21)

Seems really low to me. That on motor alone should be around 500rwhp.

ls1_chevelle

iTrader: (9)

josepy121380

iTrader: (21)

Yes I am. My car on 17lbs with a procharger. Stock cube ls1 made 810rwhp. I know its not a turbo. I would think his would be a little north of 700rwhp. I could be wrong though.

ls1_chevelle

iTrader: (9)

You know NOTHING about his combo unless I missed something. Just like I know nothing about yours. Procharger size, compression ratio, heads, fuel, intake, timing, etc.

But yes it should definitely make more steam but 500rwhp NA is a little far fetched if I assume its built how I think it is.

josepy121380

iTrader: (21)

Yeah sorry I am assuming a 10 to 1 motor. I have seem them do locally 480-500 rwhp NA of course with heads, cam Lt's. Just looked like to me hos power was on the low side.

ghost-1

iTrader: (4)

Do you have the dyno with the other turbo? Whats up with the graph crossing at like 3200 rpm's

Cam72aro

iTrader: (28)

Compressor is waay undersized for a 408, but for free its better than the last one. On 15psi with an 88 or 91 compressor it would make 100 more hp on that motor. It's just not moving enough air regardless of pressure.

ls1_chevelle

iTrader: (9)

Yea I wasn't trying to be a ***** or anything but even a healthy 10:1 with a big turbo cam will be a dog. No disputing a nice NA cam, heads, exhaust deal will make what you say.

StatoJase

To clear things up its a forged 408 with around 9to1 comp, medium sized turbo cam, turbo 400 with a tight 3000 slingshot converter, 9" with 2.75 ratio diff. car is a wb Holden statesman weighing 3800lb plus with me.
The Turbo kit I built myself, around a gt4294 I had originally planned on putting on the stock ls1 with the vortech. Which blew up due to a blow through carb issue. Knew the gt42 would probably be way too small for a 408. Made 560rwhp and ran 10.91 first run but could feel it choking so tested backpressure and stuff to confirm.
Got hold of a gt4780 for nothing and it fit without too much hassle. Got 627rwhp. Going to run it soon.
This car is a full weight street car that I drive when I am home. A Bigger turbo could be on the cards later.

StatoJase

And I didn't think the 4708 was too small a turbo when I fit it. Its bloody huge but the wheels inside obviously don't represent the size of the housings. It was free, it was in good condition, and it is not laggy or anything for a primarily street car. Full boost as soon as its at 3000rpm. So I guess later on I will be looking for something around the 88 to 91mm range to benefit from the 408 cubes.

ittwgn

that power seems fine to me mate !!! stock heads ?? I,ve run 75mm and 88mm turbo's on a 408 !!!! our aussie dyno's are a bit low compared to some figures you see !!! anyway take it back to the track and see the real difference!!! cheers

StatoJase

yeah stock l98/l76 heads from a ve ss donor engine I scored and built. I have flicked through your threads ittwgn. Nice set up. Our season in WA starts soon but at the moment I only go to the off street meets. My baseline is that 10.91 I ran last season so no matter what its quick for me. Just got to hit and leave with the 2 step this season to launch harder I think.

Cam72aro

iTrader: (28)

A dyno dynamics dyno is also pretty stingy as compared to a dyno jet. I have seen 30-40 hp less on them.

fouroff

iTrader: (2)

I’m very interested in knowing what size turbine you had for the GT4708. I’m doing a similar setup. Thanks!
Jeff