5.3 Twin On3 70mm's
Yeah i totally agree. I wouldn't think about doing twin gt45's but if he wants to do them I'm saying the nitrous would make them somewhat usable for the strip. On the street, i think it would suck *** to do twin gt45's. The on3 70's will do just fine for wicked. Me personally would do the 61's because i drive on the street all the time and want instant boost.
It's kind of hard to go against 71 chevy. He has done this and run some damn good times. A good point is the 70's would bolt right on with no modifications. The GT45's would need some modifications and definitely need the nitrous. So probably is just better to sale the nitrous kit cheap and get the ON370's. This way it would be good on both the street and the strip.
Lots of good input but I'll go ahead and give the on3 70's a shot first.
Lots of good input but I'll go ahead and give the on3 70's a shot first.
Thanks for the kind words. ive been overturbo'd and overcammed,
then underturbo'd and undercammed, and going under is more fun than going over
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From: Michigan
I doubt the box and packing adds up to 2 pounds (EDIT: I had to unpack the turbo to measure it for a downpipe V-Band flange, so I weighed it while I had it out of the box and sure enough, 33#), so this is a seriously heavy turbo. Having said that, I just read some of the recent threads on turbo explosions and it caused me to think that some mass in a turbo might not be a bad thing if it is in the turbine housing, etc...
And one other observation, I've had quite a few turbos over the years, and this one seems very nice quality in comparison to the others that I've had (most recently a nice billet wheel Precision that smoked, but did not blow up. Lol).
Last edited by Tjabo; Sep 24, 2012 at 09:51 PM. Reason: Additional information
Thanks for the info tjabo. Sux to here about precision turbos i hear their turbos are pretty badass but customer service blows. If the gt45 didnt have that small compressor id be all over it.
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I just put twin T70s on my L76 and its a laggy bitch...I was coming from an S480 1.32AR with a quick spool valve, now am running the 70s with the .68AR housings. I used to be able to foot brake whatever boost I wanted fairly quickly, but now after 4-5 seconds it'll only hit around 4-5psi. This is with 4700ft DA, but still noticeably slower spool than the 80mm. May have to grab some of those on3 61mm turbos.
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From: Felton Pa
I've spent a whole year building my 4.8 tt project and used the Ebay t70's. The turbos are so laggy, I hate them. I can't get them to make over 6psi with 8psi springs. They don't start to spool untill 3000 rpm and doesn't make full boost untill almost 4000rpm. It went a best pass 13.60 @ 103 with a 2.22 60'. HELP!!!
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Joined: Oct 2011
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From: Felton Pa
I have FMIC and the afr stays between 11.2- 11.5 and I tried timing all over the board. I tried timing it like a N/A car till about 3400 then went to 21* at one point. It's losing so much on the bottom end.
I also run 93 octane and have a 3000 stall.
I also run 93 octane and have a 3000 stall.
Zack
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Whats the CAM look like in these laggy motors???
4.10 rear gear... really???? You are letting the engine have SOOO much mechanical advantage here that the motor never loads the turbos up to make them work!!!! Get a 3.42 in the thing....
Get the air fuel up in the 12.3-12.5 range till it starts making 2-3 psi then then bring it down to 11.5. Leave ALL the timing in it till 5-6.... hell on alot of tunes i dont start pulling timing till 8!
9 times outta 10... lag isnt the TURBOS FAULT....its in the tune and setup!
4.10 rear gear... really???? You are letting the engine have SOOO much mechanical advantage here that the motor never loads the turbos up to make them work!!!! Get a 3.42 in the thing....
Get the air fuel up in the 12.3-12.5 range till it starts making 2-3 psi then then bring it down to 11.5. Leave ALL the timing in it till 5-6.... hell on alot of tunes i dont start pulling timing till 8!
9 times outta 10... lag isnt the TURBOS FAULT....its in the tune and setup!
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From: Felton Pa
I had 3.08 gears in it and it was way worse. It does have a stock cam and LS6 springs. I don't wanna go to big on the converter, it is a pure street car, and it flashes at 3000 but if I powerbrake it it starts driving through the brakes at 2200 or so. I figured my SETUP was bad, thought the turbos were just to big for a stock 4.8. When idling they stop spinning completly.
Well, they ARE 70mm turbos. You can't expect magic out of them and the turbine tech is probably not exactly the latest greatest compared to a Borg or Garret. If you were looking for full spool by 3000 rpms then a pair of T3 sized turbos or smaller T4 turbos would have been a better bet and something in the 56-62mm range.
Some things to check and try in addition to the excellent advice from LilJohn. Make sure there are no exhaust leaks. Wrap any piping leading to the turbos. Both of those will aid in spool up. But you can only expect so much from those turbos. If you want them to spool up a little quicker try putting a little stiffer spring in there to make sure the gates are not cracking open too early.
Some things to check and try in addition to the excellent advice from LilJohn. Make sure there are no exhaust leaks. Wrap any piping leading to the turbos. Both of those will aid in spool up. But you can only expect so much from those turbos. If you want them to spool up a little quicker try putting a little stiffer spring in there to make sure the gates are not cracking open too early.
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I had 3.08 gears in it and it was way worse. It does have a stock cam and LS6 springs. I don't wanna go to big on the converter, it is a pure street car, and it flashes at 3000 but if I powerbrake it it starts driving through the brakes at 2200 or so. I figured my SETUP was bad, thought the turbos were just to big for a stock 4.8. When idling they stop spinning completly.
The stock cam just does not have the valve events anywhere close to proper to drive those turbos.
I tune a 331 sbf with a 218/218 @.050 hydraulic roller that does the same thing. At idle you can reach in and grab the compressor nut on the S480 and stop it completely.
Proper cam and springs, 400 more on the stall, and back to a more proper gear.... youd be much happier with your decision to go twins.
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Joined: Oct 2011
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From: Felton Pa
Until you are prepared to put a cam in that motor... it will never do what you want it to do. Plain and simple. Had you left the gear alone and done a cam and springs you would be alot happier right now.
The stock cam just does not have the valve events anywhere close to proper to drive those turbos.
I tune a 331 sbf with a 218/218 @.050 hydraulic roller that does the same thing. At idle you can reach in and grab the compressor nut on the S480 and stop it completely.
Proper cam and springs, 400 more on the stall, and back to a more proper gear.... youd be much happier with your decision to go twins.
The stock cam just does not have the valve events anywhere close to proper to drive those turbos.
I tune a 331 sbf with a 218/218 @.050 hydraulic roller that does the same thing. At idle you can reach in and grab the compressor nut on the S480 and stop it completely.
Proper cam and springs, 400 more on the stall, and back to a more proper gear.... youd be much happier with your decision to go twins.