So im running an on3 70mm turbo right now on my 95 cobra stock motor. Only motor plans so far in the future is meth and MAYBE an f303 cam when i do my head gaskets. Ive been seeing a smaller turbo like a 60-62mm would be better for stock motor, when would i make full boost? With the 70 im getting full boost at 2600-2700 on 7lbs. But also i have a buddy selling a practically new on3 76mm ball bearing turbo...but then i see they dont make full boost until 3500+

 

usually a 60-70mm turbo works pretty good on a 302,, a 70 will make enough hp to split the block

 

+1. I think pretty much anything in that range can split a stock block. Anything bigger than a 70, and it costs you spool time without any gains.

 

One thing im confused about is when is about a 62mm supposed to hit full boost? Im hitting at about 2600-2700 with my 70 but ive heard similar for people with 62

 

Then why swap? Do you want to be able to spool the turbo by bumping the starter?

 

Im not saying im going to, im just seeing which size is most beneficial for my motor but sounds like im running a productive size so ill probably get another 70 or a 67

 

My Gt45 69mm makes 1-2psi at 2700rpm

 

Wasn't trying to sound like an asshole with that post. 67mm is a good size. If your current turbo is done I'd look into a new s366 or s369.

 

the borgs are good units, and loud!!!!

 

Its fine man haha this is my first ever build so im a bit ill knowledged to be honest. 1-2psi at 2700? How many pounds are you running and when do you shift? And to be honest i was thinking of running the 67mm ball bearing from on3 because i havent read any bad reviews and its an inexpensive ball bearing which ive heard are decently loud as well...loud is always welcome

 

I have run 14.6psi, may add a couple more in the future. 5psi @ 3k, 10 @ 3500, controller setting by 4k. Presuure taken in intake.

Green line is boost #ad

 

What's the rest of your build? Stock long block or do you have hci? Stick or auto? gears?

I saw this thread and came here to tell this guy my gt45 feels to laggy on my build haha. Now you have me wondering if I need to investigate another problem. I'm not getting into boost at all in 1st and not until about 5k in second. 3rd starts around 3500..If I stay in the gas and power shift it's a bit better but I hate doing that on the street just to see boost under 60mph....I've just summed it up to the turbine side being so huge it just takes too long to spool on a stockish 302...Your results are obviously different, now I'm curious! I've been shopping other smaller 'budget' turbos as a replacment the last few days because I'm fed up with the lag. I was looking at the on3 70mm with the .68 AR seriously as a better match. The hotside is much better sized..I know on3 has..well, a certain reputation though...haha

 

Hci. 195 heads, single plane intake, xe258 208/216 cam. Tko600. 4.30 and 3.27. Boost took a hair longer in first gear only with the 430, but the extra gearing made up for it.
2in uppipes and 3.5dp, 3in cold side.

 

Yeah, Fair to say your combo is definitely flowing better than mine. Your heads and cam are much better suited. Im still surprised how soon you have boost coming in...I'm jealous haha

I have gt40p heads e303 cam 2.5" crossover which I think is killing me and a 3" DP. Edelbrock performer knockoff / 70mm TB. I've thought about shrinking my crossover down to 2 or even 1.75 I think it would help a lot. Also contemplated the old block off one scroll trick....The car runs decent but I expected way better response. I've had the setup apart a few times for various reasons and been through a lot of tuning with very little improvement in boost response I think I just need to go smaller turbo or get some real heads. It would probably do find with an auto behind it but I just bought an A5 kit....not really an option now lol

Anyway, sorry OP for getting off track..I'd stick with the 70 you have now, I'll probably wind up with something similar or even a 62

 

Well main reason i plan to get a new turbo is because the on3 70mm i have i bought used and leaks even after resealing it twice...so i was looking into the on3 67 ball bearing but kinda interested on the borg warners mentione above, look like some real nice units

 

FWIW my HX52 (72mm turbo) made 4 psi @ 2400 and full boost at 2700.