5.3 Twin On3 70mm's
If you can afford the front cover and such, I have a LS2 cam I can send ya for the cost of shipping. It would be better than what you have. Was trying to sell it, but it seems to be not a ton of interest in it. You would need the front cover and a couple misc items to get it working.
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I appreciate the offer and sorry I haven't updated. My issue was the turbo was bad. Not sure I posted that or not. Anyways, I am done with the precison turbos. I finally got my ON3 70mm's in this past Monday and that night I had them on the car and driving. Didn't drive it much since I was heading out of town. I am looking forward to see what this will do with the chinese turbo's. I will say this. The turbo's were well packed, looked flawless and bolted right on with no adjustments. My 62's had a .58 AR and these have a .68 AR. I am excited to see what kind of numbers I can get out of it this spring.
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!!!
youve got some great advice and some horrible advice so far. pm me and i'll try to help you with this.
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Thanks. Will do. I am in Houston right now working the next few days and then will be home around Tuesday. I will get with you then.
I am sure the OP would not mind hearing the advice as well. Better to get it out for everyone to see.
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I am debating on doing a similar build with an LS1. i want to use twin ON3 70s, or a single turbonetics t88. How fast do they spool with that .68 and how well do they pull compared to the precisions? I had a single 76mm ON3 turbo with the .96 hotside and loved it! It was a great turbo!
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I was looking into LS6 cam(already have the springs) but can't nfind anything I can afford. Trade and barter system here. My stepfather's boss was supposed to give me a stock LS1 cam but I haven't heard anything about that yet. I don't wanna go too big on the converter, it would make the thing a pig to drive on the street with a th350.
Just because it wont make boost and pull from 2000 rpm?
Youve only got a 3.276 stroke.... it doesnt make the torque of the 5.3 with the 3.622. Nor does it make the same piston speed at the same rpm.
You have to be willing to set the thing up like it needs to be.
More stall will make it feel like less of a pig not more of one. That 4.10 gear actually tightened your converter up some. Combine a tight converter with a camshaft that has 20-30 degrees too late of an EVO event and its easy to see why you arent happy.
The 4.8 will need 600-1000 more rpm to do what a 5.3/5.7 will do on all fronts. Stall speed, peak torque, peak horsepower. In heavy cars... id even give it a little extra gear to help too. All these differences are attributed to the difference in stroke.
Everything in the car has to be working together... gear, converter, cam, turbos.
In all reality... if you pulled the twins off, built a Y pipe... and just ran one of those turbos...youd probably be much happier given the other aspects of the car.
Or we could see what 71 Chevy has to say. But I do agree with everything you have said LilJohn. I am just curious what he has to contribute that can't be said for the world to read.
dont have much to say, just specific questions for the guy having the issues to try to help diagnose the problem.
on the 4.8(non-intercooled on e85, 4.86 gears on a 31 inch tire - equivalent to 4.40 on a 28)
the 70mms would enter positive pressure at 3400 rpms. traded them for the 61s and they would enter positive territory at 3050 rpms. definitely had too big of a cam which hurt the spool. it took 5 seconds on the transbrake to build up to 4500 rpms and 11psi., and it took forever if one just stabbed it in first gear to build boost.the converter would only go to about 3000 NA, then it would take about 3.x seconds to get to 3500rpms, then things would start happening fast after that
what helped was upping the timing to about 28 degrees at full tilt. that definitely brought the beast out of it. I think the 4.8 can take more timing than the others.
also, need to rev it about 600rpms more than an equivalent 5.3 due to the short stroke, so needed to shift above 7000rpms, usually around 7400 with the huge cam.
so thinking about the higher rpm requirement, 99vettefrc, you probably need a converter change. somehing that will stall to allow you to make even 2 psi- for example 4000 stall. it could still be as tight as the 3000 stall in a 5.3 because as you rev it higher, it will tighten up.
so that would be my main suggestion if you want to keep that setup, is get a looser converter, and raise your revs to over 7000 and you should be golden. the loose converter will allow you to get into the power band of the 4.8, and the revs will allow you to make more power and keep the converter still tight.
hope this helps
on the 4.8(non-intercooled on e85, 4.86 gears on a 31 inch tire - equivalent to 4.40 on a 28)
the 70mms would enter positive pressure at 3400 rpms. traded them for the 61s and they would enter positive territory at 3050 rpms. definitely had too big of a cam which hurt the spool. it took 5 seconds on the transbrake to build up to 4500 rpms and 11psi., and it took forever if one just stabbed it in first gear to build boost.the converter would only go to about 3000 NA, then it would take about 3.x seconds to get to 3500rpms, then things would start happening fast after that
what helped was upping the timing to about 28 degrees at full tilt. that definitely brought the beast out of it. I think the 4.8 can take more timing than the others.
also, need to rev it about 600rpms more than an equivalent 5.3 due to the short stroke, so needed to shift above 7000rpms, usually around 7400 with the huge cam.
so thinking about the higher rpm requirement, 99vettefrc, you probably need a converter change. somehing that will stall to allow you to make even 2 psi- for example 4000 stall. it could still be as tight as the 3000 stall in a 5.3 because as you rev it higher, it will tighten up.
so that would be my main suggestion if you want to keep that setup, is get a looser converter, and raise your revs to over 7000 and you should be golden. the loose converter will allow you to get into the power band of the 4.8, and the revs will allow you to make more power and keep the converter still tight.
hope this helps
I would think that if the goal was for a torque monster on a 4.8 a pair of twin T3 56-60mm turbos would be pretty darn fun on the street. Full spool should be around 3500-3700 depending on the gear and my guess is it would enter positive pressure under 3000 rpms easily. I am also curious what specs you had on the cam and why you choose such a low gear. I am honestly thinking my 3.73 is going to be too much gear and I am contemplating going in the 3.23-3.4x range with the 4L80E.
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From: Felton Pa
I understand what you guys are talking about with the higher stall converter. I am using a nonlockup- nonoverdrive trans, so putting a Higher stall converter is going to make this thing slip too much at lower rpms (cruising around the neighborhood). I know I need some cam and I am looking for some smaller turbos. I just have to sell some things to make up some money. If I can change the turbos without a whole lot of refab work I will keep the 70s for a time when I need them. OR.... I will look for a 6.0 long block to stick in its place.I'm just trying to make this thing run better untill such a time that I can afford a bigger engine or smaller turbos.
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I understand what you guys are talking about with the higher stall converter. I am using a nonlockup- nonoverdrive trans, so putting a Higher stall converter is going to make this thing slip too much at lower rpms (cruising around the neighborhood). I know I need some cam and I am looking for some smaller turbos. I just have to sell some things to make up some money. If I can change the turbos without a whole lot of refab work I will keep the 70s for a time when I need them. OR.... I will look for a 6.0 long block to stick in its place.I'm just trying to make this thing run better untill such a time that I can afford a bigger engine or smaller turbos.
What diameter is the converter you have now? 10 inch?
Stock cam wise the LS9 is the only one id consider for you to even try.
John what do you think about that LS2? I think it is like .550/.550 lift or something like that and I forget about the duration. 20x/210 maybe?
99vette, I would just sell the on3 to someone and slap on a set of ebay T3 GT35R turbos. Just try to find one with a vband if you can. Should be plenty responsive and make very good power still.
99vette, I would just sell the on3 to someone and slap on a set of ebay T3 GT35R turbos. Just try to find one with a vband if you can. Should be plenty responsive and make very good power still.
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Sarg... id need all the specs to run the numbers and get the events.
My deal is... it takes a 228 degree lobe to give me the exhaust valve events that i like minimum. Thats a 48 open. 0 close. Use a smaller duration and advance the centerline farther to still have that same open event... and you end up closing the exhaust prior to top dead center.... you have to be careful doing that though... a couple degrees before...ok... 10... not good.
To fit this motor.. id do something like a 216/228 on a 113+4. Negative overlap at 50... good Evo to drive the turbines so itd spool... little more intake duration than stock just to let it breathe a bit better.
My deal is... it takes a 228 degree lobe to give me the exhaust valve events that i like minimum. Thats a 48 open. 0 close. Use a smaller duration and advance the centerline farther to still have that same open event... and you end up closing the exhaust prior to top dead center.... you have to be careful doing that though... a couple degrees before...ok... 10... not good.
To fit this motor.. id do something like a 216/228 on a 113+4. Negative overlap at 50... good Evo to drive the turbines so itd spool... little more intake duration than stock just to let it breathe a bit better.
