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Advice on Turbo vendor ( CX or On3) and also A/R

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Old 07-04-2018, 11:34 AM   #1  
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Advice on Turbo vendor ( CX or On3) and also A/R

Hey all,

I'm putting a turbo on my LT1 swapped ride. T56 trans. Goal is only about 500-550rwhp, stock block / lower end, just a fun street car. I know the tune will be important as to not blowing her up. Motor is about 350-375rwhp now.

Looking for advice here: CX racing turbo or On3 turbo? I know they aren't perfect but the price is hard to beat. Anyone had both and have a strong opinion?

Am thinking a T76, but wondering about turbine A/R ratio? For a fun street car do I go .81 or .96? Seem to see folks go both ways, not sure how much it matters or what. Or is a T76 way off base?

CX racing has a 10% off sale right now, so was thinking about taking advantage of that to get a lot of the hardware bought.

Thanks for any solid advice out there.
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Old 07-09-2018, 02:00 PM   #2  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

Had much better luck with on3. Have not used cx turbos however but i know the on3 is relatively proven around me.

Vs racing also may be a place to consider.

For you t76 with the p trim .96 ar will get you 500 whp. Spool very fast. Slightly better power potential would be on3 or vs 7875. Bigger turbine for less backpressure but will spool slightly slower. But not terrible. Its very popular on 4.8-5.3 ls motors up to 600-700 whp
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Old 07-10-2018, 09:03 PM   #3  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

Thanks for the input. Been doing more researching too . . .

Happened upon the whole Denmah Kit deal at VS racing, then found the Denmah thread over on LS1tech, and it got me wondering about the GT45 from VS. Sounds like the turbine side is better suited to bigger cubes (like 5.7L) than the T76 with the smaller turbine, but the compressor is a bit smaller on the GT45. But apparently it's a brute tough turbo, and tons of people use them successfully. Denmah claims its a great choice for most LS apps below 650whp. I know I'm not LS, but maybe still a good fit?

I guess the question is: Is the On3 7875 worth $100 more than the VS GT45 in my case? The On3 7875 is a more recent product I think than the "trusty" GT45, how would you rate the two of those?
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Old 07-10-2018, 09:42 PM   #4  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

On3 and vs version of the 7875 are more powerful no doubt. For under 600 hp or so the gt45 def works good. Its really better suited to small cubes since the compressor is only 69mm. I wish they made that with a bigger wheel cuz the turbine is decent

You can likely get your goal with the gt45 tho. It be pushed fairly hard tho.
T76 has done it on ls1’s
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Old 07-11-2018, 02:18 PM   #5  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

I have the ebay GT45 which is the same as the denmah kit, thing is massive and less than $200 on ebay ( I paid like $170 I think). I couldnt imagine fitting it on my car due to size and weight. I run the VS 78/75 cast which is much more compact and it will spool faster than the GT45 which on a 5.3 spools in the 4k range.



whats nice about the GT45 is the Oring seals! But small wheel and old deisel tech gets a slow spool but bullet proof.
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Old 07-11-2018, 08:10 PM   #6  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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I have the ebay GT45 which is the same as the denmah kit, thing is massive and less than $200 on ebay ( I paid like $170 I think). I couldnt imagine fitting it on my car due to size and weight. I run the VS 78/75 cast which is much more compact and it will spool faster than the GT45 which on a 5.3 spools in the 4k range.



whats nice about the GT45 is the Oring seals! But small wheel and old deisel tech gets a slow spool but bullet proof.
Slow spool + T56 doesn't sound as fun as it could be. So perhaps it is worth the extra bucks to get a smaller, lighter turbo (better hotside longevity maybe), that will spool faster. For the guys at the track with the auto, it's not as big of a deal, since they stay spooled up all the way down the track. But that't not my app.

I hate to get something that's going to give me problems though, which is why the GT45 sounded good. Like you said, seems like they are pretty tough.

Does the On3 7875 have a pretty decent track record? I wouldn't be pushing it hard at all I'd say.

Last edited by hotrodf1; 07-11-2018 at 08:17 PM.
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Old 07-11-2018, 08:14 PM   #7  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

If you had the coin, turbonetics hurricane series 7668 would be it. Fast spool and 600-700 capable

The 7875 has not given my buddy issues and i know another local guy with one that seems to work fine
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Old 07-11-2018, 08:16 PM   #8  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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Slow spool + T56 doesn't sound as fun as it could be. So perhaps it is worth the extra bucks to get a smaller, lighter turbo (better hotside longevity maybe), that will spool faster. For the guys at the track with the auto, it's not as big of a deal, since they stay spooled up all the way down the track. But that't not my app.

I hate to get something that's going to give me problems though, which is why the GT45 sounded good. Like you said, seems like they are pretty tough.
GT45 will spool faster on a bigger motor. Like a 5.7 or 6.0. On a 4.8 or 5.3 they are laggy compared to a 76/65 or 78/75. The GT45 are hard to beat for the price and are solid up to 600rwhp, the 78/75 will push that a bit further like 700rwhp and a Billet wheel will get you more. Spool should be faster with a 78/75 than a GT45 but the 78/75 is more of a choke point on the exhaust side. You can get a cast wheel VS 78/75 for $399 and eBay has 15% right now on there eBay dealer.
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Old 07-11-2018, 08:29 PM   #9  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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GT45 will spool faster on a bigger motor. Like a 5.7 or 6.0. On a 4.8 or 5.3 they are laggy compared to a 76/65 or 78/75. The GT45 are hard to beat for the price and are solid up to 600rwhp, the 78/75 will push that a bit further like 700rwhp and a Billet wheel will get you more. Spool should be faster with a 78/75 than a GT45 but the 78/75 is more of a choke point on the exhaust side. You can get a cast wheel VS 78/75 for $399 and eBay has 15% right now on there eBay dealer.
As far as a choke on the exhaust with the 7875, once I hit 7 psi, the wastegate will be open anyway in theory, so less of a choke at that point, right?

Yeah the 15% off right now has me fired up . . .
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Old 07-11-2018, 08:39 PM   #10  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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As far as a choke on the exhaust with the 7875, once I hit 7 psi, the wastegate will be open anyway in theory, so less of a choke at that point, right?

Yeah the 15% off right now has me fired up . . .
yes and no. At 7psi aka low boost your turbo isnít working hard so the exhaust isnít backing up as much. But the housing can still only flow so much exhaust at a given psi. So a larger exhaust housing could provide more power due to less restriction even at 7psi at the same boost.

Its all about engine size, spool rpm and expected HP and boost.

A 76/65 would spool faster than a 78/75 and a GT45 but t wonít like rpm depending on Engine size. The Chinese turbos are less efficient (old tech) so a precision 76/68 will perform much better than a Chinese 76/65. The 76/65 will max out around 600rwhp like a GT45 but spool much faster but wonít carry higher Rpms like the GT45. Overall in the 5.3-6.0 range itís hard to go wrong with a 78/75 given you keep Rpms within limits on bigger engines. With a manual a smaller turbo will help with spool on shifts etc. So the 76/68 or equivalent would prob be a better choice where I would jump to the 78/75 with a auto.

Fwiw on my 78/75 I run a full 3Ē highflow catback and it makes 6.5psi with a 12psi spring (cracking pressure) with a cutout I make 8.5psi and pick up a ton or spool time with no changes anywhere.
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Old 07-11-2018, 08:56 PM   #11  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

Whoa, so you're telling me you only get 6.5psi with a 12 psi spring. As in, the wastegate isn't even opening, and you're still at 6.5?

I would have figured you'd have all you wanted at WOT and the wastegate would dictate the boost level. Hmm.

Just got Corky Bells book. Haven't read it through yet. But the darn sale is over tonight LOL
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Old 07-11-2018, 09:18 PM   #12  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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Whoa, so you're telling me you only get 6.5psi with a 12 psi spring. As in, the wastegate isn't even opening, and you're still at 6.5?

I would have figured you'd have all you wanted at WOT and the wastegate would dictate the boost level. Hmm.

Just got Corky Bells book. Haven't read it through yet. But the darn sale is over tonight LOL
wastegate bench cracking pressure is different than installed pressure. Manufactures factor in exhaust backpressure pre turbo into the spring psi. So 12psi opens on a bench but when you factor in the exhaust pushing back on the valve when building boost you get it opening before hand. The amount of backpressure is based on exhaust turbine sizing and exhaust flow after the turbo (DP). Back pressure if high on mine bc I run a full 3Ē exhaust which is like 20ft of tubing, the cutout bypasses 1/2 that and this boost goes up and spool shortens. The same thing applies to turbo exhaust sizing, the difference is that if you go too small on the turbo exhaust your **** out of luck.

Since I know it takes 12 psi to open the valve and I make 8.5psi with the cutout open that means 8.5psi boost = 12-15psi back pressure to force the valve open. Thatís almost a 2:1 ratio.

Whatís the max power and boost you want to run and on what Engine and max rpm?
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Old 07-11-2018, 09:22 PM   #13  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

Looked back on ur first post, 350 lt1, 500-550rwhp and manual. I would be looking in the 70-76 / 65-68 range. So a cheap 76/65 will get you there if your budget is low. You could do a 76/68 and cost 4x as much. Or look for a 70/65 70/68 something of that exists. A smaller impeller will spool faster as well as the turbine side.
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Old 07-11-2018, 09:23 PM   #14  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

Well decided to go with the 78/75 from VS via ebay. Fingers crossed . . .

Not much option for the regular T76, as On3 doesn't appear to be on eBay.

Also picked up a 60mm wastegate, 50 mm BOV (EMUSA units), the 31x12x3 intercooler, an oil line kit, 3 2.5" stainless V bands, all for $597. All hail the Chinese speed gods. Should be plenty for what I'm doin.

The car runs pretty good for what it is anyhow, with boost it should be icing on the cake, even if a bit slower on the spool sid.e

One thing about it, I have the stock 93 2.73 ratio rear end swapped in, so she'll go 89 mph in second gear, so not a lot of shifting really before I get into trouble . . .. Sounds like I'll be OK.

Thanks for all your thoughts!

Last edited by hotrodf1; 07-11-2018 at 09:28 PM.
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Old 07-11-2018, 09:25 PM   #15  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

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wastegate bench cracking pressure is different than installed pressure. Manufactures factor in exhaust backpressure pre turbo into the spring psi. So 12psi opens on a bench but when you factor in the exhaust pushing back on the valve when building boost you get it opening before hand. The amount of backpressure is based on exhaust turbine sizing and exhaust flow after the turbo (DP). Back pressure if high on mine bc I run a full 3Ē exhaust which is like 20ft of tubing, the cutout bypasses 1/2 that and this boost goes up and spool shortens. The same thing applies to turbo exhaust sizing, the difference is that if you go too small on the turbo exhaust your **** out of luck.

Since I know it takes 12 psi to open the valve and I make 8.5psi with the cutout open that means 8.5psi boost = 12-15psi back pressure to force the valve open. Thatís almost a 2:1 ratio.

Whatís the max power and boost you want to run and on what Engine and max rpm?
Max power about 500-550 whp, 5.7 LT1 with head work and 224/224 cam, max. RPM about 6400, realistically 6200 I suppose.
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Old 07-11-2018, 09:31 PM   #16  
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Re: Advice on Turbo vendor ( CX or On3) and also A/R

It will be fine
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