Been driving the 5.3 with a VS racing gen 1 billet 11 blade 78/75 for a few years and think a smaller turbo might work better for quicker spool. Wanted to get your thoughts on my options. Currently logs show spooling starting around 3k and 13-15psi by like 4k if I remember correctly. Car is a 87 trans am with a single CX racing turbo kit which I modified with a 2.25” crossover and has a 3” vband down pipe into a 3” cutout 7ft away and then goes to a 4” mufflex catback. I have no room for a larger DP and the turbo has to fit into the same space as the normal gen 1 78/75.

5.3 stock 150k bottom end
218/228 .560/.560 114.5+5.5 cammotion blower cam
light ported 862s with Howard .600 springs
NNBS 72lb Bosch 92mm Warr TB.

2004R trans with billet upgrades 800hp/tq capable with a billet 10” 2,400 stall 1000hp converter

Ford 8.8 with 3.55s and 28” tall MT drag radials

FMIC 3” with eBay 31x12x3 IC and I spray 750ml if wiper fluid with a snow pump on AEM progressive controller.

holley term X ECM, truboost EBC 60mm HKS clone WG and 50mm BOV.

I have no access to E85 so I run pump 93 and my IATs are in the 100-115*F range driving in the hot summer and in boost drops Bc of the wiper fluid usually staying under 120*.


car is only street driven and I think I would love the boost to come in 500-1000rpms earlier. It’s not a max power build and the 72lb injectors are maxed out around 16psi or so so I don’t turn it up past 15psi which is like 700hp or so at the crank. I’ve been looking at the borg S366 or VS 66/73 cast. Do you guys think I’m crazy and it would be a downgrade or would it still work really well. The S366 or whatever would need a 3” Vband outlet and a T4 to bolt up and no bigger than a standard 78/75.

 

Perhaps a converter with a higher flash/stall would be a solution. 2400 stall is pretty tight.

 

I'd have to agree that the converter choice is a bit tight.
My son has a Gen2.5 78/75 on his 4.8 liter and with his 3500 stall, lights off almost too quick.

FWIW, when I first did my turbo setup, it started as an ON3 A/C Delete "kit", and I wrongly ordered it with their standard "too small for a 6.0" turbo, cast 70/65. I have a 6.0, with 3.70 gears and a 3000-ish stall. With the 70/65, the car made INSTANT BOOST, and I mean the car felt like my old big block Chevelle...as in instant torque/power. It was fun, but turbo was quickly done, as in out of breath.

I think for a fun 5.3 liter 100% street driven car, that turbo would be a blast, and it is ridiculously cheap, like barely over 300 bucks.
VSRacing may offer one similar, since they come off of the same boat, but HERE is the one I am referring to.

Some guys will say it IS a downgrade, but not all of us want or need the maximum horsepower possible, because there's ALWAYS trade-offs in doing so...I honestly think your car would be more fun to drive, "downgraded".

 

I was actually thinking the opposite. Tight as in it stalls to 2400 under normal medium put around town driving but give it the pedal like anything about 1/2 and it will stall/flash to 3k and thats where boost is coming on. I figured the converter is loose enough and thats why I can't build boost till 3k. driving around under 3k which is a good bit of normal driving is uneventful and wish I could start to get into boost at least in the 2500 area.

 

I had a 76/65 on the car originally with a .81 or .84 AR as thats what came with the CX racing kit. I upgraded to a VS racing cast 78/75 and was happy then pulled that for a billet 78/75 in the hopes of quicker spool. From what I read and could feel at the top end the 65 was too small for a 5.3 that revs beyond 6k and I lost no spool with a larger 78/75. Thats why I was looking at a 66/73 as it has the larger exhaust wheel close to the 78/75 but the much smaller compressor wheel would prob spool alot faster. I dont really want to go much smaller on the exhaust wheel for flow reasons and I know guys are gona tell me to step up to a 400 series probably. I like tight converters as it doesn't feel like a slug around town with the converter unlocked and I wouldnt go higher than 2800 on the street for that reason.

 

You might also check that intercooler for pressure drop also which can cut into response. You could also try a .81 turbine on the current turbo which would be the easiest thing, but ideally you could do with a bit less compressor for the combo I bet if quicker spool is what you want.

 

Just seems like a mismatched combo:
Cam made to rev- Something like a triple 12 would have been a better choice.
Super tight torque converter- 3200 would have gotten the turbo into boost sooner from a time perspective.
28 inch tire- If you're looking at going down from a 78/75, there's no reason you need a 28" tire. Going to slow you down combined with the tight converter.
None of this discusses tuning either.

 

No measurable pressure drop from the IC. I did some tests with the reference of my WG and EBC and it didn't make a noticeable difference going from the compressor housing to the intake manifold. My IC is extruded tubes which basically have no cooling fins where the charge is goes through so there isn't much restriction.

 

Cam was designed for the motor and same overall combo but with a centri supercharger (since then I've gone turbo and left the cam) spec'd by cam motion (custom grind) they also said for my current setup they wouldn't change the specs see our back and forth below.
28" is for a decent tire to help load the engine and make the 3.55s act like a 3.23 ish rear gear as I was having traction issues with a 27" tire before (non DR tho). The car doesnt feel slow at all and from a standstill on a dark highway along I use my 1/4 feature on my speedhut gauges and saw 11.93 at 120mph but with lots of wheel spin off the line and on the shifts plus I was letting out a bit early and this was at about 10-12psi. At 8psi I did similar 11.9-12.0 @ 113.9mph as the lower boost helped with traction a bit more.

My original email/form submission:
I have a custom cam from you guys, think its a 218/228 .553/.553 115+4.5 that was spec'd for a 5.3 with a centri supercharger. The car has been turbo's (single 78/75 billet T4) for a few years now and wondering if this cam is holding me back. Car only has a 2,400 stall (flashes to 3k) and I street drive it so lots of 1500-2300rpm highway with a locked 200r4 and lots of 3000-6k street driving. I have been spinning the motor up to 6500ish lately and banging off the rev limiter but I don't spend the alot of time above the 6k+ range. What cam would you spec for my setup? its about 3400lbs 87 trans am with 3.55 rear gears and a 275/45r18 MT drag radials (28" tall tire).

Bobby @ cammotion's response:
After looking at the valve events on this camshaft i really like the specs for this setup and dont believe there is much more to be had from a camshaft standpoint.

My follow up response:
Hey Bobby,

Thanks for your response. Was I right on the cam specs? Not sure if you can see my original order but assume you can. My concern is that the cam has a big split 218/228 which is a 10* difference combined with a wide 115+4.5 LSA. I typcially see this in PD or supercharger applications because the exhaust is usually free flow. However in a turbo application I normally see closer duration 212/212, 212/214 )0-6* difference) and a shorter LSA 113-116. Any reason none of those would make a difference?

His Final response:
only reason to take exhaust duration away in a turbo application is when you are fighting back pressure issues. In a setup like this with this size turbo taking exhaust duration out of it will likely rob power

 

You want boost coming in 500-1000 rpm's sooner. Launching from a dig for a 1/4 mile pass is hardly the same as rolling into it and when you hit positive pressure. You're a stalled auto with a big tire, it should be leaving in boost before you let go of the brakes. If you want better transient response I told you the changes I would make. There's nothing wrong with 3.55 gears and you can't compare a 27" non-DR to a 28" DR.

 

What do you think of the summit stage 2 turbo cam? - Stage 2 Pro LS Turbo Cam. 226/230 Dur., 113+4, .600/.575 Lift, 3-bolt

Kinda wish they offered a stage 1 turbo cam so I could be in the triple 12 area. My 5.3 current has howard 98113 springs which I don't think will be enough
Valve Spring Set Series:
 Beehive
Style Of Spring:
 Beehive
Outer Overall Diameter:
 1.280
Outer Inside Diameter:
 1.035
Inner Overall Diameter:
 .900
Inner Inside Diameter:
 .650
Damper:
 No
Closed Pressure:
 115 @ 1.800
Open Pressure:
 332 @ 1.265
Rate:
 412
Max Lift:
 .600
Coil Bind:
 1.150

 

They have a ghost cam , a bit less duration than the stage 2 . Cam motion has a 214/214 113 +3 and .570 /.550 IIRC . Very close to a triple 12 . Not hard to order a custom cam , pick core , lobes , lsa your done . I'm sure they could walk you through it at isky or hit up JFR for one.

 

Ghost cam looks close to what I have currently. 218/228 .561/.561 115.5+4.5

 

What's the tune look like when tryin to get into boost?

 

Timing - 93 pump, FMIC and spraying 750ml of wiper fluid progressively

Fuel

AFR

 

these are slightly higher res

 

Can't see the rpm axis of the timing graph but timing looks soft if I'm guessing right. AFR looks ok.

 

sorry, see new pic for the rpm axis.

 

Wow I didn't realize the rpm columns were in such small increments. That does look ok.

 

Yea, I like the holley software much more robust than the fitech I was running. I honestly thought my tune was fine and maybe a tad aggressive for the cheapest 93 I can find but the car runs and drives great. I'm still trying to figure out the holley datalog side but the learning and quick apply to base is a game changer! For the most part the tune is within 1-2% after a 40min drive but I won't have data logs till the spring when I can take the car out again. I might be able to rummage through some fitech logs to see when boost starts but I remember it being around 3k.