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2.48 first x 3.25 out back is 8.06 starting line ratio (SLR). For a street car that's plenty of gear.
When it comes to converters, the general rule of thumb is, shift drop of +1200 is okay for a street car and <1200 is what you'd want for a drag car. So once you start hitting it with your planned boost, and let's say the shift drop is 1400, it's okay for a street oriented combo. To go into more detail, it's all about what you want. Folks will generally want the shift drop to keep you in the best part of your power band, and to also dropping you say down around peak torque where you have timing pulled.
I raised my shift points to keep the rpm from dropping into the rod bending portion of the rpm band.
Not true, I paid over a grand for a custom Continental Converter that was designed to work with a rowdy 600hp BBC 454 and 250hp shot of nitrous.
It drove terrible on the street, wouldn't hardly flash, it would hit a wall at 3,000rpm which was way outside its happy zone but with the bottle turned on, it was a completely different animal.
There's a reason people use PTC, FTI or Circle D regularly and not Jegs.
You may very well need to throw more power it as well.
My current converter wasn't locking up very well shifting at 6,500rpm, very little rpm drop, I moved my shift points out to 7,000rpm and it got much tighter which was visible in the rpm drop on the logs.
I don't think the dyno is that far off either, a stock LS 5.3 makes 270-290chp.
Factor in cam and heads and say you're at 350chp, -20% for drivetrain losses through the 4L80 and you end up at 280whp.
13 psi is nearly double atmosphere so you're right on at 550whp.
You've got a little engine that needs rpm to spool up and the converter enables or inhibits that.
If you aren't using an EBC, start there, those bring the boost in down low way faster than gate alone.
I know you can basically pay as much as you want for a converter. When not on sale this converter is pretty inline costwise with FTI and Circle D single disc these days ($935). Right or wrong its not really saving any money! Lol I did get a helluva deal a few years ago and paid $580. But if I bought one today I would go FTI or Circle D, you guys aren't wrong. Word is this converter is made my Transmission Specialties, they are supposed to be pretty good. Anyhow, duly noted, if I can't fix this with a tune and troubleshooting converter is on the list.
I do have an ebc, its actually a dual solenoid. Something else to look at.
2.48 first x 3.25 out back is 8.06 starting line ratio (SLR). For a street car that's plenty of gear.
When it comes to converters, the general rule of thumb is, shift drop of +1200 is okay for a street car and <1200 is what you'd want for a drag car. So once you start hitting it with your planned boost, and let's say the shift drop is 1400, it's okay for a street oriented combo. To go into more detail, it's all about what you want. Folks will generally want the shift drop to keep you in the best part of your power band, and to also dropping you say down around peak torque where you have timing pulled.
I don't have tall tires either, ~25" or so, close to stock height. 315/35/17s
Tall gearing adds load and will actually assist with building boost and TQ earlier. Def possible to have too much gear, but that would only help in terms of getting the converter to stall higher. Nothing wrong with a 3.25 IMO. 1st gear is pretty tall on a 4l80e. Hold the brake and stomp the gas. If it doesn't flash past 3k, there's not much you can do. Spool time will always suck. If it goes past 3 then you have something to work with tune wise, or possibly have a leak.
Unfortunately its going to be a minute before I can do that test. I am in line to get a new downpipe/exhaust welded up. Right now it has no downpipe.
So I have a nitrous kit sitting here from my last car. After all the troubleshooting and tuning I could just hit it with a little 50 shot. That's 88ftlbs at 3k plus whatever it does to turbo spool. I'm getting ahead of myself again but that would certainly wake it up.
I know you can basically pay as much as you want for a converter. When not on sale this converter is pretty inline costwise with FTI and Circle D single disc these days ($935). Right or wrong its not really saving any money! Lol I did get a helluva deal a few years ago and paid $580. But if I bought one today I would go FTI or Circle D, you guys aren't wrong. Word is this converter is made my Transmission Specialties, they are supposed to be pretty good. Anyhow, duly noted, if I can't fix this with a tune and troubleshooting converter is on the list.
I do have an ebc, its actually a dual solenoid. Something else to look at.
With the turbo you're using, you should be seeing positive pressure by at most 4,000rpm easy, my S484 starts building positive pressure by 3,500rpm.
So for the tune, the timing should be setup for NA until around 5 lbs. of boost.
The timing in my current tune is pretty aggressive even for NA from what the experienced tuners on here have told me to help light off my bigger S484 turbo, then the timing should dip at peak torque then roll some back in.
Check your EBC settings too, there all kinds of settings you can play with to roll the boost in sooner.
You mention dual solenoid, are you using an external pressure source like compressed air or CO2?
Looks like Holley instructions require an external pressure source for dual solenoid use, might be a quick test to change your setup to a single solenoid and see if that helps?
You could very easily move the lines around to test this.
Maybe contact Transmission Specialties also and see if they can tweak it for you.
I had this done through Circle D, ask them for a shipping label too so you don't pay an arm and a leg for shipping.
With the turbo you're using, you should be seeing positive pressure by at most 4,000rpm easy, my S484 starts building positive pressure by 3,500rpm.
So for the tune, the timing should be setup for NA until around 5 lbs. of boost.
The timing in my current tune is pretty aggressive even for NA from what the experienced tuners on here have told me to help light off my bigger S484 turbo, then the timing should dip at peak torque then roll some back in.
Check your EBC settings too, there all kinds of settings you can play with to roll the boost in sooner.
You mention dual solenoid, are you using an external pressure source like compressed air or CO2?
Looks like Holley instructions require an external pressure source for dual solenoid use, might be a quick test to change your setup to a single solenoid and see if that helps?
You could very easily move the lines around to test this.
Maybe contact Transmission Specialties also and see if they can tweak it for you.
I had this done through Circle D, ask them for a shipping label too so you don't pay an arm and a leg for shipping.
No CO2 or anything, that could be s problem...
My last car was a Neon with a Megasquirt I built and I had an ebc on it. This is Holley Terminator X with MAC valves. I'm familiar with the concepts but have to learn a lot more about this set up. Another reason its better to do as much as you can yourself instead of paying others but water under the bridge now.
Last edited by ScottStaypuff; Sep 20, 2024 at 12:13 PM.
My last car was a Neon with a Megasquirt I built and I had an ebc on it. This is Holley Terminator X with MAC valves. I'm familiar with the concepts but have to learn a lot more about this set up. Another reason its better to do as much as you can yourself instead of paying others but water under the bridge now.
Simple fix my friend, just move those lines around to use one of the solenoids using the Holley instructions.
Plug the rest, sounds like this may be the issue because if the port that is supposed to feed external compressed air is open which it looks like it is, your boost may be escaping or causing it to build very slowly.
Also consider the wastegate spring, I tried using a very light spring (3-4lbs.) in my last car so that if I hit a safety, it would dump all the boost.
Problem was that my backpressure was high enough to push the wastegate open early and made building boost very, very slow.
I moved up to a 6-7lb. spring and boost came in way faster and harder.
I also have a .030 over 5.3, but I'm running AFR Enforcers and Summit Pro LS domed pistons for 10.5:1 compression. Engine was built to run on E85 from the start, so I didn't even consider going low compression. I'm running a previous generation BTR Stage 2 Twin Turbo cam, which seems pretty similar to their regular Stage 2 turbo cam except with more exhaust duration. It's 226/235 with .610/.614 lift and 113+5 LSA. Only went with it because BTR had it for a screaming deal in their garage sale section. I'm not disappointed, that's for sure. My car is only street tuned as of yet, and it absolutely rips. Pulls straight to 7500 with ease, so quickly that even with a 6900RPM shift light, I hit the limiter in first gear ( @7500 ) by the time I can react. I can attest to the disadvantage of having a steep rear gear. I'm still running 4.30's in mine, and while I have a stick shift, my first gear is similar to a 4L80E (2.66 vs. 2.48). Even at 7500, I'm only hitting 50 MPH. The engine revs so fast it outpaces the turbo and it never builds much boost in first gear. But man, once I shift into second, it's like a freight train. I'll have to look at my logs to see where it starts making boost, but it definitely doesn't feel laggy at all. I've got a Gen 2.5 78/75 with a 1.25A/R. I'll be swapping to 3.73's over the winter, 4.30's are just too much. I'd venture to guess you have a lot more left in your tune, but from my past experience with automatics and LS engines in general, I'd say a 3000 RPM converter might be a little too low, especially with a turbo combination. More testing and adjustments will tell the tale for you.
Good info. I do think I have way more important things to deal with than a cam swap, but back to the original intent of the thread. I am really trying to see how much overlap people are getting away with on various turbo combos. There must be a point where it hurts you but the cam manufacturers seem to err on the side of caution causing the power to be a bit "flat" versus a NA cam. Simple solution though, add more boost.
You have domed pistons as well? That sounds about right, my heads are 62CC, so that would account for the increase ( mine is 10.5:1 ). Just remember, that calculator doesn't take gasket bore diameter or ring land volume into account. You can add 1CC for ring land volume as a general rule. Getting the bore diameter of the gasket into the equation will give you a more accurate final number.
You have domed pistons as well? That sounds about right, my heads are 62CC, so that would account for the increase ( mine is 10.5:1 ). Just remember, that calculator doesn't take gasket bore diameter or ring land volume into account. You can add 1CC for ring land volume as a general rule. Getting the bore diameter of the gasket into the equation will give you a more accurate final number.
I have Summit domed pistons as well, sounds like exactly the same. I can run either 93 octane or e85 with flex sensor.
I broke in my engine on 93, but I'm going to run it solely on E85 unless I'm putting it in storage for the winter. I don't want to break something pushing it on 93. I had a couple close calls already.
I broke in my engine on 93, but I'm going to run it solely on E85 unless I'm putting it in storage for the winter. I don't want to break something pushing it on 93. I had a couple close calls already.
I’ll chime in since I have a 5.3.
222/235 112+5 .620 or so lift.
799 heads I ported. 9.5:1 CR
Pro Flow intake.
Martin Smallwood designed my cam.
Turbo is a Forced Inductions S476, billet wheel, 87mm exh.
PTC 9.5” torque converter.
I can foot brake this to 3400 standing on the pedal. I have rear drum brakes. Disc brakes just don’t work.
Anyway, depending on boost, the converter will flash between 5-6000. Yet drives around just fine. I agree that the torque converter, and tune are key.
Footbraking my car runs easy 8.80’s and has hit just shy of 158. With this baby cam.
I now have a 1-2 leave transbrake. Wholesale suspension upgrades snd have been quite lost with the combo. A story for a different post.
I’ll chime in since I have a 5.3.
I have rear drum brakes. Disc brakes just don’t work.
Don't agree with this at all. I have a foot brake only fox mustang. Had drum brakes on it when I bought it but I put on strange rears. They definitely are the same if not better than the drum brakes. I'm able to foot brake mine up to 3800 rpm on the 2 step. Biggest difference with disc brakes is that you can find good compound pads that have huge bite when hot after a burnout. I've never looked but I don't believe you can get a performance pad for a drum brake.
Can you guys share your setups and what cam you are using? The more info the better but engine size, intake manifold and turbo specs would be appreciated. If you can describe how it spools up, horsepower, how far you rev to and if you are satisfied with the results that would be awesome.
My cam is a LJMS stage 1, 222/227 and 113lsa +3. My set up is a .030" over 5.3, cnc'd ls6 heads, flat top pistons, huronspeed, ls6 intake, 4l80e no transbrake, 3.25 rear end gears, 3000rpm stall converter, 25" tires, the basic cast $400 VS 7875 turbo with .96ar turbine housing.
It revved to 6200rpm and made 550whp on 13psi. Bottom end is lacking imho, can barely get it to spin tires, probably could use some more tuning before I would even think about swapping cams. (I have been thinking high lift truck type cam)
Since all that, I swapped over to a VS G42 clone - 80mm journal bearing turbo with a 1.25ar housing and a 4" bumper exit exhaust. Getting bigger injectors/more fuel. I can update after the new set up is done. I want 700whp and good torque, enough to be a little scary. Sounds like I can get there pretty easy with correct parts and tune.
Going to a bigger cam from the one you have listed will make your problem worse. I've been proven over and over bigger cams give up low end power and tq and make more up top. So going to a bigger cam will only make your situation worse.
What intake manifold is on it? A short runner manifold will make this 100x worse. A stock LS6 intake would be perfect for your set up and what you are saying is wanted.
Overall I do agree with others that converter should be your biggest concern (get a custom spec converter from a rep company - Jegs aint it) and then you need to look into the tune (can also make a huge difference) and boost control.
I’ll chime in since I have a 5.3.
222/235 112+5 .620 or so lift.
799 heads I ported. 9.5:1 CR
Pro Flow intake.
Martin Smallwood designed my cam.
Turbo is a Forced Inductions S476, billet wheel, 87mm exh.
PTC 9.5” torque converter.
I can foot brake this to 3400 standing on the pedal. I have rear drum brakes. Disc brakes just don’t work.
Anyway, depending on boost, the converter will flash between 5-6000. Yet drives around just fine. I agree that the torque converter, and tune are key.
Footbraking my car runs easy 8.80’s and has hit just shy of 158. With this baby cam.
I now have a 1-2 leave transbrake. Wholesale suspension upgrades snd have been quite lost with the combo. A story for a different post.
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