Why is my truck slow?

[rlovell383]

I see a few things... you do not have much gear & I'm guessing you have a decent sized rear tire, further killing the gearing.

You added a larger cam that favors higher RPM power that you may not be able to take advantage of.

Also LS engines respond well to being leaner. 12.8-13.0 is common & should pick up some more power.

I agree the gearing isn't helping my situation. And yes, I have big 28.5" tall tires in back. If I can pickup 3 tenths or so in the 60 foot, that should get me near 13.7-13.8, which is closer to my goal but still not good enough.

My main concern is why its only getting 97 MPH in the traps, and not pulling as hard as I expect in the meat of the power band. MPH is an an indicator of HP and its quite a bit lower than I expect. I have a feeling its a combination of things.

I'm running about 12.5 A/F and like Andrew said should be well into the ball park with my TBI setup.

[Vimes]

Dual 3 inch on a normally aspirated 5.3? Way too large. 2.25 duals or 3 inch single is the largest I'd go on that. A 5.3 is a small engine. Dual 3 inch is what you use on a supercharged engine. Years ago I had dual 3 inch on an NA 350, and it was a dog. Had the 3 inch after the axle replaced with 2.5, and it helped it out quite a bit. The problem is a lack of scavenging. Exhaust scavenging is something you get when the exhaust is sized correctly. When the exhaust valve opens and the pulse leaves the cylinder, it draws a vacuum inside the cylinder just in time for the intake valve to open. This gives a mild supercharging effect as it allows the cylinder to receive a larger fuel/air charge than it would otherwise. When the exhaust is too large, the exhaust pulse essentially dissipates into free air, so the cylinder can'teven clear all of the exhaust out of the cylinder before the valve closes. Walker Quiet Flows also don't clamp down on the inside like you were told, in fact that's their whole selling point - the same flow as a high performance muffler only without the noise. I run them on vehicles I do for my wife, so I've researched them pretty well. If they did though, it would actually help the engine. Since you plan on doing the entire exhaust anyway, prove me right or wrong - have the exhaust after the axle replaced with 2.25 inch sections, and see how you do. Should do a little better, but the entire exhaust needs to be correctly sized to get the full benefit.

Tall tires and high gearing also kills, as others said. Then there's the 2.50 1st gear on that TH400, when combined with the tall gear and large tire you're killing your times. 4.10s would be the correct gear for that to make up for the tire size and the 2.50 1st gear. Not to mention, a TH400 take a lot of power by itself to run. Yes, it's strong, but it's also slower than other options. A 200-4R with a 2.74 1st gear and 4.10s would be a much better choice as it will easily handle the power and doesn't need computer control. I'd even suggest a 700-R4 with its 3.06 1st gear and 3.73s. Both of these transmissions take far less power to run, and don't need a computer.

[rlovell383]

Dual 3 inch on a normally aspirated 5.3? Way too large. 2.25 duals or 3 inch single is the largest I'd go on that. A 5.3 is a small engine. Dual 3 inch is what you use on a supercharged engine. Years ago I had dual 3 inch on an NA 350, and it was a dog. Had the 3 inch after the axle replaced with 2.5, and it helped it out quite a bit. The problem is a lack of scavenging. Exhaust scavenging is something you get when the exhaust is sized correctly. When the exhaust valve opens and the pulse leaves the cylinder, it draws a vacuum inside the cylinder just in time for the intake valve to open. This gives a mild supercharging effect as it allows the cylinder to receive a larger fuel/air charge than it would otherwise. When the exhaust is too large, the exhaust pulse essentially dissipates into free air, so the cylinder can'teven clear all of the exhaust out of the cylinder before the valve closes. Walker Quiet Flows also don't clamp down on the inside like you were told, in fact that's their whole selling point - the same flow as a high performance muffler only without the noise. I run them on vehicles I do for my wife, so I've researched them pretty well. If they did though, it would actually help the engine. Since you plan on doing the entire exhaust anyway, prove me right or wrong - have the exhaust after the axle replaced with 2.25 inch sections, and see how you do. Should do a little better, but the entire exhaust needs to be correctly sized to get the full benefit.

Tall tires and high gearing also kills, as others said. Then there's the 2.50 1st gear on that TH400, when combined with the tall gear and large tire you're killing your times. 4.10s would be the correct gear for that to make up for the tire size and the 2.50 1st gear. Not to mention, a TH400 take a lot of power by itself to run. Yes, it's strong, but it's also slower than other options. A 200-4R with a 2.74 1st gear and 4.10s would be a much better choice as it will easily handle the power and doesn't need computer control. I'd even suggest a 700-R4 with its 3.06 1st gear and 3.73s. Both of these transmissions take far less power to run, and don't need a computer.

Well.... I'm not sure I agree with the exhaust sizing suggestion, but I do appreciate the suggestions. I think it would be faster if I ran straight headers and no exhaust. My Walker Quiet flows do neck down inside, I saw it with my own eyes. Its considerable, probably down to about 2 inches or maybe even less. The mufflers have actually discolored to purple from the heat/backpresssure! That simply can't be good.
Next year I might experiment with dropping out the exhaust at the track and running just the manifolds/head pipes.

I agree on all points about the gearing and transmission. Its getting 4.10 gears this winter and a T56 when funds allow.
Originally I built the truck with a Cadillac 500, and decided it didn't fit the personality I was looking for. Hence the LS swap. Future plans are to bore/stroke the 5.3 to a 383 and up the compression with better heads and a tad more cam. That should get me where I want (theoretically)

[68Formula]

Actually the statements and technical explaination about the exhaust being too large are valid. I too have experienced going way too large in my younger days. A properly designed system will produce same peak power as open headers with no loss of torque.

That being said, since you're planning on a 383 down the road, might as well stick with the dual 3" and do the other enhancements first. But had you planned to stay with the 5.3L, I would've suggested no larger than 2.5" with a crossover to balance (either X or H) and non-restrictive mufflers (something that flows at least 80% of an open pipe the same size). Or a single 3" all the way.

[andrewb70]

I strongly agree with adding either an H or X pipe. The X will smooth out the pulses more and generally have a quieter note. I went from straight pipes to a X pipe and it changed the note and added noticable torque down low, although I did change mufflers as well...:-)

[Lonnies Performance]

You have little gearing (3.25) in conjunction with a tall tire & minimal first gear (2.48) in the trans.
A 5.3 is not a torque monster to begin with.

You are at 97mph, but not even topped out in 2nd gear with your setup at the 1/4 mile.
That big tire also takes a lot of power to turn... I've seen guys slow down a .1- .2 by going to a 28" over 26" tire in a typical 400hp Camaro by running too much tire.

Even most stock pickups with 5.3's are running 3.73 gear & a 4l60E with a 3.06:1 low gear which is 40% lower than your current first gearing.

You would like 4.10's except for the current lack of a overdrive trans.

[Vimes]

https://duckduckgo.com/?t=ffab&q=how...st+size&ia=web

Plenty of links on how to determine the correct exhaust diameter. Exhaust requires the correct diameter, and too large is not any better than too small. Too small backs up the engine, too large kills scavenging. Both kill power. For dual 3 inch exhaust to provide proper scavenging for your 5.3, you'd likely have to be turning somewhere around 12,000RPM. For a 5.3 that never goes more than 6000RPM and has no supercharger, 2.25 duals is plenty. But even then, you still need to do something about the TH400, 29 inch tires and 3.25 gears.

[rlovell383]

You have little gearing (3.25) in conjunction with a tall tire & minimal first gear (2.48) in the trans.
A 5.3 is not a torque monster to begin with.

You are at 97mph, but not even topped out in 2nd gear with your setup at the 1/4 mile.
That big tire also takes a lot of power to turn... I've seen guys slow down a .1- .2 by going to a 28" over 26" tire in a typical 400hp Camaro by running too much tire.

Even most stock pickups with 5.3's are running 3.73 gear & a 4l60E with a 3.06:1 low gear which is 40% lower than your current first gearing.

You would like 4.10's except for the current lack of a overdrive trans.

I plan to get a second set of wheels and drag radials 26" tall at some point. Yea the 5.3 is a dog below 3500 RPM. I never considered the tall tires slowing it that much though. Wonder if MPH would improve much. Between 26" slicks and 4.10 gears I bet it will pickup a fair amount on the ET. I'm not worried about the high cruise RPM because an T56 tranny will be going in before too long.

[rlovell383]

Ok, so the consensus is keep the 3 inch exhaust, or maybe drop to 2.5 inch for the 383 build, but put better mufflers in, and an H/X pipe. Between that and gears/tires it should put me where I want to be.

I have a 67 Camaro with a gen 1 383 I built that dyno'd 581 HP@6600 RPM. I have dual 2.5 inch pipes with an H pipe and Flowmaster 2 chambers on it, and it freaking rips. The M22 is also much more efficient than a Th400 that's for sure. The exhaust doesn't seem to be much of a factor on that one.

[Vimes]

Ok, so the consensus is keep the 3 inch exhaust, or maybe drop to 2.5 inch for the 383 build, but put better mufflers in, and an H/X pipe. Between that and gears/tires it should put me where I want to be.

I have a 67 Camaro with a gen 1 383 I built that dyno'd 581 HP@6600 RPM. I have dual 2.5 inch pipes with an H pipe and Flowmaster 2 chambers on it, and it freaking rips. The M22 is also much more efficient than a Th400 that's for sure. The exhaust doesn't seem to be much of a factor on that one.

Heh heh... the 383 rips on dual 2.5 inchs, and the 325 (5.3) is a dog on dual 3 inchs . I realize you don't believe me on this, but just replacing the section after the axle with 2.25s would help although not as much as a full exhaust would. But, I'll stop bringing it up. It's your truck, and you should run the exhaust you want .

[rlovell383]

Heh heh... the 383 rips on dual 2.5 inchs, and the 325 (5.3) is a dog on dual 3 inchs . I realize you don't believe me on this, but just replacing the section after the axle with 2.25s would help although not as much as a full exhaust would. But, I'll stop bringing it up. It's your truck, and you should run the exhaust you want .

The 2 inch choke in the Walker mufflers aren't accomplishing the same thing?

[Lonnies Performance]

Lets try to clear some thing ups... you do not need restriction.
Restriction is always bad.

You are trying to achieve sufficient velocity for scavenging & to prevent reversion during cam overlap with an appropriately sized exhaust.
To a point you want a small enough pipe for velocity, but just enough to be effective, whereas, too much it then becomes a restriction & a resultant power loss.
Keep in mind you can also over-scavenge, pulling some of the air-fuel out the exhaust when running cams with significant overlap.

Scavenging SHOULD be accomplished primarily with the headers.
The exhaust is a secondary effect which can help somewhat at part throttle of with mid-range power, especially if you have shorty headers which basically do little to tune the exhaust.

Personally I would not worry about 3" exhaust as much as I would about using a properly sized full length header.

As the exhaust travels down the pipe it loses energy, which causes it to condense & require less volume/pipe size.
Downstream of the muffler (where most of the restriction & energy loss occurs) additional pipe is virtually worthless & only directs the gasses for a safe exit from the vehicle.
Keep in mind this additional tail pipe can be smaller & often helps with sound control but is not the place to make power.

I recently did a 06 Chevy pickup with a Trick Flow 5.3 top end heads/cam package. It is supposed to make 450hp.
It was initially installed with stock exhaust. You could feel a big increase as rpm climbed over stock, but it was evident that you needed to rev it higher to take advantage of the power. It was shifting at about 5500 & laying over after the shift, so I raised the shifts to 6200. It made a big difference keeping the RPM up.

Also the factory tune was calibrated very rich at 12.2 leaning it out to 12.5 made a big difference & even again at 12.7.
You could actually hear the sound of the engine change at full throttle.
I hesitated to go further as this vehicle may also do some towing & did not want to risk a meltdown.

Next we added long tube headers with a full 3" dual exhaust. I noticed no real drop in mid-range power, but it picked up significantly at higher revs.
Not pleased with the noise level but performance was respectable. This was not my primary choice in exhaust, but was too good of a deal to pass up.

[rlovell383]

Lets try to clear some thing ups... you do not need restriction.
Restriction is always bad.

You are trying to achieve sufficient velocity for scavenging & to prevent reversion during cam overlap with an appropriately sized exhaust.
To a point you want a small enough pipe for velocity, but just enough to be effective, whereas, too much it then becomes a restriction & a resultant power loss.
Keep in mind you can also over-scavenge, pulling some of the air-fuel out the exhaust when running cams with significant overlap.

Scavenging SHOULD be accomplished primarily with the headers.
The exhaust is a secondary effect which can help somewhat at part throttle of with mid-range power, especially if you have shorty headers which basically do little to tune the exhaust.

Personally I would not worry about 3" exhaust as much as I would about using a properly sized full length header.

As the exhaust travels down the pipe it loses energy, which causes it to condense & require less volume/pipe size.
Downstream of the muffler (where most of the restriction & energy loss occurs) additional pipe is virtually worthless & only directs the gasses for a safe exit from the vehicle.
Keep in mind this additional tail pipe can be smaller & often helps with sound control but is not the place to make power.

I recently did a 06 Chevy pickup with a Trick Flow 5.3 top end heads/cam package. It is supposed to make 450hp.
It was initially installed with stock exhaust. You could feel a big increase as rpm climbed over stock, but it was evident that you needed to rev it higher to take advantage of the power. It was shifting at about 5500 & laying over after the shift, so I raised the shifts to 6200. It made a big difference keeping the RPM up.

Also the factory tune was calibrated very rich at 12.2 leaning it out to 12.5 made a big difference & even again at 12.7.
You could actually hear the sound of the engine change at full throttle.
I hesitated to go further as this vehicle may also do some towing & did not want to risk a meltdown.

Next we added long tube headers with a full 3" dual exhaust. I noticed no real drop in mid-range power, but it picked up significantly at higher revs.
Not pleased with the noise level but performance was respectable. This was not my primary choice in exhaust, but was too good of a deal to pass up.

Ok, that makes sense. I was always under the impression that any scavenging that was happening is done in the headers. Since everyone in this thread universally agrees there is power to be found SOMEWHERE in my exhaust, I'm going to completely re-build it this winter. Make (or buy) some mid length or full length headers and couple them to 2 1/2 inch exhaust with free flowing mufflers. It works in my Camaro so it should work in my pickup.

[Vimes]

I wasn't going to post on this thread anymore but since you asked a specific question - that small crimp is not enough, as on a 3 inch inlet it wouldn't be more than a tiny drop to 2.75 inch diameter. When I ran my dual 3 inch on a Gen 1 Chevy 350 I had horrible low end and terrible mileage, and just replacing the section after the axle with the dual 2.5s boosted low end to midrange performance considerably. It was with that that I learned that exhaust should be properly sized, and bigger is not necessarily better.

An 8ft section of 2.25 is about 30 bucks at the parts store, and clamps are a couple of bucks each. Since you plan to replace your exhaust with your new engine anyway, what do you have to lose to give it a try? When you see that you gain low end, it will at least give you food for thought on the correct size for the new engine. Exhaust systems and carburetors are the same, go too large and your racing engine loses to econoboxes on the strip.

[rlovell383]

I wasn't going to post on this thread anymore but since you asked a specific question - that small crimp is not enough, as on a 3 inch inlet it wouldn't be more than a tiny drop to 2.75 inch diameter. When I ran my dual 3 inch on a Gen 1 Chevy 350 I had horrible low end and terrible mileage, and just replacing the section after the axle with the dual 2.5s boosted low end to midrange performance considerably. It was with that that I learned that exhaust should be properly sized, and bigger is not necessarily better.

An 8ft section of 2.25 is about 30 bucks at the parts store, and clamps are a couple of bucks each. Since you plan to replace your exhaust with your new engine anyway, what do you have to lose to give it a try? When you see that you gain low end, it will at least give you food for thought on the correct size for the new engine. Exhaust systems and carburetors are the same, go too large and your racing engine loses to econoboxes on the strip.

I very much do appreciate your input and apologize if I seem skeptical towards your ideas. I'm totally open to learning new things about hot rodding! I have a pretty well calibrated eye-ball as a former machinist by trade, and the restriction in MY particular mufflers is significant. Likely close to 2 inches or less at the neck. If you look at the Summit reviews it confirms my estimate....

https://www.summitracing.com/parts/wlk-21856/reviews

I wouldn't have worried about it if it really was just 1/4 inch drop. That being said, I plan to upgrade one thing at a time and test in between.
This winter I'll be re-gearing the 9 inch to 4.10 gears. In the spring I'll take it back to the drag strip and test. After that, make up a new exhaust for it and see what that does. It will be fun to see and I'll be sure to post my results if any of you are interested!

By then the chassis and tuning should be pretty well sorted out for a good platform to make a wicked 383 out of my 5.3.

[69cutlassrkt]

upgrade to a high stall torque converter and install full length headers.

A high stall torque converter will make it faster than changing the rear end gear. I have a 3" exhaust on my 5.3 with dougs 1 3/4 headers. I remember a while back ls1 guys were seeing better numbers with 1 7/8 headers. I agree with adding an h or x pipe.
When I had a 3600 stall torque converter in the 4l60e whenver I would floor it it was in the power band. Though now with the 4l80e it definitely feels like it could use a lower rear gear. The car has always had a 2.78 gear.

My car with 4l60e, stock converter, bigger cam and 15% torque management ran an 8.88 at 84mph in the 1/8. It ran a 9.0 in the 1/8 with the stock cam and a 2500 stall torque converter. With a 3600 stall torque converter and drag radials and no torque management(I think) it went 8.2179 at 86.79mph in the 1/8th.

[Lonnies Performance]

upgrade to a high stall torque converter and install full length headers.


My car with 4l60e, stock converter, bigger cam and 15% torque management ran an 8.88 at 84mph in the 1/8. It ran a 9.0 in the 1/8 with the stock cam and a 2500 stall torque converter. With a 3600 stall torque converter and drag radials and no torque management(I think) it went 8.2179 at 86.79mph in the 1/8th.

8.88 converts to approximately 13.9's in the 1/4
8.21 is roughly 12.9's.

[rlovell383]

upgrade to a high stall torque converter and install full length headers.

A high stall torque converter will make it faster than changing the rear end gear. I have a 3" exhaust on my 5.3 with dougs 1 3/4 headers. I remember a while back ls1 guys were seeing better numbers with 1 7/8 headers. I agree with adding an h or x pipe.
When I had a 3600 stall torque converter in the 4l60e whenver I would floor it it was in the power band. Though now with the 4l80e it definitely feels like it could use a lower rear gear. The car has always had a 2.78 gear.

My car with 4l60e, stock converter, bigger cam and 15% torque management ran an 8.88 at 84mph in the 1/8. It ran a 9.0 in the 1/8 with the stock cam and a 2500 stall torque converter. With a 3600 stall torque converter and drag radials and no torque management(I think) it went 8.2179 at 86.79mph in the 1/8th.

Header upgrade- yes
Converter upgrade... meh. LOL

This is the first hot rod I've built with an auto and it will be my last. Its just not as fun to drive. Its getting ripped out for a 6 speed ASAP. I know it won't be faster but fun factor is much better. My 2500 converter is annoying to drive as it is, I can't imagine higher.

Thanks... Thats all good info, and your times make sense.

[rlovell383]

upgrade to a high stall torque converter and install full length headers.

A high stall torque converter will make it faster than changing the rear end gear. I have a 3" exhaust on my 5.3 with dougs 1 3/4 headers. I remember a while back ls1 guys were seeing better numbers with 1 7/8 headers. I agree with adding an h or x pipe.
When I had a 3600 stall torque converter in the 4l60e whenver I would floor it it was in the power band. Though now with the 4l80e it definitely feels like it could use a lower rear gear. The car has always had a 2.78 gear.

My car with 4l60e, stock converter, bigger cam and 15% torque management ran an 8.88 at 84mph in the 1/8. It ran a 9.0 in the 1/8 with the stock cam and a 2500 stall torque converter. With a 3600 stall torque converter and drag radials and no torque management(I think) it went 8.2179 at 86.79mph in the 1/8th.

What are your cam specs, and how much does your car weigh?

[69cutlassrkt]

What are your cam specs, and how much does your car weigh?

EPS 222/226 112 lsa ground 4 degrees advancedlift .596/.605, EPS/LXL lobes

I'm guessing the car weighs 3800lbs or more. I haven't ever weighed it.

I understand about the converter. My 2500 almost drove like stock, although it was a nice lockup protorque converter. With the 4L80e it has around a 4000 stall torque converter. Haven't driven it much since the trans swap, but it's defintely loose.