[JonD]

Originally Posted by oldman

Um it ain't me asking for dyno proof of a subjective part throttle low RPM issue.

I believe I did a terrible job with my choice of wording

To tell people a smaller header is better because you’re having lower part throttle issues seems to be subjective without proving it’s not the tune.

Is that a possibility?

[Whocares05050]

Generally* 1 7/8 has been the go to for all motor builds and 2 inch for boosted applications. My 5.0 lost a lot of low end with 2 inch headers and i went to 1 7/8 and it was night and day. Both re-tuned afterwards. But every applications different

[18ss376]

Wish someone made a 1-3/4" for my 455h.p. LT1

[squish72]

Originally Posted by 18ss376

Wish someone made a 1-3/4" for my 455h.p. LT1

https://www.phastekperformance.com/B...ders-17293.htm

[oldman]

Originally Posted by JonD

I believe I did a terrible job with my choice of wording

To tell people a smaller header is better because you’re having lower part throttle issues seems to be subjective without proving it’s not the tune.

Is that a possibility?

Actually, without cats for the stock header or my LT there are part throttle issues.

It is an OBJECTIVE FACT that a smaller header will maintain exhaust velocity better. I have nothing to prove. I've listed my mods, don't think it is the tune, do think a 2" header with no cats would yield even worst low speed part throttle performance. I've seen it happen on many engines over decades.

[oldman]

Originally Posted by Nicul15

Yes I love driving in low rpms and skipping gears during commutes. I haven’t noticed a change and you can bet your ass we would rip the LTH right back out if it did

Prob will add msd to the car at some point so maybe that may add some more data to the situation

Will be testing the L86 intake first tho


I really hate to speculate like this but I have notorious paranoia of vacuum leaks. Tuning the MAF to inenvertily allocate for a vacuum leak will send transient part throttle driving to hell

How knows, the point is there are no issues with cats. I don't see myself going back to stock intake and stock TB. I could as I'm boosted and the 103mm TB and MSD are really worthless unless of course, I was going to install an 8 point dual inject.

Heck I even like the truck manifold for boosted setups. Figure the Procharger can use some more midrange grunt. It can produce more boost than my fuel system can supply on the top end... or the short block take. Looking forward to the results...

Oh and let's go to sound, the engine sounds like sluggish with no cats, it is not fart pipe on a ricer bad, but it is not crisp either. With cats... the engine is louder than stock because of the headers, but not very much louder and the sound is crisp like a high compression V8.... With cats the engine is quiter all the way around and smoother / crisper in the low to mid range. Don't know how much HP, as I got no traction in any normal speed anyway.

[JonD]

Originally Posted by oldman

Actually, without cats for the stock header or my LT there are part throttle issues.

It is an OBJECTIVE FACT that a smaller header will maintain exhaust velocity better.

LOL, you’re a true forum guy

[RobbyBeefcake87]

Originally Posted by oldman

Well there are a few that delete the secondary cat that includes the rest of the x pipe all the way to the stock muffler. They are not unreasonably expensive.
That said the general consensus is that the primary cats are the biggest restriction.

Yea I've seen those but I believe the end at the mufflers of the original mid pipes have to be cut though, I'm under the impression it's one piece after the cats. Texas speed or especially speed engineering seem like good ways to go there without breaking the bank.

[Umbriel]

Originally Posted by Nicul15

My personal car is with cats but I’ve never driven a car that was catless that was tuned right and lost power

Never heard of it either. Every car i have ever owned that was modified was cat less and never had any issues. Engines do not need back pressure to run correctly, it's a myth. I would look into the tune if my car was doing this.

[18ss376]

Originally Posted by Umbriel

Never heard of it either. Every car i have ever owned that was modified was cat less and never had any issues. Engines do not need back pressure to run correctly, it's a myth. I would look into the tune if my car was doing this.

Back when I had my 1987 Corvette with a Lingenfelter 383 I ran it with open headers then with full free flowing exhaust with Borla mufflers. It ran faster with the full exhaust & I still don't know why it ran better than open headers

[Umbriel]

Originally Posted by 18ss376

Back when I had my 1987 Corvette with a Lingenfelter 383 I ran it with open headers then with full free flowing exhaust. It ran faster with the full exhaust & I still don't know why it ran better than open headers

Tuning maybe? Only thing I can think of, changing the airflow so much it throws the tune off all speculation at this point with that. I know every car I have ever owned and modified has never had any issues running no cats and open exhaust. The car I have now is running 2 inch headers and no cats and runs perfectly fine with no issue at all and a very noticeable increase in power.

[6spdhyperblue]

Originally Posted by 18ss376

Back when I had my 1987 Corvette with a Lingenfelter 383 I ran it with open headers then with full free flowing exhaust with Borla mufflers. It ran faster with the full exhaust & I still don't know why it ran better than open headers

The key is freeflowing maintaining velocity and scavenging.

[Umbriel]

Originally Posted by Nicul15

The key is freeflowing maintaining velocity and scavenging.

Yep. A lot people confuse scavenging and velocity with back pressure.