1995 K1500 header install

[Roadknee]

Just got back from a 25 minute loop I like to take when I'm tuning, which includes a flat section of highway where I can run a 0-60 mph pull. I was curious whether the headers would require any changes to the VE tables. Nope. The BLM average were in the 122-128 range; where they've been for the last year. The WOT 0-60 mph run yielded the same 10.0 second time it always has. So my bone stock LO5 shifting at 4,400 rpm sees no benefit at all running a good set of headers and a 2-1/2" Y-pipe as compared to the stock iron manifolds and 2" Y-pipe. Can't say I'm disappointed, or even really surprised. It does sound better. And I'm certain this exhaust system will be much better suited to support the 300 hp engine, once I get around to finishing and installing it.

[JeepsAndGuns]

I too contemplated on a set of headers for my cherokee for a long time. I did end up going ahead and buying some. Mine are full length and I did feel a noticeable difference in power and sound, both for the good. Sorry to hear yours did not make a difference.

[Fast355]

Just got back from a 25 minute loop I like to take when I'm tuning, which includes a flat section of highway where I can run a 0-60 mph pull. I was curious whether the headers would require any changes to the VE tables. Nope. The BLM average were in the 122-128 range; where they've been for the last year. The WOT 0-60 mph run yielded the same 10.0 second time it always has. So my bone stock LO5 shifting at 4,400 rpm sees no benefit at all running a good set of headers and a 2-1/2" Y-pipe as compared to the stock iron manifolds and 2" Y-pipe. Can't say I'm disappointed, or even really surprised. It does sound better. And I'm certain this exhaust system will be much better suited to support the 300 hp engine, once I get around to finishing and installing it.

Primaries are too small on your headers to see any real HP gains. There is a reason the aftermarket all use 1 5/8" or 1 3/4" primaries. I had a set of Flowtech 115000 1 1/2 primary, 3" collector headers into dual 2.5" exhaust with a X pipe on my 305 and later 350 in my 83 G20 with TBI swap. Going from manifolds to headers and a good exhaust was VERY noticeable even with the small factory marine cam (200/212 @ .050", .400/.410 on 110 lsa) I had in the 305 at the time. I was putting down about 180 RWHP and 270 RWTQ from the 305. I swapped a stock TBI 350 gm crate engine into the 305s place after overheating it an popping a head gasket. Made 178 RWHP and 262 RWTQ. I did a few extra bolt-ons (TBI spacer with open center, power bowl, 454 TBI, 1.6:1 full roller rockers, and an underdrive pulley) )and got it up to 210 RWHP/310RWTQ. When I got serious with the 350, I swapped to Doug Thorley Tri-ys with 1 5/8" primaries, 2" intermediate pipes and 2.5" collectors using the same 2.5" dual exhaust. Even before the cam swap the header change alone was once again very noticeable. With a production LT4 cam, 1.6:1 rockers and my setup I was cranking out 255 RWHP and 320 RWTQ.

[Roadknee]

Primaries are too small on your headers to see any real HP gains.

This can not be any further from the truth based on the experience of professionals that make their living designing and building custom headers and exhaust systems for winning teams

There is a reason the aftermarket all use 1 5/8" or 1 3/4" primaries.

There is a reason and it's because companies are in business to sell product, and the belief of majority consumers that bigger must be better.

[Fast355]

This can not be any further from the truth based on the experience of professionals that make their living designing and building custom headers and exhaust systems for winning teams

There is a reason and it's because companies are in business to sell product, and the belief of majority consumers that bigger must be better.

Actually what I wrote is pretty accurate. Plenty of dyno data out there that supports what I posted as well as personal real world experience. The LT1 cammed 1999 Suburban picked up very noticeably with Hooker 1 5/8 primary long tubes with 2.5" collectors into a Hooker 2.25" dual exhaust setup running thunderbolt 5" spun metallic core cats and hooker aerochamber mufflers.

My Titan gained almost 30 RWHP on a Mustang dyno stepping up from the factory manifold cats to catless 1 3/4" 14 gauge T304L mid length headers with 2.5" merge collectors into the 2.25" dual exhaust. It was a monster after headers for a 5,800 lbs 4x4.

The 305 Vortec in the Corvette had a set of stock L82 Ramshorns on it and I put 1 3/4" primary, 2.5" collector headers onto the same dual 2.5" exhaust it had with the ramshorn. Ran 2-3 tenths quicker in the 1/8 with zero other changes.

[Fast355]

I was running 0-70 in 8 seconds in nearly 100*F weather in a 5800# truck with a 5.6L engine and 1 3/4" primary headers. It got out of its own way pretty quickly.

http://www.youtube.com/watch?v=lELdtvmah2A






I also towed with it, plenty of low-midrange grunt over stock.


The Express has Thorley Tri-ys and gained noticeably as well even shifting at only 4,900-5,000 rpm in Tow/Haul mode.




Doug Thorley even used dual 3" pipes to mate the headers to the factory Express van exhausts. I reduced from 3" to 2.75" to 2.5" at the cats and used a dual in/single out muffler.



The van has a huge gearing disadvantage compared to the 5spd in the Titan yet it still pulled down a respectable ~8.xs 0-60 and 11 sec 0-70. For a 6,200 lbs beast with only a 3.73 gear and a 4L80E it is not short on torque by any means. The 4L80Es tall 2.48 1st and 1.48 2nd gear ratios are like having a 3.00 rear gear with a 4L60E in first and a 3.23 in 2nd and the 60 lbs stock 13" torque converter also doesn't help the off the line jump very well either, despite having a dual stator and 2,200 rpm stall speed. When you go WOT from idle it kinda lags, hesitates for a second, then takes off like a proded bull!

http://www.youtube.com/watch?v=-6DZhPN7VHQ

Finally the 99 Burb....0-80 mph in 13 seconds on an uphill onramp in 90*F weather.

http://www.youtube.com/watch?v=LYdyu501Z4Y

Like I said I think I have a little first hand experience at making these engines run pretty strongly.

I also had both 1 1/2" long tubes and 1 5/8" tri-ys on the same engine in my G20, the larger tri-ys blew the smaller headers away from off-idle through redline.



When I put the healthy TPI enging into the G20 I was glad I had the extra headroom to make more power.

[old truck guy]

Im no expert but I've done a ridiculous amount of research in choosing headers for my build. The general consensus on primary size is where you want your power, smaller = low and mid range while larger = more top end. Port alignment and collector size/design are every bit as important as primary size. Just because you saw gains with larger primaries doesn't mean it is because they were larger, its the complete package that makes a difference.

Superchevy has an article on a header test using a smeding 383 and 4 different size headers. The 1 1/2" primary, while intended to just establish a base line for the test, supported well over 400 hp and ended providing the best overall power curve below 5000 rpm. The larger sizes didn't pull ahead until 4500+ and at the sacrifice of low end. Headers by Ed states that there is no point in having a primary size larger than your exhaust valve so if you have a typical svc with 1.5" valves, no need. Unless you're building a high rpm motor, bigger is not better.

If your talking vortec heads, the biggest problem is port alignment. Unlike standard sbc heads, vortec's have a raised port (approx 60% of the port is above the bolt centerline) so smaller primary headers tend to cover the top of the port. Bigger primaries while uncovering the whole port present sealing problems at the bottom of the flange.

I myself went with a set of flowtec 11508 flt headers (less than $150). Basically the same headers in superchevy's test, 1 1/2 primary and 2 1/2 collector. Replaced the wimpy 1/4" flanges with a set of 3/8" cnc cut flanges that I bought on ebay from Hells Gate Hotrods. He sells a set of sbc for $45 and made me a custom set for the vortec port alighnment for less than $100. I went a step further and bought a set of Meg's weld on merge collectors from cone engineering for $125. After finish assembly I sent them to a place called pro kote Indy in Indianapolis and had them professionally cleaned and ceramic coated for $220. Just got them back and they look awesome. For less than $600 I got ceramic coated, perfect fit headers with perfect port alignment and plenty of sealing surface.

Assembling motor now. Let you know how the do when I get it running.

[BLG355]

Assembling motor now. Let you know how the do when I get it running.

The cam in your signature is one of the ones I considered using. It actually came down to the that one and the one I am using now which has much less lift. I'd like to hear how it works for you.

BLG

[old truck guy]

Im no expert but I've done a ridiculous amount of research in choosing headers for my build. The general consensus on primary size is where you want your power, smaller = low and mid range while larger = more top end. Port alignment and collector size/design are every bit as important as primary size. Just because you saw gains with larger primaries doesn't mean it is because they were larger, its the complete package that makes a difference.

Superchevy has an article on a header test using a smeding 383 and 4 different size headers. The 1 1/2" primary, while intended to just establish a base line for the test, supported well over 400 hp and ended providing the best overall power curve below 5000 rpm. The larger sizes didn't pull ahead until 4500+ and at the sacrifice of low end. Headers by Ed states that there is no point in having a primary size larger than your exhaust valve so if you have a typical svc with 1.5" valves, no need. Unless you're building a high rpm motor, bigger is not better.

If your talking vortec heads, the biggest problem is port alignment. Unlike standard sbc heads, vortec's have a raised port (approx 60% of the port is above the bolt centerline) so smaller primary headers tend to cover the top of the port. Bigger primaries while uncovering the whole port present sealing problems at the bottom of the flange.

I myself went with a set of flowtec 11508 flt headers (less than $150). Basically the same headers in superchevy's test, 1 1/2 primary and 2 1/2 collector. Replaced the wimpy 1/4" flanges with a set of 3/8" cnc cut flanges that I bought on ebay from Hells Gate Hotrods. He sells a set of sbc for $45 and made me a custom set for the vortec port alighnment for less than $100. I went a step further and bought a set of Meg's weld on merge collectors from cone engineering for $125. After finish assembly I sent them to a place called pro kote Indy in Indianapolis and had them professionally cleaned and ceramic coated for $220. Just got them back and they look awesome. For less than $600 I got ceramic coated, perfect fit headers with perfect port alignment and plenty of sealing surface.

Assembling motor now. Let you know how the do when I get it running.

[Roadknee]

Like I said I think I have a little first hand experience at making these engines run pretty strongly.

I don't think you'll find anyone who will disagree with that. I've personally been very impressed with your results for about a decade now. I simply don't agree with your opinion that 1-1/2" headers are holding back my stock LO5. FWIW, I don't think it would gain or lose anything measurable with a decent set of 1-5/8" headers either.

[Fast355]

I don't think you'll find anyone who will disagree with that. I've personally been very impressed with your results for about a decade now. I simply don't agree with your opinion that 1-1/2" headers are holding back my stock LO5. FWIW, I don't think it would gain or lose anything measurable with a decent set of 1-5/8" headers either.

Its possible your stock cam has a choke hold on the engine and it just can't move any more air through the valves but honestly I have never not seen gains with headers.