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Help with disappointing dyno results

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Old 07-10-2018, 04:15 PM
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fast.asleep
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Originally Posted by 856SPEED View Post
I have been down this road before but long ago; 2002-2003. I still have the car. Itís a one off 85 with the 91-96 rear bumper Gen I SBC with a nice exhaust note and runs 12ís with street tires and ZF6 tranny...love the car along with the white face Autometer gauges...Itís a C4 that GM never made......However......


Going back to what you said....I donít know I would do this project today....why????

I had no idea muscle car era 2.0 was going to the levels we are seeing today....technology has has grossly improved in the new cars and they do everything so efficiently with a huge aftermarket. Donít get me wrong, this car will stay with me since itís a quality build....but If I were you, buy an LS with a whole car wrapped around it. Computers and televisions from the 80ís and 90ís were great at that time, but could you imagine trying to convert one to your big screen HD set??
I totally agree with everything youíve said. I could have had a decent c5 by selling this car + what Iíve spent so far. BUT the car has huge sentimental value to the point that I can honestly say I will never sell it. While I love the engines in the c6, the styling just doesnít do it for me. Love the c7 but Iíll wait a few years and let someone else deal with the depreciation
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Old 07-10-2018, 05:03 PM
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Originally Posted by ddahlgren View Post
If you want a 10 second car build a 9 second car add 20k at least to the budget and plan on maintenance travel and lots of seat time unless you race 9 second cars already. Needs a cage and back half at least and aftermarket electronics or carbs or a good turbo. Not a cheap date and yes everything you have done is money down the rabbit hole.
Fair enough. Iíll stop with the blower and start saving for a c7. I guess I was just hoping for more considering all the posts I see about how headers add 50 hp to a stock l98...
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Old 07-11-2018, 10:11 AM
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Originally Posted by fast.asleep View Post
Fair enough. Iíll stop with the blower and start saving for a c7. I guess I was just hoping for more considering all the posts I see about how headers add 50 hp to a stock l98...

people say a lot my friend!


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Old 07-11-2018, 10:27 AM
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If GM could have gotten a 20% increase in headers for a few hundred bucks don't you think they would have made it an option? In my mind a TPI is better suited on a 305 than a 350 in the first place right along with the exhaust manifolds and cylinder heads. My bets are if you put all the L98 parts on a 383 the best you might get is 385 ft/lbs and 270 hp
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Old 07-11-2018, 10:31 AM
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will the type of intake make much difference once I add the blower?

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Old 07-11-2018, 10:56 AM
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YES the blower adds torque and hp the intake exhaust heads cam set the torque curve. The same intake that adds power NS will add power with the blower up until a point. But if not shooting for 1000 hp I would use that guideline. If you can buy a converted LT1 intake for 400 with rails it would be a virtual gift. It will allow more cam and get the heads ported to at least 195 w/ spings for the cam and blower as you need to add spring tension on at least the intake side for the blower.
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Old 07-11-2018, 12:24 PM
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Originally Posted by ddahlgren View Post
If GM could have gotten a 20% increase in headers for a few hundred bucks don't you think they would have made it an option? In my mind a TPI is better suited on a 305 than a 350 in the first place right along with the exhaust manifolds and cylinder heads. My bets are if you put all the L98 parts on a 383 the best you might get is 385 ft/lbs and 270 hp
Think about a car made in 1920 compared to 1960
No think about the car from 1960 and compare it to one from 2000.

40years make a big difference. We are talking about a fuel injection and engine designed 40 years ago, produced on manufacturing methods from 40 years ago.

Not only the technology, but emissions, CAFE, ability for the engine to fit into different platforms... etc. It's not so easy to just offer as an "option". There is a reason why cast manifolds are still used and it is not because it is the easiest way to make power. It's a series of compromises resulting in an acceptable solution to many constraints.
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Old 07-12-2018, 08:29 AM
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In C4 L98 they are bending and welding 8 tubes for the intake and 8 tubes for the exhaust the length of the tubes are meaningless. The L98 only had to fit 2 platforms, Corvette and Camero. Your argument interesting but really does not hold water for me.Adding 20 inches of tubing costs pennies compared to adding them as a 200 dollar option if they really add 50 hp. GM did not bend the tubes for the TPI and probably not the exhaust either. I did business years ago with the tube bender in MI that did do the ones for the TPI.
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Old 07-12-2018, 08:58 AM
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Originally Posted by ddahlgren View Post
In C4 L98 they are bending and welding 8 tubes for the intake and 8 tubes for the exhaust the length of the tubes are meaningless. The L98 only had to fit 2 platforms, Corvette and Camero. Your argument interesting but really does not hold water for me.Adding 20 inches of tubing costs pennies compared to adding them as a 200 dollar option if they really add 50 hp. GM did not bend the tubes for the TPI and probably not the exhaust either. I did business years ago with the tube bender in MI that did do the ones for the TPI.
What Tubes are you talking about? Both the intake and exhaust manifold are cast units.

Somethings I know very well. Longer intake runners make more power down low. Hence the name "Tuned Port" you can tune the ports for certain RPM ranges. Same for head port length and cross sectional area.

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Old 07-12-2018, 09:02 AM
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Plenty of Long Tube vs. Shorty headers test out there showing long tubes make more power. I would say both on intak and exhaust tube length not only matters it is a primary concern.
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Old 07-12-2018, 10:57 AM
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Originally Posted by ddahlgren View Post
If GM could have gotten a 20% increase in headers for a few hundred bucks don't you think they would have made it an option? Adding 20 inches of tubing costs pennies compared to adding them as a 200 dollar option if they really add 50 hp.
Your logic or deductive reasoning here is way off. No, I don't think GM would have offered headers "for a few hundred bucks" for many reasons:
1. Cost. "A few hundred bucks" is a ton of money to add to a cars COST (not price). I guarantee you that the ROI isn't there; most people wouldn't pay what the Retail would end up being on that part.
2. To meet all of GM's criteria, the headers would have to cost more than "a few hundred dollars", most likely.
3. Fitment
4. Under hood heat
5. Durability
6. Cat light off time
7. Passenger compartment heat
...for starters.

Dyno tests have shown the value of LT headers on the L98, both in F-bods and 'Vettes...since those cars came to market, so for there is about 30 years worth of data on this topic.

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Old 07-12-2018, 01:42 PM
  #72  
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1. Have you ever seen the speed of a CNC bender that will bend and cut to finshed size?
To go 20 more inches at least for a 91 is trivial as is the cost of tubing when buying tubing in the volume used already.
2. I don't run GM's engineering department possibly you do or have personally read their spec's for an exhaust system and can point them out verbatim.
3. Every Y body and F body is the same as they don't make any other partspecifically for each car.
4. A couple of heat shields as needed already changes little. By nature it is not loaded with precision dimensions beyond normal stamping equipment.
5. My 91 had original exhaust when I got it as a 17 year old car my Pontiac has 16 year old exhaust. I suspect OEM exhaust is wildly better than any after market one.
6. You mention all this heat to deal with so pretty much takes care of light off especially with heat shields to hold it in and out of engine compartment.
7. Compared to the cat right under the center of the passenger compartment it does not seem overwhelming as a problem and if it showed up fixes are very simple and cheap.

The ability to do accurate work and do it cheaply is what building anything in volume is what factories can do when dealing in tens of thousands of identical part. Current aftermarket headers and custom exhaust is expensive and at times has problems fitting due to low volume and implied value tht the customer will tolerate.

My take on it do with what you will. My only experience in the automotive world making multiple identical parts is with the Calloway B2K engines. I managed the shop floor producing the engines as a subcontractor shop. 435 more or less (it has been a long time ago) engines and even at that level buying pallets of plain boxed parts is wildly cheaper than might be imagined.. The actual work of building them was much cheaper than you could every do one two or a dozen. We had milling and boring machines that the setup did not change for years.

My thoughts free so take them for what it is worth rather than a debate and personally adding 50 HP as claimed by header companies and their shills on a stock L98. If it was that easy GM would find a way to do it as the big sell on the LT1 was 300 hp last looked 250+50 is the same 250. Not up for a debate but I don't think things are as black and white as you allude to.
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Old 07-12-2018, 05:05 PM
  #73  
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Originally Posted by ddahlgren View Post
1. Have you ever seen the speed of a CNC bender that will bend and cut to finshed size?
To go 20 more inches at least for a 91 is trivial as is the cost of tubing when buying tubing in the volume used already.
2. I don't run GM's engineering department possibly you do or have personally read their spec's for an exhaust system and can point them out verbatim.
3. Every Y body and F body is the same as they don't make any other partspecifically for each car.
4. A couple of heat shields as needed already changes little. By nature it is not loaded with precision dimensions beyond normal stamping equipment.
5. My 91 had original exhaust when I got it as a 17 year old car my Pontiac has 16 year old exhaust. I suspect OEM exhaust is wildly better than any after market one.
6. You mention all this heat to deal with so pretty much takes care of light off especially with heat shields to hold it in and out of engine compartment.
7. Compared to the cat right under the center of the passenger compartment it does not seem overwhelming as a problem and if it showed up fixes are very simple and cheap.

The ability to do accurate work and do it cheaply is what building anything in volume is what factories can do when dealing in tens of thousands of identical part. Current aftermarket headers and custom exhaust is expensive and at times has problems fitting due to low volume and implied value tht the customer will tolerate.

My take on it do with what you will. My only experience in the automotive world making multiple identical parts is with the Calloway B2K engines. I managed the shop floor producing the engines as a subcontractor shop. 435 more or less (it has been a long time ago) engines and even at that level buying pallets of plain boxed parts is wildly cheaper than might be imagined.. The actual work of building them was much cheaper than you could every do one two or a dozen. We had milling and boring machines that the setup did not change for years.

My thoughts free so take them for what it is worth rather than a debate and personally adding 50 HP as claimed by header companies and their shills on a stock L98. If it was that easy GM would find a way to do it as the big sell on the LT1 was 300 hp last looked 250+50 is the same 250. Not up for a debate but I don't think things are as black and white as you allude to.
Fair enough... I am enjoying this... so now reason out why not one manufacturer uses long tube headers on a large volume produced car.
1. Have you seen long tubes made? It's more than just the bent tubes, it is also the welding and flange flatness. Then cleaning up the weld beads at the flange. The time to produce them is a lot more, requires a lot more material, and require more specialized equipment. As an Automotive Engineer that actually has worked for OEMs, Tier 1 and Tier 2 suppliers... a lot in CNC Machining of cast parts and welded assemblies I can assure you... a cast manifold is cheaper and not by just a few hundred bucks.
2. Have you installed long tubes on many cars? Space is a major issue often requiring the removal and re installation of many components. Starter, steer shaft, steering rack, Air conditioning... I have done it on a few cars. In the mass production world, the engine has to be a drop in on the line and once a part is on, they don't remove it for something else. This does no apply to very limited production or conversion vehicles. This is why you could get cars from SLP with headers. It was done after the car left the assembly line.
3. Emissions... how many long tube headers do you know... true long tubes, that actually get an CARB ID?
4. Factory exhaust on most cars are still mild steel... mild steel is mild steel and stainless is stainless and aluminized is aluminzed. Depending on what you buy or your car is equipped with, the results are based off material.

There is a reason a set of coated long tube headers that actually fit and don't blow out gaskets every 2500 miles are north of $2500. There is a reason why hot rodders have been using long tubes for over a half century and OEMs are still not. It is not because they don't make more power. It is because of fitment, cost, and emissions.

Last edited by KyleF; 07-12-2018 at 05:06 PM.
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Old 07-12-2018, 06:53 PM
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Originally Posted by ddahlgren View Post
6. You mention all this heat to deal with so pretty much takes care of light off especially with heat shields to hold it in and out of engine compartment.
'll avoid the rest of your ignorance, but this? If the heat leaves the exhaust and heats the engine bay (and related components)...what do you suppose is happening to the heat that was supposed to light off the cats? THINK.
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Old 07-12-2018, 11:38 PM
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Nm .

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Old 07-12-2018, 11:56 PM
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Originally Posted by ddahlgren View Post
If GM could have gotten a 20% increase in headers for a few hundred bucks don't you think they would have made it an option? In my mind a TPI is better suited on a 305 than a 350 in the first place right along with the exhaust manifolds and cylinder heads. My bets are if you put all the L98 parts on a 383 the best you might get is 385 ft/lbs and 270 hp
Long tube headers would have been difficult. It is not just making the headers themselves, it is installing them on the car where they would have slowed down the production line quite a bit when the workers had to fit them versus just dropping in an engine. Also they tend to leak a lot more than short tube manifolds, meaning more warranty claims.

Also I don't know that they had a whole lot of CNC machines in the mid 80s and even with modern CNC we still have cast pistons, cast heads and cast engine blocks in the vast majority of vehicles built today. If the cost difference was really trivial those parts would be forged from billet.

The other problem with long tube headers is space and fitment. You would need different headers for F bodies and Y bodies meaning different full up engine subassemblies. To be honest production variances might actually make it impossible to do in volume. I have never installed long tube headers on either an 80s vette or camaro, but I have installed them on a lot of other cars and you get two identical cars, same year, same engine and two identical sets of headers and they will fit on one car like a glove and need to be modified for the other car. Not anything major but you would need to dimple the header here or grind off a small part of the cars frame there. That kind of fitment process is routine with headers but would cost thousand of dollars on a moving production line. Maybe an OEM could do better in volume, but none have yet to my knowledge for a high-volume application.

Last edited by auburn2; 07-13-2018 at 12:13 AM.
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