moparmat2000
Well-Known Member
I am back on the 408 stroker deal. I posted the temp use 318 deal on a different thread.
340 HP's vs headers
- Thread starter Saetun
- Start date
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To kill a 150 hp on a 450 hp engine would back to stock 340 hp numbers. Air compresses my cousin's stock car engine pulls to 7000 rpm with a 2 bbl making well over 400 hp. Nascar makes 800 hp with restrictor plates with dime size holes.
Obviously manifolds aren't the best idea for performance. But with a little planning can't see why you can hit your goal of 400+ hp.
Obviously manifolds aren't the best idea for performance. But with a little planning can't see why you can hit your goal of 400+ hp.
I have been following this old thread you revived. I just bought a pair of early HP 340 manifolds. I would also like to liven up my 318 in my Swinger. I have a LD4B and a assortment of 600-650 cfm carbs. I would like to follow up with TTI exhaust or at least get the front pipes from them and finish out the exhaust. This combo seems to help the teen's performance. I may put in a little cam while I'm at it.
I think with a stroker it would be best with headers of some kind. The engine is just a big air pump and a stroker uses quite a volume of it. It has to get out as fast as it came in. Keep us posted on what you do and the outcome. tmm
I think with a stroker it would be best with headers of some kind. The engine is just a big air pump and a stroker uses quite a volume of it. It has to get out as fast as it came in. Keep us posted on what you do and the outcome. tmm
MopaR&D
Nerd Member
Headers are more about tuning the exhaust pulses than overall flow capacity. There are some magazine builds out there where they added a set of longtube headers to a stock 300-HP 5.9L Magnum crate engine and it picked up like 3 HP. Put the same headers on the 380-HP crate with the big cam and it's more like a 20-30 HP boost even though the displacement is the same. I liken it to tuning a 2-stroke; when you have both the intake and exhaust passages open to the cylinder at the same time (like in a 2-stroke or a 4-stroke engine with a high-overlap cam) the ability of the high-inertia exhaust gases to move quickly out of the cylinders and help pull more fresh intake charge into the cylinder is critical. A 408 stroker will work fine with manifolds, you just have to build the engine with that excessive high-RPM backpressure in mind so it will (in my mind) need a short-duration split-pattern cam with extra lift and duration on the exhaust side compared to intake. Also check out the episode of Engine Masters where they bash a set of headers to oblivion and it didn't affect HP at all, showing that the length and overall diameter of the tubes is way more important than the actual cross-sectional area of the tubes which is what everyone intuitively points at for making more power (bigger tube=flows more air).
Comparing it to intake restrictor plates isn't quite the same because in reality those NASCAR engines take advantage of the massive negative pressure exhaust pulses produced by the tuned headers to pull air through those tiny intake holes as hard as possible. When you mess with the exhaust side and take away that tuned scavenging affect it throws everything out of whack and kills massive amounts of HP. Granted most of what I'm saying comes from literature (David Vizard's How to Build Horsepower) not from my own testing unfortunately.
moparmat2000
Well-Known Member
Got a set of hedman block huggers coming. I will make my own downpipes. Off thesr while on my 318 mockup motor.
The 318 runs great, and is stock, i will prob do what others have mentioned, and put a good timing chain on it, install those 340 exhaust manifolds on it, get an LD4B and an eddy 600 and drop it in my kids car. For now it will still be doing mockup duty for the downpipes for this car.
Anybody know where i can get 2&1/2" diameter muffler tube mandrel bends that i can cut apart and make my own down pipes out of. I'm thinking i can do this, and buy the header type exhaust kit from summit, and add another set of collector flanges to tie it together.
The 318 runs great, and is stock, i will prob do what others have mentioned, and put a good timing chain on it, install those 340 exhaust manifolds on it, get an LD4B and an eddy 600 and drop it in my kids car. For now it will still be doing mockup duty for the downpipes for this car.
Anybody know where i can get 2&1/2" diameter muffler tube mandrel bends that i can cut apart and make my own down pipes out of. I'm thinking i can do this, and buy the header type exhaust kit from summit, and add another set of collector flanges to tie it together.
MopaR&D
Nerd Member
You're definitely gonna need a pair of these: Header Reducer Set, Angled There's simply not enough space to have straight collectors and try to have the pipe go back up and over the steering linkage, at least with my stock stuff. I'm a little leary of changing the pitman and idler arm lengths because that might screw with the steering geometry (bump steer etc.). I also had to use one of those premade exhaust pipe "donuts" like this one, only way to get tight enough bends for it all to fit: Mandrel Bend Donut 2.5" 2.50" 2.5in 2.50 2.50in Exhaust Intake Stainless Steel | eBay
moparmat2000
Well-Known Member
Aaaah the donut. And just cut pieces out to make a tube wedges and weld em up. The angled collectors will definitely help. Thanks for showing me those Khalid. I never knew those existed. I guess i got to get the headers mocked up on the teener under the hood first, and then see where to go from there. My chuck is filthy, and i just had lower back surgery 3 weeks ago, cant lift over 10lbs yet so i'm not moving it around to clean it up and temp install it just yet. At least not till i get a clean bill of health from the doctor.
The longer pitman and idler arms only mess with ackerman angle when steering wheel is in full lock. Thats only going to happen when parking it. No bump steer issues. This was how Chrysler got fast ratio steering on the T/A challenger and AAR cuda back in the day, no joke. Old racers trick. You do that, and use the pressure valving off a slant sux saginaw pump, and lower the line pressure, and you get a fast ratio steering chuck that feels like a rack n pinion. Problem w moving center link back is certain long tube headers tend to not fit, but this may make a little more room to augment the header downpipes
The longer pitman and idler arms only mess with ackerman angle when steering wheel is in full lock. Thats only going to happen when parking it. No bump steer issues. This was how Chrysler got fast ratio steering on the T/A challenger and AAR cuda back in the day, no joke. Old racers trick. You do that, and use the pressure valving off a slant sux saginaw pump, and lower the line pressure, and you get a fast ratio steering chuck that feels like a rack n pinion. Problem w moving center link back is certain long tube headers tend to not fit, but this may make a little more room to augment the header downpipes
MopaR&D
Nerd Member
Cool good to know about the steering, I know the AAR-T/A cars had something like that but I didn't realize it was that simple. I put one of the Firm Feel Stage 2 P/S boxes in my Duster, with that, smaller steering wheel and proper caster at the wheels it felt like a modern car. I remember showing it to an older friend of mine (relatively, I'm 26 he was like 53?) and he was shocked by how much better it felt than stock steering, he had never experienced a Mopar with that kind of steering feel with "stock" components.
moparmat2000
Well-Known Member
I think the plan for the teener will be the LD4B, a eddy 600 and those 340 hi po mannys, and some 3.73s in a 69 notchie. That should be plenty for a teenaged driver.
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moparmat2000
Well-Known Member
Yep they were sloppy as heck back then. About half the problem is the way overboosted assist. Dial the line pressure down a bit and it tightens up. I think in a mopar action article they said its about 1,600 psi stock, and dialing it down to about 850 psi. tightens it up. Not 100% on the numbers though. Find the article on the net, and check it out.
moparmat2000
Well-Known Member
Well in another thread similar to this one , and this one i mentioned that i hate headers, but pulled the trigger on these shorties. So i guess i'm gonna eat crow over this one. Maybe these are better made. I will use copper gaskets. Guess i will find out.
MopaR&D
Nerd Member
The Hedman Tight Tubes are good quality, head flanges are nice and thick I believe 3/8", tubes are pretty thick gauge steel and the welds are nice too. The driver-side fits nicely around power steering stuff, they also come with some nice small-head bolts that use like a 3/8" wrench. IIRC I used the gaskets that came with the headers from Hedman and sprayed them with copper sealant then tightened the header bolts evenly bit-by-bit. NEVER had a leaking issue after initial install and I put 25k hard miles on that 360 until it kicked the bucket (tuning errors, too much detonation). Main downsides were the exhaust routing which it sounds like you got covered, and high underhood temps but that happens with any uncoated headers, unless you got coated ones?
moparmat2000
Well-Known Member
I may either get em jet hot coated in dark gray, or wrap em in header wrap.
moparmat2000
Well-Known Member
I think i did pretty good on those hedmans today actually. A guy had em on evilbay for $175 with an awful silver spray job on em. Said he ran em on a dyno on his small block, then went big block. I offered and got them for $150 shipped. I will sand blast em at work, and spray em w a high heat coating.
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LOL... I didn't realize this thread was old. I was answering the original OP's question.
moparmat2000
Well-Known Member
Its all good, i forgot it was someone elses thread lol. I will still be doing the bit to the 318, but now will put it in my sons car when we build that project. An LD4B is a pricey vintage piece now, an i see em with a bunch of corrosion in the water jacket areas, so hows a Weiand stealth stack up against it? I kinda like squarebore manifolds myself, i think the eddy performer is a spreadbore.
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Ok, I didn't go back and see what all your plans are for the 318, but in comparison to the LD4B, I think the Weiand Action Plus is a great intake for 318's. They do have a spread bore design, but a square bore carb bolts straight on top of 'em. I like them better than the eddy performer. Pretty easy to get second hand, and cheaper to buy brand new. Great intake on a stock 318, and a great intake on a 318 with a mild cam, headers, and some head work including 340/360 heads.
moparmat2000
Well-Known Member
Engine ran great out of 74 dart parts car. No smoke, didnt knock, decent oil pressure. I was gonna change seals, gaskets, core plugs, water pump, clean out and reinstall the oil pan. Add 340 exh manifolds, and a nice aluminum intake with a 600 carb, electronic ignition w GM HEI.
If you are not going to do head work or swap cams, then a lot of intakes would do you great service. Here is a short list of easy to find and easy on the wallet, but there are others as well:
- Factory Cast 4 bbl
- Old Holley Street Dominator (I just bought one for 30 bucks). I'm talking the one without the divider in the plenum
- Edelbrock performer
- Weiand Action Plus
If you're patient you should be able to find a LD4B at a reasonable price (less than $200). Most of the ones on eBay now start at $200 or $250 and still need work. Clearly some folks are paying that amount for LD4B's since most of them are not relisted.
moparmat2000
Well-Known Member
I dont mind a weiand action plus, or a street dominator. Will need to hit next swap meet and look 4 one.
One of the Weiand's is almost an exact copy of the LD4B but I dont recall which one. I looked at buying a new Weiand if I couldn't get a good deal on a LD4B.
why people over pay for the LD340/LD4B is beyond me, unless they want the retro-old school look (which I understand). Plenty of intakes that will match or exceed them for less money.
moparmat2000
Well-Known Member
It doesnt have to be an LD4B. It can be something that flows just as good. Maybe a weiand action plus will fit the bill.
myduster360
Well-Known Member
Everyone thinking about if headers are "worth it" needs to get this "HEADER DESIGN INFOPAK" from Headers by Ed
I first ordered it over 25 years ago. It was the most eye opening, practical advice on testing and design I've ever heard. I can even say it played a part in inspired me to go into Mechanical Engineering.
Get More Header Design & Construction Information
I first ordered it over 25 years ago. It was the most eye opening, practical advice on testing and design I've ever heard. I can even say it played a part in inspired me to go into Mechanical Engineering.
Get More Header Design & Construction Information
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