so for the most part i haven't been very active on the form due to my project taking a back seat. (87 t/a gta) but I've finally started getting parts together and the new motor is about to be swapped in. so my task now is to choose some headers i was going to go with long tubes but decided i do not feel like dealing with the problems they bring for 8-10 extra hp. so im going to go with shortie headers instead. now for every day street application is going to a 1 3/4 worth it ? or should i just stick with 1 5/8 pipe diameter. here are the specs of my car

350sbc
forged pistons
forged connecting rods
edlbrock rpm performer cam
eldbrock rpm performer intake
305 heads with full race port and polish
holley 700 double pumper carburetor
plan on running full 3' exhaust all the way back if it can be done but were not sure yet. also want to try to run true dual but again not sure of the possibilities the most common way I've seen on here is run both pipes down one side of the car. so were exploring that option.

 

1 3/4in shorties from Dyno Don or SLP's if you can find them. 305 heads are going to choke the engine.

 

1 3/4 and ditch the 305 heads.

 

Right!

 

Thanks guys I'd like to ditch the 305 heads but it's what I got atm since the 350 heads that are on the current motor won't fit the new motor due to the intake bolts being different. I'd like to get a set of camel humps or get a set of edlebrock rpm performer heads to match the cam and the intake but I don't really have an extra 800-1k laying around anyway we went with the 305 heads to boost the compression which is right around 10:1 ish atm I have looked around on forums though and people have had varying degrees of success some say they work amazing others say the heads make the motor run hot. Anyway thanks for the info I'm going to a huge parts swap meet next week so I'll keep an eye out for some camel humps or some after market heads.

 

Here's a chart that'll help with your selection. You'll the need the exhaust cfm at full lift and the vehicle application to make the proper determination.
Using Vortec heads as an example, at .500" lift, they flow 160 cfm (according to most sources) so in a street application, a 1.5" I.D. pipe (about 1 5/8" O.D.) is your best bet.
If you step up to an AFR 195 competition head, they flow 224 cfm at .500" lift. Now a 1 3/4" header is better.

 

camel humps suck and it might be worth your time time to oblong the 2 center bolts. unless the 350 heads are vortec then use them and get a new manifold.

 

As has been said, the 'camel hump" heads aren't worth it when the chances of finding something aftermarket is just as liklely. If you HAVE Vortecs, then spend the money on a manifold. If you come across the Edlebrocks, get them if only because they're aluminum (and flow reasonably well with a smallish intake port volume) and there are a few advantages to using aluminum over iron. If you have any choices, you won't be far of the mark to choose the smallest intake port that delivers the best flow. That's pretty general but it works for the most part.
Then once you have the heads, you can work on the header size.
If you're sticking with the 305 heads you have for any length of time, and you have a choice in primary pipe diameter, smaller is generally better in any given street application.

 

There not vortec heads the transplant motor that's going in the car was built by my dad's friend. It's out of a 71 chevelle. The motor only has about 1500 miles on it. He put the 305s on there in order to bump the compression ratio up. I originally only bought it for the bottom end but it was mutually agreed by myself my dad and a few other people that a full carburetor swap over from tpi (I hate fuel injection to much computer crap) to a carburetor setup would be best. I had looked into vortec heads but I was unable to locate them anywhere ever junkyard I went to that had cars/trucks with vortec anything in it was generally missing and on eBay (besides the fact shipping would kill me) I've seen them run anywhere from $400-800 which for a few 100 more I can get the edlerock heads to match the cam and the intake but as stated I'm going to a swap meet next week I'll keep and eye out for some heads and see what I can find thanks for all the help

 

Compression ratio to match the cam more specifically (but you've got that figured out).
As for the help, the point I was trying to make is that header size is linked to cylinder head flow and vehicle application. It's not a case of one size fits all. Your 305 heads, despite being ported, might work best with a smaller primary tube. Then again, if they were ported by Roger "Dr Air" Helgeson, it may take a larger pipe to work best.

 

Nope lol nothing specially like that just my local machine shop. As luck would have it all as he deals in is sbc. So it worked well for me lol. But hangout for the input I'm going to look around some more and see what I can find it kind of seems like 1 3/4 might be the way to go due to the port on the heads I also want to see about what I can do to get the compression up just a little higher not to much more as it's already at about 9:1 but I'd like it to be somewhere in the 9:5 range. I know I can use a different head gasket but that's a entirely different forum lol.

 

Here ya go...PM for details

 

^^ pmed although I'm really just looking for the headers I don't need the y pipe or anything else as I'm going to try my hand at a true dual setup

 

I would REALLY suggest you reconsider that horrible idea. There are REALLY good reasons that poeple go through teh trouble of paying big money for well-built y-pipes in these cars.

 

^^ I'm not to worried about it I have unlimited access to a shop, pipe bender, pipe and a lift. My finances uncle owns a shop.

 

The piping isnt the concern. It's the frame of the car. It's in the way. That and the transmission. It's much more difficult and impressive and functional to build a y-pipe to a catback in the factory location.

Go measure the distance between the ground and your transmission crossmember, then subtract the diameter of the pipe you want to use and see how much you have left.

That's why most guys who are just hell bent on doing duals well will do something like this. This is the Nelson Racing thirdgen camaro:



But when you run duals like this without the crossover you lose the scavenging effects of a crossover that an x-pipe or h-pipe or a Y pipe will give you.

 

Not once have I had an engine run better with a Y-pipe and single exhaust. X-pipe is preferable to a H pipe but both help equalize the exhaust backpressure (AND FLOW) between banks which help improve scavenging.

 

There is nothing about your combo that would benefit from a true dual vs a single 3".

 

There is no substitue for an exhaust system that develops ZERO backpressure. It's also critical for the exhaust to flow close to 2 cfm per horsepower delivered at the crank.
That's why some of use can get away with a single 3" and others can't. On a modest 400 chp engine, that's a muffler that'll flow 800 cfm minimum. Duals make it easier.
The scavenging (as opposed to an exhaust that doesn't flow well) doesn't really enter into the picture until the cam overlap gets into the range where an exhaust induced induction cycle can begin and THAT won't happen unless the exhaust system has more to it than zero back pressure. That's where you get into pressure wave tuning and as you all know, that's a different story altogether. I don't think that's the OP's objective.
At any rate, zero is the target.

 

Well that was a fun read...

 

Do I detect a hint of sarcasm?

 

Maybe a little.

That's a neat chart. Is that one of Vizard's ?

-- Joe

 

Yeah, that's one of Vizards.
With so much misinformation out there, for the guy who's looking for some simple advice (as in primary header size) he's easily tapped for the fundamentals.
Of course and their brother has an opinion....

 

Yep, he simplified things for basic builds.

I found the thread kind of funny that he had this debate over pipe size when the rest of the build is fundamentally flawed.

Then InfernalVortex comes in with the x-pipe science and I almost lost it. (not because the information was bad, but because it should go to someone building a 10 second car).

350 non-roller block, 305 heads, 'carb'. This thing is gonna be a speed demon!

-- Joe

 

I suppose we all have to remember when WE were at that stage. Using what parts we had to build what we could because that's what we had. Witness my first build. About 40 years ago I put some "double hump" heads on a 307. Combined that with my Holley Street Dominator intake, a set of "BlackJack" headers and a rebuilt 4160 Holley and I was good to go. Put that in a 68 Chevelle with a powerglide and 3.08 gears and you can imagine I was hot stuff.
Then I packed it all into a 400 block with some kind of aftermarket cam and I was hotter still.
Fast forward to my "hot rod renaissance" about 30 years later and I started with Hedman shortie headers, some Vortecs and an aftermarket cam on a 350 in my new to me 86 IROC-Z...
Anyway, I guess the point is, I'm willing to give a little guidance to any of the rookies. As long as I have a little personal experience and research to draw from.

 

So am I, but his mind appears set on a number of things and it's because he's trapped in the following bad scenario:

1) Young and not enough money
2) Couple of real old farts who don't like "fuel infection" telling him to carb it
3) Non willingness to learn 'modern' hot rodding

And I used the term 'modern' loosely, because we're quickly approaching the point where carb's have not been on a new vehicle in 30 years.

When he's done the car probably won't make as much power as it did stock.

-- Joe

 

All valid points Joe although in this case it was a simple matter of the OP asking what size headers would be best.
As for the EFI vs carb debate, personally I embrace both approaches.
I like carbs because I think I know them well. Models based on the 4150 style at least.
FI because I understand the adaptablility and what it means to fitting it into a given project. Example being is that I'd like a (roots style) supercharger on my next build but I can't say I'm a fan of having my fuel mixer on top of the blower. I like the compact look of the throttle body in front of the blower.
Regardless, good luck to the OP in his build.
As for modern, the carb is going to be around for a while yet. Hell, guys still race flatheads!
Spread the hot rod word...

 

A few years ago I met an old engine builder that actually preferred to use 305 heads on hot street motors. Of course he would port the snot out of them first. I don't think he built off of theories either, as he had spent a lot of time testing on a flow bench and dyno testing everything.

If the OP's machine shop hogs out those heads anything like the guy I met, they might actually be a decent set of heads.

 

LOL, just trying to talk the guy out of doing duals...

I had a dual 3" X-pipe setup back in the day and I'll never do it again unless Im actually making enough power to need it. It was way overkill for my setup and a huge pain in the butt.

 

Duals can be a pain and I agree most of the times not needed or worth it. Having said that though I have never ran a single/Y pipe system on a third gen in over 15 years of messing with these cars. All of mine have been duals.

 

This doesn't make sense to me. The labor costs involved with hogging them out far exceed what a set of bolt-on aftermarket heads cost.

-- Joe

 

But that's in today's world. 15, 20, 25 years ago it was very hard to find aftermarket heads that flowed 240+ cfm and when you did the price was out of range for most of us.

I can fully see and understand porting power pak, double hump, fuelie, 305 HO heads 20-40 years ago and getting 210 to 240 cfm out of them, but not today when you can go buy any used vortec truck heads for a couple C notes, flow 230 cfm and make 20-40 HP more than your other stock heads

Or drop a grand on a set of alum heads that flows 260 cfm.

In todays market it just don't make sense to go backwards and use a poorer style head.

When the double hump heads or the 305 HO heads was in production, they was thought of as the best production head of the time.. So thats one reason they was used... Now that's the vortec heads

 

It's true. Way back when, around 1999 or so, when I first started my 355 project, everyone kept insisting I keep my 305 heads to put on my 355. I think most liked that method for the compression boost.
I didn't end up going that route regardless, and I'm thankful for that, as I scored some Eddy RPM heads used and dirt cheap.

 

This guy is very set in his ways. He is semi-retired and literally builds Chevy small blocks and big blocks for the fun of it, so the time involved isn't a real big deal to him I guess. He had a 2-car garage packed full of assembled engines ready to go, all of them were for sale, but he wasn't actively trying to sell any of them.

 

Appropriately sized duals can be slightly better but a well built single exhaust setup with the right size mandral bent piping and an adequately sized/flowing muffler can still run great.

You can make a single system support a good HP number and be relatively quiet but it takes alot of space under the vehicle and a well thought out system. I have a pretty healthy Vortec 350 in my Express van that has a nicely constructed exhaust system and it does its thing pretty darn quitely as well for a cammed/heads/headered small block.

My exhaust starts with Thorley tri-ys with 2.5" collectors into thorleys 3" headpipes meant to match up to the factory 3" pipes on a 1-ton Express.







The 3" pipes reduce into mandrel bent 2.75" stainless pipes havested from a low mileage newer chevy truck and flow into dual 2.5" spun high flow cats. The pipes exit the cats at 2.5" and flow into a 36" x 8.75" Walker Dynomax school bus muffler built 3 chamber turbo muffler style.







The exhaust is then channeled through a 3" mandral bent tailpipe over the axle to the stock exit location.

My 84 year old grandmother would not object to riding on a highway roadtrip in it and it still makes over 400 hp. Its actually a bit of a sleeper in that it will spin the tires and get up and go without much engine noise.

 

That's a good looking exhaust system!.

Yeah, single fits much better under a third gen for sure, but with me I'm "old school" I like the look and sound of true duals and mine is a mid 10 second car N/A, once the nitrous goes on, looking at high 8's. So max exhaust flow is a major concern for me.

Not the prettiest exhaust by any means, but it works and fits pretty good. At my lowest point I can still fit a coke can under it. I didn't have a way to bend up the pipes at the time and done it in my yard with no lift, so I used the 3" flex repair pipes to get my bends/angles and welded all the other together.

Hedman long tubes, summit 3" X pipe, dual 3" pipes, dynomax ultra flow 3" mufflers.
I lowered my trans crossmember down by 2", spaced up my trans mount by 2", and ran pipes over the trans crossmember. Mufflers are placed in very rear of car under/side of the trunk storage well bottom, then 6-8" of 3" pipe angle cut added to finish them off and look/act as exhaust tips.

I had many other 2.25" and 2.5" dual setups in the past, and never had as much ground clearance as I do now with my 3" dual system. It's all about thinking the whole setup through.

The 1 thing that gave me the most clearance was dropping crossmember down. My old 2.25" duals ran right below the cross member and only drug every now and then, so I figured dropping Xmember 2" would be a safe limit and gave me the space to go up and over with pipes

 

Duals in what sense? A pair of mufflers dumping under the car? I'd like to build what my old Chevelle had. Two mufflers in the traditional location and tail pipes over the axle and exiting the rear. With a lowered 3rd gen, that takes a lot of work...and a few compromises. This isn't to say it hasn't been done. It's just not easy.
If I were to build a dedicated drag car, I'd go for glass packs or race bullets that serve as header collector extensions. Then you could easily build a tuned exhaust to work with the cam overlap. Unfortunately, in a street car, that noise gets really old, really fast...

 

Oops. Should have read that before I asked what kind of duals you had.

 

Ahh. The luxury of having a little real estate to work with.

 

That is a 4L80E too, lol! Too bad the engine compartment is anything but roomy.

 

I'd like an 4L80 as my next transmission. I understand they'll fit in a 3rd gen.
As for working on the engine in your van, I've had several Astro/Safaris. Love 'em except for engine work. What a PITA!
Now my old '67 Dodge Fargo van. Mid engine with a dog house, that when removed, exposed everything!

 

Dyno Don, do you have anymore 1 3/4 header and y pipe combos? If so how much? I'm looking for new headers for my semi mild 406.

 

Have you looked into the stainless 1 3/4" OBX headers? I've done the ceramic coated thing a number of times and they always look like crap and rust through eventually. I don't know what your 406 is going to see for EGT's, but I've tipped 1800+ a number of times on earlier 355 builds and the coating never recovers from that.

-- Joe

 

I just looked the OBX ones up, and they are sweet. I only worry about long tubes since my car is lowered, and is driven on the street as well as the track. I was going to buy the 2460HKR headers from Summit along with the matching y-pipe. They are 1 5/8". My 406 is breathing through a set of Bowtie Phase II heads, so now I ask the recommendation of the people I trust on this board, should I step up to the 1 3/4? Or will I be fine with the 1 5/8?

 

Yeah, I try not to generalize but long tubes on a lowered car probably won't be a good idea.

I'd probably just run the hedman 68470 or whatever the number is. It's not worth paying 3 times as much for mild steel headers just because they are a hair larger primary diameter. I ran 120mph in the 1/4 on those headers for a number of years over 10 years ago.

-- Joe

 

Quoted for "absolute truth".

 

Yes, PM me for details

 

so I didn't want to necro the crap out of this thread but here it goes. I did take everyone's advice and went out and found some vortec heads for dirt cheap however they were on a very dirty motor so I have elected to rebuild them. since they need machine work anyway for my cam springs to fit. and I need the $$ for the intake. so for now the 305 heads which are now fully ported thanks to a friend of my fathers who owns a machine shop. I have learned allot over these past few months part way because of this fourm. I did elect for carburetor because quite frankly its a personal choice easier and cheaper to work on and I only live about 7 min from my work. I am still set on going on true duals however as everyone has said, to say its been challenging, well that's an understatement.

here is an updated build list from when I got the motor till now
spr flat top pistons with valve reliefs
eagle connecting rods.
dual chain timing gear
comp cam thumper cam 479/ 479 lift with 107 degree lobe sep (wanted to retain stock vacuum for a/c and the like)
comp cam springs
comp cam lifters
full ported 305 heads
steel eagle crank
bm hole shot 2000 rpm stall converter
700r4 fully rebuilt to about 600 hp thanks to a friend who works for monster transmissions.
stage 3 shift kit (thanks to the same friend)
fully rebuilt rear end with 373 running gears.
all new bushings suspension brakes etc.
Holley electric fuel pump.
edelbrock rpm performer intake.
holley 700 dp carb
1 5/8 inch headman shorty headers
2 core aluminum radiator. and upgraded electric fans.
full msd ignition setup.
chrome pulleys and the like.

im sure there is something I am forgetting.
its been a long road after i wrote this thread and saw the replies i realized i was in way over my head. so i sat back did a ton of research and reading planned out my build and my parts list and this is what i came up with. thank you for all the help guys your knowledge has been invaluable to me.

 

Back in the day when I had more kids in the house than money, I would use 305 heads to do a budget build on a 350. It was a short cut to higher compression, so you could run a little wilder camshaft. With a little porting, they ran good enough for some street racing and mild strip duty, especially in a light car, such as the '79 Monza I was running at that time. Of course that was during an era that didn't have stock cars coming off the showroom floors with 300+ horse power. Now that I'm on the back side of 50 and actually have a Man Cave and a budget to run it, I build them in a more straight forward way, but I still fondly look back on how us poor boys built fast cars when we were younger.

After running the Monza for a few seasons, the body twisted bad enough to cause cracks to start across the top of the car; which gave me an excuse to build my first camaro; it was a '67 and I wish I still had it.

 

I will never understand why anyone would go to the trouble of installing heads with 1 5/8 valves and then use a header that has in inside diameter of 1 1/2".

Surely you must realize 1 5/8 is 1.625 and has an inside diameter of 1.500

1 3/4 is 1.750 and has an inside diameter of 1.625 like the valves.

It doesn't matter how well you have run with 1 5/8" headers, you probably could have done better with 1 3/4" headers.

Just my $.02