70 Impala 355 header question - Impala Tech
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post #1 of 10 (permalink) Old 01-05-2014, 07:36 PM Thread Starter
 
 
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70 Impala 355 header question

I have a nicely built 355 in my 70 impala and just finished it and now want to take out the ram horns and add full length headers. I have heard there is an issue becus of the turning box being mounted on the frame and near the drivers side header. Is there a set of headers that is built to avoid having to bend or dent the header and will clear this issue?? Thanks guys
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post #2 of 10 (permalink) Old 01-05-2014, 09:14 PM
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Welcome to the Team Chris!

Headers are made to fit a stock car just the way it left the factory. This includes the stock Saginaw steering gearbox.

When headers start to give fitment problems is when the car or motor are modified with aftermarket parts. An example is the raised exhaust ports on aftermarket big block heads on a motor installed on the wrong small block frame stands. The exhaust ports were reshaped and relocated to make the engine breath better so they make a lot more power, but now the headers will be raised and placed at a different angle hitting the car's chassis in the process. This is further aggravated by the frame stands which has the motor out of the stock location (which is lowered to counteract the two inch taller big block). It is interesting to hear owners of such cars complain even though they may or may not admit to not first reading the "foot notes page" that advertises all known fitment issues.

If everything is stock I would expect them to either drop in or slide up from the bottom without having to do anything other than removing the spark plugs. That said some companies are better known for their performance image offering large tube equal length primary tubes such as Hooker, while others have a reputation for their nice fit and easy of installation such as Headman headers that use unequal length tubes with fewer bends and made out of thicker steel but with smaller inside diameter tubes. There are companies like Doug's and Cyclone that try and find middle ground.

Big Dave
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post #3 of 10 (permalink) Old 01-05-2014, 10:15 PM Thread Starter
 
 
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Thanks Big Dave I have just heard from other that its a problem on the 70 because of the placement on the upper part of the frame instead of down further like most other cars. It seems to be directly down from the middle 2 exhaust ports. My car is a factory 350 car and all I hve done was take the old engine out and build up below and add it.

02 vortec block 30 over hyper flat tops arp throughout, coated bearings, and all balanced and blueprinted compression 10.1 to 1

AFR 195 eliminator comp heads, port matched eddy performer rpm air gap with 1 in spacer

Mike jones custom speced jones cam hyd roller with jones roller lifters .228/.228 dur .580/.545 lift 108 lobe sep, 105 center 1.6 roller rockers, 5/16 .080 wall hardened pushrods, roller chain,

Quick Fuel 680 VS carb with GM HEI with MSD cap, rotor, coil, 8.5 wires, crane adjustable vac can set at 10 degrees connected to manny vac and NGK plugs. Inital is set at 18 degrees and 16 degrees mech in dist with screw stop mod.

exhaust is mandrel bent 2.5 dual with x-pipe out magnaflow mufflers and right now its using rams horns with 2 in outlet tht have 2 in pipes connecting to the 2.5 in until I find some headers but I know this has got to be choking it some.

I have 2 transmissions trying to decide which to use both built and ready 700r4 and a turbo 350 but i hear pros and cons for both. I have a custom stall being made as well tht will do great for a daily

have 2 sets of gears depending on which trans I go with 700r4 was gunna do a 3.73 gear and posi, turbo 350 is a 3.42 and posi

So was just looking for anyone thts already done headers on a 70 with a sbc and had no probs and what kind they used tht was all.
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post #4 of 10 (permalink) Old 01-06-2014, 10:20 AM
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The frame on the '70 is the same as the 1966-'69. If they can use headers so can you. It won't be the frame that is the issue but your heads. The heads use the Vortec's fast burn "D" shaped exhaust port:

http://www.pro-touring.com/threads/9...roller-rockers

The holes in the head that mount the headers are in the stock location, but the exhaust ports are actually raised. Because of this the top of the "D" shape is very close to the edge of the flange with it's 1.5 inch square hole so you will have a continually recurring exhaust leak were it burns through unless you use a header designed specifically for these "D" shaped ports.

The 700R4 is a TH350 that has an overdrive gear added to it. Many of the internal parts interchange. So in terms of strength there is no advantage. Where there is an definite advantage is the 700R4's overdrive that will drop your motor down thirty percent lower than trying to cruise with the TH350. You will need the 3.73 gear set to keep your cruising RPM above the flash point of your unspecified custom stall speed torque converter. The 700R4 utilizes a lock-up converter: I suggest you tell your custom converter maker to include that option. It provides an additional 5% to 7% increase in gas mileage, and contrary to what he says, will not affect your car's drag racing performance (it can be locked out with a switch on the dash if he insists upon it). The only down side is the added weight to the converter but it is worth it unless this car is going to live on a trailer and only drag raced.

I had a 582 with a 4L80e transmission and I used a lock-up converter as it was mostly street driven. I tore the lock-up lining off the inside of the converter once when racing with slicks, but since it was under warranty I sent it back and got a new one. After that I disabled the lock up function when ever I bolted on huge slicks.

Big Dave
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post #5 of 10 (permalink) Old 01-06-2014, 11:19 AM Thread Starter
 
 
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thanks again dave i contacted my converter guy n explained i wanted the lockup feature i will be using the car daily so id like the extra mpg n the overdrive as well so 700r4 i think is the way to go.

As for the heads the link u posted was the old 195 afr heads the new eliminators are light years ahead of them n employ a much better exhaust port. Below u can see the difference between mine n the ones u posted. These are more square not D shaped i posted a pic of both below.

Also i know this is the same frame but the older models didnt hve the steering box up so high on the frame heres a link to show u what i mean http://www.hotrodders.com/forum/1970...ems-98316.html seems this is an issue only for the 70.
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post #6 of 10 (permalink) Old 01-06-2014, 11:41 AM Thread Starter
 
 
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Doing alot of research and looks like the hedman 68170 should fit and clear the steering box gunna give em a try cant hurt their only 175 new lol
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post #7 of 10 (permalink) Old 01-07-2014, 07:47 AM
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I just installed a set of Flowtech headers in my 68 and they fit nice. One tube is very close to one of the steering box bolts but I plan on grinding the bolt just a bit to get me about a 1/4" of clearance. I have aluminum Trick Flow heads which are D port and angle plugs BTW. The passenger header practically fell in by itself.
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post #8 of 10 (permalink) Old 01-08-2014, 05:32 PM Thread Starter
 
 
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very cool to know I got the hedman headers coming they will be here tomorrow and installing them on sat so will let ya know how they work. But if they dont go well guess the flowtech may get a chance lol
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post #9 of 10 (permalink) Old 01-15-2014, 11:13 AM
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Quote:
Originally Posted by 70imp355 View Post
Doing alot of research and looks like the hedman 68170 should fit and clear the steering box gunna give em a try cant hurt their only 175 new lol
I had these headers on my 65 Impala with a 383 with Edelbrock Victor Jr heads that have raised exhaust ports. They fit much better than the Hooker, which uses the same part number for Impala 65-76, Monte Carlo, Chevelle. Hooker's also have the left side hanging down farther than the right to clear single exhaust trans cross members. They got hit on every speed bump and dip in the road.

The Hedman's tucked up very nicely and the engine cross member would hit the ground before the headers got touched. They also have ball/socket style collector, not gasket to blow out.

One thing to note on the Hedman's. It is necessary to remove motor mount bolt and jack engine over towards passenger side to get the left side in from bottom. A bit annoying, but worth the time to have a nicer fit.


I wanted 1 3/4" headers for my car. I ended up having to make my own in the most bizarre way. I bought a set for a Mopar 383, knocked the flanges off and bought

If you are looking for headers larger than 1 5/8" primaries, you are out of luck except for custom and Stahl. Stahl has a template for '65-'70 Impalas with 1 3/4 to 17/8" stepped primaries. I was quoted $1300 for them.

1965 Impala SS, 383, 4 spd
1970 Caprice LS-4 454, TH400

Last edited by Scott Liggett; 01-15-2014 at 11:34 AM.
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post #10 of 10 (permalink) Old 01-15-2014, 12:44 PM
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At $1.300 you are approaching custom header prices which is what I use in my exotic installs where there is no off the shelf application (like a 2-1/8th primary tube long tube header for a BBC in an '85 Impala.

Even though there was an off the shelf application for my 406 cid SBC in an '89 Caprice I chose to have a stainless steel header kit welded up out of U, J, 90, and 45 degree pipes (and of course straight pipe) for a full SS exhaust system from port to bow tie exhaust tips at the rear bumper. I forgot that I had paid out $2,400 to have that system made at an exhaust shop in West Tampa when I recently crushed the car; I should have saved at least the headers off of it, I but didn't think of it until just now.

Big Dave
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