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I'm installing Doug's stainless steel side mount headers on my 70. Yep...they don't exactly fit...but they come close! In all fairness the BB engine and heads are not stock GM, Keith Black and Brodie. I need to lower the engine to get the headers to fit under the frame. Anything would be great; 3/8, 1/2 inch. Another problem may be the motor mounts elevating the engine slightly. Does anyone know if there are motor mounts that will lower the BB in a C3 frame?
The problem is basically with one tube on the driver's side. I can also grind away some of the frame (!). Just dropping the engine a fraction of an inch would either solve or greatly alleviate the problem. BTW. The headers are absolutely beautiful. They look like polished chrome, when there are actually polished stainless. Don't want to dimple them! Oh...the crank vibration damper is 7 inches in diameter versus 8 inches for the stock, so that gives me more than 1/2 an inch of play, at the damper/front crossmember, with engine height.
Thanks. Pretty obscure question but maybe someone has an answer. Yes. if push comes to shove, I'll look for a frame repair shop to lower the frame motor mount horns. Thanks
I'm thinking someone used spacer plates on their headers at the head mounting surface to get proper clearance, but it may have been a SBC . Just a thought.
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Make sure that if you lower the engine mounts, that the fan does not hit the shroud. My big block Chevelle had poly motor mounts in it and when I installed the factory shroud and the fan hit it. I installed factory mounts and all was well. So, to answer your question, the Energy Suspension poly mounts I had will drop your engine. Jerry
I had the same issue. I heated the offending header tube and using a flat bar and big hammer made an indention about 1/4 inch deep to clear the frame. This will not degrade performance and being under the car it will not be seen. Much better plan than grinding the frame.
I don't think there are mounts that lower the engine, even the solid mounts. Seems it would throw the driveline geometry off with even a tiny amount of movement.
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If you use solid mounts without the spacers they will lower it a about 1/8th to 3/16s but the bolts wont slide though easily yo would have to open up the through bolt holes a thousandth or 2. Other than that its notching the frame or massaging the headers...massaging is the smarter way to go and it will not effect their performance, its just that you have to make them a little less perfect which sucks. doing anything major to your frame without repairing that cut would weaken it in that spot, however minimal, is still a weak spot. If its in a part that is boxed then you are in better shape
Make sure that if you lower the engine mounts, that the fan does not hit the shroud. My big block Chevelle had poly motor mounts in it and when I installed the factory shroud and the fan hit it. I installed factory mounts and all was well. So, to answer your question, the Energy Suspension poly mounts I had will drop your engine. Jerry
. Thanks for the comment. I will be using an electric fan. Goodby to the stock BB fan shroud. It's tough to get that thing in and out on a fully assembled engine compartment.
Originally Posted by Jebbysan
Where exactly does it hit?
Jebby
The tube from the #3 cylinder (the cylinder adjacent to the #1 cylinder) hits the inside edge of the frame where the frame is bending inward to make space for the front wheel. I'm surprised that the passenger's side header fits OK! This tells me that the Keith Black block and Brodix heads must be very similar to the stock BB's exhaust port geometry.
I'll try to attach a photo later. This part of the frame is pretty close to that large hole on the other side of the frame...the hole that allows you to install/remove the bracket for the power steering ram. If I notch the frame, I'll definitely have someone weld a plate to add strength...maybe weld a plate over that big hole.
Thanks for all the great comments. Here's some photos The blue tape on the frame indicates the interference. The appearance of tape on the tubes are reflections. Overall engine view. The headers look like chrome. The engine dyno'd at 630 hp at 7000 rpm. 496 cubic inches. Calles crank and H beam rods. Fuel Tech 550 sequential port injection.
I'll call Doug's Headers Tuesday. Looks like they may have a factory in Irwindale California. I'll be interested in hearing what they say. Maybe they can mod them? I like the idea of cutting the offending tube section out and re-welding. The frame should not be the offender. It's a NOS frame purchased from GM Parts in ~1980! I ordered a replacement 1969 frame for a 69 BB I had at the time. The 69 was later stolen, leaving me with the frame. I found out a couple of years ago, the frame is actually for a 1973, the 73 frame being a service replacement for the 68 through 73s! The 73s being rubber front bumper cars means a relatively easy mod has to be made to the front frame extension horns to attach the front chrome bumper.
Last edited by 68/70Vette; Sep 17, 2023 at 01:30 PM.
I don’t think anyone here is advocating cutting and modding your headers; rather just dimpling them to gain the clearance. If you are running solid motor mounts it takes very little clearance to make it work. Since yours are stainless, there’s no chance of cracking the chrome, so if you dimple them with a bit of finesse, and re-polish them after, it will look like it was engineered that way.
The reason it doesn't fit is because most all good aftermarket heads have a raised exhaust port.....so Doug's isn't going to be able to tell you anything really.......
Given your picture.....I would flatten the pipe in the affected area.....
Even with stock everything this occurs due to offshore manufacturing variations. In other cases it has been suggested after bolting the headers to the head bend the pipes by using body weight on the collector.
The reason it doesn't fit is because most all good aftermarket heads have a raised exhaust port.....so Doug's isn't going to be able to tell you anything really.......
Given your picture.....I would flatten the pipe in the affected area.....
Jebby
This is not discussed much, but Jebby is correct, most aftermarket aluminum heads the exhaust port location is not the same as the factory heads and can affect header clearances. Something to always consider on choosing heads. Manufacturers like Brodix makes heads with the factory location. In your case, flatenning pipe may be the only option. Good luck.
I would do as others have suggested and just flatten or dimple the header tube where it contacts the frame.
You only need a little and if you do it right, you’ll never see it.
I’ve read threads where people used a larger diameter socket, dimpled the tube and it looked like it was done by the manufacturer.
If you are worried about it effecting performance, it won’t.
Engine Masters did a segment where they not only dimpled a set of headers, they mangled the primary tubes and ran them on the dyno, showing there was no loss in performance at all.
Motor Mounts to Lower Engine?
