HP limit with 1-5/8 headers

-
6

66dartman

Well-Known Member
Joined
Apr 25, 2005
Messages
1,164
Reaction score
11
Location
Littleton, CO
Since the headers that I just bought for my 66 Dart 360 project have 1-5/8 primaries and 2-1/2 collectors, what do you think will be the hp limit of the engine? Can I still make 450+? The engine will be more strip oriented with 12:1 compression and eddy heads. I don't know if porting the eddy heads will be limited by the header primaries
 
With the compression and the heads I would use 1 7/8 hedders for the 450+ HP. IMO


BJR Racing
 
It's difficult to give specific numbers, but the 1 5/8" primaries and 2 1/2" collectors will definitely restrict your HP. Personally, I've always found it better to be on the conservative side. I have TTI stepped headers that go from 1 5/8" to 1 3/4" with 3" collectors and I can run in the mid-11's while weighing well over 3,500lbs! Different weight-to horsepower calculators give different #'s. Not sure what the actual HP is, but it's up there. The step gives the best of both worlds - bottom end torque without being restrictive at higher rpm's. Some custom race headers start out about 1 1/2" or are shaped to the actual port opening! But they do step up quickly to 1 3/4" and/or, sometimes, 1 7/8", depending on the application. You will see a benefit by getting rid of your existing headers.
 
I kind of gotta agree with the fellas here. Though the smaller tubes can still make power. I wondering about the rest of the build and intended use. Sometimes smaller is better.
 
Well the problem with having a red headed stepchild 66 dart is that the headers are few and far between. I really didn't want fenderwells, so I bought the Doug's headers.
I guess in the future if tti makes a step header for this chassis I will have to break down and buy them.
Thanks
 
Hey 66dartman, don't dispair. Read what this article has to say about stepped headers vs. headers that are too large or too small. I'm not saying I agree with everything it says... I'm not sure I even understand all of it. But it does make you scratch your head and think about it.

My bet is that any off the shelf header has the potential to perform better on one engine than it does on another. To put that another way, just because a TTI step header works wonders on one guy's 7500rpm screamin' 340 does not mean that same header will perform as good on another guys 416 stoker with a 5500rpm readline. Just my opinion, but if you really want to get the absolute most out of a set of headers, they must be custom designed for that particular engine/chassis combination.
 
If you have the headers, I'd use them. They might even improve on low end grunt.
 
GotDart said:
To put that another way, just because a TTI step header works wonders on one guy's 7500rpm screamin' 340 does not mean that same header will perform as good on another guys 416 stoker with a 5500rpm readline.
Click to expand...

Just for reference, I shift a little over 6,000 and go through at around 6,500 rpm. My compression is less at around 10-1 and heads have OEM ports, but the rest is similar.

For what it's worth, my opinion on stepped headers was influenced by the fact that many of the high-rollers in NHRA and IHRA Stock spend a lot of money and dyno time getting custom stepped headers made and that's one reason they have VERY fast race cars within the rules! While I'm not in a position to do that, I got these after seeing magazine tests and the same headers on other cars in my class performing very well. And these are "on-the-shelf". They work well on the track AND on the street!

Like any part, adding it may alter what the rest of the combination likes and may require some fine tuning. (i.e.: jetting, ignition timing, etc.) "Shelf" parts aren't "perfect" for many combinations. But they are usually designed to work well in a wider variety of applications. So GotDart is correct. But getting that perfection is beyond most of our resources. (Design, build, dyno, track, redesign, etc.)

Unfortunately, TTI doesn't have headers for the early A-bodies. Also, the 1 5/8" headers won't make the combo run "bad". Sometimes you just have to make the best of what you have. But if it becomes feasible to get different headers, a bigger size would make an obvious improvement overall in 66dartman's combo.
 
Will they afect the power in a negative way? To some extent, yes. Will you notice it? I seriously doubt it. It takes a lot of sorting out to get to the point where swapping to custom or longer or larger tube/collector will make a feelable difference. Does it make a difference, defiantely..But on a street car, you wont notice it much. At t he track, you can feel ET changes in the .10s, but a street car on the street, it's hard to notice a change of .5, unless you're racing a consistent car and you can gage against it.
 
1 5/8 verses larger tubes. With larger tubes, and 12 to compression, you arn't going see much, if any loss of low end torque. With the 1 5/8 tubes your upper end power will suffer . I agree with what has been said.. any serious street or strip performer will benefit with the larger tubes. I feel 1 5/8 is too small for hot well built 340/360. Torque (low RPM) motors (limited to 5500) will be fine with them. Stepped headers are good also but EXPENSIVE. 1 7/8 would make great hi-rpm power, 1 3/4 would work well also if you can find them for your chassis engine combo. Good luck and keep us posted. Terry.
 
FWIW,

The larger the tube diameter on headers the higher in the rpm range the torque peak occurs. The length of the tubes will rock the torque curve around the torque peak. Longer tubes enhance the power below the peak, shorter tubes above the peak. To a point longer collectors will enhance power below the peak and larger diameter will enhance the power above the peak.

Read an article in Popular Hot Rod about a month ago where they tested 8 different styles of headers on a stout 454 big block Chevy. The reported average power over the test rpm range which as I recall was 3k to 6500 rpm. Anyway, the average power for all the styles of headers was within 1 or 2 HP of each other. They tested tube diameters of 1 3/4", 1 7/8", 2" and 2 1/4" and step headers.

What this means is when you pick up power on the top end you loose it on the bottom end and visa vers but the average's essentially stay the same. So just like picking cams, carb sizing and what type of intake to use you have to know your operating range. I would venture to say if you won't be spinning the engine past 6000 rpm that the smaller tubes would be a better choice but if you plan on looking for max power above 6000 rpm the larger tubes would be the way to go.

Remember, Horsepower is just the torque the engine produces, times the rpm, times a constant.
 
I read the article that GotDart posted and it is very interesting what Ed's headers says.
One very important factor is where I will be running the car-Bandimere Speedway is at 5800' in altitude. That is why I am using 12:1 static pistons, however the cylinder pressure will be more like 11:1. It seems to me that it is very easy to over do it with cam, carb and ports up here. I will be experimenting all the way until I sort my combination out. My goal of 450 hp is more like 400 up here, and I am really looking for the most mid range torque I can get. I feel it will be easy to overpower my 8" wide drag radials with too much low end. I went with 4.30 gears and I hope I haven't over geared the car.
 
I run a NHRa stocker with a low compression 340. I ahave tried all the different types and tube sizes. I ran the 1 5/8 at first and tried the 17/8, the 15/8 was run for the torque they make over the 17/8. I have three sets of headers for my car and pick the right ones for the track and air. My 340 ran 10.83 in bracket mode ar Rockingham in Oct. 1.38 60ft and 6.80 in the 1/8. With the 360 spend the money for headers on a convertor and other needs first before the headers. The gain might be much for the money spent. The step headers that cost 1500.00 are worth about 10hp over your 15/8, the 17/8 are worth about 5hp and a set of custom stainless that costs 3000.00 are worth about 20hp over your 15/8.
 
thanks jmk426, I needed some hard numbers for comparison. I will spend my money on a good converter instead of new headers next year.
 
You must log in or register to reply here.
-

Back
Top