'59 Cadillac 390. I'm building custom headers, in which for show purposes the smaller the tubing is, the better. One exhaust port will be joined by the next which will then be joined by the next. Will 1 3/4" be too small? Performance is not the first priority, but I don't want to choke the engine and I don't want to hurt anything. I'm running them open, no mufflers or baffles. Thanks.
I just can't see 1-3/4" being too small for primaries. Granted, I'm not familiar with Caddys, but I know a lot of powerful Chevys and Fords running headers no larger than that and putting down big power. Some run smaller than that (1-5/8") and still make big power.
1.75 should do well on there. The way I usually tell from a performance standpoint is take the cross sectional area of the tube and the port. A little less on the tube won't hurt you on a non-performance engine.
The primary tubes are fine in 1 3/4. Maybe I'm just an old fart but if you are building log style headers like the real old ones I'd have the tubing up to 2" at the end with a 2" header pipe to the muffler. It's not that hard. I personally think that they look better than a tiny 1 3/4 header pipe. When you build a log style manifold it was common practice to increase the size of the log as more gasses were added to the system. I don't get all rapped up in specifics. It's not that hard to run 2" so crimping it down to 1 3/4 is not a desirable IMHO
so at the end of the header you will have all 4 merging into 1.75 diam. pipe ? & will have 3 "Y" s . that cant be any worse of a restriction than the manifolds. i would think that every Y should jump up a size on the one leg going to the next Y since it passing more gasses with the same size (probably 1.5) off the head Imo 1.75 is too big for 1cyl , and too small for 4 clyinders
It will look something like this. Please excuse crappy drawing. I have some cool ripple tubing I'm gonna use for the end and it's 1 3/4". I want to keep a sort of continuity with the sizing. Will be chrome.
Sorry, I misunderstood. I thought you were building long tube headers and using 1 3/4 for the primarys and then going into a tapered collector. Now I'm not sure if your plan is a good one or not.
It would be like having a 4 cylinder with 1 3/4 exhaust or a V8 with 1 3/4 duals. On the small side but will work. Especially on a basically stock motor that does not rev too high. Have you considered 3 pipes on each side or have you got enough ripple tubing?
Ooh... I didn't realize that 1-3/4" would effectively be the collector size. I thought it was just the primaries. I guess I misunderstood, too. It would seem to me that 390 cubes would be a lot to be deployed into such small headers. Couldn't that adversely affect scavenging? Might be better with a stock sized cam? I know it's not so much a "performance" application, but still... If you chrome them it wouldn't surprise me to see the chrome get quite discolored if those gasses spend too much time in there.
That'll work fine, it won't be the best performing set of cad headers, but you won't be choking it or anything.
Street driving, the torque will be great, upper revs is where you would likely benefit from a bit more diameter. If you can 'flow' the #2 and #3 pipe joints, each one smoothly into the 1st, then the scavenging would be helpful. Looks possible w/your sketch.
How about using 2" pipe from the center "main" tube, and 1 3/4" pipes for the two end ports, blending into the main tube.
I could, but would need to rethink the look. Haven't come up with one I like where the center tube is the man tube. And the rippled tubing is 1 3/4"...
It should be ok for just a driver, but you are cutting performance at upper rpm a bit. Lots of stock V8s through years came with 2" singles, 1 3/4 duals flows slightly more so should be ok.
The 454 SS came stock with 17/8 pipes. Yes more power could be made with a more open EX. But for Looks not power I think 13/4 will be fine. I like the sound a small pipes gives a nice crisp crack out the pipes
The Jalopy Journal
