Matching Header diameters

Carl- I posted this a while back but here it is again- 1 1/2" will do to almost 6,000rpm. I'd say you're on the borderline here; do you want to emphasize lower end/mid range or peak power? Do you know what cam is in the engine? And you're planning on putting 1.25 rockers on it? The rockers will extend the peak by 2 or 300 rpm and since the engine is large enough (> 2 liters) to have lots of torque, you could use the larger exhaust, but it really depends on what you're looking for. How high does it rev to in 3rd gear now? And yes going too large can negatively affect the powerband (and mileage, a little bit), but you don't really have to worry here.

Hey thanks Al...Great information!

Somehow I missed that previous chart posting.

My driving puts me smack dab in the 1 1/2" column...which is good since that's what I have.

The number of times I've touched 5 thousand rpm, (In three and a half years), I can probably count on my fingers and toes...and then I was showing off in third gear!

As you know, I'm unable to visually identify my rocker ratio...but I've got a new set of 1:25's that will eventually be installed for wrenching practice.

I've got that chart stored in "My Pictures" file so it's easy to find. Right click on it and save it to Pictures. Sorry Carl, but you're going to have to refresh my memory; what brand of exhaust is on the car now? I figured the 1 1/2" was about right for your driving style, but thought I'd let you know the options. With the 1 5/8" you might not even feel the small reduction in lower end power, but if you never rev it high enough to matter then what you have is the best fit. Lots of guys with bugs do run 1 size higher tubing than what's optimal for their combo and claim it works great (and it does work fine), but (especially with engines in the 1600-1800cc range) the missing bottom end/lower midrange makes itself felt as slightly poorer mileage (you're pressing on the pedal more) as you're tooling around town.  

Carl, as Al mentioned with your driving style a 1  1/2" exhaust system is perfect.

Al,

My exhaust system is described as "German exhaust by Classic Speed Parts"

(CSP?) supposedly an expensive system with two cylindrical mufflers scavenging 1&2 and 3&4 separately...and mounted so closely to the valve covers that the rocker arms are partially obscured. #2&4 are very, very, difficult to access. Simply little to no space to squeeze my hands into and also see what I'm fiddling with....so for 2&4, especially, I'm basically valve adjusting blind and by feel

That's right! Now it comes back to me...

I have a 2110 with an A1 1.5" header and it flies past 6000 with tons of low end also.  I know in the old days it was said that you will lose more power with too large a header than you will with one that is too small. This is because most of your street driving is below 4000 unless you are completely nuts!

fpcopo,

Come this Spring on a clear cool early Sunday morning I'm going to grit my teeth, buckle up tightly, and intentionally "touch" a hair over 6k rpm on the freeway (in 3rd gear of course!) just so I can legitimately say "It flies past six thousand rpm with plenty of low end torque"

That's the joy of a larger engine- you can build it to rev a little higher and yet it's size creates low end and midrange that's perfect for the street (where we do most of our driving). Do you know how high past 6,000rpm it will rev with power? And you're right, Frank; a header that's too large will not have good airspeed until higher up in the rpm range. Displacement can make up somewhat for a higher revving engine's poor lower end performance, but there's really no point in going bigger than necessary.

I know the aircooled performance stuff from a mis-spent youth, drinking too much beer and playing with bugs for the first 15 years or so of my driving career, and in my early/mid 20's ran a Cal Look bug for 6 or so years. It was a 14 second car when I sold it, with a short close ratio gearbox (4.37 r&p, 1.48 3rd and 1.12 4th) and a 6500rpm 1750 with 44IDF's, 40x35 heads, Engle W125 cam and 1 1/2" merged exhaust. It was a great combo- idled like a stocker, easy to drive on the street and made the power I was looking for. Even today I think a 78 or 82mm crank (and the resulting increase in displacement) would have made it the perfect street/strip engine.

I only mentioned the above because I think the perfect Speedster engine (for most guys) is a little different; ideally for a toodling around town, long slogging highway engine we want something with as much displacement as possible that doesn't rev quite so high, which puts the torque curve closer to the 3,000-4,000rpm zone where we spend so much time in. A 2 liter engine can make 140-145hp and a 2276 can hit 160hp, all in by 6,000rpm and with a killer torque curve for highway driving.   

Torque is it.

With a 2110 in a street car, a 1-1/2" header is a nice trade-off. The problem is "what kind of 1-1/2" header"?

Marty asked what a "merged" header was a couple of weeks ago, and I explained it there. I'm coming to believe that the collector is at least as important in a header as the primary tube diameter. If you have to give up one or the other (and you usually do), a decent merge seems to work better than ideal primary tubes of the ideal size/length. That's the thing with an A1 header-- the length of the tubes is all wrong-- but they all have really, really nice merged collectors. You pick your poison.

The problem with the 1-1/2" CSP header Carl's got is the collector-- it's not merged. A header with ideal-length tubes, and a nice/long collector is going to look very similar to an A1 "low-down" or a Bugpack/EMPI merged header-- and the collector is going to stick out the back and look stupid. There's not a lot of real-estate back there to work with. 

So... before anybody runs out an buys a different exhaust (I'm looking at you, Carl), it's important to note that almost any exhaust in a speedster is going to be a compromise. I didn't want to hear that a couple of years ago, but it's just the truth. I've tried no less than 4 different headers on my car, all with custom exhausts behind them. It gets pretty expensive, and none of them are "perfect". I've been looking at a CSP "Python". That header has equal-length tubes, a decent collector, and it all fits behind the apron nicely... but the primaries are 48-ish inches long. That's a  l o n g  primary tube, and really sets up some strange resonance in the exhaust. There's no free lunch.

The only exception to the "compromise rule" I can think of is the Tangerine Racing tri-Ys a very few of the Type 4 guys are running. Those exhausts have it all-- ideal size/length and great packaging. It all fits, and it all works.

Forewarned is forearmed.

Yeah Stan, I can feel those eyes on the back of my neck!

Fortunately my pocketbook won't cover a Type4 bolted up to a Tangerine Racing tri-Y...I'll simply have to live with what I got.

The header is an A1 with merged collector. Pat Downs said he ran the dyno pull to 6500 and it still had good power. I believe him because I've ran it past 6000 in 2nd gear and it was still pulling welll. I haven't taken it to 6500 though, I'm still breaking it in.

I like your simple setup, Ed. With that Cherry Bomb I bet yours and mine will sound about the same.

It's a bit too loud for my taste, actually. But no worries.