My IM has a CB performance engine built in 2004. 1776 that I punched up to 1835 with a larger P&C set. I also took the dual 40 idfs and added the cb venturi kit that smooths out the venturi  to give it a bit more air flow and hp.  I have been playing with the velocity stacks and took them to 3" where the engine did not like it. Then down to 2.5" and all is good. Great sound a tad more torque...

I say all this because I have done nothing to the exhaust.  It has a "stock" Porsche 356 Dansk replacement muffler. 

I feel like this exhaust is constricting the potential. It may have done fine at 1776, but now with the carb upgrade and the larger cylinders..., I don't know for sure.

Any info on exhaust size vs engine size?
Is there a specific size for specific engine or ...?

I see CB now offers a sidewinder with dual tips. (I want to keep the traditional appearance as possible), but the sidewinder is a costly experiment.



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Thanks Alb. That chart is great.  Where did it come from?

I will answer the questions best I can. I did not get much info on the engine when I got the car. And I hate to bother Pat or Henry about a 15 year old car/engine they built. Doubt they would remember anyway.
Here  is what I have : dual relief case, CB 044 heads, solid lifers...
Cam ? It had heater boxes but I changed  to J pipe. The J pipes are wrapped not, but best I can tell from the heater boxes, they have a 1 3/8" ID.

Power comes in around 3k rpm and tops out at 4k. So ... I'ld say it was a "mild cam".
It will continue to rev on up, but not much 'push' after 4k. I believe the tips do have resonators. It has a nice throaty sound, not like straight pipes.

Right now the car is packed away and a bit hard to get to.


Yeah, I doubt either Pat or Henry will be able to help you with what's in the engine. The chart was put together by an enthusiast engine builder/Hot VW's reader and was published in an article in the magazine in 2012(?). How high did the engine rev with power originally? When you replaced the 90.5's with the 92's did the deck height or rocker geometry change?  Even with the increase in displacement, the heads and carbs should still let it make power to it's original redline (or very close to), but the only part that's marginal is the exhaust. Both CB Per. and A1 do Sidewinders with dual tips.

Re-reading your posts, I noticed you said the engine has 044 heads. I don't think CB Perf. ever equipped those heads with stock (35x32 mm) valves, so this leads me to believe that the engine has bigger valves. They are probably 40x35 mm, as Pat wouldn't put heads with 42x37 mm valves on a 1776 unless the thing was cammed to make power somewhere above 7500 or 8,000 rpm. With 40x35 mm valves, again, this leads me to believe that the engine is set up to make power to 5500 or 6,000 rpm, which means the exhaust on it is definitely too small and it needs 1 1/2" primaries (the tubing coming off the heads). I'm doing a lot of assuming here, as there's no information about what's actually in this engine. It's easier to upgrade when you know what's in the thing (valve sizes, porting, camshaft, and compression would be nice too!). I'm not criticizing, as this is all the info you have, but only pointing out how this would be easier if we had the proper information.

A couple of questions- how high did it rev with power before you put the bigger pistons and cylinders and 1.25 rockers on it? Would it go to 5,000 rpm? Higher? When you bolted on the rockers did you check geometry at all (you use an adjustable pushrod) or just bolt them on with the pushrods you had? The reason I'm asking the last question- if the rocker geometry is wrong the engine may not be getting all the valve lift it should be (it might not even be getting as much lift as with the 1.1-1 rockers you took off, although this is a very extreme case) and may be contributing to the problem as well. Any engine with dual carbs (even with a stock camshaft and stock rockers) should rev to 4500 or so with power, so you saying that it "tops out at 4k" is raising a little bit of a red flag here. 

It has been a couple of years since I put the larger pistons in the engine. There was a lot wrong with the car when I got it. It at least needed rings, so I thought if I had to pull the engine and take it apart, why not upgrade the P&C too without making it a stroker. I phoned Pat, he did not remember the engine (of course) but said the 92s would be max and bring the engine up to 1835. 
So ... I honestly never experienced the engine running in good condition before I redid it.  I did not put in adjustable push rods, but that is great advice and will be on my shopping list. I did work quite a bit with the shims when installing the 1.25 - also with elephant feet (911 style). 
I found this exhaust and will probably give it a try when it warms up in the garage a bit. No heat and a tad cold on that concrete. It's affordable and might do the trick. The engine "feels" like it is choked off and not giving me all  it can. But that could be wishful thinking.  :-)
You are giving me a lot to go on. I certainly appreciate all your knowledge Al! 

An adjustable pushrod  is for figuring out pushrod length only, and is a great help when working out the rocker geometry (especially with wider stroker engines). Were you using the rectangular shims that go under the rocker stands? If so then you've probably got the geometry in the ballpark, and the elephant's foot adjusters make pushrod length somewhat "forgiving". Did you shim the side play of the rockers as well (with the round shims that go on the shafts)?

The merged Sidewinder is exactly what you want; make sure to use the drop boxes so it gets tucked up higher for a Speedster, and you can get dual tips as well. Al

PS- 1 more question- are you sure you're getting full throttle at the gas pedal? Have someone hold the gas pedal down while you check at linkage on the engine. You wouldn't be the first to be tripped up by this...

I did use the square shims and got them positioned correctly with the side shims. I did it over and over until it seemed right.
Throttle is a good idea too. I'll check it out. I  redid the linkage with an Empi system that lowered it, so I could make the engine look more like a 356. (photo). So that is worth looking at again.

I decided to go with the single tip exhaust to help keep the heat down, and add a couple of faux exhaust ends through the bumper-ettes... to continue with the 356 look. (My car is a roadster not a speedster).

So now I am going to subscribe to Hot VW. 

I have another question - what is a "drop box" ? 
( I am not using heater boxes on this car.)


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