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Discussion Starter · #1 · (Edited)
Hi Friends,

Its official I have the seemingly dreaded smog manifold on my otherwise perfect USA-spec 1968 130 B18B (w/BW35, no I don't plan on swapping the transmission I live in a high traffic city and the auto works beautifully and shifts like butter). I have a brand new set of carbs that will be going on to replace the tired ones on the car. I figure after going through all that I might as well investigate installing a 1967 style one piece cast intake/exhaust manifold. Before I do, I have a few questions to ensure I've properly done my due diligence (the more info the better, I'm here to learn from the experts). I hope you don't mind.

What are the disadvantages of switching the "smog" manifold?

What are the advantages of switching to the non-"smog" manifold?

Will the non-smog manifold worsen my fuel economy (assuming of course the carbs are properly tuned, etc.)?

I have a rebuilt set of HS6 AUD94s (off what I believe was a 1966 B18D) and the car currently has a set of HS6 AUD252s with DX jet needles (I plan on getting a set of new needles and swapping them). From what I've heard, the DX needles seem to be the best of both worlds, more efficient in the lower end/idle and more aggressive in the higher RPMs when you really get on it.

Will the manifold bolt right up or will I need to source any additional stuff (besides a new gasket)? Part numbers would be fantastic and would make my life uber easy!

For context, I don't race the car or drive it too hard, the car is only used in summer and I'm basically looking for a decent balance of performance and fuel economy. Thank you so much!
 

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cvf;

How's your hotstart? If you're not experiencing miserable hotstart after heatsoak, or inconsistent idle, and secondary throttles are tight and don't let in any/much False-Air, then you can leave well enough alone...but if you're like many, who have experience those symptoms (all else being OK), then you might consider making the intake part a new anchor for your small watercraft!

See also:http://www.sw-em.com/manifolding_notes.htm#dual_throttle_manifold

Cheers
 

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Discussion Starter · #3 ·
cvf;

How's your hotstart? If you're not experiencing miserable hotstart after heatsoak, or inconsistent idle, and secondary throttles are tight and don't let in any/much False-Air, then you can leave well enough alone...but if you're like many, who have experience those symptoms (all else being OK), then you might consider making the intake part a new anchor for your small watercraft!

See also:http://www.sw-em.com/manifolding_notes.htm#dual_throttle_manifold

Cheers
Hey Ron,

So far the car has been running great. With regards to hot starting, a wise old man always told me to depress the throttle and turn the key so I guess I've always done that and its always fired up without issue hot or cold. Took a look at your wonderful article and I had some additional questions besides the ones listed above.

Will I gain more power by doing the manifold swap or will I not really notice much? How about the carb needles. I guess as the manifold is factory I won't need the stepped washers if I simply convert from the smog to non-smog 1967/1968 manifold correct? The AUD94s don't have the TOVs. Am I really missing anything by eliminating them? The motor is running smooth but I'm getting about 18 MPG or so (22ish) combined over several fill ups like as a result of a mixture dial up to smooth out the idle. Thoughts?
 

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Discussion Starter · #4 ·
Also, the car has a Girling brake booster. Could the intake vacuum leaks cause the brake pedal to get a little spongy? Like it feels like there is minimized pedal resistance and they start to bite at 3/4 or sometimes 1/2 pedal, once you hit that point the pedal resistance is great and the stops the car well, it's just a little odd. For example, if I'm stopped at a light or even underway, let go of the pedal to creep up a little and then get back on the brakes very quickly they feel a little spongy. Could it be the carb Throttle Overrun Valves that are causing this? There is plenty of fluid in the reservoir (not sure the last time the system was bled though)? Would the non-TOV throttle plates on the AUD94s or swapping manifolds largely fix that (presumably because there would be more vacuum with throttles fully closed than in the smog unit?). Or am I hunting in the wrong forest on that issue?
 

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cvf;

There is some performance increase, but without a dyne, it's tough to quantify...its also very much outside temperature (air density) dependent...

I think pedal feel is less influenced by manifold type and any possible minor vac leak, and more limited to the Brakes and Booster themselves...the huge volume of the booster acts as an accumulator (evening and smoothing) for the vacuum...

TOVs are (normally) open only during engine braking, so they will not cause this...and if they are (abnormally dislodged and jammed) open at idle, this would be immediately noticeable as it would also result in an elevated idle...

Cheers
 
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