Cam timing adjustment GTSi US spec to EU spec?

On my ‘82 GTSi we had the Digiplex reworked including rev limiter. Cam timing set to EU and CIS head rebuilt. That combination without cats works very well.

 

Somewhat similar situation for me. I swapped my 801a modules for a pair of NOS 802a's maybe 15 years ago. Simple plug and play, no related modifications required, and a notable performance gain. And since I have no smog requirements, I also considered adjusting my exhaust cams, too, as you have mentioned.

But I ultimately decided not to alter the exhaust cams from their USA degree settings for a couple of reasons. I doubted my ability to be able to -accurately- adjust these cams by what I believe to be only 4 degrees while the engine was still sitting tight in the car. And I was informed that altering only these cam's timing really did not end in very much of a potential performance gain.

Instead, I've located a pair of early Euro exhaust cams which do have a significant increase in lift. I've held off on installing these cams for the moment as my exhaust valves are still the OEM hollow sodium ones, and increasing their lift via the Euro cam would also cause them to close with greater force against their seats. And I don't wish to take a chance of one of these old valves fracturing at this point in their long 40+ year life.

My Euro exhaust cams are therefore sitting on my shelf, awaiting that future day when I do a cylinder head overhaul. At that time new solid exhaust valves will be used along with these Euro cams (and to be adjusted to Euro degree timing).

Hope this helps - DM

 

The early cams do indeed offer better breathing,

The Euro vs US advance timing is a matter of the orienting the gear dowel pins, during the degree process

 

Could you please post measurements of the lift of these euro 2Vi exhaust cams (and the lift of your US 2Vi exhaust cams when you have access). Cam lift is one thing that F rarely states in its documentation. (Of course, if you have some F documentation showing the exhaust cam lift differences, please post.)

The SPCs show euro 2Vi and US 2Vi use the same intake cams, but it surprises me that the euro exhaust cam would be significantly different than the US exhaust cam (just because the durations are the exactly the same and the stated BHP difference is small enough to be explained by no cats vs cats and the ignition map differences). Not saying that they don't have more lift, but would like to have some measured values (for the US cams, too!). TIA.

 

Of course, Steve, I'm always happy to add whatever modest info which I can to the overall knowledge base!

I measured four (4) cams: The intakes are USA spec OEM's, with embossed model numbers as shown (and with distributor rotor mounting provisions on the far end, as can be seen). The exhausts are 'mystery cams' in that there are no model numbers shown. I'm "assuming" that they are early Euro spec, simply because there's no provision on the end of either cam for the smog pump pulley.

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For all cams, I measured the peak-to-peak distance as shown in the picture below, slightly rocking the cam back and forth so to catch the peak. I measured the 8 intake and the 8 exhaust cams individually, adding these values together for each set, and then dividing by 8 in an attempt to alleviate any minor lobe-to-lobe variations and/or operator measuring errors:

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Does this info help?

Cheers - DM

 

Yes, much, and seems a reasonable difference only being ~0.7mm. Can you also please give the dimension 90 deg to what you already measured for each (i.e., the diameter of the base circle of the lobe)?

 

For sure, but it'll need to be done tomorrow-ish.

I won't forget!

 

I’m just curious to what is the duration of the Euro and the US cams

 

The durations given in the respective OMs are exactly the same for both intake and exhaust, but the US exhaust cam setting is retarded 4 deg crankshaft relative to the euro exhaust cam.

The 308i-2V SPCs do indicate that the euro exhaust cams are somehow different than the US exhaust cams. The 1-4 US exhaust cam is obviously different because of the need for the air pump drive, but the 5-8 US exhaust cam also has a different F part number than euro 5-8 exhaust cam so that must be something in the lobe itself. I'm a little suspicious about Dave's "euro" exhaust cams not having F part numbers on them (might be an aftermarket cam) -- can someone with a euro 308i-2V post whether there are F part numbers shown on their exhaust cams, or not?

 

Well as Steve S is indicating per Factory diagrams, "not much" except for year to year..

But as these cars age i think "anything goes" as th emods is really the case..

 

Recall that even in 1976 they were struggling to meet the US DOT unburned CO vis a lot of low tech apps...

Not sure what they hoped to be gained by the exhaust cam lag, but it was also coupled the the microswitch off the carb lingaee and the r1 and r 2 points sytem???

 

They retarded exhaust cam timing to increase exhaust temps and increase catalytic converter efficiency at low RPM's.

 

And that retardation for the sake of increasing exhaust temps cost about how much hp?

 

Generally speaking advancing or retarding a cam doesn't change HP much but moves the power band up or down. Retarding the cam moves the power band down in RPM's. Peak power occurs lower in the RPM range.

 

Just done. As before, these base circle diameter numbers are the arithmetic average of the eight (8) lobes:

OEM Intake: 24.16 mm

"Mystery Cam" Exhaust: 24.18 mm

Both appear to me to have been originally designed to be essentially the same.

DM

 

Thanks very much, Dave. Agree that the nominal base circle target diameter was/should be the same (and that small actual difference isn't significant). From your measurements:

Intake lift = 31.56 - 24.16 = 7.4 mm (was/am a bit surprised that this is even less than the '78-'79 US carb intake lift of 7.7 mm)

Exhaust lift = 32.29 - 24.18 = 8.1 mm (still hoping that someone can respond about the stock euro exhaust cams having, or not having, the F part number stamped on them)