What is the difference between early carbed 308 and later carbed 308

The older carb cars do have different cams. They also don't have as much in the emission department. Removing the cats will make some difference.

The easiest and cheapest fix is to buy a newer car (328 or newer).

If you really want to change the car you have do some searching here, there are lots of threads on improving 308 HP output.

 

Ben,
There have been several threads on the subject, bottom line there are many differences. Cams, timing, carb jetting-set up, and exhaust. No easy or cheap fixes. Removing the cats will have little effect. I did it, along with richer jetting, removal of most of the air injection and other smog equipment and K&N air filter....gained only a few hp on the dyno after much tuning.

 

The cams are different, but the later cams (78 & up) AFAIK are also timed goofy. The intake is opening late (16* BTDC) and the exhaust is closing (14* ATDC) far to early. Thats only 30* of valve overlap! If I had one I would alter the valve timing, at least the exhaust.

The later exhaust cam is only 10* less duration than an early cam, yet they pushed the opening point to 50* from 36* BBDC. It could easily be retarded 10-15*.

The intake lost more duration, 16 degrees, but could still be advanced 5 degrees or so. This data is comprised from various sources so dont quote me.

In other threads where valve timing has been discussed, to many think simply aligning the cam marks is good enough. Yeah, it will run okay and its supposed to pass emissions that way, but only by degreeing the cams can you zero in on real performance. As has been pointed out, several 308's, including my own, were found to be 3 degrees retarded at the flywheel AFTER the indicater plate was pushed over as far as it would go in its slots. If your trusting your flywheel timing marks without any knowledge of true TDC you could be losing significant power. At a bare minimum, find true TDC with a piston lock and reference it at the flywheel. Only by degreeing your engine can you have any idea what cams you have and how they are timed.

Also, valve clearance plays an important part. Having your valves adjusted to the lowest (tightest) clearance settings will give you the greatest amount of valve lift and duration. Then set your ignition and make sure its working properly and fully advancing and only then go after the carbs.

We all read this stuf and go yeah yeah yeah. I myself have been guilty in my younger days, trying to tune a carb to correct an ignition fault, or trying to change ignition to make up for faulty valve timing. We are all lazy. Take the time to gain perfection and you will be paid back in spades. Trust me, its quite hard to get that front exhaust cam to time exactly where you want it. It took me over an hour of taking that front sprocket off and putting it back on, contorting my old body to force myself to see my marks and find a pin hole that worked. So many times I wanted to just stick it on the index mark and call it good. I am so very glad I perceviered and did it right. Not one of my index marks is aligned properly, and that thrills me to no end.

So, check and or correct you TDC flywheel marks, check and or alter your valve timing and valve clearance, check full speed advance, check or change your jetting, and finish by syncing your carbs. Youll be glad you did. And if you dont want it to backfire, lose the air injection, plug the ports, and make sure all your exhaust system gaskets are sealing and there are no cracks or holes anywhere.

Oh, you might want to look inside your aircleaner snorkle for sound deadening and remove it. Might be worth 5 HP?

Will a stock late carb make as much power as an early carb? Nope. But with a bit of work and tuning it might run better than 95% of all the other cars, and therefore yes, it could make more power than an early 308. Especially seeing most arent tuned anywhere near like the above examples.

 

Paul,

From what you are saying about the the '78 & '79 USA cams, we might be better off setting the intake to open at 21 BTDC and the exhaust open at 36 BBDC?

 

I dont know, somewhere in there. At least it would be closer to the early events.

A discussion on max compression brought up maximum advance timing. Something was brought up that made me open up these books and it blew me away.

I went back in and looked in both the GT4 service manual as well as the early carb owners manual. Its 34 +/- 2 degrees at 5000, but it dont stop there. The curve shown in the shop manual stops advancing at 13 degrees total distributor degrees advance at 3400 distributor RPM. That would push total advance to 38 +/- degrees at 6800 rpm. Unless of course the manual is wrong? The owners manual shows an entirely different curve that stops at 3000 distributor RPM with 16 degrees of distributor advance. Both graphs show 9 degrees at 2500, so they match for 34 at 5000, but they sure cant both be right.

I asked over in the Vintage area to see if anyone had advance curves from other older cars to try and see a comparison. Seeing how retarded valve timing and ignition timing have trended since the inception of emissions, along with running overly rich to feed the cats, I am guessing that the earlier cars had the highest total ignition advance.

 

If early emissions Ferraris are like my early emissions Lotus, the entire car was designed for no emissions at the factory in the day, and later had to have changes made so it will pass when the laws changed. Cam timing, extra plumbing, carb jetting, exhaust and ignition timing were all altered for emissions, not for power. The factory had to take an enigine desinged to run one way and alter it to ways it wasn't intended to be, hence power losses.

I imagine that engines designed with emissions in mind made better power and also ran more efficiently.

Ken