308 Performance Mods During Major Service

Hi All,

I'm doing a major service (belts, valves, carb rebuild, etc) on my '78 GTS. Are there any recommendations on updated parts or adjustments while I've got everything apart?

Thanks

Henry

 

Previous year's cams had better profile.........but that would add major $$$$.

Have them degree them to Euro spec timing, in any event, that'll help!

There's rumor decking the block down will raise compression, have you searched on the Micholetto Rally Engines??

There was a Bill of Material for the Chinetti GT4 Lemans engines that is pretty good.......

 

Just getting the carbs correct, you'll be amazed at the difference......

 

What's involved in doing this? This is a U.S. car.

 

I'm also going to try 135 main jets. The stock are 125's. I've opened up the intake and exhaust, so hopefully this will help. A/C is 200, idle 55, and F36 ET's.

 

It involves setting them to euro specs, using the same cams, to get a little better performance.......I'm not a techie type engine guy, but mine did run better for it.....

I'm happy if the car's not on fire........try a search and also check out the LeMans Chinetti stuff......

You are still running catalyst type exhaust??? I'd imagine properly sized modern design cats would be a great improvement for you....

 

Modify the distributor internals with a spacer ring inside the centrifugal cam heels, to have a reduced amount of total advance... and run about 15-18 at idle with max of 33-36.

 

Doesn't 15-18 at rest make for harder starting?
Tom

 

I used 140 mains, with otherwise stock carbs (K&N air filter). The 135 may be a better compromise...making any further richening by changing the A/C jets. Be sure and use at least an NGK 6 to prevent plug fouling. You may even need to go to a hotter 5, but start with the 6.

What ignition are you using?

 

By "valves" do you mean an adjusment or removing the heads to do an actual valve job? An engine with only 10,000 miles on it can benefit greatly from making sure the valves are closing and sealing properly. You won't make horsepower without that.

Higher-compression after-market pistons are available for your engine.

Making sure the ignition system is working at peak efficiency and that dwell angles and advance curves are syncronized (multiple ignition points and multiple distributors) is critical.

On US cars, enlarging the idle jets from 55 to 60 helps at the bottom end.

Perfect carb set-up is a must but don't bother with it untill everything else (valve timing, compression, ignition, etc) are perfectly set up.

Wil

 

Does anyone know what I have to do to get it to euro spec valve timing? Will I have to purchase new/different cam sprockets?

As for the cats, I did replace them about 8 years ago. They were a direct replacement. They are a honeycomb design and are supposed to flow a lot better than the stock ones (especially since one of those had a meltdown). Aft of the cats is just piping and then Ansa tips (no muffler).

 

Hey Dave,

Yeah, I thought I would be better off trying the 135's first. As for the ignition, that's all taken care of. I've been running an Electromotive DIS for about 8 years now. Runs better, better drivability, better fuel economy, and no more $250 distributor caps.

 

No valve job, the heads are staying put. If/when I rebuild, then I'll consider the pistons. I'll see how the 135's work and go from there. Besides the idle jets are easy to change. Thanks for the tip though.

Henry

 

Phil, can you give us a sketch of you modified sleeve with the dimensions. As I understand it, you have limited the total amount (band width) of advance the distributor can put out and then adjusted the static position of the distributor so as to have about 14 degrees at idle, and no mare than 35 degrees at 5000 rpm.

The following is my experience. After a DIY major service, I set up the distributors with a timing light at the flywheel at 14 degreesat idle, and then took the car aroung the block to warm up the oil. The car ran better that ever before at low RPM. When I got back home I re-timed the distributors for the specified 34 degrees BTDC at 5000 RPM. Had to retard significantly, and now ended with about 7 degrees BTDC at idle. The driveablity went way down and the car displayed the same flat spot that it it always has had coming off idle.

So Phil, I think you are on the right track. Can you share the dimensions of your bushing with us?

Thanks in advance,
Martin Jansen
75 308 GT4
Agoura Hills,
So Cal

 

My shop set up my 1977 308 GTB timing to euro specs without any major issues on their part......they just pulled the information off the web and spun it on the dyno a few times......a subtle improvement.

 

I just want to caution some folks who try 14-degree BTDC setting at idle, you may idle too fast with this setting, especially with carb cars.

When I set up the Electromotive system with vacuum advance, to try and improve gas milage, I set the initial electronic advance to about 8-BTDC. Because the vacuum advance added to this during the high vacuum idle condition, the idle speed crept up to about 1500 rpm and would not go lower. I don't recall the total advance under this condition but managed a rather unique fix. I refitted the R2 microswitch to interrupt the vacuum advance electrical signal to the MAP terminal on the Electromotive systen when the throttle was on the stops. This modification effectively disabled the vacuum advance at idle, reverting to 8-degrees BTDC. Not all cars will have this issue, but just be aware excessive ignition advance at idle may result in too high an idle speed.

Bill

 

I dont have the info in front of me but one of the cams is differnet euro to US. I believe its the exhaust profile that is different so, you cant time US cams to Euro specs unless you have a magic wand. You can change the timing but cant duplicate the euro without a euro cam and the difference would be hardly noticable for all the trouble involved. If you want a significant gain then bump the compression with pistons, install custom ground cams from WEB in CA, rejet, recurve the distributor and upgrade exhaust. Cost $$$$. Its tough to get any great gain from a 308 otherwise.

 

I can't do a sketch, but all you do is make an alloy ring that slips over the shaft in place of (or over the top of) the thin plastic tube thats there already..

Simply turn up some alloy to push fit the shaft OD, and have a spacer OD that suits your particular distributor.

I won't say a size, because no two are the same. Use a shop that has a dist tester and a lathe, and make it custom to get perfect accuracy.

Very crude ball park wall thickness of spacer.... 3-5mm.

This then drops INSIDE the heels of the bob weights, limiting the amount of RETURN action available.... and means the upper advance curve remains stock.

I've even seen some locked at 30 degrees... meaning 30 at idle and 30 max. Ran well, with no problems, but needed high octane fuel.

There is no issue with idle speed whatsoever. You just need to tune the whole engine to suit.

FYI, 365BB (which have same bore/stroke as 308), have 18 deg at idle as std.

It dramatically improves low rpm torque, and makes no difference to power at max rpm.

 

If you remove the cat, and open up the exhaust, you might want to run .60 idle jets. I was getting a lot of popping at idle and at low RPM, this eliminated it, and also gave me some bottom end torgue. I barely have to tap the gas when letting out the clutch in first.

 

Changed AC jets from 220 to 200. Works (pulls) much better on the high end. Mains are 135 and idles are 60.

Another issue. Just did major service including valve lash adjust, timing belts and cam seals. Every thing was fine untill I was resetting the static timing on the distributors. Next thing I know, the cam seal on the front exhaust bank had come out of its housing. Darn. Pulled the front (5-8) valve cover (again) changed gaskets, cleaned the seal, dimpled marked the seal cavity in the cover, and re-installed with new gasket. Mounted distributor where it was before. After a week, drove the car with some good hard pulls to 7500 rpm. Back at home everthing looks good and the cam seals are where they belong(fully seated).
Go to set the timing again with a timing light, front and rear at 5000 rpm (looking for about 36 degrees BTDC). After I finish I noticed that 3 of the four cam seals had moved (pumped out about 1/16 to 1/10 inch) Darn again. Got a big breaker bar and using the timing belt cover as a fulcrum point gently levered them back to the fully seated position (easy to do). Drove the car some more, including "on it". No more problems. Got to thinking about why. Here I think, is the answer. When reving the motor (to 5000 rpm for timing) with no load, there is very little load on the rings to seal them against the bores (especially with an older motor), and so there is a lot of ring blow-by.This pressurizes the engine block and the cam seals are pumped out of place. The crankcase vent hose system is probably not big enough. IN contrast, when the engine is at high RPM and the motor is under major load, the rings are pressured into contact with the cylinder, and no (less) ring blowby.
Lessons learned;
1) When setting distributor timing remove the oil filler cap, (so as to relief pressure) and dont take too long.
2) When driving on the street, dont run at high RPM and light throttle.

Martin Jansen
75 308 GT4.
Agoura Hills,
So Cal.