TEST DRIVE VID. Finally. 308gtb with P6 cams and 10.5:1 cpr

Will do that this weekend pending the weather. I suspect the top end is just fine, it just feels "stronger" with the 135's. I'll do the test and report back, thanks for the tip.

Geno

 

plus, i can tell its just much leaner at idle, it doesnt smell as gassy

 

Not to hijack your thread, but I put the 55's in along with the 135's and spent the day driving around, tuning, sync'ing etc. My conclusion is this, my car likes the 60 idles. I have the carbs perfectly synced, and i just cant get enough fuel in the 1-3k range to make it run right, little hesitation, carb wheezing, not a big deal but its just not smooth off idle into the main jets. Put the 60's back in, and it runs perfect. A little rich, almost like I could use 58 idles if there is such a thing. I know people say the idles only control fuel at idle, but i kown they are contribute enough gas to make a difference in the mid range.

So, i'll conclude for my car its 60 idles with the 135 mains (until its emissions time anyway),

next weekend I am going to the plug trick you mentioned to see how things are.

 

excellent sound!

 

Carbs rule.............I miss my 1977 308 GTB.............

 

I followed a few others with the V12 project, so really haven't been here much, but lurk on occasion. I apologize that I missed this thread.

Yes, its awesome to see some validation for a change, its been a long time coming. I am a bit surprised to read you couldnt put your foot fully into it below 3000 without sputtering, though. I didn't have that problem. I did have a moment of hesitation near idle, like when you booted a fat cam big block, but once it caught it just went. Perhaps you mean the sound is different? I do recall strong gurgling and valve seat noise in the lower R's that got washed out by the exhaust once it got above 3K and started hauling.

I understand that the situation became troublesome with cooler weather, and John swapped out the cams and never dyno'ed the car. That is unfortunate, as all we have for reference are the dyno runs at Carobu. My thoughts are that the mixture was just a bit too lean. Not damaging lean, but lean enough the motor didn't like the cooler weather. With big cams, if you dont want to keep re-jetting everytime the temps and weather change, you have to stay richer than you probably would like, taking a hit in peak power for better driveability. In this instance, EFI or a good mechanical injection system would work better than carbs.

It is interesting in the video that you actually see the dramatic increase in performance. In the last half, you see the car effortlessly accelerate from around 80 mph to over 120 in a very short time. There are a lot of 308 videos on You Tube, but they all seem pretty anemic compared to this one. Fun to watch.

 

It was more fun to experience...



PDG
(the guy behind the camera on this one)

 

Just a heads up in case anyone is interested, I have a set of P6's on eBay ending today.

 

When you put your motor together with the Borgo's, how far down in the liner did they come up to TDC? Mine stopped .055" below the deck.

Just to refresh the memory banks, the pistons and cams (Borgo 9.7 pistons and P6 cams) in this car are 100% identical to the Michelotto GT4 LM engine that ran at LeMans in 1974 in the production class. The only physical difference between the LeMans engine and ours, was that they ran 208 heads. But the valves were the same as ours. My understanding is the exhaust ports on the 208 heads are what was needed. Heck, they even ran points ignition!! And you may find this interesting, but they used a lot more advance, around 44 degrees in the top end. And plain old 40 DCNF carbs.

The next issue is that quench area. I cant for the life of me believe they put a motor together with the pistons stopping that far below deck. This leads me to believe they milled the block in the LeMans car.

There are many mysteries to that engine that we will probably never know. I have heard the motor made over 340 HP, but there is really nothing to back that up. Its all fun though just the same.

 

First of all I was off, it was 42 degrees not 44. Second, our fuel was a lot different in 1974 than it is today. As to where I get these figures, the manuals for the early USA 308 clearly show the distributor advance curve peaking at 3000 distributor RPM and that the distributor has/had 16.5 degrees of total advance. This would be 33 degrees total crankshaft advance, and would be fully advanced at 6000 crankshaft RPM.

Now recall that we time these engines at 5000 rpm, and this would actually be 2500 distributor RPM. On the graph, this would indicate 14 degrees distributor advance/28 degrees advance crankshaft. Also recall that 5000 is supposed to give 34 degrees advance on the flywheel. If the distributor is going to gain an additional 5 degrees crankshaft at 6000, you would then have 39 degrees.

However, the euro engines had different advance curves, with full advance coming in at 3600 dist RPM, 7200 RPM crankshaft. The LM docs shows an S 159 A with R1 points only. The curve for that distributor shows 9 degrees dist advance at 2500 dist rpm. Docs show the LM was timed to the same 34 degrees at 5000, now add another 8 degrees of crankshaft advance at 7200 rpm.

Some other notes of interest are the carbs. Standard 40 Webers DCF, 36mm Venturis, 160 mains, 175 air, F6 E tubes.

Again, the crap fuel we have today does not burn like the stuff we had 30 years ago. To come close we would probably need to get some 100 octane Av gas. Slower burning fuel should be able to take more advance.