66 Sat
Well-Known Member
When my 354 Poly (318 with a 3.48" crank) went on the chassis dyno the dyno operator reckoned the factory 4 barrel cast iron intake manifold was holding it back. After consulting with poly guru Gary Pavlovich, I was advised to open up the 4 hole plenum to a divided opening, and port the runners while I was there. I wanted to pull the intake anyway as it had the felpro steel shim gaskets which are not great for sealing and I suspected oil was being pulled through the gasket on at least 1 cylinder. I ordered some fiber gaskets from Best Gaskets and used them instead (from Ebay seller CARS LLC Antique Auto Parts).
The opening up of the plenum was the hardest part - dremel, angle grinder, hacksaw (mostly) and carbide burr to finish off. Porting the runners was relatively straightforward, I worked out a slower drill speed works much better that fast - this was all done with a carbide burrs on my cordless drill. This is the first time I've done this so I was being very careful.
Anyway, put it all back together, put the distributor back in close to where I'd taken it out and went for a short drive. I wanted to warm it up to set the timing properly, but got to the end of my street and the car was running so poorly I couldn't get up the hill to get back home. It was getting dark and I was highly embarrassed being stranded so close to home so called my son who came to the rescue, holding the car at 800rpm while I set the timing to 14°. Car was running ok now so put the vacuum gauge on it, tweaked the carb, and then put it away for the night.
The next day I took it on a long run to the city and really wasn't impressed. Poor throttle response low down and no better up top, in fact it felt worse than before. Just had no fizz at all, felt dead. I was worried that opening up the plenum had somehow screwed things up and was felling pretty down about it - I had ruined a perfectly good, fairly rare, factory manifold, and spent hours of my time doing it!
Well this morning I was still fretting about it when it suddenly came to me. What an idiot I am. I'm running Manifold Vacuum Advance and in my haste to get the car home on the first night I set the timing without plugging the vacuum line. So today I jumped in the car, warmed it up, plugged the line and then put the light on it. I was only running about 3° initial(!) (the MVA was adding 11°). I set the timing properly then went for a spin - the bottom end is restored to as before - opening the 4 hole into a divided opening hasn't hurt it at all, and the top end feels great.
I should get to the track at the end of the month and will update if the ET/mph is improved but at least I haven't gone backwards.
The opening up of the plenum was the hardest part - dremel, angle grinder, hacksaw (mostly) and carbide burr to finish off. Porting the runners was relatively straightforward, I worked out a slower drill speed works much better that fast - this was all done with a carbide burrs on my cordless drill. This is the first time I've done this so I was being very careful.
Anyway, put it all back together, put the distributor back in close to where I'd taken it out and went for a short drive. I wanted to warm it up to set the timing properly, but got to the end of my street and the car was running so poorly I couldn't get up the hill to get back home. It was getting dark and I was highly embarrassed being stranded so close to home so called my son who came to the rescue, holding the car at 800rpm while I set the timing to 14°. Car was running ok now so put the vacuum gauge on it, tweaked the carb, and then put it away for the night.
The next day I took it on a long run to the city and really wasn't impressed. Poor throttle response low down and no better up top, in fact it felt worse than before. Just had no fizz at all, felt dead. I was worried that opening up the plenum had somehow screwed things up and was felling pretty down about it - I had ruined a perfectly good, fairly rare, factory manifold, and spent hours of my time doing it!
Well this morning I was still fretting about it when it suddenly came to me. What an idiot I am. I'm running Manifold Vacuum Advance and in my haste to get the car home on the first night I set the timing without plugging the vacuum line. So today I jumped in the car, warmed it up, plugged the line and then put the light on it. I was only running about 3° initial(!) (the MVA was adding 11°). I set the timing properly then went for a spin - the bottom end is restored to as before - opening the 4 hole into a divided opening hasn't hurt it at all, and the top end feels great.
I should get to the track at the end of the month and will update if the ET/mph is improved but at least I haven't gone backwards.
