I'd like some thoughts on this. I have a local friend with a 70 Hemi Superbird clone. Really nice car. He's been having lots of trouble pretty much ever since he got the engine in the car and has wanted me to see if I could get it running better for quite some time and we were just now able to get together all day yesterday afternoon.
Here's the engine rundown. 512 Hemi based on the 2nd generation (426) design. 10.5 compression. Aluminum heads, hydraulic roller camshaft, 243 and 255 @ .050. 2 Edelbrock 750s. Passon 5 speed transmission and 3.73 gears. He's always had trouble with the car chugging at part throttle, being difficult to start when hot and just generally running very poorly.
So I got to checking everything. The first thing I noticed was the timing seemed "funny" somehow. I could not get a good reading on it with a light. I finally said "screw it, I'm gonna try setting it by ear" and I did. I kept backing the timing down about 2 or so degrees at the time until I got to the point where the engine started running MUCH smoother and you could actually hear the camshaft. When I did that, I hit the balancer with the light and BAM there was a SECOND timing mark. They had been using the WRONG timing mark the whole time.
Just to make sure, we found TDC and sure enough, that second mark was the correct one. So now we had a good base reference for timing. Here's where it gets "a little" strange. This engine is VERY happy with "only" 6 degrees initial and "about" 26 "or so" total. And I mean it will get down and boogie. It will slap light um up now and he said it's never done that before. Starts very easy when hot, idles good and you can really hear the camshaft countin um off. It sounds really good. We have a little tuning to do on the carburetors as it's still rich at idle. I put in some lighter springs to get the metering rods on the lean step at idle, but they need some bigger metering rids to lean it down more. He also has a pair of Edelbrock 600s and we may go to those, if it looks like we will have a lot of trouble tuning the 750s.
But what about that timing? Can we attribute it to the Hemi heads being so efficient? The aluminum heads? I would have THOUGHT it would need more than that, but you can tell the timing is RIGHT now. Seems strange, but I admit, I've not tuned on that many Hemi engines.
Here's the engine rundown. 512 Hemi based on the 2nd generation (426) design. 10.5 compression. Aluminum heads, hydraulic roller camshaft, 243 and 255 @ .050. 2 Edelbrock 750s. Passon 5 speed transmission and 3.73 gears. He's always had trouble with the car chugging at part throttle, being difficult to start when hot and just generally running very poorly.
So I got to checking everything. The first thing I noticed was the timing seemed "funny" somehow. I could not get a good reading on it with a light. I finally said "screw it, I'm gonna try setting it by ear" and I did. I kept backing the timing down about 2 or so degrees at the time until I got to the point where the engine started running MUCH smoother and you could actually hear the camshaft. When I did that, I hit the balancer with the light and BAM there was a SECOND timing mark. They had been using the WRONG timing mark the whole time.
Just to make sure, we found TDC and sure enough, that second mark was the correct one. So now we had a good base reference for timing. Here's where it gets "a little" strange. This engine is VERY happy with "only" 6 degrees initial and "about" 26 "or so" total. And I mean it will get down and boogie. It will slap light um up now and he said it's never done that before. Starts very easy when hot, idles good and you can really hear the camshaft countin um off. It sounds really good. We have a little tuning to do on the carburetors as it's still rich at idle. I put in some lighter springs to get the metering rods on the lean step at idle, but they need some bigger metering rids to lean it down more. He also has a pair of Edelbrock 600s and we may go to those, if it looks like we will have a lot of trouble tuning the 750s.
But what about that timing? Can we attribute it to the Hemi heads being so efficient? The aluminum heads? I would have THOUGHT it would need more than that, but you can tell the timing is RIGHT now. Seems strange, but I admit, I've not tuned on that many Hemi engines.
