Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Seconary rod suggestion?
55 Tony:
--- Quote from: Cliff Ruggles on May 07, 2018, 03:59:30 AM ---Pretty high pressure readings for 454 CID with a 230 @ .050" cam on a 110LSA. I'd suspect the true static compression is higher than you have calculated or the cam is advanced further than you think it is, or a little of both.......Cliff
--- End quote ---
Yes, I believe the head was milled a little or lot more than I accounted for. I really wish I had known about cc'ing them. It was my first build ever. I have replaced timing chains before and I'm pretty darn sure it's 2* advanced and no more. In your opinion, if I have all the low end torque that I can use, would you suggest setting the cam straight up? It's not an easy job with a BBC in a 55 chevy. Although the cam says 1500 to 5500 and I redline it at 5500rpm anyway. Comp told me the 2* advance would lower the power band about 500rpm at each end, but I know the guys on the phone are hit and miss. Oh, and by the way, the motor has almost 8000 tough miles on it with no problems so I guess all in all I did a few things right?
Cliff Ruggles:
Advancing camshafts to improve low end power is a highly inaccurate assumption.
It gets regurgitated over and over on the Boards, but I doubt if very many folks have actually done any testing in that area to see what really happens with moving cams around in terms of engine and vehicle performance.
It is true that advancing the cam or lowering ICL closes the intake sooner, but it also moves the exhaust to cylinder scavenging is effected, often adversely.
Several years ago I decided to test that sort of thing and moved the cam I was using in my 455 4 times to see what would really happen.
It started out installed at 109ICL per the cam card. I had many hundreds of runs on the car so accurate comparisons could be made. I also logged many thousands of street miles so would also compare street performance as well.
First move was to 111ICL. It really didn't effect it much anyplace, just a very slight reduction in vacuum at idle and maybe just a tiny bit "lazy" at very light throttle openings. At the track it ran almost exactly the same at every point as it did at 109ICL.
Next moved it to 113ICL, and that really took some "snot" out of it. Idle vacuum dropped a solid 2" at 750rpm's, noticeably "lazy" right off idle, and it lost nearly almost 2 tenths and 2 MPH at the track.
Moved it to 107ICL next. The vacuum at idle returned, and it "felt" little better on the street, with slightly improved throttle response right off idle. It didn't really "feel" any better past about 2000rpm's, but when you are working with a big 455 engine that makes TONS of torque anyhow, "seat of the pants" evaluations are a bit difficult right to start with. Anyhow, race day came and at the track it KILLED it everyplace, slower in 60' and ET and MPH at every point.
Lesson learned, advancing a cam doesn't necessarily improve low end power, engine power across the loaded rpm range, or vehicle performance at any level......FWIW......Cliff
55 Tony:
So ... read the card, set it and forget it?
Something else I *think* I realized. Bare with me, I don't know cam shaft lingo. But some of the numbers on roller cam specs make it look a bit wild when comparing it to a flat tappet cam. But since the flat tappet is, well, flat, the cam lobe hits it sooner and holds it longer than with a roller on the same cam. Is that right?
Cliff Ruggles:
There are limitations with flat cams not present with roller designs.
The roller cams can get the valves up to full lift quicker/sooner and hold them there longer.
Flat cams would chew up the lobes trying to do the same thing........Cliff
55 Tony:
Let me ask a different way. When stating specs for cams, do they give the actual lift of the cam lobes or the lift of the lifter and rod as it travels over the cam lobes?
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