I am in the process of setting up a rolling chassis for my '50 styleline. I'd like to mock up the engine and exhaust soon. I've been looking at both the Fenton and Nicson manifolds available and was wondering which would be better for a mild 270 build? The Nicsons look much beefier and have 2-5/8" collectors vs. the 2" ones for the Fentons. Conventional wisdom would say that the Nissans would flow better, but realistically, I think I will be running 2" exhaust tubing at the most in order to keep up velocity. Would the larger ports of the GMC be negated by necking down to the smaller sized exhaust tubing? Any advice here on the manifolds and tubing size would be appreciated. Thanks.
Look at how the exhaust leaves the head and enters the manifold. This was done to miss the stock intake. If I'm not mistaken the Nicson hits a flat spot before exiting down. The Fenton flows in a sweep as I remember. That may help in your choice. I have original Nicsons so I would probably use them and at the flange I would neck them down anyway for the street. Good luck
I have run Fenton stuff in the past and have always been happy with the results. One thing to remember is that exhaust can be too big just like too small. I probably wouldn't run 3" pipes behind a flathead but I may run 2.5s behind a y block.
Fentons for a GMC are modified Chevy castings so the ports may not align perfectly. Nicsons were designed for GMC, and will flow better than stock. What other mods to the engine are you planning?
Use the nicson headers, the fentons are a chevy part that dont fit the gmc very well......I will find a pic of mine here somewhere...
Real Fenton headers fit the GMC with a very small amount of port match. Don't know about the recent Chinaman castings, but when you grind on them they don't make many sparks ...
Thanks for the responses guys. Plans for the jimmy are lightweight pistons in 8.5-9.5 static CR range depending on which cam I choose and the dynamic compression. I want a really small cam, my goal is smoothness and torque as this is for a custom. I have a 419 small port head that has been rebuilt but has stock sized valves. I may resize the valves larger and do a little pocket porting and cleanup but haven't decided. Will balance the entire rotating assemble and do all oil mods. I have both a McGurk 2x1 small port intake and an 2x1 Ellis intake, will most likely go with the McGurk and use the Stormberg BXOV-2s that I have. This will be backed by a Saginaw 4 speed and fed to a '57 chevy rear which I have both 3.08s and 3.55s for. I'm still undecided which gear ratio to use. I see the Fentons are less expensive and far more available than the Nicsons. I only see Nicsons offered up occasionally on the Inliners site for around $500ish. I would prefer Nicsons, but was unsure about necking them down to a smaller exhaust tubing being too constrictive. What size exhaust tubing would you recommend? thinking of going with Porter mufflers, I don't want too much rapping noise but more of a classy deep burbling sound for this ride.
My GMC motors don't rap like the Chevy motors do. I don't know why. Larger valves won't be an advantage on a motor thats not reving to the moon. Stock GMC cams are really good for a street motor. Use a v8 Fluid damper on the front and adapt your pulley to it. 3.08 would be a great highway gear, if you have the 3.50 low gear Sag. . Go with the headers that fit the head. There's a big step trying to fit Chevy ones on the GMC. Maybe it's good for anti-reversion!LOL.
I guess I did say enough about the Nicsons, yes the flange is big but right out of the head the exhaust hits a flat at 90* 1" out of the head then redirects down. In their day and for the street the are fine an definatly look period correct but sh--ty for performance and no intake manifold heat. I also agree GMC's are throaty not rappy. If you can find a large port intake use it on the small port head by using a 45* end mill and taper it into the port. There is plenty of meat at the edge of the head for this. For efficiency this velocity is fantastic when the valve first opens and small valves are a plus here too for the low end torque. I helped a guy using a 270 small port and single 4 barrel large port and he was really impressed using what you would call a RV cam. Good luck and I'm glad to see another Jimmy on the street.
Thanks for the advice. How do you adapt the fluidampr? Is there a particular v8 model that fits best?
I have tried them all. Right or wrong they were all for SBC V8's. I believe someone is making one for the 292 6 which would work fine I'm sure. At one time I used a 1/8" spacer ring first but not any longer. I relate everything to how well the flywheel stays tight. Remember I'm racing mine. TCI Rattler was the worst. Fluid Dampner and a Fisher were both good along with the stock Chevrolet 7". The best is the ATI Super Dampner. All my pulleys mount on the front like modern engines. Once I did take apart a stock water pump to remove the pulley. I mounted a vee belt pulley from a hardware store to line up. Today I only use electric water pumps and prefer the Meziere. Good luck
Yes you can. Remember nothing is directly bolted on. Use studs and not bolts. Set each manifold as close to center as possible and mark centers. Set the gasket on the cylinder head over the studs and mark centers. Then set the gaskets on the headers with the marks lined up; you will see where you need to grind off some of the cast iron on one side of each port. Take only what you need and angle the grinding in the exhaust manifold. Or you can just line them up the best you can a don't do anything. I use 2 piece large self aligning washers from McMaster Carr or the stock elongated hold downs on the studs. Good luck.
you can buy new Nicson Headers to suit a Jimmy - If you're interested, ring buffalo Enterprises, as he is an agent for them
DO NOT USE the fluidamper. Go to BHJ Dynamics. they make a 2 groove damper for these engines. Yep old thread but as long as its bumped, Ill throw this in
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