Setup and Tuning 351c 2v

I have a 73 mustang with a 351C 2v that's stock internally as far as I'm aware. I'm not sure what year my cleveland is based on because it has been completely replaced at least twice since i've had it (6 years now).

Up until about a year ago it remained mostly stock except for long tube hooker headers and dual 2.5" exhaust. Then, due to a hefty 35% discount i purchased a 670cfm holley street avenger and a weiand X-celerator. The distributor is stock, and hasn't been recurved at all, but is fitted with a pertronix ignitor module. Wires and coil are MSD and i removed the ballast resistor. I also swapped the open rear end gears from 2.75 to a traction-loc 3.5 about a year ago as well. Without tuning, this setup measured 15.5 second quarter mile, chiefly due to a broken/poorly shifting FMX I had at the time that required lifting off the gas a good deal before it would shift to 3rd.

About a month ago I had the p.o.s. FMX (that i've had rebuilt twice) replaced with a C4 with full manual valve body and B&M 2400 stall holeshot converter.

For most purposes, my car runs and starts fine. It accelerates without stuttering, maybe a mild build up after stomping the gas using the heaviest (black) secondary spring included with the holley carb. However, I do find that the car stumbles and misfires if i drive approaching 4000+ rpm ( I believe that's about 80mph+). On heavy acceleration, the stumbling and misfiring seems to go away, and it seems i can't rev in any useful way above 5000rpm. This car has always had poor mileage- like 10street/14hwy and after the gear change it's about 8street/12hwy.

Could this be that my stock cam just isn't made to cruise at that engine speed? Or is 670 too much carb for the otherwise stock 351c 2v?

I'm considering purchasing a plenum divider for the single plane weiand (weiand lists 7460 and 7461 but no details on differences on either?). Or upgrading the stock distributor to one that i can recurve easier like from MSD or similar. Manifold vacuum reads 15 idling at 800-900rpm.

I've ordered a jet kit & secondary spring kit so i can test different settings. I plan on upgrading the cam within the next 2-3 months or so, and changing the stock distributor sometime before that.

Currently the car weighs 3450lbs without driver, and I plan on changing the frontend to fiberglass & possibly the doors and trunk since it's prettmuch the same cost to buy a kit than seperate hood and front end.

Right now i'm looking for ideas to fix the stumble and misfiring at freeway speeds, any setup or tuning recommendations are appreciated. Cam suggestions are also welcome. I don't care for streetability much or idle quality, and will eventually make this car more of a weekend car anyways.

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One thing that stands out about your setup is the single plane weiand intake on a stock 2V engine and I am assuming a stock Ford camshaft.Also the670 cfm carb is much too large for that engine as it sits now. Also your gear change didn't do much for you either in regards to your problem. The 351c cam barely makes any power past 4000 rpm. In other words you are trying to run the car consistently at the top of its power band. One thing you can doublecheck is the timing. Typical for this motor is 8-10 initial with full advance at 36, 38 absolute max.A rather quick advance curve is good for stoplight to stoplight power. These engines really like alot of inial timing.I have worked wit thse 2V Clevelands alot and this is what worked for me.

Edelbrock Performer 4bbl conversion intake
Comp Cams 268H hydraulic grind
Crane pushrod guideplate retrofit kit and stud kit
Msd Billet distributor and 6AL box
600-650 cfm holley for max power( vacuum sec's)
Or a Holley 500cfm 2bbl on aspacer on the Performer intake for better streetability. Yea, it really works
timimg- 10 12 degrees initial total to 38
Use 2nd or third quickest advance spring set up in the MSD distrib.

Anyway, as far as the mis fire and stumbling goes you were right on the money with your camshaft rpm statement. I am willing to bet that your plugs are getting pretty black and sooty due to the single plane intake and the big carb. That would definitely create misfiring also. Sounds like a simple case of mismatched components.
By the way that 670 you have would probably work real well on the setup I mentioned above. Hope this helps you out.

I forgot to mention that if you want to eliminate the highend miss, simply pull back on the initial timing aabout 2-3 degrees . You will lose a little low end power but should help with the highend problem

I don't think I want to switch out any of the components. I purchased them a bit on the large side in anticipation for upgrading to a roller cam. I should be getting the jet kit tomorrow which includes two of each 64-99, so i'll probably lower the primaries to 64 from 65 and maybe two down on secondaries to start out with. I'm also ordering a plenum divider kit for the weiand intake, (7460 is square bore and 7461 is for spread bore). Hopefully that'll get rid of some of the misfiring. Anyone else have suggestions or tips?

I ordered the plenum divider kit. hopefully it helps a bit till i can swap out a cam. Has anyone here had any experience with Lunati cams? Their tech recommended a 31103 grind. Can anyone recommend a roller cam for a 2400 stall converter? I'd be willing to suffer a bit on street and swap gears out to 3.9 or 4.11 at the track.

Are you sure it isnt valve float?

Otherwise, I wouldnt lean it, rich mixture is safe and doesnt cause a surge, and going leaner might burn a piston if it is a lean surge

I would guess that you are over advancing with a stock distributor or valve float at that RPM

I doubt it's valve float because before I changed the intake, carb & rear end I would cruise at around 4000 on the freeway for long periods of time without any strange misfiring. I get the plenum divider this monday and i'll post the results of that.

I've also been looking into building another block from scratch and keeping my current one as a backup block. Is it worth it to order an aussie spec block? I read they have higher nickel content than us built cores. As far as cams go, a Lunati tech advised a 31103 cam which is their 280in/300ex advertised duration, 228@.050in/235@.050 ex. How would this rank against a 280h comp cam? I would spring for a roller cam if it seems worth the money.

That 31103 cam will liven the car up. It is similar to mine but my setup is a 1100kg car with a manual. The lift is about 550, the LSA is 109 but it still idles at 700rpm with a nice lope. Peak HP is at 5800 BUT you need to talk to the cam manufacturers and match it to your CR, diff, weight and application but I would suggest be bold the clevelands love to breathe.

<font size=-1>[ This Message was edited by: speedar on 1/23/06 2:29pm ]</font>

<font size=-1>[ This Message was edited by: speedar on 1/23/06 2:31pm ]</font>

When you change the cam it will run much better. If you are building another engine, it might be good to get a roller. They generate more power and you sont have to worry about wiping out lobes. I currently have a b303 in my 302 and works great, power comes on strong at 3500 and goes untill 6000 rpm. You might want a little more duration because of the increased cubic inches. The cam you mentioned sounds good to me, or you could try a 274HR from comp cams if you want a roller.