What are the symptoms of having a cam and/or carb that are too small for the application? I ask because I have worked out all the bugs in my setup, but now seem to get to 5000rpm very quickly then get a slight bit of hesitation or faltering. It continues to rise in rpm, if I want it to, but it "feels like" it is running out of gas (getting insufficient fuel flow) when I get up there, and continues to accelerate at a much slower rate. I have Edelbrock 600cfm, with 3 stages richer metering rods, and am just now starting to get the cocoa color on my plugs, even though it is still kinda light colored, which is why I am wondering about being undercarbed...I am not able to get enough gas into the engine. Even at 2 stage rich metering rods, plugs were clean and white. My cam is off-brand equivalent to the Edelbrock Performer Plus, supposed to be good up to 5500 rpm. Heavily ported Torker 289 intake, mildly ported exhaust GT40P heads with stock rockers, Hooker long tube headers, Edelbrock Performer 351 mechanical fuel pump (advertised good up to 550 HP, I am guessing that I am still under 300HP). Stock distributor with Accel Super Stock coil and 8mm wires. Any suggestions?
I doubt it is the heads, since they are the same heads used in Lightning trucks and Cobra Mustangs, and I am pretty sure they can handle twice the flow and HP than what I am putting through them. Now, the valves may not be lifting the way they could with better 1.7 rockers, but again, same rockers that were in Cobras and Lightnings. Do you know something I don't about the heads? But, that sounds like one vote for "undercammed"
I agree with Stockhatch, the head I think will start topping out at 5600-5800 RPM's alone with you saying the cam is rated at 5500 RPM.
What are the specs on the cam? I doubtit has a very aggressive profile, and the p heads are good, but have small ports so they flow pretty well at low to mid range rpms, but choke out up top. BTW, the 1st gen lightnings and cobras used true gt40 heads. Only the explorer/mountaineers use the p heads.
Have you tried the next higher set of "rods" for your carb? I know nothing about Edelbrocks, but a 600 dp holley will support way more power than what you are making.
Im thinking cam also, unless your fuel system is plugged the pump and carb can run way past that. the cam says 5500rpm(sounds like the one im installing) but that is counting on springs, lifters, and rockers that dont start to lose a little before then. how fast are you hitting that rpm anyway, just wondering for a rough estimate on my app.
I get to 5000 in first gear within a second or two. I hit 80 mph in 3rd gear around 6-7 seconds. Shifting at 5000 since it slows down after that.
scooper... is it possible the springs are allowing the valves to float..... im not a head expert.. but i have been told.. anyhting over 5000 rpms and a decent cam and you should be running a higher spring rate for valves.... you said you upgraded the heads and headers... this could be the issue.. or the mechanical fuwl pump isnt putting out enough pressure at high rpms..
Now I did not think about that. On my GT40 heads I did get new springs that was matched with my cam. My cam has more lift than Ford's stock cams.
I doubt his cam is floating the valves. The stock springs arent great for .500+ lift roller cams, but a flat tappet low lift, low duration cam shouldnt make them sweat.
I would recommend more cam. I think that is your biggest limiting factor at this point. Your intake wants to rev, your carb should be good for alot more power, your heads are much better than stock...I would get a bigger cam and some good springs for the heads. Somewhere along the lines of 220-225@.050 duration and as close to .500 lift as you can get without going much over it. The p heads wont flow much after .500 anyways. This is just MHO, and Im not saying it isnt something else giving you the soggy feeling up top. Once carb jetting is eliminated as an issue, I would go for the bigger cam regardless.
scooper ...t he cam i leaning towarsd.. xe264h.... .512 lift intake and exhaust... since you and i are close together.. and you have a better set of heads than i do.. that cam would be the best i think
My current lift is .478, I think. I really need to go with 1.7 rockers, maybe roller rockers... I just really wanted to make sure that I was running my engine at top performance, and not losing out due to something minor like fuel flow. I really cannot complain, as it gets to 5000 rpm so quickly...I used to cross the 1/8 line still in second gear, since it took 2/3 of that track to even get to 4000 rpm, where I used to shift. Now, as soon as I hit the gas, I am already flexing my arm for the shift. And, 2nd ain't too shabby either. I need to find a track to get some real numbers. and a dyno... ST, I like the sound of your cam! But I think I am done with "major" engine upgrades until I do an overhaul, and stroke it to 347ci. Then bigger cam, 10.5:1 compression, etc. Until then, I am running a 33 year old engine with stock pistons and rods (and bearings) and 58,000 miles on it, and I don't think I should press my luck on pushing it too much further. I am pretty sure I have at least doubled the stock horsepower, which is plenty for me for now. I "should" be satisfied with that
