Im lost, the only other suggestion i havent checked is my comp could be low but even with low comp pistons i should be 8.7:1 but my cam is rated 8.5:1 and higher. o No: :ball:
Low compression might make it a little doggy at low rpm, but wouldn't kill the top end with that cam. This weird. Silly question, have you run it without an air filter?
Kody checked his comp and the cyls are all around 125....which is not bad but in my opinion is a bit low for the performance he is looking for. We have chated about options to correct this such as shim head gaskets and milling the heads so that he doesn't have to really pull the motor apart. I also believe that the cam should be dialed in as when it was changed to straight up it ran alot better....for all we know with stock old springs the valves could be floating. There are alot of things that can cause the motor to fall over....
Mark, when the cam was straight up it ran horrible. No power at all. It was takn me almost 13 seconds to hit 60mph. Its much better at 4 advanced now which is what TA told me to do. It says on the cam card to install it 4deg advanced which is what i have it at now. The springs shouldnt be stock. They should have less than 20k miles on them. And should be TA or poston.
What about checking your valve spring pressures? My car had sat for a few years and when I put in the new cam, I had the springs checked at the machine shop I got my porting done at, came in light, so we threw new ones on. Might be having some valve float issues?
Mark i tried it with no air filter and lost power. I have a new twist to add to things. When i run my stock GS cold air cleaner my peak hp comes in between 4400 and 4500. Why would this be? How do my plugs look with this new holley?
WOW those plugs are out of a running engine? I would guess that it is starving out of fuel now for sure. The reason it gained power with the stock style air cleaner is that it had the effect of enriching the mixture slightly. We are getting somewhere now. I would throw in some bigger jets (against our prior thinking) and see how it responds. It seems weird that it is looking so lean with those jets in it though.
Yeah those plugs probably have 200 miles on them as well as a bunch of 0-60 runs and 10 1/4 mile runs. i wonder why my motor wants so much more fuel than Arties? He set his with a wideband and 68 primaries and 72 secondaries are perfect...and thats with a 1in spacer! Im not running a spacer anymore. so what jets do you suggest? if im runnin lean this could kill my powerband...no?
if all your time with those new plugs are as you say...sounds like the secondaries are open more than an average motor. I would maybe try up 4 in the back and 2 in the front , jest are cheap and easily reuseable.
Leaning out will definitely kill your power and in severe cases (as mentioned) will cause surging and coughing, sometimes backfires. You can seldom tune an engine like someone else's and have it be right. Artie's has a stock cam, and I don't know if yours has been overbored at all. More cubes, bigger cam, more fuel needed to feed the higher rpm. I still haven't seen a convincing ruling out of fuel delivery though. You mentioned some tests, but was there any correlation between the power dropping off, and changes in fuel pressure? It might not be totally startving out, but just not getting enough. My truck's fuel pump is going bad, and I can punch it, and it just lays down after about 3500rpm. No surge, no sputter, just no more engine. It is usually a screaming monster, big block, headers, torquer intake, cam etc, but without enough fuel, it just wimps out. Jets are cheap though, so start there and if after a couple steps up nothing improves, we need to look elsewhere.
I agree....with the looks of those plugs it surely wont hurt to bump up the jetting.....dont think fuel pump is the culprit and surely you cant compare motor x with y as each is independent with its combo and vehicle. bet if he goes up in the secondaries at least to a 79 ( he has 75 in now ) we will know exactly what is happening.
To test my fuel pressure i ghetto rigged 3/8 fuel line to a T that i put in my primary fuel line in front of the carb and attached a guage to the end of it. i took out a ram air scoop and taped the line to my window and watched it. at WOT it never went below 2-3 psi. your truck sounds like exactly what my car does. no surging, sputtering, caughing. it just run out of motor.
I've just been reading this thread for the first time today. I have a 750 Holley vacuum on my 350 and have it jetted at 72 front and 78 rear and it works great. That may sound a little rich but the plugs are a perfect light tan color. Your plugs look a little too clean for my comfort, but keep in mind that it is much harder to get a good reading with unleaded gas. Try some race gas in it if you can, or possibly a lead additve in the tank when you're reading plugs. Bill
good suggestion i will add lead next fillup. i just went and got a set of 79 holley jets for the secondaries. hopefully this will help solve my problems.
I see you did a cranking compression test and they were around 125 psi. Were they consistant? A better test would be a leak-down so you could hear where the leakage is, if it is substantial. I had a motor one time where the pressure was leaking badly around the valve seats... resulting in peak power a good 600 rpm below where it should have been. After redoing the valves all was well.
no it was not consistent. i was anywhere between 115 and 140. but the motor was not hot. i didnt know to run the motor for 10 minutes before...that wouldnt have worked ne ways because the headders would have burnt the hell out of me. ill look into a leakdown test.
Not anymore, swapped it for the Comp 260H mid-season. Stock cam had seen better days, so I threw in the Comp because it was here. I just went to a 70 jet on the primary side, richened it up to the 12.0 range on a/f but it should be about right when the air gets cooler. Since I'm running brackets every weekend, the slightly rich mixture seems to be a little more consistent as well.
