Looking for some help on my build. Basically, it feels like this engine just isn't making as much power as I would think. I feel like I'm just forgetting something basic, or maybe I overestimated what I could do with a street naturally aspirated 250.
It's a 250 I rebuilt about 5 years ago. I did 1.94" intake valves, and 1.6" exhaust, had the head and block milled, and put in 307 sbc pistons to raise compression to about 9.3:1. Cam is a Howards cam with 213 deg duration and .502" lift on both lobes. I'm running an offy intake with a 500 CFM Edelbrock AVS2, and some hedman long tubes. Timing is 16 deg initial, with around 36 total.
I did not, however, lump port the head. Why? I'm not sure, probably should have, but didn't feel like spending the extra time messing with it, and figured I'd be happy enough with the other mods. Well I was wrong, and after 5 years I finally was bothered enough by how slow it was to do lumps.
So about a month ago, I bought the T6G2 kit and did a DIY lump port job in the garage. Once it was all back together, I was surprised to find that the lumps made... no difference. It doesn't feel any faster, and taking some times it seems really no better than it was.
Just to give some perspective, my 0-60 times are like 10-11 seconds. Both before and after the lumps. That's in a half ton short bed 67 c10, with 3.54 rear end, 235/60/15 tires and I currently have a T5 from an 80's V8 F-body. I do have to shift 2nd-3rd for the last few mph, so I'm sure that hurts the time a little but still. Is that all I should expect? Are my expectations just way off?
So what am I missing here? Before the lumps I just thought it was slow and that's that. Regardless of what's going on you'd think at least doing the lumps would've made a noticeable power increase. But it doesn't seem that way. So now I'm thinking something must have been wrong since day 1 that's holding it back but I'm not sure what. The engine otherwise runs great. I've put around 10,000 mi on it and even did power tour this summer. AFR gauge shows fueling is good, plugs always look good when I check them, doesn't burn oil, etc.
A few things I've checked or am thinking:
-The fact that lumps made no difference makes me think there's a restriction somewhere so I'm just limited on airflow. But I wouldn't know where. Carb and intake are good, I had those off to do the lumps, no obstructions. All my exhaust was clean when installed. I can't imagine long tube headers and tubing/mufflers are somehow plugged after a few years. Might pull it all and check.
-I've checked compression, it's about 150 psi on all cylinders, which is what it's always been since I rebuilt it. Is that too low?
-I checked over my ignition system today to make sure plugs were gapped ok (0.040"), and wire resistances seem normal. Ignition timing checks out, etc. I do run a cheap amazon dist that was like $60 and parts store plug wires. Could try an expensive name brand distributor and wires, just not wanting to spend the money if it may not help.
-Are the 1.94" valves too big? I know the 1.84" is recommended for a street 250. Not sure why I went with 1.94, just thought bigger is better I guess.
-Did I botch the lump port job? Seems like if they're in there they should be good. Pictures attached. I've thought about pulling the head and trying to run it without the lumps now just to see.
-Was the 500 edelbrock the wrong choice? I could try a holley 390 but they're pricey, or just another 500 eddy if mine's somehow bad. I would think more cfm wouldn't hurt peak power as much as kill economy or make it idle rough.
Any other thoughts, suggestions? What am I doing wrong with this engine. Thanks!
