Inliners International Forums General Discussion Engines What am I missing?

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!

sjburk I sent you PM

You say the fueling is good. What is the AFR @ WOT? @ cruise?

sjburk

It was good to chat with you yesterday.

Thanks, you too

I used to have the cruise dialed in at the 15:1 range for economy, lately with messing with jets, it's a little richer, more like 14:1 when cruising.

WOT, in the 12:1 range, does vary some while it's settling out.

Have some screenshots of datalogs with AFR, speed, MAP, and wheel speed, if you're interested. These are 2nd gear pulls, 1st one just going wot, 2nd trying to smooth out the transition.

From what I have found, WOT around 13 cruise 13 and idle 13. These have a terrible chamber design and do like extra fuel at idle and cruise. Your pics show WOT in the 11's It is too rich.

Thanks, I'd always seen most engines I've messed with run best WOT at around 12-12.5, but every engine is different, so always good to see what they like. I did change the secondaries, and have the AFR in the 13:1 range now. Did a few pulls today, seems like the times are a around 0.05-0.1 sec better than what I'd been getting (2nd gear pull, 2800-4800 rpm). 3.7s vs 3.8s before.

For anyone reading, I'm going to make sure I have timing dialed in as well, per twisted6 recommendation. Maybe try an aftermarket ignition module as well. I have 36 total advance, which the engine seems to like. Though I do think it's coming in a little late, probably full advance at 3000 rpm, so it may like it to come in closer to 2500 rpm. Played around with different spring kits in the past and can't ever seem to get timing to come in early enough without it being too early or getting way too much at higher RPM. I'll have to keep playing around and find the balance.

Will post with any updates if I find some more speed.

Might not be that something major was wrong as I was thinking, maybe it's some small things stacking up, fuel being a little off as mentioned above, timing not quite perfect.

Anyone else with a similar engine setup let me know how yours runs or what kind of times it does (1/8, 1/4, 0-60, dyno graphs etc). I don't have any good comparisons, so maybe it's performing better than I think. I don't have official drag times or dyno numbers. Not really a race build, just a fun street engine for a truck. But still want to make sure I'm getting what I can of it after putting in all the work on this build!

If you run a vacuum advance. You can change it out to an adjustable one. As we talked about you can also use springs with different tenson on the weights Or one weight lighter than the other. There is nothing in the rule book that they have to be the same. But keep a log of what you change, and do one thing at a time.

The fuel curve looks better. Timing all in by around 2500 will also help the mileage, watch out for detonation. 1 light spring and 1 heavy or medium spring to tune the timing curve. Use stock GM weights. If in a HEI.