Lack Of Power On 331

Discussion in 'Classic Mustang Specific Tech' started by John Grunwald, Jul 13, 2013.

  1. Hey guys I need some help with my combo, this is my set up:
    331 all forged with keith black pistons and I forgot what brand on the crank and rods
    I have a weiland intake with a 600 holley
    Rollin thunder cam with like .587 lift on int and exhaust? I can remember the specs exact I'll copy the link to eldebrocks cam card
    10.4 cr
    190cc procomp aluminum heads with alot or machine work done ( ported and polished and cleaned up)
    Msd ignition
    8.8 31 spline with a 3.73 gear
    C4 trans with a shift kit
    3200 tci stall

    So the suspension sucks I know that, but off the line I'll spin the tires up to 30+ but from like 45+ I don't feel like it goes like hell , I know most of my power should be at the upper end but even gunnin at highway speeds i could get passed by cars I should be slaughtering, I feel like my carb is too small for my set up because I know the ports on my heads were pretty big and my cam has quite a lift on it, or i might have some problems with the c4? Its out of a maverick that had an unknown amount of miles and it was never rebuilt and sorry I don't have the dyno numbers yet I'm just passing it off of people that have pulled on me on the street
  2. start with the carb. which weiand intake is it? just because a set of heads has had work done to them doesn't mean they will run better. not to mention the pro comps don't have the reputation of having the best casting/parts quality ootb. verify everything is setup correctly then start looking to improve parts selection.
  3. This cam?
    I agree, start with the carb...what size exhaust pipe are you using?2 inch, 2 1/2? Does the engine run OK by itself? Does it pull all the way through the power band, or can you feel it start to starve out? Where is the engine timed at?
  4. I feel like it kinda starves out but it's hard to explain because it's not always consistent and I don't think the heads are the problem we had all the ports measures to be the same, the valve train was changed out. And That is the cam I'm using I can't remember what it's timed at though and the exhaust is 2-1/2 and the headers are these Chinese headers on eBay hahahaha I'll grab the link i wanna swap them out soon
  5. I was just driving it but ya it feels like its in the upper end at 3rd gear more like 60+ not 45
  6. as the others have indicated, start with the carb. next check your timing, both initial and total timing, along with your advance curve. you should have 10-14 initial, with 32-36 total timing, and have it all in by 3000-3500 rpm.
  7. Is 750 too big? And what about a single plane victor intake? I have a dual plane I think weiland stealth? I'll check it later

  8. Has your carb ever been tuned? If its bone stock out of the box, its too lean and you need to up the jet numbers up into the 70s to get it in the ballpark. If it has a Power Valve, increase primary jets by 4-6 and use secondary jets that are +8 larger than the primaries. For example...stock jets are 66s. Use 70 primary and 78 secondary for starters. Now your in the ballpark.

    A 750 is not too big for a 331 IF the engine is being revved to 7000. To 6500 then a 650 is good. Single plane is good IF you are revving to 6500 to 7000 minimum. If your cam is not good to that rpm, stick with the Weiand stealth.

    Check timing as mentioned by others. 12-16 BTDC initial and 34-36 total all in by 3000 or so will get you in the ballpark.
  9. Is this your cam?

    Its a pretty god size cam. Should provide peak HP in the 6000s with usable HP up near 7000 if the springs are up to the task. A dyno will tell the story. I think you need a 650 minimum and maybe a 750 if the engine produces usable HP to 7000.
  10. Just another note.

    For comparison sake, the 331 in my car has a .528 lift, [email protected] duration solid lifter flat tappet cam. Advertised HP range was 2000 to 6000 rpm. Actual is more like 2000 to 7000 rpm with peak HP at 6500 in my particular setup. Peak HP drops by only 30 HP at 7000. Shift points are 7000 to 7200 rpm. When I had a Weiand Stealth, shift points were a bit lower at about 6800.

    Your cam is bigger than mine in lift and is nearly identical in duration @ .050 and is probably bigger than my cam for duration @ .200 (another common duration info point besides @ .050). Your setup is a bit different so your engine characteristics will be different.

    Your cam is hydraulic and a roller though. Pushing a hydraulic roller to 7000+ can be done but it requires a bit more attention to details such as adequate valve spring rate compared to a solid flat. Your lifters are heavier and your cam ramps are more aggressive. This requires stouter valve springs to keep things under control
  11. The 600 has been tuned and the jets altered I also set up a metering block in the secondary with I think 78 jets in it and theyre dual springs I can't remember the strength it's been a while but I know the valve train is very stout
  12. that's a decent intake. I wouldn't bother changing it. a good 750 is not too big. buy an AED or if you need a choke a quick fuel. holley's metering is jacked. carb sizing has more to do with the relationship between cross section vs. cylinder displacement vs. lobe area than using some antiquated rules like xxx cfm for a xxx cid at xxxx rpm. a lot of that is from people having to mask holley's stupid metering by running too small of a carb for the last 40 years. its just not that simple. you cant look at cfm ratings. its about having a small enough venturi to have good carb signal while balancing enough venturi size to feed the engine effectively. ive seen good known 650 HPs that wouldn't run worth crap on a big head/cam/358" pump gas combo. then put a new 750 HP on it and the problem got worse, then put an AED 750 on it and all the problems went away and the car picked up a 1/2 second in the 1/8 mile. its not about cfm, its about having the correct carb for the application. that being said, I would read the plugs first and look for ignition issues before spending a bunch of $ replacing parts.
  13. The carb is small, but I think the tune is also a problem. Sometimes a car feels faster after a change, but when you take it to the track it is actually slower. When my car was normally aspirated I tuned it to an A/F ratio I was told it would make the most power. When I took it to the track I ended up putting 4 jets in it front ant rear and going .4 and almost 4mph faster. I now use the wideband for shaping the curve and time slips to verify whether or not a change helped. I only look at plugs for detonation and heat. IMO most people get it wrong reading plugs alone. Reading plugs is only a small piece of tuning for me. Measured performance is all I base tuning on. Oh, and I don't trust dynos because they don't accurately load the engine like real life.
  14. Well thanks for all the help guys I'm going to try to bring it out to the track soon if I can find one here in southern California.. Does any one know a reputable dyno in the SoCal area?
  15. different cams influence the brake specific fuel consumption as well. on NA combos we read the plugs to make sure its not lean and tune for the highest trap speed. IMO that's the best way to do it because you can tune it on the dyno for greatest hp and then go to the track and itll be slower than the 'track tune'. forced induction combos need the wideband however, we tune them for the desired a/f curve and then they run what they run. it keeps them alive assuming the fuel is consistent.
  16. The heads are not the problem. Alot of people that dont have them will repeat what they heard, not what they have experienced.I have Pro Comps but had them CNC ported and put new valvetrain.The castings are ok, but can be worked to be great.I would at least step up to a Holley 650HP.

    For a dyno check out Superior Tuning in Anaheim off the 57 or my buddy own Racers Edge Tuning in Downey, but caters more to mod motors/fuel injection.

    Also you can run at Irwindale every thursday 4-10pm, $20 bucks to race or $10 to watch.
  17. I would say it depends on your individual set. I have a friend with a set, we weighed them vs my rhs both bare ootb and his pro comps are 4lbs lighter than my rhs per head. talk about a porous casting. he has had all kinds of problems with guides pulling out and seats falling out. as far as port work, it depends on who did the work as to how good it is.
  18. That is true.Ive had mine for about 4-5 years now and havent any issues and they are good enough to support over 500hp at the wheels.My buddy with AFR's broke a rocker stud within the first 6 months on a "better quality" head. Sometimes its just luck i guess.
  19. the buddy I know that has a set are 3-4 years old. I have been told by are a very reputable source that the Cleveland pro comp casting is a really nice piece for the $.