Need help with engine combo

Discussion in 'Engine Topic' started by TheSkippy, Oct 18, 2012.

  1. TheSkippy

    TheSkippy New Member

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    I am wondering where I can make some more power. My engine combo is:

    350 stock bottom end 4 bolt untouched; had 8.3:1 original compression with 76cc heads
    AFR 0916 180cc Heads with 65cc chamber making 9:1 compression; I am measuring 150-160 cylinder pressure.
    Comp Cams XE262H Xtreme Engery cam; .462/.469 lift, 262/270 duration, 110 lobe seperation
    670 Holley Street Avenger dual feed, vacuum secondary
    Edelbrock 7101 performer RPM intake
    1 5/8 headers, 3" collectors, 2 1/2 dual exhaust with converters
    1.5:1 rockers
    Timing set at 12 initial, 33 mechanical all in at 3000
    Stock stall converter with TH400 trans
    342 rear gear, 26" tires
    77 camaro, 3500 lbs
    running 14.1 at 99mph
    I figure the engine is making just about 300hp. I hoped this combination would make 350 or so. My goal is low 13 1/4 mile. I am thinking not enough cam. Considering 1.6 ratio rockers. I did reuse the original timing gear/chain set which looked like new. I am also considering new timing set and installing using the 4 degree advanced keyway. Any thoughts about the combination or what I might change?
     
  2. 1980RS

    1980RS Veteran Member

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    I would put more cam in it with those heads like a 280h CC and a 750 dp. If you are only running 33° timing in the motor now try bumping it up to 36 than 38 and to 40° to see if it helps. I went from 36 to 42° and my car weny from 11.90's to 11.70's with that change. Try it, what's the works you would have to do? set it back. I ran a 600 holley 2 years ago and ran 12.36 switched to the 750 dp and went 12.15 but if you do a lot of street driving the 670 may be better.
     
  3. 1BAD78

    1BAD78 Veteran Member Gold Member

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    I probably wouldn't go much bigger on the cam with that low of compression. The xe268 is about max. That with a 2500 stall should help. I'm around 10.5:1 with the xe274 and Brodix IK 180 heads with a 3000stall and I'm in the low 13s.
     
  4. 1980RS

    1980RS Veteran Member

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    9 TO 1 low? Mine is 9.7 to 1 and I have a 292h Comp Cam in it and the car runs great. As I reread his specs it looks like he went from 8 to 1 up to 9 to 1
    A 280H would run fine and if he wants more street manners just call Comp and get it ground on a 114° LCA. Alittle less low end tq. but a bunch more driveability.
     
  5. hhott71

    hhott71 R.I.P 11/19/18 Lifetime Gold Member

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    The cam is big enough for the 9:1 compression.
    The 33* total timing is RETARDED. Add 3-11* of timing in 3* increments until you see it decrease in MPH. If you judge by et only check the 60' times as that will show the tire spin. MPH going up and up means its pulling harder, dial it back to where it does the best mph.
    Why the 400TH, way too heavy for your application.
    Keep what ya got, changing it back to the 350TH. Get the timing all in by 2500 and get a 2800 rpm-3000 rpm converter.
    The carb is fine. If you don't have the EZ-adjustable secondary kit on the cab, get it. Again testing it with MPH readings and the BOG You don't want it to bog, and you don't want it be strangled by not opening properly.
     
  6. TheSkippy

    TheSkippy New Member

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    Thanks so much for the quick replies. I have tried advancing the timing and get deisling or run on when I shut if off along with it having a tough time turning over when hot. I can probably get 3 more degrees, but not much more. I have advanced it to as much as 40 degrees and did not see much difference except for the problems mentioned above. I will try it again and see how it acts. It is mostly street driven. I was actually thinking about going with the XE274 cam. Looked to me like the largest I could get away with 9:1 compression. What do you think about just going with 1.6:1 rockers to get more lift out of the cam I have in it? The trans came in the car and is built strong so I havn't done anything with it yet. I have a 700R4 in the garage waiting for its turn in the car. Gonna cost 2K to get it built and installed so it is waiting for just a bit until I get the engine sorted out.
     
  7. Damon

    Damon Veteran Member

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    Don't touch the cam unless you are going to change the converter at the same time. You're already borderline.

    99 MPH (assuming you run at Cecil) seems a bit slow for that combo. I've run similar combos at similar MPH with far crappier heads than you have (but with a less power-consuming TH-350 trans).

    I agree there might be more in the timing- 33 total seems a bit low. I suspect you have vacuum advance adding in more timing than the engine will tolerate at idle/part throttle so you're having to pull the initial/total back below optimum to prevent problems. Am I anywhere near reality with that guess?

    I'd also check to make sure you are getting to true WOT when you put the pedal down. For sure check the throttle arm to make sure it's getting wide open, then play with secondary springs to make sure you're getting full secondary opening as soon as possible, just short of a bog.

    Any chance you're outrunning the fuel system and flattening out in the upper RPMs? A stock fuel pump and stock lines is good for about 14.0s before it can get a little dicey.
     
  8. TheSkippy

    TheSkippy New Member

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    I have not heard any pinging as of yet. Just the run on and hard start. I do have the vacuum advace hooked up right now. I did try not using it at all. The car didn't run great without it. Felt like it was hesitating. The vacuum advance is adjustable and I have it adjusted to give the least amount possible. It advances to 48 degrees with the vacuum connected. I'll try adding 3 degrees and see what it does. I will also check the throttle and secondary springs. The fuel pump is mechanical; edelbrock or holley. It has 5.5 psi at idle. Not sure at top end. If I had it on a dyno I could tell; the gauge is under the hood so I can't see it. Doesn't seem to drop much at all just revving the engine. The fuel lines are stock.

    I really wasn't looking forward to a cam change. I do think I want to do something with the rockers. I have comp cams roller tip 1.52 right now. I know the push rods were close to the head on a couple cylinders so I took them out this morning to see if I had any rubbing and the rockers have a purple haze on them at the base and see some scaring in the cup. I think I want to switch to all roller. Do you think I should stay with 1.52 or switch to 1.6?
     
  9. my24ktrat

    my24ktrat Veteran Member

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    ...I'd keep that cam , just dial in your combo a bit more , you should already be 13's easy , did you change out the stock sec. spring in the holley , try a yellow one, also what's your converter, a 2400 stall will help,also agree get rid of the turbo 400 . A thinner head gasket would've given you a little more bump in compression. Try a number 10 vac. canister on your distrib. and an advance spring kit, hope that helps, DC:bowtie:
     
  10. Damon

    Damon Veteran Member

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    Understood about the ignition advance curve. If you've got 33* total and 48* max with the vacuum advance hooked up that means you've got 15* of vacuum advance in the canister (48 - 33 = 15*). That's a bit much, but not by a ton. I shoot for about 10*, maybe 12* at the most. But it's not totally out to lunch nor is it likely to be robbing you of 5 MPH through the traps (which is about how shy of full potential I think you are).

    Also understood about the fuel pressure gague.... nobody ever mounts one where they can see it. Which is a shame, since idle readings are nearly meaningless. Get hold of a kit to mount it remotely and see what it's doing wide open in the upper RPMs. If you're outrunning the fuel system it will be obvious. And you don't need to mount it permanently like that- just a couple runs through the gears at WOT on a back road with the gague duck taped to the windshield temporarily will give you the info you need to determine if you're outrunning the fuel system.

    Also wondering.... any chance those cats in your exhaust are experiencing that "not so fresh feeling"?? I hate to point the finger at parts that rarely fail, but cats behind a performance-tuned carb engine (as opposed to a stock/emissions engine) are not known for longevity.
     

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