My new engine is a dog!!

Discussion in 'Classic Mustang Specific Tech' started by crushnut, Oct 6, 2004.


  1. crushnut

    crushnut New Member

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    My engine has no power at all. I has just barely enough to get the car moving. I could probably be beat by a Geo Metro or something :notnice: This is a fresh build w/rebuilt heads, torque rv cam, stock crank, sealed power pistons, weiand stealth intake and 500cfm Edelbrock performer carb. I have it tuned the best i can do it with the tools i have. This kinda ****es me off, i mean i had more power/acceleration and seat of my pants feel before i rebuilt the engine, and that was with 8.... yes, 8 cracked pistons :rolleyes:

    Anyone want to make any guesses as to why it is lacking in the power department? :shrug:

    Thanks a bunch :worship:
     
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  2. C0V3R

    C0V3R Member

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    What do you have the initial advance at? Is it running rich? Vacuum leaks?
     
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  3. C0V3R

    C0V3R Member

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    Oh also, have you checked all cyclinders are firing?
     
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  4. latamud

    latamud Founding Member

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    You could always add a supercharger
     
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  5. NorCal66

    NorCal66 New Member

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    Is that 500cfm enough to keep up? Maybe you're not getting enough fuel.
    :shrug:
     
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  6. ratio411

    ratio411 Founding Member

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    Have you checked compression?
    You said in another post that you went from a 68 to 74 block.
    I don't remember the dates, but in the early 70s Ford added about .020" to the deck height on the 302. It was just 3 or 4 years, but that block would put your pistons further down in the block. If you started off with 9 to 1, then added 4.03" of .023" additional deck height, it seems to me that you would be down on compression.
    Just a thought.
    Do some research on that year block. I am 80% sure it had the taller block.
    8.206" 221-302 deck height
    8.229" early-mid 70s 302

    Dave

    Edit:
    I want to make it clear that I don't think this is you immediate problem giving you fits... but it well could be a contributing factor that will never go away after you fix your current issue.
     
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  7. 1320stang

    1320stang Founding Member

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    What's your 20? What do the plugs look like? Fire in all cylinders? if no vacuum leaks, it sounds like the cam is not installed right and your timing may show to be right but its actually off.
     
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  8. 390Fe

    390Fe Founding Member

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    Does the engine feel like it doesn't want to rev at all? Feel "flat"

    I agree, I'll bet you have a timing issue - timing chain off a tooth, distributor off a bit, cam 'retarded' when installed. That RV cam - is it a standard 302 firing order or is the the 351/HO 302 firing order?
     
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  9. oz

    oz Founding Member

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    I don't like the sound of that .023" of extra deck height but cars in the '70's had 8:1 compression and ran (not fast, but they ran...).
    Since your comp ratio is in question, the first thing to do is to check your compression (and leak down while you're at it) and get back to us.

    What year are the heads? If they are '74, then you probably have big chambers and increased deck height... = about 7:1 compression :doh:

    What are the specs on the cam?

    How did you tune the carb (vac gage method, tach method, etc)? Do you have the kit of needles and seats from Edelbrock for your model carb?

    What ignition do you have? Plug gap?

    Does the engine idle? It what RPM? Does it shake?
    How much vacuum at idle? Is it roughly constant?

    ...more info please.

    My newly rebuilt 302 (+.030", Speed Pro, stock '69 ported heads, Edelbrock Perf RPM, cam, intake & 600 cfm carb, roller rockers on studs, etc) felt like a dog first out too. I had a 2.5" exhaust put on it and that (to my surprise) made a big difference. I have been playing with the needles / seats to get a little more out of it. I still have the stock 2.79 gears so it's not going to be quick by any means until I change them to something more reasonable.
     
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  10. 66P51GT

    66P51GT New Member

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    I agree with the others. You either have a timing issue or compression is low.

    I've created an Excel spreadsheet that determines Static and Dynamic compression ratios. Static is a good baseline but Dynamic is a better indication on how much compression you have since it is based on the camshaft and the Intake Closing Point ABDC. You will have to refer to your camshaft specification card to determine the degree offset At Bottom Dead Center (ABDC).

    Only modifiy the bold fields to determine your compression. The "Boss Rod" column is for the engine I am currently building.
    Compression Ratio Spreadsheet. Enjoy!

    Make sure your total advance is at or near 36*. If you have a vacuum advance, make sure the diaphram isn't ruptured. Timing makes all the difference. When I installed my MSD, i ran the stiffest springs and the engine was a dog. I swapped the springs to get a quicker advance curve and behold, the engine never felt more powerful.
     
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  11. crushnut

    crushnut New Member

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    I had the intial at about 10, but now im not sure what it is because i adjusted it so i would get the best vacuum about 18 inches at idle, and when i put it in gear it drops to about 14 and the needle is kinda shaky. I dont think it is running rich, but i will check my plugs anyways and that all cylinders are firing. Also will check for vacuum leaks (around the base of the carb and intake front and back, the rpms should increase if there is a leak, right?) Ive been told that 500cfm is plenty. The taller deck height is interesting, i didnt know that and the machine shop didnt say anything about it. The heads are 1966 54cc chamber heads.

    The engine does feel flat like 390Fe said, i thought i installed the cam/timing chain properly, but maybe i didnt. The cam has a standard 302 firing order. I can do a compression check and get back to you guys with the results but i dont have a leak down tester, is it really important to check that also? The carb was kinda tuned with a vacuum guage, tach and what some people on here told me to do.

    The cam specs are:
    Cam Lift, Int-.281, Exh-.296
    Valve lift, Int-.450, Exh-.474
    Lobe ctr, Int-102, Exh-116

    Adv. Duration, 280 Int, 289 Exh.
    .050 Duration, 204 Int, 214 Exh.

    Its a pretty small cam so i dont see why i would be having problems with it :shrug:

    I had a Pertronix Ignitor with stock plug gap. The engine does idle, but not very well when cold, but gets better when warmed up. Rpm at idle is about 800+-, 18 inces of vacuum at idle (with timing probably way advanced) and 14 with a shaky needle in gear.

    I hope this is enough info :) I will check the things you guys mentioned and get back to you. Thanks :nice:
     
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  12. crushnut

    crushnut New Member

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    Thanks, but i dont have Excel, do you know where i can get it without buying it? Im cheap :)
     
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  13. blascrw

    blascrw Member

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    Excel viewer

    you can get an excel viewer from MS go to microsoft webpage and do search for excel viewer
     
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  14. crushnut

    crushnut New Member

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    Yeah i downloaded that, but it is only a viewer you need the full program to edit and change the fields to use 66P51GT's spreadsheet.

    Thanks anyways
     
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  15. 66P51GT

    66P51GT New Member

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  16. 66P51GT

    66P51GT New Member

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    #16
  17. crushnut

    crushnut New Member

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    According to the calculators i have approx. a 9.6:1 static and 9.2:1 dynamic :shrug:
     
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  18. ratio411

    ratio411 Founding Member

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    That cam you spec will actually increase compression...
    Not static, so I must be thinking dynamic.
    The technical term is that is a cam that builds 'cylinder pressure'.
    Dave
     
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  19. 66P51GT

    66P51GT New Member

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    Dynamic compression is a better measurment for engine building because it takes into consideration cam timing and overlap of the intake valve. This overlap has the effect of shortening the stroke.

    E.g. - If you have a 3.00" stroke and have an intake valve overlap of 34* ABDC, it has the effectiveness of shortening the stroke by .187". This is the distance the piston will move up into the cylinder wall while the intake valve is closing on the compression stroke. On a 4" bore, this translates to ~38cc less air in the combusion chamber.

    Formula for determining Effective Stroke (in the spreadsheet link above):
    SE - Effective Stroke
    S - Stroke
    R - Rod Length
    A - Angle in Degrees ABDC
    SE = (S ÷ 2) + R + ((S ÷ 2) × cosA) - SQRT ((R2) - ((S ÷ 2) × sinA)2).

    Through my research, dynamic compression is always lower than static. You can't increase dynamic compression by changing the cam. The only way I know of increasing dynamic compression higher than static is to add a Turbo, Supercharger, or NOS.
     
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  20. 66P51GT

    66P51GT New Member

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    To address your statement...
    I think what you were saying is that cams affect dynamic compression. Since the one specified has a low overlap, this cam will have less of an influence on the loss of dynamic compression?

    Static - Dynamic
    9.5 - 9.3
    vs. a high overlap cam that may be more like
    9.5 - 8.9
     
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