Shouldn't my engine Rev higher?

Discussion in 'Technical' started by ESampson, Nov 14, 2014.

  1. ESampson

    ESampson Member

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    Well it's a Decent little 347 with 180cc RHS heads, 650DP (switching to a 750 next season to see if i pickup any ET) Performer rpm intake, msd ignition/dizzy. The cam is a XE294 which is a 2800-7000 powerband Duration @ 50 is 250 intake and 256 exhaust valve lift .554 & .558 lobe lift 347 & 349 with 110* lobe speration. i have all the matching parts that go along with the cam, what would cause my car to fall flat at 6400ish and start to get valve float? shouldn't i be able to take this thing past 7000, even if the power starts to drop off?
     
  2. aussie maverick

    aussie maverick Member

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    I have a similar set up to this, using a stage4 trickflow with 592 lift. 3000-7000rpm range. This cam was designed for 5.0 so in saying that you can take off a couple of hundred revs(compensating for the longer stroke). Mine was falling over at 6400.....until I dyno'd it and found out my taco was 1000rpm out! Oops... Power curve peeked at 5800 and stayed level through to 6700
     
  3. Bryant

    Bryant forgot more than learned

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    the larger displacement of the stroker kit will move the same amount of air as a 302 at a lower rpm. the cam and intake advertised rpm band is based on a 302. so a 347 will run out at a lower rpm.

    i dont know if it will fall off 600 rpm earlier but it is a factor. were the valve springs installed heights verified for the cams requirements?
     
  4. ESampson

    ESampson Member

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    they were ordered as a matching package from compcams, i only checked part #'s once it arrived, then i went ahead and just put it all together.
     
  5. aussie maverick

    aussie maverick Member

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    When you say you just put it together, I assume that you did dial the cam in? The 5.0 cam won't have a difference of 600rpm
     
  6. ESampson

    ESampson Member

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    I had the shortblock assembled at a shop because of the stroker kit, rods only came semi-finnished ect. i put the heads together for this one..the last one that blew up, i put together lol. if they didnt "dial in" the cam, could this cause it?
     
  7. aussie maverick

    aussie maverick Member

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    It could, and probably would, but if it was a reputable machine shop, I'm sure they would have dialled it. It may still pay to ask them.
     
  8. ESampson

    ESampson Member

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    i went to my box of recipts and checked to see what they charged me for...nothing on it about degree'ing the cam...so could this really be the issue? the last thing i want to do it pull my motor and degree it....i'd assume if they didn't degree it, it would be installed "straight up"
     
  9. Bryant

    Bryant forgot more than learned

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    just because the springs were recommended for the cam doesnt mean you can just install them. you need to check the installed height on the heads.

    it could be the cam not being degreed properly or not enough spring pressure to get past that rpm. i would expect the cam being in wrong would not limit the rpm it can rev to. the valve springs not being installed at the correct height can easily lead to valve float and that will limit rpm.
     
  10. 71gold

    71gold Frank Cooper Supporting Member

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    I would look at the valve springs...(valves floating).
     
  11. groberts101

    groberts101 Member

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    The simple fact of life is that cubic inches ALWAYS eats up cam duration. Put that same cam in a 427 windsor and watch another 4oo rpm fall off the top.

    Things that can work against you for extending power past peak rpm.

    1. Too much ignition lead can easily make a motor fall over faster past peak power.
    2. Not enough air flow for the cubic inches/rpm. Slightly smaller than required carb, dual plane intake, and wrong air filter base combined with too short/restrictive of a filter element.
    3. Not enough exhaust flow for the cubic inches/rpm. Street style headers with small'ish primaries/collector size along with chambered mufflers(INCLUDING unpacked mufflers like flowmasters) and/or too long of a collector/too many bends/too small a pipe all add up to snuffing out a top end in short order.
    4. Unported 180's are marginal for the rpm's you're shooting for here. 200+ cc heads would be best and porting those heads would give you power everywhere. Especially up top on a stroker motor. Conservative estimate would be in the range of about 25 horse.
    5. If you have steel retainers?.. move to titanium ASAP. Same springs with Ti retainers will feel like you upgraded the springs with another 200-300 rpm for the money spent. Heavy(large diameter) springs and steel retainers can lead to spring surge well before valve float sets in. Surge will kill rpm without giving you the tell tale signs that float will. Kills springs faster too.

    My suggestions. Take some total timing lead out(those RHS's chamber shouldn't need much more than about 38 total and you might even try 36 to see if you gain anything on top. Uncork the exhaust. Take off the air cleaner.
     
  12. 71gold

    71gold Frank Cooper Supporting Member

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    would any of this...float the valves...:huh:
     
  13. 71gold

    71gold Frank Cooper Supporting Member

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    would any of this...float the valves...:huh:
     
  14. groberts101

    groberts101 Member

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    I thought that #5 above clarified potential problems but how did we come to the final conclusion that he's floating them?

    It could be a little bit of.. all of the above.
     
  15. stroker mav

    stroker mav Member

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    what was your et and mph with that combo?
     

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