|12-19-2011 01:22 PM|
|12-18-2011 11:05 AM|
here is a low compression 454 on the dyno.
|12-18-2011 05:53 AM|
Cranking PSI isn't a very good indicator of how an engine will perform. Wear and ring/valve sealing aside, a radical cam will tend to pump lower than a stock cam but will have much more top end power. A tactic that has long been used by some engine builders is to change the cam timing in relation to the crankshaft in order to get the highest cranking pressure. This isn't a cure for a poorly selected cam, but could help, regardless. I repeat could help- there are a LOT of things that enter the picture so this is not an absolute by any means.
One reason overlap/LSA is mentioned in regard to cylinder pressure is because the intake closing point is not a spec that is as 'advertised' by the cam makers in their ads or in brief catalog descriptions. But it stands to reason a cam w/long duration at 0.050" is going to have a later intake closing point than a shorter duration cam, all else being equal. Hence the connection between the two.
What a lot of overlap/tight LSA can do that causes a poor idle or "lope", is it tends to decrease the vacuum at idle and can add to reversion. Either/both of these things will cause a poor idle.
|12-17-2011 11:21 PM|
|streetbruiser||I stand corrected|
|12-17-2011 07:50 PM|
yes, torque and horsepower goes up with more compression. But be careful, BBC don't tolerate compression as well as a sbc.
FYI, valve overlap doesn't effect cylinder pressure, as the engine isn't trying to make cylinder pressure during this part of the 4 stroke cycle. The intake closing point is what effects dynamic cylinder pressure (what you would measure on a compressing gage). And a "longer duration cam" will tend to have later intake closing point, the extra overlap is often wrongly accused of reduce pressure as more overlap typically accompanies longer duration cams.
Actually extra overlap can be used to increase torque (as in circle track engines). For example...Two cams with the same duration, but one has a tighter LSA (more overlap), will close the intake sooner in the compression stroke and develop more torque. Advancing the cam will have a similar effect.
|12-17-2011 09:48 AM|
|12-16-2011 10:48 PM|
|streetbruiser||This is part suggestion and part question. If you ran a compression test and it reads less than 140 you probably aren't making good power; too much overlap of valves being open suggesting you either increase compression or go with a smaller cam. What do some of you other friendly car guys think of this diagnostic strategy?|
|12-16-2011 10:32 PM|
say you had a 425hp engine with 10:1 cr, Then dropped the compression ratio down to 8:1. Then the engine would lose 6.5% power or 27.6hp in this case.
Shortening up the mechanical advance slot and running a lot of initial ignition timing helps low compression engines gain more throttle response. What does your timing curve look like?
|12-16-2011 06:53 PM|
|starnest||Good natured ribbing is the intent.|
|12-16-2011 04:13 PM|
|12-16-2011 01:54 PM|
It sounds to me like you are satisfied with the performance you're getting from the motor, so I have no further suggestions concerning that. I don't have enough basic information to make an intelligent suggestion anyway. Most fellows will start at the wrong end of the truck, adding pieces to the motor when they should be improving the rear suspension and installing gears and a locker together with wheels and tires that are chosen toward a goal. So, that would be the next thing I would work on.
I regret getting sideways with you, but you have just enough smart*** in you to get on my nerves. The guy in the Mustang may or may not have been on the loud pedal, but it's a moot point anyway. I can't respect street racing anyway. What I can respect is a timing slip from the dragstrip. That's where the rubber meets the road.
If, for instance, you were to make a quarter mile pass at 14.70/96, then changed some parts or did some tuning and went 14.40/98, then you have meaningful data.
There are many things I could teach you and you wouldn't have to take someone else's opinion on another forum about what cam to use, you could work it out for yourself. Either way, I wish you the best of luck.
|12-16-2011 01:27 PM|
|nfreas313||As far as the cam the one that I have is in the range that I have been told on many forums will produce a very torquey engine such is what I'm going for and that is why I chose it, it wasnt just a guess but what cam would you recommend?|
|12-16-2011 01:21 PM|
|nfreas313||And I give respect when it is deserved, and talking down to someone does not earn respect|
|12-16-2011 01:19 PM|
|nfreas313||If u wanna drive up here be my guest, ill outrun that in my gtp with a v6 lol|
|12-16-2011 01:18 PM|
|nfreas313||Torque wins races bud, that's why something with higher HP can lose to a vehicle with higher to a vehicle with more torque, and the mustang is a heavy *****|
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