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Old 08-11-2010, 12:57 PM
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Quote:
Originally Posted by oldbogie
My SCR calculator (static compression ratio) gives you 8.6 to 1 with flat tops and these heads with a zero decked block and .019 gasket. My conversion to DCR dynamic compression ratio gives you a useful ratio based on intake closing point and what that does to mixture density is 6.4 to 1 which is way low, the DCR needs to be around 8 to 8.5 to one. The Fireball 290 is an old design cam with too much overlap, a very late closing intake combined with relatively low lift. You really have to be careful of pistons as has been mentioned, there are short deck pistons designed to maintain stock compression with decked blocks, if you have a set of these the static compression is in the sevens or less.

A quick and dirty improvement could be to advance the cam you have from 4 to 8 degrees. You need to check for cam to valve interference before firing the engine but with the low lift that's probably not going to be an issue. This cam has a nasty sounding street idle but in the big picture is no great shakes as a performance item, it has all the bad features (rough idle, weak torque curve) and few of the good ones (top end power output). Actually you intake and carb selection are pretty good considering this bump stick.

The carb's small for this combo and the Performer leaves a lot of power on the table, the Performer RPM is a much better unit. The carb and intake you have really aren't a problem till you wind this up and this doesn't sound like it was built to wind high so changing them right now is a moot point. If you change any of this start with the intake not the carb.

I don't understand what you're saying about the ignition timing, my first impression is that's it's well F'ed Up, but that comes from my intreperation of your description. Some questions to help me;

What is the static setting in degrees?

Does it have a vacuum advance? If so how much advance for how much vacuum?

Sounds like it has a centrifugal advance, that brings the question as to how much? When does it start in RPMs? What is the rate of increase in degrees per 1000 RPM?

Do you know how much total advance there is when it's all in, that is measured degrees against RPM not guesses and not some brochure data, but real measures.


Recommendations:

I'd start with advancing the cam from 4 to 8 degrees. This results in ending the intake cycle sooner against crank degrees which will help the bottom end but hurt the top. Then! Them heads gotta go, you spent a lot of money on those things making a silk purse out of a sows ear. They're now just a shiny expensive sow's ear that's as useless as before. And give me some real ignition timing data. This cam makes for a weak cylinder charge on the bottom end it takes a lot of compression and ignition lead to overcome at least some of that. Cut back on the octane to see if you can get this thing to ping, the fact it doesn't isn't telling me what I want to know. Don't worry for a street engine it takes a lot of pinging to do any harm.

Make one change at a time and test, don't rip it apart and do a bunch of stuff then hope it all works, then you never know what did and didn't work for it.

Bogie
Ok, Thanks everyone for the input and opinions let me start by trying to answer some of the response questions.

(1) Yes it is a close ratio 4 speed winds out in 1st gear about 55 mph with a 3:72 posi.

(2) It is a Zero decked blocked but is not using short decked pistons it is using the actual factory .60 over forged replacement pistons.

(3) The 290H Cam was picked due to its nasty sounding old school street profile along with the fact Cranes profile and tech's assured me i could get some low end grunt with it.

(4) The car pulls real strong from 3k rpm on to about 5500.

(5) the intake is the performer rpm sorry i left that part out.

(6) Timing static is 18 degree BTDC +4 cam advance and the mechanical advance is factory +20.

(7) Advance is active at 850 rpm from off idle ,All in at 3200 rpm for a total of 42 degrees BTDC.

(8) There are no headers just factory logs into a 2.25" magnaflow system true dual from logs out.

(9) This a Non A/C Car so no accessories other than water pump and alternator.

****Anytime you turn the car off you smell gas--NO LEAKS or DRIPS--And you always have to depress gas pedal one time prior to starting cold or hot***

PS---Anybody has a good set of small block heads etc that WILL help my cause i have a bunch of Mk IV BBC I MIGHT be interested in trading some of it--stuff like Ross forged 51cc .60 over Pistons, Trw hyperkin .60 over, Edelbrock 7075 polished with bird catcher top, BBC Dimple rods,1971 factory replacement rectangular port heads bare castings plus manley ss valves and crower springs-plus other stuff was going to build for this car BUT think going to stay SBC....
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