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biggest cam for stick 305!!!!!

I love my Chevy Chevette!
Posts: 1
Joined: 03/05
Posted: 03/26/05 08:26 PM

does anybody know what the biggest cma for a 305 is with out havin to change valve springs or a stall cuz i out a 280 intake 510 valve and it runs but its just lackin fuel at idle and i caint lower the timming enough with out it dieing .should i get a power chip or a powerprogrammer or something help!!!  

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I mow my lawn and find Chevys
Posts: 1985
Joined: 10/03
Posted: 03/26/05 08:58 PM

even though from your first impression you really sound like i shouldnt respond, i will

why are you camming a 305? 305's are not performance engines, when GM built the 305 the last thing in their mind was performance, if you have a 305 powered car, leave it as is and drive it for the good gas mileage that they achieve, if you want a performance engine save up and get a 350 from a junkyard, and there will be much more possibilities

also trying to get the biggest cam in a engine will soon lead you to poor performance, i suggest getting some basic knowledge on the subject wheter it be from books, magazines, or any reliable sources.

with what you said you dont want to change valve springs and you dont want to change converters, well that takes your choice of aftermarket cams to about zero, especially valve springs is something that almost is required to be changed when camming a engine and if you want any sort of duration for top end power at all you will need to change your stall converter

more than likely the problem with your overcammed 305 is that it needs a overly rich idle to combat the drop in manifold vacuum also if its computerized this drop in vacuum might be effecting the MAP sensor and causing fuel problems, but i am not that informed on fuel injection, one more thing, cammed engines will need more initial advance, to combat the drop in cylinder pressure at low speeds, not less



Edited 3/26/2005 8:00 pm by GibTG  

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I mow my lawn and find Chevys
Posts: 1195
Joined: 08/03
Posted: 03/28/05 02:32 PM

OK Memphis88, you've gone and done it this time.

Actaully I'm guessing this is an 88 something or other. Knowing what this is could lead us to transmission type, gear ratios, tires and wheels, type of fuel injection. All these things come into play.

When I was a young fella the speed shop in the little Southern California town I grew up in had a banner that hung over the counter. It read, "Speed Costs Money, How fast Can You Afford to Go". It appears you've got yourself into the practical application of that statement, trust me we've all learned this one way or another at one time or another. The smart guys gave up and got married, the others became motorheads and plowed on through, married or not actually.

A 280 degree cam is a lot of cam whether its measured at .050 lift used by cam grinders or at the SAE position of .006 inch. This is a case of a wild cam or a really wild cam. The problem with wild cams is that while they really let an engine develop plenty of power, all that power shifts up the RPM range. This shift in the power band leads you into all kinds of problems from keeping the beast cool to wheel and tires that are speed compatible and a help move the overall gearing into the new higher rev range required by the engine.

If this is an 88 someting or other, you can pretty much expect its configured around low emissions and high fuel economy. That means computer controlled injection of some sort and ignition. It means low compression in the low thru middish 8 to 1s. It also means a high ratio rear axle like a 3.08 teamed with an overdrive transmission such that the engine turns a rather lazy 2000 RPMs at 70-75 miles per hour.

Your whomper stomper cam has now moved the torque peak from 2000/2500 RPM up to say 3500-4000 RPM. The fuel injection system has no way to know this, your off the fuel map and need some custom programming. Depending upon what you have roughly from 95 and older you'll need a new PROM chip in the computer. For 96 to the present you'll need to either reflash the computer memory or will require a preprocessor to get the fuel map and sensors talking again. This will put the mixture straight with operating conditions. The difference comes sooner for Corvettes and LT-1 Camaro/Firebird/Impala than other models.

But wait that's not all. The 8ish something compression is too low. These long duration, high lift cams hold the valve open a long time. They're designed to come on in upper rev ranges by using the developing gas inertia within the intake and exhaust ports to "supercharge" the cylinder. Really pack'n those air and fuel molecules in there. The down side is at low RPM there isn't much gas inertia so large portions of the incoming charge either leak past the exhaust valve during overlap or get pumped back into the intake tract with the late closing intake valve. Yes this happens with port injection and the latter reversion even happens with sequential port injection. To overcome these two occurances the calculatable or "static" compression ratio needs to get boosed to around 10 to 1 and the advance needs to come in sooner to help make up for lost bottom end torque. Advance ain't quite that simple, books can be written on this subject.

The gas inertia thing and the compression thing lead you to gear ratios and that includes wheels and tires. The engine wants to turn faster to get up into it's torque peak RPMS when the vehicle is at cruise speed on the highway. That means for example the 3.08s come out and 3.5, 3.7, 4.1 to 1 something on that order go in. Kiss your gas milage goodby. The gears lead back into the computer programming, etc, etc. 

See how this goes, it's a system a change anyplace in the system demands a change in all the other places. It costs a lot of money, time and effort. Some one suggested that you replace the 305 with a 350, your right back here, maybe a different spin, but simply putting in the larger engine sends you into the computer, etc, etc. All with a bit different spin, but mostly the same bases.

--- and we ain't even delt with a high stall converter, high flow exhaust and cats, not to mention all those other parts that bust under higher loads and speeds like the transmission, U-joints, rear axle, mounts, springs, shocks, etc, etc.

So we're back to  "Speed Costs Money, How fast Can You Afford to Go". Pity, some of us class this as fun. Best of luck, stay in touch.



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I have an SS396 tatoo
Posts: 270
Joined: 08/04
Posted: 03/29/05 08:15 PM

If you are gooing to swap cams you should always consider new springs. Even if you are useinf

g the same amount of lift. It does no good to go to a long duration cam only to have the valves float at 4000 rpm . It has ben done before .


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