Alright guys ive been reading through these forums trying to make an educated decision. Not having any luck. i would like to replace the cam in my 85 sport coupe. 305 q-jet. Not having any problems with the one in the car and the engine and car only have 85000 miles but i would like to generate more power and still claim the 305 ya know. the real question here is; am i kidding myself to think that i am going to put a descent cam in this thing and not get new heads? can i change a few things in the heads for a new cam? i dont want a 5.7 cause i know someone is gonna say just get one. no disrespect intended just would like to run 14.5 or so and say i did it on a 305

 

Just take my 305, it did a 14.39 in my car last year at a 3600lb race weight through a dana 60 axle. Anyway, the stock heads can only take about .450" lift for the retainers to hit the guides. My 305 has a 600cfm Edelbrock, Performer RPM intake, cheapy summit cam 204/214 dur @.050 .420"/.442" lift. Just for the hell of it, I slapped the blower on it and made a 12.7 pass on probably 9-10psi.

 

ya im kinda workin on a posi now with some ... i think 343's ???... but not sure anyway, ya i would like to put a descent cam in. i got plenty of breathing room i think ... hooker 2055's with hooker 3" cat back ... im looking at intakes too but the whole deal is i want to be able to run my stock q-jet with the new intake and so far only really found intakes that i would have to use an adapter for. so do i need to get any kind of specs or numbers or anything off my block before i go to purchase a cam or no? do i need to buy other parts for instalation? springs, rockers, rods??



thats 3.43 gear i guess sorry. still pickin this stuff up

 

Any cam for a small block chevy will fit. It'd probably be better to get new pushrods, rockers, springs, double roller timing chain, maybe scew in studs, but when I did it I just got the cam and lifter kit. Before I put the blower on, I put some better springs on for the boost, but still otherwise stock. The one I got is SUM-K1102. BTW, I remembered that before the cam the car ran a 15.0 followed by a 14.7 with the new cam.

With the gears, I'd hold off until you see what mph the car is capable of in the 1/4mile so you can get the best gear possible for the setup. To set it up for the best 1/4 mile time, I'm betting the combination will want a 4.11 gear. This gear should get you spinning 5300-5500rpm through the traps at 94mph.

 

i think gm puts a torque converter that stalls at 2200 to 2400 rpm stock on a either 91 or 92 s-10. would that be an acceptable torque converter or am i just wasting money on something that i will need to upgrade later.

also will changing the cam take away the cars ability to advance itself correctly. cause that is computer controlled right? not real sure maybe i dont know what im talking about but figured id ask

 

GM puts a torque converter stock on every automatic.

 

ha ha. ya i hope so. no i was just thinking that torque converter in particular would bolt up on my car. and if i buy an aftermarket torque converter for my car that stalls at that rpm, seems like im gonna be paying a lot more for it. kinda seems like a good deal. brand new for 130$.

 

I'd go for a 3000 stall if you even get one, but it's not really needed. I had a 2000 stall with mine, which is almost stock and it was fine. Just saying if you even bother with a converter, go at least a 3000 to have room for future stuff; plus it should make it launch harder reguardless of cam. BTW, you want to get a lock-up converter if your looking for one.

 

how do i know if i need a flat tappet or roller cam? there is a big difference right? all cams are pretty much manufactured the same way right? so i dont need to go with some big name brand, or does it make a difference?

 

Sometime in 1987 the started putting hydraulic roller cams in motors, so yours being an 85, assuming a factory stock motor, would have a hydraulic flat tap.

 

cool thanks. i know this is a lot of questions but how do i know how much lift, lobe, duration, seperation (and some other high speed terms) my engine has or i guess will happily except?

 

I don't know any duration numbers as those are more difficult to measure, but I believe my stock cam had .390 lift or less, might have been even .365. I still have that cam and lifter set sitting on a shelf somewhere that I wrote lift numbers on.

 

so more lift more compression or less lift more compression or do they even go together? more lift you have to have bigger chambers in the heads or something right?

 

Lift, static compression and chamber size have nothing to do with each other.

 

The more duration and lift you have, the more power you're going to make. The duration pretty much determines where the power band will be. Like the 204/214 duration cam makes peak power around 5500rpm give or take some depending on size of motor. Now the cam that's in my 383 is 264/271 duration, and thus makes peak power at 7400rpm. The lift of the cam is a good factor for how much power it can make, to a certain point with all SBC heads but we'll ignore that for now. The heads will flow more air with the valves open more, again to a point, so the more lift the more power. The problem with huge duration is that it makes for crappy dynamics of the motor when idling and what not. So, as can be seen with newer motors like the LSX motors, they try to run a low to medium duration, but lots of rocker arm ratio up to 1.8 or so instead of 1.5. That way they have a cam with the same say 204/214 duration, but instead of .440" lift, they get around .600".

With compression, again it's a more=more power. Usually this means running a smaller chamber head or a domed piston. The quality of fuel is the limit here; too much compression and the air/fuel mixture gets hot enough that it blows up on its own usually before the spark plug tries to explode it. That is where big problems happen like engine parts outside the engine.

 

ok cool so like there is really no limit to the cam you put it, you just have to be smart about it and not put to much. ok so these cams all come with lifters. so that is because i have to replace my origional lifters with the new ones for airflow? and the ones that come with the cam will complement it the most correct? hmm so should i buy rockers to help match the cam or should i just settle for what my stock heads can take? if i got new rockers i would need new springs too right?

 

There are limits to the cam size, sometimes people have to machine their pistons so the valves don't hit them. More cam also makes for less actual compression. If you have 2 identical motors except for cam size, and did a compression test, the smaller cam motor would read more psi. Once both motors reach their respective power bands, the compression is probably about equal, but the smaller cam will have more low end power from the higher cylinder pressures there.

Not all cams come with new lifters, but you do need new ones as they wear individually to each lobe on the cam. On flat tap cams like that there is actually one side of the lobe that's taller so it grabs the lifter harder on a side and spins it. This wear characteristic is why a good proper break in is crutial for flat tap cams. I'd just leave the stock rockers in there, but new ones wouldn't need any different parts anywhere else unless you go for a 1.6 or higher ratio instead of the standard 1.5 ratio. Each cam usually has some part number for the recommended spring for it, and is also a good thing to follow. If the spring isn't strong enough, it might not be able to close the valve fast enough resulting in loss of power and possibly a bent/broken valve if it is weak enough. Too much spring pressure though, and the cam will wear out quicker.

 

ok cool. would i get any more power out of my new cam if i were to put full roller rockers on? or would the amount of money i would be spending outweigh the benefits if any? so where do i find out what exact measurments are on my cam now do i have to pull it apart or can i look at some kind of code or something?

 

Someone probably knows where to find the cam specs from some option code or something, but I'm not too good with that. I just measured my cam when I took it out. You can measure valve lift from the rocker, just have to cycle the motor a few times and bleed out the oil in the lifter to get it accurate. With the cam out, just measure the difference in diameter from the skinniest part of a lobe to the widest/highest point of that same lobe. Take that and multiply it by rocker ratio to get valve lift. So a cam with .450 valve lift will have a .450/1.5= .300" tall actual bump on the cam, now if you were to multiply that by 1.6 this same cam would make .300x1.6= .480" lift and slightly more duration. Or you can multiply the given valve lift by 1.06667 to get the 1.6 ratio lift when given a 1.5 ratio lift.