What's the largest lift cam I can put in a 289 with stock heads/pistons? What if I put different springs in the heads? 
How big?
- Thread starter 1967coupe
- Start date
I think the biggest factor in lift is compresson, you cant run much lift at all with out a hefty amount of compression. And the biggest lift doesnt meen much, its not like its directly related to horsepower. You need to concider the rest of the cam too. I have a mildly hoped up 289 with around a 9:1 CR, im running a 480 lift isky cam ( not to shure on the duration) but im aound 260hp and 280 ft/lb. My best advice would to look up some engine builds simalar to what your shooting for and see what kind of cam they are running, ask some one at a good machine shop, or just call the cam company and ask!
Good luck!
P.S. your going to want a valve train to match, especially new springs!
Good luck!
P.S. your going to want a valve train to match, especially new springs!
NorCal66
New Member
Well...I'm running a .496/.520 lift cam on my 302. As far as I know (what the PO said) I have stock pistons and compression as well. Maybe THATS why it feels sluggish sometimes lol :damnit:
Clears though if that's your question...stock rocker arms as well.
Clears though if that's your question...stock rocker arms as well.
I think the compression issue is pinging. If you have a weak CR then you need race gas, around 520-530 lift is max for stock CR. My 351 im building is in the 9.2:1 area and max would be like 540 I think? (went with a 519 524 lift) But with some beefy springs. My 289 was pretty sluggish too but fattened up the secondaries and lost that problem. Allthough my gas mileage went down the crapper!
I guess what I'm getting at is I would like to have approx. 300 hp (flywheel) with the stock heads. I already have the Air Gap intake w/600 carb and a good exhaust. I plan of getting AFR 165's in a couple of years but I don't know if I should wait to get a different cam then (probably the RPM) or if it would work with what I have now.
NorCal66
New Member
If you plan on 300 on stock heads you're going to need them ported. With a high lift cam and good flowing intake, the heads are really going to slow you down by not letting the engine breath enough. That's the problem I have right now even though the stockers are ported and polished to hell.
I also had problems with my stock head now flowing enough. I found a pair of 4v 289 heads and spent too much on them and was still dissaopointed with the result. I wish i would have waited and just bought some aluminum head. The cost difference wasnt that much. If you really want to get a little more put a small shot of nitrous on it. I ran a 125 on mine with stock piston and when i took it apart to replace head there was no pits in the pistons.
LMan
Founding Member
a hot cam with stock heads is a waste of time and money. You will be disappointed -in all likelihood you will run slower than before, with less driveability.
Head work comes with or before a cam change, IMO. Port the stockers, oversize valves, good headers (full length/Tri Ys, if you can get them in) first. Alum heads are great if you can afford them and the valvetrain they require.
The cam has nothing to do with CR. Thats a function of the heads, cc's, stroke, bore, etc. It DOES have everything to do with piston-2-valve clearance, however. My 10.5:1 motor stays the same CR no matter what cam is in it.
I would look at, minimum, a porting job (most of the cleanup you can do yourself, save 100s of $) and better valves, combine with a slightly hotter cam, IF your exhaust is up to snuff. Remember, if you cahge heads entirely your CR may very well change due to cc diffs between the heads. Also, oversize valves dictate that you check the P2V clearance before reassy.
Head work comes with or before a cam change, IMO. Port the stockers, oversize valves, good headers (full length/Tri Ys, if you can get them in) first. Alum heads are great if you can afford them and the valvetrain they require.
The cam has nothing to do with CR. Thats a function of the heads, cc's, stroke, bore, etc. It DOES have everything to do with piston-2-valve clearance, however. My 10.5:1 motor stays the same CR no matter what cam is in it.
I would look at, minimum, a porting job (most of the cleanup you can do yourself, save 100s of $) and better valves, combine with a slightly hotter cam, IF your exhaust is up to snuff. Remember, if you cahge heads entirely your CR may very well change due to cc diffs between the heads. Also, oversize valves dictate that you check the P2V clearance before reassy.
...hehehe...what they said...hehehehe
Really, you can get a huge-lift cam to fit without piston-to-valve clearance issues on a stock motor. So big (for those heads) in fact that it will hardly run at all. In addition to total lift you need to look at the duration as well to judge the performance of a cam, many have long duration with low lift or vice versa.
Really, you can get a huge-lift cam to fit without piston-to-valve clearance issues on a stock motor. So big (for those heads) in fact that it will hardly run at all. In addition to total lift you need to look at the duration as well to judge the performance of a cam, many have long duration with low lift or vice versa.
Not entirely true. While the cam choice does not affect the static compression ratio, ie the one calculated using head cc's, piston cc's deck clearance etc. It does have a enormous impact on the compression that the cylinder actually sees. A high lift/high duration cam can actually bleed of some of the pressure in the cylinder prior to the powerstroke, thus cars with huge cams will oftentimes have a lower measured compression PSI, even though they have a high static CR. I posted a graph of valve lift vs crankshaft degrees a while back that shows what i'm talking about, it should still be up.
brianj5600
Active Member
Agreed. You can see a sizable power gain with a cam change and stock heads. Too much duration and valve opening timing can bleed off cylinder pressure. The intake you have probably wants more duration than the engine can tolerate with stock compression ratio. A cam company can help you with selection. If you have a stock cam there is a ton of room for improvement. Let your favorite cam company pick it and don't look back. Anything they pick will most likely require new springs. They can be changed w/o removing heads, but if you pull them they can be milled. The cost adds up quickly though. It will sound nice too.
NorCal66
New Member
I'll just give you a little more on what I have since that's pretty much the disucussion at hand: big cam and small heads. My cam should pull good through 6500rpm, but the heads just don't flow enuff. From 2500-4000 or so it screams and hauls ass, and even off idle it will roast em no problem and pin you back to the seat, but after like 4500 or so it runs out of steam big time -doesn't flow what's needed. It's fun for short little bursts but would be useless on the strip. It's very streetable however in my opinion...
Anyways good luck, and I'd just go with your current plan, wait on the heads first.
Anyways good luck, and I'd just go with your current plan, wait on the heads first.
