azpetewave

I am building a 351W for the street (aggresive) but I cant decide which cam to use. I am looking at the Comp Cams xe274 (.519/.523) or a Comp Cams XE284 (.541/.544). I have a an Edelbrock RPM Air Gar Intake manifold (1800-6500) and World Products Windsor Sr. Heads Cast Iron (200cc Intake, 2.02/1.60 Vavles, and 64cc Comb Chambers). What should my compression ratio be? I was thinking (9:1 or 9.5:1) for mostly street use and cast iron heads. Should I use 1.6 or 1.7 rockers? I'M LOST!!

azpetewave

Correction!! I am doing a 10:1 Compression ratio

Indy

I like your set-up!

Comp Cams should be able to recommend a compression ratio for each of those camshafts. IMO, 10:1 compression is plenty for a pump gas street machine! As far as the rocker ratio... increasing the ratio over the stock 1.6's (which is what manufacturers will spec the theoretic valve lift at) will change lift and duration of the cam (you prolly already know that). However, going to the 1.7's may create some unwanted valvetrain instability in the upper RPM's. Mind you it looks like you're set-up is staying below the 6500rpm mark. Also, 1.7's might be a little more work to correct the valvetrain geometry. I'd stay with 1.6's cause those cams already "got it"!

I think both of those cams are pretty sweet... idle quality on the XE284 may be a little rougher that the other (may be marginal). I would pick the one which best matches your intake and cylinder head operating range, even if it is not the "larger" cam.

However, these are my opinions only. Good luck! Keep us posted!

Indy

azpetewave

Thanks Indy, I think you are right. Since the xe284 cam is good betweeen 2300-6500 rpm and my intake tops out at 6500 rpm it is kinda pointless to have a cam shinning at 6500 and an intake manifold dying at 6500 haha. I will go with the smaller xe274 (1800-6000) with 1.7 RR. I think that will be a much better street setup. But i will definately call Comp Cams to double check but i think i am on. thanx again.

Indy

So... If you go with the 1.7RR on the XE274, your valve lift will actually be .551" intake and .555" exhaust! So you see now, the XE274 cam combined with the 1.7:1 rocker arms (instead of the 1.6:1) you will be creating higher lift than the XE284. You will also effectively increase the camshafts duration (you would have to ask Comp Cams by how much).

I'm not sure if you want to go with the XE274 + 1.7RR to create "big lift" numbers. Plus create some potential valvetrain instability. Also might be more work to figure out pushrod length to correct the valve geometry.

or;

Just go with the bigger XE284 camshaft and use 1.6RR?

or;

Find a camshaft that will give you the .551"/.555" lift and the duration you want on the 1.6RR.

Does this make any sense to you? I'm just thinking in terms of time and money, that's all.

Keep us posted. Good luck!

azpetewave

Ok I am getting this. I will stay with the 1.6's but how do you think the xe284 will act on the street? I have a toploader 4 speed manual.

Indy

Hey,

Unfortunately, I have no experience with this particular cam. But IMO, a 240/246 deg. duration @ .050 is not over the top by any means. So, as Comp Cams describes it, it will probably idle rough with a fairly low vaccum (maybe 10"hg or lower). Nothing sounds more like you mean buiseness then a "lumpy" idling cam! As far as drivability, with a 4 speed manual you will be able to control the revs in the operating range of the cam on the street (need to pass? downshift it!!!). You might need to change rear-end gear ratios to keep you cruising at around 2000 rpm.

Bottom line is... What would you consider streetable? Some people can tolerate more than others.

Anyways... Let us know what you go with. Good luck!

Arrid Extra Dry

both of those cams are good for street strip, look at the ford motor sports X cam and Z cam
they run good too

Arrid Extra Dry

just thought of this....
why dont you just build a 408, more power , and costs about the same as a 351 build
if you use good I beam rods, you dont have to do any grinding on the block, everything goes together just like a 351 does.

azpetewave

ACTUALLY I GOT A GREAT DEAL ON 302/ 347 STOKER BUILD UP AND I AM GONNA USE THE XE284 CAM. THANKS FOR THE SUGGESTIONS AND HELP!!