Hey guys, here's a quick brief of my build...

Roller block, fresh 383, edelbrock performer heads, Comp cams 08-501-8 roller cam, ported lower base, ported upper plenum, slp runners, headers, msd distributer, etc... Everything new, 10:1 Comp Ratio...

Here's the link to the cam...

http://www.summitracing.com/parts/CCA-08-501-8/

I originally wanted 1.5 or 1.52 full roller rockers, but I'm a fan of buying stuff second hand since it's easier on the budget. I see some great deals on 1.6 ratio rockers left and right.

I know my springs will handle it since it's a modest cam. And I'm pretty confident I won't have piston to valve interference with the larger ratio rockers. I'm building the motor as a torque grunt with the cam working between 1200 and 5200. I'll be mainly looking for power between 1200 to 3500, I don't plan on revving higher than 4000 ever.

How will running 1.6" rockers effect my build? I know it will give more lift and a slightly greater duration, but I don't understand exactly how it effects my goal powerband...

 

If you want it to peak at 3500 and shift at 4000, which seems laughable to me, then why the heck did you go so big on the cam? And why those heads?
Yes, get the 1.6:1 rockers, but then change the cam to the 08-407-8.

 

Haha hey now that's even the cam that you suggested back awhile ago in my build! Maybe it was worded differently or something, but it's almost the same as one of the torque monster 383 in Atilla's engine building library just with a different LSA.

I appreciate the input however I already have the cam so I'm not going to go backwards in the build. I just don't have rockers now and I see there's always people selling 1.6 ratios but not 1.5 ratios.

Will running 1.6's hurt my build? I'll admit I don't know all the ins and outs of rocker arm ratios. Running 1.6s increases valve lift, and slightly changes the duration. However I don't understand how this will effect me. Air will be moving slower into the cylinders since it's more volume of air? And this would increase HP but take away some torque??

 

The extra ratio gives you extra "window" area, so you get more cylinder filling when there's adequate draw. Being a 383, there is adequate draw. The new effective intake closing is only 1 degree later, so it only extends the rpm range by 100 rpm. However, you're effectively gaining 2 degrees of overlap, which that 383 will really like.
Bottom line: more torque in the mid-range, with slightly better top end.
And thanks for pointing out my consistency, it's good to know. I had forgotten that we had already gone over the cam.

 

By the way, you really should consider Hedman 1.625" long tube headers, preferably ceramic coated, at least on the inside.

 

Thanks for checking back in. That description was great. I felt it would do the 383 decent without killing any low end. Just wanted to double check my intuitions... Got a set of Comp cams 1.6's on the way

I'll put a set of calipers on my headers and see what the ID reads. Good point on the header upgrade with the better breathing engine.

Thanks for your help. Hopefully someone will come across this in their search.

Now I just have to get the pushrod length measuring tool and get the idea push rod length since there's so many variables in the build so far.

 

There's another clearance issue that so many people forget about. The heads need to be set up for the higher lift. That means the springs need at least .060" between the coils at full lift plus the bottom of the retainer can't hit the top of the valve guide/seal at full lift. The distance from the pedestal to the valve tip won't change so to get the higher ratio, the pushrod is located slightly closer to the pedestal. The pushrod slot through the head needs enough room for this relocation. Most aftermarket heads don't have a problem but production heads may need to be clearanced.

Technically, going from a 1.5 roller rocker to a 1.6 roller rocker will only give you about 5 more HP. It's not uncommon to do half a swap. 1.6 rockers on the intake and 1.5 on the exhaust. It depends exactly what kind of performance you're looking for. Could be why you usually see 8 rockers for sale. Doing a ratio change is a poor mans cam swap. You'll get better results with a cam ground to what you want.

You can change your rpm powerband around by changing the cam timing. Advance it for more bottom end, retard for more top end. You'll see many street cams with built in advance since they generally operate at lower rpm ranges. Drag cams don't have this build in advance because they operate at high rpms but they can still be installed advanced, retarded or just straight up. Changing the cam timing 4* can move the powerband a couple of hundred rpm. More than 4* and you need to really check piston to valve clearances.

 

Thanks for posting. The Elderbrock heads have only guideplates not the smaller rectangular port like factory heads. But I will be double checking that when I get the pushrods in. Same with the valve springs, they say it's good up to .600 of lift, so I should be fine there.

When you say built in advance are you talking about it's actually ground into the cam or are you talking about when you clock the timing chain gears at 4* increments? Do people still bother advancing the cam via the timing chain set since the electronic distributor and programming can take care of all the timing one will needs anyways? If they do, howcome?

 

Built in as in ground into the cam. If you take a cam with 4* of built in advance then advance it with the gear another 4 then the cam timing is 8* advanced.

Cam timing and distributor timing is not the same. Cam timing is when the valves open and close. Distributor timing is when the plug fires in relation to the piston and camshaft position. Cam timing can be affected by worn parts such as the timing chain. If the valves do not open and close where the cam card says they should be then the cam isn't going to give the same performance it's intended for. You can fine tune the cam performance by changing the powerband window as mentioned above.

 

i just came across this in my search, very useful you are right.