Help with cam choice
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Help with cam choice
I am looking to put a very mild cam in my LT1 while it is apart. I want it to retain the stock type idle so I want to keep the duration short. I am looking at the following 2 cams from comp cams, Can anyone explain to me the differences in how they might act? They look so close to me I am not really sure they wont run about the same. Will the idle on #2 still be smooth with the narrower centerline and longer duration intake? #1 is 210/220 500/510 on a 114 centerline. #2 is 212/218 488/495 on a 112 centerline. Thanks.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Longer duration with lower LSA means more overlap and so a lumpy idle, though I don't think even #2 would be lumpy. Actually I'm thinking you might want to go with a little more agressive cam.
To determine overlap look at the advertized durations (at zero lift) for each cam. Add the advertized duration for int & exh together, divide by 4 and subtract LSA to get the overlap. If overlap is 30-55deg you should have good power and a decent idle with a 350cid SBC.
For example the ZZ-9 cam has:
282/287deg-advertised duration
212/226deg-duration at .050"
.483"/.520"-lift
112deg-LSA
Here we have (282+287)/4-112 = 30deg overlap.
To determine overlap look at the advertized durations (at zero lift) for each cam. Add the advertized duration for int & exh together, divide by 4 and subtract LSA to get the overlap. If overlap is 30-55deg you should have good power and a decent idle with a 350cid SBC.
For example the ZZ-9 cam has:
282/287deg-advertised duration
212/226deg-duration at .050"
.483"/.520"-lift
112deg-LSA
Here we have (282+287)/4-112 = 30deg overlap.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Thanks for the formula. Using that formula gives me 21.5 for one and 21.25 for the other. This looks to be right in the middle of the stocker and the Hotcam which is about what I wanted to accomplish. It sounds like either one should idle nice and smooth. So once again I dont really see much difference.
I appreciate the reccomendation but I am not real concerned with getting aggressive on the cam. I have another go fast car and for what I use this car for I really want it to behave just like stock while having a bit more stuff. So is there any difference between these two? Comp gives the RPM range for #1 as 1000 to 5000 and # 2 as 1200 to 5200. Will # 2 slant the powerband upward just a tad because of the narrower centerline? Thanks again.
I appreciate the reccomendation but I am not real concerned with getting aggressive on the cam. I have another go fast car and for what I use this car for I really want it to behave just like stock while having a bit more stuff. So is there any difference between these two? Comp gives the RPM range for #1 as 1000 to 5000 and # 2 as 1200 to 5200. Will # 2 slant the powerband upward just a tad because of the narrower centerline? Thanks again.
Melting Slicks
Joined: Mar 1999
Posts: 2,535
Likes: 2
From: Rochester NY
CC cam is much cheaper and those are very mild. I used to run LPE219 cam. 219/219 @.05 .560/.560 LSA 112 with my 1.6 rr. It idle smooth and made good hp on my old combo head/cam 93 LT1. It sound means. This cam will idle 750rpm but I set mine to 900rpm and it sound means.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Another way to compare cams is to subtract the duration at .050 from the advertised duration. The SMALLER the difference, the more aggressive the ramps, which is what you want in an engine with streetable concerns.
With aggressive ramps, you can make the same power with less duration which keeps the vacum up and the idle under control.
Just make sure that all the cams you compare have their advertised duration measured at the same lift, usually .006 and that valve lift is similiar.
Jake
With aggressive ramps, you can make the same power with less duration which keeps the vacum up and the idle under control.
Just make sure that all the cams you compare have their advertised duration measured at the same lift, usually .006 and that valve lift is similiar.
Jake
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
These are pretty close........ both look like good cams.
THis is JMHO but for what you want go for the one that tends to increase lift rather than duration. Of these two cams #1 would likely be the one you would like the best.
#2 would suit me better. I don't mind the engine shaking at traffic lights,in traffic, etc. And I LOVE that lopey idle sound, jusy LOVE it.
Be sure and check your valve springs and clearance form the spring retainer to the stem seal when you use those cams with over .500 lift. Don't want to break or bend anything in the valve choo-choo.
THis is JMHO but for what you want go for the one that tends to increase lift rather than duration. Of these two cams #1 would likely be the one you would like the best.
#2 would suit me better. I don't mind the engine shaking at traffic lights,in traffic, etc. And I LOVE that lopey idle sound, jusy LOVE it.
Be sure and check your valve springs and clearance form the spring retainer to the stem seal when you use those cams with over .500 lift. Don't want to break or bend anything in the valve choo-choo.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Thanks for the input everyone. I think I am going to go with cam #1. I was originally concerned that it would have isufficient top end because of the 114 centerline. I have since found that the stock cam is ground on a 116 centerline however. So with a narrower centerline, more duration, and substantially more lift I think it will accomplish what I want to do.
