AMC Eagle Den Forum

The Mighty 258 => The Engine => Topic started by: Canoe on September 19, 2012, 11:48:18 AM

Title: 258 block with 7120 head: which cam?
Post by: Canoe on September 19, 2012, 11:48:18 AM: (Nest search is nuts)

So much info.

Machinist says that his book shows a 4.2 and 4.0 cam so close to each other that there'd be no difference in performance. That 4.0 cam also comes with a fuel pump lobe. I'm thinking the book he has is for a much earlier 4.0. He's got a performance book, but says he's had problems with everything he's ordered from them (offshore crap) with no effort for them to make it right.

So, for a daily driver (90%), with some trailer towing (7%) and then some unimproved road and mild offroad for the rest, which cam?
Title: Re: 258 block with 7120 head: which cam?
Post by: carnuck on September 19, 2012, 01:48:40 PM: Going with carb or EFI? The profiles are different. Renix cam and HO cam are the same, BUT cam timing was altered by retarding the cam gear on the HO to delete the EGR valve.
Title: Re: 258 block with 7120 head: which cam?
Post by: Canoe on September 20, 2012, 01:09:55 PM: Carb.
Stock for now. 2100/2150 later.
Title: Re: 258 block with 7120 head: which cam?
Post by: eaglefreek on September 20, 2012, 02:35:44 PM: I'm running the Comp Cams 68-232-4 and I'm happy with it. I used stock replacement springs instead of the ones recommendwd since they require machine work. I have almost 3 years and 30,000 miles on the engine with no cam problems. The Mopar cam would be a good choice also. http://m.summitracing.com/parts/dcc-4529228ad
Title: Re: 258 block with 7120 head: which cam?
Post by: BenM on September 21, 2012, 11:31:45 AM: They're quite different. The 1982 spec is not from a TSM, so it's rounded; it's also the one I'm least sure of; I'd have to double-check the 1996 against a TSM as well. Lift should be lobe lift for the 258 & valve lift for the 4.0 (divide by 1.6).

Code: [Select]
Year Vehicle Disp Carb Adv.In Adv.Ex [email protected] [email protected] I Open I Close E Open E Close Overlap I Cent E Cent LSA I Lift E Lift 1978 All 232 1v * 256.92 256.92 12.12 64.8 53.12 23.8 35.92 116.34 104.66 110.50 0.232 0.232 1978 All 258 2v 263.37 263.37 14.58 68.79 55.59 27.78 42.36 117.11 103.91 110.51 0.248 0.248 1980 Jeep 258 2v 263.37 263.37 14.58 68.79 55.59 27.78 42.36 117.11 103.91 110.51 0.248 0.248 1982 All 258 2v 262 262 9 73 57 25 34 122 106 114 0.253 0.253 1987 Jeep 4.0L Renix 270 270 197 197 21.5 38.5 22.5 5.5 46 112 0.424 0.424 1996 Jeep 4.0L HO 253 259 188 192 20 28 16 4 43 107 114 0.408 0.414 2003 Jeep 4.0L FI 253.3 259 188 192 19.3 54 70.8 8.2 41.6 107.3 121.3 114.3 0.408 0.414
Title: Re: 258 block with 7120 head: which cam?
Post by: Canoe on October 01, 2012, 10:58:19 AM: For better for worse, machinist looked at the numbers and we've selected a ~~Growler~~ ~~Crowler~~ Crower Baja Beast Level II.
We'll see what it does.
Title: Re: 258 block with 7120 head: which cam?
Post by: BenM on October 01, 2012, 11:57:45 AM: Let us know how you like it. Odd that it's a 280/280 advertised duration and only 208/208 @.050.

Here's a comparison of cams with similar range ratings:

Code: [Select]
Name/Grind/Part Range Adv.I Adv.E [email protected] [email protected] LSA I E (Lift) Isky 256 Super 133125 1500-4800 256 256 202 202 111 0.281 0.281 Hesco RVOB 1500-5200 264 264 214 214 110 0.294 0.294 Lunati 63502 1600-5800 262 268 220 226 112 0.317 0.329 Crowler 280HDP 44915 1800-5000 280 280 208 208 112 0.280 0.280 Isky Dual Pattern 133125/26 1800-5000 256 262 202 208 110 0.281 0.278 Crowler 278HDP 44245 2000-5000 278 284 212 218 112 0.289 0.297 Isky 262 Super 133126 2000-5500 262 262 208 208 110 0.278 0.278