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258 Hi-Perf build with pics. |
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2drwgn 
AMC Nut 
Joined: Jul/02/2007 Location: Ocala, Fl. Status: Offline Points: 248 |
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 Posted: Oct/11/2013 at 7:36pm |
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Gotta add a couple of comments to this.
With an overly agressive cam lobe ramp and high spring pressure, you will most likely experiance cam bearing failure at the #3 cam bearing. There is a lobe on either side of bearing, only a few degrees apart adding additional stress. Also, the blanks that almost all cam grinders use are from the 1960's 199!
There are no new blanks. Mother mopar increased the diameter in 2001 with the AB block--has cam thrust plate. I believe that this was done to eliminate some vibration. The shaft is larger by over .080. I have seen the #3 bearing worn enough to lose 8+ lbs of oil pressure! I have sent an AB cam to be reground for a stroker I'm doing know.
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1966 American convert
4.0 FI AW4 |
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Pdok
Supporter of TheAMCForum 
Joined: Apr/03/2011 Location: Alabama Status: Offline Points: 1025 |
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Posted: Oct/11/2013 at 8:09pm |
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I'm running pretty much the same cam/springs as the OP. I've got less than 5K miles on the combo, and I'm using a zinc additive. I love the cam, idles strong, pulls freaking hard all the way past 80 (where I can't stand it any more).
What's the real effect if I switched springs to the Mopar Performance springs and kept the Comp X4 cam? What difference is it going to make, performance-wise. I get it that it reduces seat pressure and wear on the cam, etc., but does it have any other effects that might not be good? I'm assuming the seat pressure is needed because the lobe might be a little aggressive. I'm personally OK with the reduced lifespan of a performance cam as such, since this car isn't a daily driver as much as a toy.
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76 Grem X 258/904,4.0 head/MPFI, Comp X250H cam, Hughes springs, Clifford header, serpentine swap.
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uncljohn
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Joined: Jan/03/2013 Location: Peoria AZ Status: Offline Points: 5394 |
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Posted: Oct/12/2013 at 10:51pm |
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I've more or less an engine similar to what you are either finished with or contemplating. I pretty much agree with "Frank and the cam and springs. I use the Isky 256 Super cam and it will work well with the OEM springs and such. The engine can run well with the next size up but I initially picked that cam for a slightly different reason. I was at the time using the OEM BBD Carter 2 barrel and the OEM smog configuration. And I wanted it to not only be a better street engine but also pass smog. And it worked, The AFB will work, I have one and the intake frank is mentioning to go on a 232 I am building. For my 258 I have the MOPAR designed port injection fuel injection and it is a Speed Density system and is pretty much an electronic equivalent of the Carter AFB. Now that the year of the car I am driving no longer has to pass smog I would have picked the next Iskenderian cam which also works well with OEM valve train. I have not done the porting work so can not really comment on it except it looks like you did a nice job.
I am satisfied with the performance of my 258, it is estimated out at 180 hp. It will turn over 5000 rpm with no problem and I have shift points selected to take place at 4500 rpm with the automatic transmission. As the premium gasoline in my area is 91 octane, I built the engine to have a smidgeon over 9:1 compression. As far as I am concerned it drives and runs like a new V6. I have put about 45,000 miles on it since finished with a number of cross country trips. I like it. Yours should be pretty much o.k., except I too think you have more cam then you need and it seems to require something other than OEM and Frank pretty much identified the disadvantages of it. |
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70 390 5spd Donohue
74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam |
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tached_out
AMC Nut
Joined: Feb/08/2008 Location: Vancouver, BC Status: Offline Points: 328 |
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Posted: Oct/13/2013 at 12:20am |
The rocker shaft head looked good because it had big port openings. From a performance stand point, it went down hill from there. The cross section was good, but the turn was too sharp, the boss to big, the throat too narrow, the valve too small and the valve stem too fat. Not to mention, you were stuck with the 1.5 to 1 rockers and the solid pushrods weighed a ton. They could be made to work, but it took a lot of work. The pedestal heads with their smaller ports were probably a better overall head in stock form with a little less potential for all out flow. The 4.0 head is a masterpiece. It truly is. Among it's attributes are large ports, better shaped ports, big valves, skinny stems and best of all, it's a true twelve port head. I have no first hand experience with the Hesco head, but it's advertised to be virtually the same head but made of aluminum. Same port and same valve. It's claimed advantages are it's light weight, it has lots of meat, so you can go nuts porting and shaving if you want and it has a large holes that you can remove the lifters through. At $2,000. however, I'm not stepping up to the plate.
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tached_out
AMC Nut
Joined: Feb/08/2008 Location: Vancouver, BC Status: Offline Points: 328 |
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Posted: Oct/13/2013 at 2:04am |
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I'd like to thank everybody that has commented so far.
I'd like to talk about my valve spring choice and hopefully set aside some concerns that you might have. Comp recommends their 926 valve springs and 744 retainers with every AMC six cylinder cam they make. Even their smallest High Energy grind that is only a little more than a stock replacement. That spring has a brutal 415 lbs./in. rate. I already had a set on the shelf and a set of 740 retainers witch are identical only they use 10 degree locks instead of 7 degree. So I checked the pressure at my installed height of 1.760 and came up with over 125 lbs. At maximum lift I had 330 lbs. That would be fine if I was spinning this motor to 7,000 rpm but I'm not. I'm using the stock bridged rockers in this build and I never plan to let this get to 5,000 rpm. on the street. In fact, when I get it to the track I'll sneak up on the rpm of the shift points that give me the best ET. I have a feeling it won't be much higher. For that reason I wanted a more sensible spring. I plan to do a lot of cruising on nice days with this car. And I don't want to be worried about it destroying it's self. I chose the Comp 940 spring. It fits perfectly. It has a much friendlier 239 lbs./in. rate. It has one more coil and is made of a smaller diameter wire. I also used the 740 retainer and finally decided on the 616 locks that give an additional .050'' of installed height. I ended up with 115 lbs. @ 1.810'' installed height and 235 lbs. @ maximum lift. I think this will do the job quite nicely and I think the rest of the parts will thank me. Here is the installed set-up.  I'm using Joe Gibbs BR camshaft break in oil for the initial cam break in and the first five hundred miles. from then on I'll use an additive or a zinc oil. |
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tomj
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Joined: Jan/27/2010 Location: earth Status: Offline Points: 7544 |
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Posted: Oct/19/2013 at 6:38pm |
YES YES YES! it's so refreshing to read a balanced approach to an engine build. this is a great thread. design has to be correct for the application. in 2013 absolute-max-HP is limited only by money, it's not a reasonable goal. very sweet engine you're making. the mix of attention to detail and pragmatism is refreshing. |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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GreggR
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Joined: Aug/21/2009 Location: Painesville, OH Status: Offline Points: 1267 |
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Posted: Oct/20/2013 at 9:04am |
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5 minutes in the penalty box to tomj for using big words...
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No matter where you go, there you are... Buckaroo Banzai.'75 Hornet Hatchback
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tached_out
AMC Nut
Joined: Feb/08/2008 Location: Vancouver, BC Status: Offline Points: 328 |
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Posted: Oct/21/2013 at 2:31am |
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Another stumbling block I've come across.
When I went to tighten the rocker bolts, I had less than 1/4 of a turn of lifter preload. It's because the Fel-Pro composition head gasket I'm using is about .030'' thicker than the original steel gasket. I was concerned (since I'm using all new parts), once everything wears in I might have no preload. I didn't want to buy new longer pushrods so I shortened my rocker pivots instead. I wanted to be precise, so here's how I did it. I made a little fixture so I could grind the bottoms of the pivots using the side wheel on my valve re-facer. This is the wheel used to dress the tip of the valve stem. I used a letter O drill bit as a pilot and a nut as a spacer. I know not very ingenious, but kind of resourceful. I took .025'' off each pivot.  Shortened pivot on the right.  Shortened pivot on the top.  The whole thing is back together now and I have 3/4 of a turn of lifter preload.
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tached_out
AMC Nut
Joined: Feb/08/2008 Location: Vancouver, BC Status: Offline Points: 328 |
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Posted: Apr/06/2015 at 12:52pm |
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Just a post update. I have FINALLY found some time in my personal life and am getting back to this project.
As present, the engine is wrapped in a bag and sitting on the stand awaiting installation. The intake manifold and headers will go on after the engine is in place. I'll be running a Z spec T5 transmission with Pro 5.0 shifter and a Centerforce clutch. The car already has 4.44s out back. The weather is nice and there is a guy in town with a six cylinder `71 Maverick that keeps driving by my place really slow. Then he romps on it. It sounds great. I so want to get out there and do battle with him.
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amxdreamer
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Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8509 |
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Posted: Apr/06/2015 at 1:03pm |
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How long before you get to teach him a lesson Glenn?
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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