hot rodding a 258?

[CJim7]

Chevy valves/p&p. 272 cam. hi comp pistons.

This was my 3rd build on this motor and one I don't talk about for a variety of reasons.

1. It is uber-expensive, headwork alone.
2. I don't have a lot of faith in component strength. I broke out a piston skirt which I think was direct correlation to the almost 11:1 compression I was running.
3. Again, I think a stock 4.0 head is plenty of an upgrade for those wanting power increase....and I don't trust the amount of stress put on an engine built for low RPM torque. The last thing I want is to encourage someone to do a very expensive build and have everything go up in smoke.

I try to forget about this mod...

 

[rr41mag]

I brought the die peneatrant kit home and did my head. Everything was ok

 

[Goatboy4570]

To get 300 hp they would have to run the x4262h cam.

gutthams with his 270 hp version most be running comps x4254h

I think what ever cam anybody runs it will have to be daul pattern for sure

 

[Goatboy4570]

You might want to look at the spec sheets that Golen Engine Services posts on their website. They have a good breakdown of reliable Hi-Po parts for their 300HP and 4.6 builds.

I am currently running one of their 270 hp/4.6 motors, and it runs within 20 ft.lbs of the MUCH MORE expensive 300hp version.

The dyno grafph starts at 300 ft pounds and 2500 rpm, whats the motor like off idle and can you still lug it like a stocker?

your cam could work well even in a less modifided motor

 

[gutthans]

The dyno grafph starts at 300 ft pounds and 2500 rpm, whats the motor like off idle and can you still lug it like a stocker?

your cam could work well even in a less modifided motor

I ran the X 4x4 254H cam on both a .060 over AMC 258 i6 / 4.2l w/ 4.0 head and the 4.6 stroker...I was/am able to consistently drive in 5th @ 800 rpm and pull from a dead stop in 3rd with both motors. It's a well rounded cam that I can set idle @ 650 w/o issues.

 

[Goatboy4570]

Maybe I should have said torque instead.

If you or anybody who reads this whats to they can go to the comp cams website and download for free "Camquest6"

CC6 is a more basic version of "Dynosim5", im guesing comp pays a small lisine fee, CC6 runs only comp cams grinds, the to programs even though related cant file share. You can get cyl head air flow numbers form Stan Weisses web site.

none the less you can run two of the best cams made fore the AMC 258 i6 / 4.2l , the X4256h and the X4262h.
I ran half dozen similer cams in DS5 from isky howards and lunati and the X4262h ruled from idle to redline, only the howards pulled a we bit more topend, but witt a corresponding upper bottom loss.. The 262 even out pulls the more RV like grinds off the bottom.
The sim also shows how the AMC 258 i6 / 4.2l absolutly loves a small tube header! even off idle.

If the 262 is as good in a engine as it is on a dyno sim then there simply is no other choice.
Cheack it out.

 

[rr41mag]

Well I've started on this head and now am having second thoughts I can get a newer head for 41 bucks. So what year year head should I look for out of a junkyard?

 

[Goatboy4570]

Well I've started on this head and now am having second thoughts I can get a newer head for 41 bucks. So what year year head should I look for out of a junkyard?

is it a newwer AMC 258 i6 / 4.2l head? cause if it is just buy it. or are you thinking of going down the 4.0 head swap road?

Whats wrong with your present cyl head?

 

[gutthans]

IIRC the casting you want is #7120. I believe that is around 94 - 99

 

[rr41mag]

I have a 1976 AMC 258 i6 / 4.2l complete motor. I started with the head. I got it hot tanked and die pen the head no cracks then started porting and polishing. Now come to find out I don't think I should have ported it. I was thinking of going the 4.0 way since I can get a head for $41 at my local pic and pull

 

[mtnwhlr]

You want one from a High Output 4.0 I think '90-95

 

[Goatboy4570]

I have a 1976 AMC 258 i6 / 4.2l complete motor. I started with the head. I got it hot tanked and die pen the head no cracks then started porting and polishing. Now come to find out I don't think I should have ported it. I was thinking of going the 4.0 way since I can get a head for $41 at my local pic and pull

Porting the head was not a waste of time if you learned something, you can carry that knowlege forward.

So the 4.0 head we need is ether a 91-95 "7120" casting or a 96-99 "0630" casting. there both high port heads with the 0630 not having a place to screw in a temp sender.
for me im gona grab the one with the lowest miles, if its a 0630 ill just take coolant temp from my intake which im carrying over from my AMC 258 i6 / 4.2l .
I'm staying carberated.
The exhaust manifold or header has to be 4.0 for the center ports to work.

 

[gutthans]

Porting the head was not a waste of time if you learned something, you can carry that knowlege forward.

for me im gona grab the one with the lowest miles,....

Not sure that I would care about the mileage, in fact I would be happier with a higher mileage head... Reason being that the metal is more 'seasoned' and less prone to any cracking or shifting than a less proven piece. Also, you're going to be milling and reworking it any way, so mileage defects really aren't important (unless of course it's trashed)...but I would already be planning to replace guides and plane it rather than 'trust' it.

That seasoning thing was pointed out to me over 40 years ago by the Barnett Brothers and Smokey Yunick, both of who's names you may know. Both frequently utilized used pieces in their race motors and claimed that higher mileage pieces were inherently more stable under stress than 'green' parts. I can't prove that, but I wouldn't want to argue that point

 

[rufus1138]

i heard a story about european manufacturers like prosche and bmw doing the same kind of thing by setting/soaking/burying the blocks and heads, not sure anymore of the exact procedure but it definitely developed a reputation for older european motors being seasoned like you mentioned and very tough.

 

[Supertrunk]

These folks have been the experts in inline-six hot rodding for almost 50 years, Clifford 6=8:

Clifford Performance: Jeep & AMC Cars

Lot's of eye candy too!