4.0 head change dyno results

[tinman]

Just got back from the dyno, and while not exactly a straight swap, it's pretty close.

First pull was back in April with a stock CA AMC 258 i6 / 4.2l engine, but with all smog stuff gone. It did have the 2100 carb and HEI for the test, but everything else was stock.

166.1 ft-lb@ about 2250 RPM's and 88.1 HP@ about 3300 RPM's.

Today's test had an '84 block, bored .030 over, '95 7120 head(rebuilt, but stock), and a comp 252 duration cam. Same carb and HEI, but I did replace the muffler with a new magnaflow one.

224.3 ft-lb@ 2500 RPM's and 140.3 HP@ 3500 RPM's.


So, a gain of 58 torque and almost 52 HP with mostly just the head. I'm not sure how much the cam, the boring, and the muffler added, but I was pretty happy with the results!

Now I need to get off my rear and start a build thread I guess. I still plan on doing some sort of FI sometime, just not sure when, or what kind.

 

[coldair]

Do you have the dyno sheet? I would love to see it.

 

[tinman]

The description for the red line should read 81 CJ7 with the AMC 258 i6 / 4.2l , instead of 82 and a 4.0.

Looks like everything moved up about 200 rpm's. Is that primarily due to the cam?

 

[73CJ]

Thanks for the info.

Mine is close to your build. I sure can tell the difference on and off road but really couldn't guess what difference it was in HP.

 

[coldair]

The cam could have a lot to do with the HP/rpm range.

 

[CJim7]

The headswap is probably the best upgrade you can do for the AMC 258 i6 / 4.2l .
When I did mine, I went with a 262 duration cam and flat pistons. A Clifford intake and 500cfm Edelbrock. A healthy P&P on the head and I dynoed at just under 300hp. It was rather impressive.

A few people I know have gone to the full extreme of milling the head for larger chevy valves and jumping to a 272 duration cam with results well over 300hp.

My only issue with my set up was offroad performance lacked with the carburetor I was running. Some tunning and re jetting would have probably helped it out but I was having to much fun at the stoplight with the ricers

 

[IOPort51]

Did you have problems with a fast idle? I notice your charts start at a higher RPM after the head and cam swap. The last person I remember having a dyno after a head swap gained about 30 HP as I remember, I thought that was well worth the effort.

 

[1986cj7]

The headswap is probably the best upgrade you can do for the 4.2.
When I did mine, I went with a 262 duration cam and flat pistons. A Clifford intake and 500cfm Edelbrock. A healthy P&P on the head and I dynoed at just under 300hp. It was rather impressive.

A few people I know have gone to the full extreme of milling the head for larger chevy valves and jumping to a 272 duration cam with results well over 300hp.

My only issue with my set up was offroad performance lacked with the carburetor I was running. Some tunning and re jetting would have probably helped it out but I was having to much fun at the stoplight with the ricers

What kind of torque #'s did you see and at what rpm's? Also what octane gas did you have to run? What kind of compression where you running?

 

[Incommando]

If I was a guessing man I'd say that one poster was using gross numbers at the flywheel using an engine dyno and the OP was using net numbers at the rear wheel on a chassis dyno.

 

[tinman]

Did you have problems with a fast idle? I notice your charts start at a higher RPM after the head and cam swap. The last person I remember having a dyno after a head swap gained about 30 HP as I remember, I thought that was well worth the effort.

You know, I'm not sure why that starts at a different RPM. I'll have to go in and ask him, but I never had a problem with the idle, so who knows.

And yes, my test was done on a chassis dyno.

 

[1986cj7]

You know, I'm not sure why that starts at a different RPM. I'll have to go in and ask him, but I never had a problem with the idle, so who knows.

And yes, my test was done on a chassis dyno.

I wasn't questioning your print out, it is far closer to what I would expect to see, then the 300PH stated by anther poster.
Cjim7 just what are the specs of your build, what components did you have to use to get that hp, I know it's possible to get that out of a 4.0L stroker but your looking at changing the displacement closer to 4.8L or 5.0L. I think the compression and all would require high octane fuel or race fuel. I'm looking at building a motor. I"m not sure if I want to build a 4.0L stroker or just build a AMC 304 . I know theres no replacement for displacement, but I think for what I want 230-250 hp would be plenty. I"m looking more at torque then just plain hp. Just would like to get good power and mpg, and the best bang for the buck.

 

[coldair]

HP is expensive when building a motor. I went on Comp Cams cam selector entered all my specs for my AMC 258 i6 / 4.2l build they estimated mine at 225 hp 289.9 foot Lbs of torque. I havnt been able to back those number up yet because of unforeseen personal problems. But when I get the motor broke in with a few oil changes I will dyno it on a chasis dyno.

 

[CJim7]

Yes, this was gross hp at the flywheel. I installed flat pistons after a .040 overbore along with the 262 Comp cam boosted my compression ration to 11:1. I left the valvetrain stock except for the tighter valve springs recommended by Comp Cams. I was able to run 87 octane which is still a huge mystery to my...everyone I know running 10:1 or higher experienced pinging with anything but premium fuel. I was just lucky I guess.
I P&P'd the 4.0 head and used an XJ header with the Clifford aluminum intake. Kept the exhaust free-flowing with a glasspack. I completely de-smogged the engine which gives back a lot of robbed raw power. Mid-80's california smogging was archaic at the best even under perfect working condition.
The 500cfm Edelbrock was a perfect combination with my engine build.
Most of the AMC 258 i6 / 4.2l 's powerband lies at between 2000 and 2500rpm, this stayed true to form with my engine

All this was a healthy contributing factor to my T-5 being replaced with a T-18 . I couldnt keep the T-5 together anymore.

As great as this build was, my 401 turned out to be a masterpiece as far as keeping something user-friendly and yet exploiting the optimal power output while still staying on a budget.
AMC V8's are capable of huge power, the architectural block strength and design leads way to upgrades many engines cant handle mechanically without further upgrades. The biggest drawback is a poor oiling system which is easily solved with the addition of a cheap diverter.

...But this is about inline 6's. Im a huge fan of them and was extremelly happy with my AMC 258 i6 / 4.2l hybrid. I would DEFINATELY do another one.

 

[Barry2]

The headswap is probably the best upgrade you can do for the 4.2.
When I did mine, I went with a 262 duration cam and flat pistons. A Clifford intake and 500cfm Edelbrock. A healthy P&P on the head and I dynoed at just under 300hp. It was rather impressive.

A few people I know have gone to the full extreme of milling the head for larger chevy valves and jumping to a 272 duration cam with results well over 300hp.

My only issue with my set up was offroad performance lacked with the carburetor I was running. Some tunning and re jetting would have probably helped it out but I was having to much fun at the stoplight with the ricers

Heh aheh Heh! Aint it fun tho?