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360 experienced engine builder please help.

8.7K views 36 replies 11 participants last post by  Mach  
#1 ·
Looking for some input from the engine builders on here.

I rebuit a 360 Magnum motor in a Durango RT Clone, it’s a SLP+.

Botton end is stock.

I used the following components

New EQ 318 Heads:
2.02 stainless intake
1.625 stainless exhaust
.042 mopar head gasket
New stock head bolts
New stock lifters
M1 2bb intake
Fast Man 52 mm throttle body
8mm wires
Pioneer Spring 810102 installed at 1.66 height.
KN air filter
Comp Cams XR264HR with 212/218 and .480/.480 installed straight up / which is ground with 4 degrees advance.
Comp Cams 1.6 Roller Rockers with Comp guide plates.
Edelbrock hardened 6.93
1.5 inch shorty header thru. Custom 2 inch into 3 inch flow master in and out. High flow new cats
SCT tuner /tuned by Hemifever
Edge 2600 stall billet cover
MSaine valve body.


Computer Engine Dyno shows this combo making 351bhp at 5000rpm and 402 ft lbs at 4000 at the crank when I use ultra conservative inputs. Thats 100 hp over stock and what i was shooting for with heads, cam, intake and headers.


Here is my dilemma: I am missing 60 BHP and TQ at the wheels. Even if computer dyno is over estimating I should make 275 rwhp 320 rwtq with this combo.

The comp roller kit came with 6.8 pushrods, which looked good in the valve train set up as far as geometry goes. But I'm not a valve train expert.

The motor ran well but pulled a disappointing 222 rwhp and 273 rwtq. Valve train was loud.

When resetting the lash to 3/4 turn past zero lash I noticed several were below zero lash? I re-measured and the stock pushrods looked better on the roller tip. (Again I'm no expert). 6.8 seemed small. I ordered stock size but hardened for the guide plate compatibility. So 6.93 are in there.

This woke the motor up some and eliminated some of the sewing machine ticking noise. Still there at idle, could be there at higher rpm just can't hear it if it is.

My second pull was 243rwhp and 293 rwtq.

Here is my issue my peaks are way to low. At 5000 this thing is done. Dyno guy shuts it down, graph drops and line goes erratic. I can post graph is anyone can read these things. Peak HP is around 4500 rpm. Torque is highest at 3000 when the converter catches, and nose dives at 4000 rpm.

Cylinder pressure was good before the build but I will check again.

There are no misses or stumbles anywhere. Plugs good but I will check and re gap anyway. Fuel pressure is good and the motor gets fat when it dies off a little so there is fuel there. No valve damage from short push rods. Bind is at 5.44, not close to that.


valve float? But I have 125 and 310 for pressures. Comp says it is good for the cam. They recommend at least 115 / 300. Pull a spring and have tested? Did I get wrong items shipped?

Pushrods still undersized? The XR is a small base circle cam did I measure wrong twice? Use 7.05 or more and check for clearance rotating by hand, set lash and do a pull.

The motor works really well. Pulls nice and smooth and will toast the 275/60 17.

I just cant figure out why its running out of steam early?

Any thoughts would be greatly appreciated. Thanks all.
 
#5 ·
As far as the pushrods, get a measuring pushrod and check for proper length. With my re-ground cam and Edelbrock heads, I ended up using a 6.93 Edelbrock hardened pushrod. Actual measurement came out at 6.95 for my combo. Every combo is going to be different.
 
#6 ·
When it comes to fuel sync as duner mention. Mark the cap/rotor with a marker where it is at stock, so you can always set it back to a reference point. You can also find a shop with a modus or snap on or drbiii scanner and you can visually see on the scanner where the sync is at # wise, and the # will change as you rotate the dist, making it easier for you. By all means try it manually, but at least mark it so you can find a reference!!
 
#7 ·
Degree the cam. If you just install it "straight up" without checking the tolerances with a degree wheel, you have no idea where you're at.

I found that my last timing chain set was off by around 12 degrees when I checked it.
 
#9 ·
I'm not a pro builder by any means, but I'd take the computer program results and toss em in the trash, and the only thing a Dyno is REALLY good for is tuning...Or giving you a base to work off of, and then it's only good if the DA is exactly same everytime you dyno.

I only Dyno at 315 RWHP, and that's corrected RWHP, up here it's probably 50RWHP...But I can run 12's all day.

Degree the cam, check your valve train geometry and stay away from the Dyno.
 
#10 ·
As said, degree cam and check fuel sync.

As far as pushrod length, due to tolerance stack up, different part combinations, ideal pr length will vary. Just make sure the preload is the same each time you measure for pr length and that you are in the same spot on the base circle of the cam also. I, personally, would bottom out the lifter pluger, check for length, then subtract from the length to get correct preload on a hyd lifter.

Another thing I noticed is the smallish 1.5" primary shorty headers. I'd like to see, at least 1 5/8" primaries. Not sure I understood the rest of your exhaust setup.

Need to make sure ignition is in excellent working order and get your tune(a/f ratio and ignition advance curve) dialed in but an LM2 would help with acquiring data to see what's going on.

I think 1.7 rockers would help a fair amount also. The flow curve on those heads keeps going until .600, then flow starts to drop.
 
#11 ·
To measure push rod length, you use an adj push rod, mark the top of the valve stem, set the valve lash as normal, hand torn the motor over a few times, pull off the rocker and look at the tip of the valve stem. Centered = good. If not centered, change the pushrod length and repeat till it is centered.
 
#18 ·
Then he could just find the total travel of the plunger then subtract the difference. Ex. .100 travel-.020 preload= .080, the number to subtract from pushrod length when correct pattern is present on stem with plunger bottomed out while measuring.
 
#15 ·
Thanks for the positive replies. I really appreciate the info. I will get the sync set asap.

The 1425 comp roller rocker conversion has 5/16 studs that convert the top part of the stud to 3/8. If I'm not mistaken the 1.6 roller rocker in the kit is a Chevy rocker?

Does anyone know if i can use 1.7 Chevy adjustable rollers rockers with this. That will bring my lift to 5.12?

If not anyone know what 1.7 will work with the kit?

Thanks again.
 
#16 ·
Get it running right as it sits first, then change things afterward.

After reading the initial post again, it seems like your cam timing is advanced too far. You may need to retard it to raise the powerband up some.

Check it out with a degree wheel. Your cam card should tell you where they recommend installing it.
 
#17 ·
I noticed that besides the SS valves and hardened pushrods, you haven't lightened anything else up in the drive train. Ever consider titanium retainers and/or locks as well as lighter springs? Or are those components not available for the Magnum engines?
 
#20 ·
Computer Engine Dyno shows this combo making 351bhp at 5000rpm and 402 ft lbs at 4000 at the crank when I use ultra conservative inputs. .

Theres your problem. While I agree with most that you probably should have degreed in the cam there is probably some tuning that needs to be done on the dyno to get the full potential..with that being said the program you used to simulate the engine should really only be used for fun. I have yet to see any of them that were close to being accurate
 
#24 ·
Looking for some input from the engine builders on here.

I rebuit a 360 Magnum motor in a Durango RT Clone, it’s a SLP+.

Botton end is stock.

I used the following components

New EQ 318 Heads:
2.02 stainless intake
1.625 stainless exhaust
.042 mopar head gasket
New stock head bolts
New stock lifters
M1 2bb intake
Fast Man 52 mm throttle body
8mm wires
Pioneer Spring 810102 installed at 1.66 height.
KN air filter
Comp Cams XR264HR with 212/218 and .480/.480 installed straight up / which is ground with 4 degrees advance.
Comp Cams 1.6 Roller Rockers with Comp guide plates.
Edelbrock hardened 6.93
1.5 inch shorty header thru. Custom 2 inch into 3 inch flow master in and out. High flow new cats
SCT tuner /tuned by Hemifever
Edge 2600 stall billet cover
MSaine valve body.
Is that right above bold? 2" what? don't like this if it means 2" Y-pipe into 3" flowmaster.
Also the smart peeps around here have pretty much got you where you should start first.



DEPUTY
 
#26 ·
On the exhaust, I had shop make the y pipe from two inch pipe and then redo a y that goes into a single 3 inch pipe thru the a new cat and a single flowmaster suv 50 series muffler.

I am going to check the fuel sync at a shop in the am. My truck almost never sees 5500 rpm. Shift are set at 5400. The smaller cam and 114 lsa were chosen to maximize a flat torque curve for it's weight and to try and bring HP peak into a usable rpm for what I use it for.

Thanks all for some great starting points.
 
#27 ·
That 2" Y-pipe is smaller than what I would like to see with your current mods.I would preffer a 21/2" Y-pipe into the 3" exit pipe to the muffler,but the 2" y isnt your problem.
That 114 lsa is more for top end bud not bottom end,motor cams are typically 108-110 lsa and blower/N2O cams are more 112-114 lsa.What did your cam card call for on installed centerline of the cam??? it will be in crank degrees and is what you should have the cam degreed at.I would like to see some where in the neighborhood of 108* crank centerline with that cam in that durango.


DEPUTY
 
#32 ·
I made the same exact numbers on my 5.2l with the same cam.You should be making more than 240rwhp. I would start to look at the aforementioned mechanical issues before you do any further mods...
 
#34 ·
My 408 looks like it will perform well NA but would respond to spray. It's 114lsa installed at 110ICL. Power is quite flat and does'nt vary much, 473 lb ft from 3300 to torque peak of 496 at 5100. Hp peaked at 6100 and 6200 at 526hp. It's a turd, lol. It should be more like 550hp and 520lb ft. I'll bump the compression some. It's about 10.2-10.3 right now with a 236 @ .050 xfi lobe cam. The short midlengths didn't help and the collectors were kinda aimed to the walls of the 8" exhaust fan scavengine tubes. Want to address some valvetrain geometry too. I'd hate to spray it and break the cast crank. Maybe a little shot won't hurt.:D
 
#35 ·
Nice. I'm running my 390 at 11.0:1 with a forged crank, pistons, and h-beam rods, so it will handle a lot more spray than I'm throwing at it.

It definitely propels my little ******* 4x4 down the track nicely so far.
 
#36 ·
Could one of your tell me what rocker I would need that is adjustable. I want to try and keep cost down by reusing the guideplates and 5/16 to 3/8 conversion studs that came with the 1425-kit from Comp. I won skimp on a quality rocker just don't want to by an entire kit again. Would prefer 1.7 but will settle on 1.6 if they dont make a 1.7 that will work.
 
#37 ·
For the 1.7 ratio, which is actually not too common as you would think you can either get Harland Sharps (check their site) that use studs and are for the Magnum or use Scorpion sbc 1.7's. I went with HS's due to the smaller body, lighter mass of their rockers on my bolt on 360 in the truck. The Scorpions are bulkier and heavier and thus the 950lb open pressure the body will take. A 3/8 stud will not though so it's overkill. They're only about $220 and have a lifetime warranty though. They're nice rockers. I used the 7/16 version Scorpion 1.7's on my 408.