Gen One and Gen Two Dodge Viper Camshaft Specifications 708 & Stock Gen One

[ericj96]

Gen One and Gen Two Dodge Viper Camshaft Specifications 708 Cam & Stock Gen One

I have looked all over for good data on these cams and after looking throught the International Registry and the cams specs listed I got frustrated because the specs conflict with themselves. Open and close events dont fit the avertised durations. The lift basis is not called out as .002" or .006" or .050" etc. Overlap does not fit the events given either. The one cam grinder that lists the 708 cam calls out the intake lobe as 212 deg at .050". With a lope like that they have got to be kidding.

I needed to spec a new cam for my gen one that is at the machine shop because one of the lobe crest has the special treating worn off. So I rounded up damaged viper cams for free and sent them in to Comp cams to be "cam doctored".

These were the results:

Gen one bone stock cam:
Duration at .006” lift intake = 285 deg
Duration at .006” lift exhaust = 278 deg
Duration at .050” intake = 218 deg
Duration at .050” exhaust = 212 deg
Intake Center line = 117 deg
Angle between lobes = 114 deg
Intake lift at lobe = .308
Exhaust lift at lobe= .291
Intake closing event was 77 deg after bottom dead center----translates these cams do not have the exact same lift and close rates on the lobe if what comp cams is reading is correct.




708 Cam:
Duration at .006” lift intake = 288 deg
Duration at .006” lift exhaust = 296 deg
Duration at .050” intake = 220 deg
Duration at .050” exhaust = 230 deg
Intake Center line = 117 deg
Angle between lobes = 114 deg
Intake lift at lobe = .321
Exhaust lift at lobe= .321

 

[JonB]

Thanks for sharing the G1 vs G2 research.... is there a question?

The Gen 1 and 2 engine chief from Team Viper is an owner/member here......seldom posts. But I can forward a question ???

 

[ericj96]

Well yes, What are the specs that Dodge has on these cams and are they the same as what comp cams estimated? Also are these cams non semetrical lobes?


Thanks

Eric

 

[coupe]

Wow... thanks for sharing that!

The 117º installed intake centerline on a 114º lobe separation angle is quite unusual... I would've thought those numbers would be reversed.

You must be registered for see images attach

 

[ericj96]

We have very long intake manifold runners and the late closing event on the intake lobe allows the long column of air that is still trying to get in the cylinder do so even after the piston starts back up the bore. If we had a short intake runner or a dual plane intake then the late IVC would be a problem.
Our cam manifold combination is black magic got to test it to get it right kind of system. I noticed the the gen one cam, 708, and the posted Greg Good cam all have a IVC event at .050 of about 45-47 deg ABCD.

 

[plumcrazy]

call greg good if you need a cam. there are much better ones available than the 708

 

[ericj96]

After much research I went the conservative route. I do not want higher dynamic cylinder pressure than 8.0 to one (otherwise stated as about 185 psig cranking cyclinder pressure) on my 10.2 to one compression motor and I want the thing to have a low toned melodic rumble that is smooth at idle. This is what I had comp cams grind for me and I have no doubt most of you guys would think its a little conservative:

Comp Cams Dodge Viper Camshaft Single pattern with 3051 lobes:
Duration at .006” lift intake = 274 deg
Duration at .006” lift exhaust = 274 deg
Duration at .050” intake = 220 deg
Duration at .050” exhaust = 220 deg
Intake Center line = 117 deg
Angle between lobes = 114 deg
Intake lift at lobe = .320
Exhaust lift at lobe= .320
Intake closing event was 74 deg after bottom dead center.


My line of thought went like this. These long intake runner engines like a late closing of the intake valve. My stock cam, the 708 cam and the Greg Good spec cam card I could find all had a late closing of about 45-47 deg ABDC at .050" lift and a .006 intake closing event about 74-80 deg ADBC. This late closing helps keep dynamic cylinder pressure down too. Comp cams standard grind cams were closing the intake way too soon and the dynamic cylinder pressure models and cranking cylinder pressure models were showing 8.5+ and 200 psig respectively and that tends to indicate racing gas and you......

The stock gen one cam has a 218 deg at .050" and the 708 a 220 deg at .050" duration on the intake. The stock gen one cam does not have a rough idle so I was comfortable with a 220 deg at .050" intake lobe with a 117 center line that yields what looked like to me the prefferential closing event timing. The 3051 is very close to a stock 708 intake lobe in lift and durration at .050” but it is a little faster acting so it should pull a little harder early and about the same late.

The exhaust lobe on the gen one was 212 deg at .050” lift and the 708 is 230 deg at .050” lift. I have had the opportunity to hear the after market rocker/708 cams with high compression and low restriction exhaust combo and they have a much more pronounced lope than the factory cars do in my opionion. So the question was for me how far can I push the exhaust lobe and still get a chop free idle? On 4” bore v8s with 3.48-3.75” strokes 218 intake 218 exhaust cams with 110 lobe separation are just starting to get rocky idles. We have slightly longer strokes on our motors so we should be able to carry a little more duration especially with our 114 deg lobe separtions. I came to the conclusion that 220 deg exhaust duration at 050” would work provided I stayed with the 114 lobe separtion.

Without prejudicing the Comp Cam Tech I asked him how he would describe the above specifications and he said you are going with a baby magnum cam that will be smooth but not perfectly so.

So to make a long story short I stayed with a intake lobe much like a 708s and used it on both the intake and exhaust lobes thus getting rid of my seriously crappy 212 deg low lift exhaust lobe.

 

[NI-KA]

I can't resist asking a question. (For a reference point I know very little about CAM profiles)

On my 1997 GEN II (I do not know what kiind of CAM I have I just know it isn't stock)

What portion of the set up on the CAM causes the "lopey" rocking of the car? Especially on start-up. Smooths out after warm up.

It is a heads and CAM car. Others who know more have commented they can hear the overlap built into the CAM.

Don't get me wrong I like the "lopey"ness of the car etc. Just curious.

 

[ericj96]

The lope mostly comes for the period of time when both the intake and exhaust valves are open (TDC) and how early the exhaust valve opens. Having both valves open at low speeds causes the engine a loss in flow control thus the rocky idle quality.

Overlap = (intake .006 dur + exhaust .006 dur)/2 - lobe center angle x 2

SO

The above 708 spec has cam doctor numbers = (288+296)/2 –114x2 = 64 deg at .006” lift. That’s quite a bit and it shows up in idle behavior. Also the 708 has a exhaust valve opening event that is very early and the piston is only about half way down the bore when the exhaust valve opens and burning gases blow into the header. This is due to its 296 deg exhaust lobe.

Notice that duration at .050 overlap is zero on most high performance street cams.

 

[NI-KA]

Thanks ericj96

 

[ericj96]

The end result was 491 RWHP at about 5,500 rpm and 551 RWT at about 4200 rpm.


440 RWT at 2000 rpm

530 RWT at 3500 rpm

550 RWT at 4200 rpm

510 RWT at 5000 rpm

470 RWT at 5500 rpm

Car has a stock idle with a low melodic rumble and is quiet when in 5th or 6th at highway speeds. Other gear heads who have driven it say that after 3 grand at WOT the car sounds like the "wrath of ***". The car's sound track has a split personality.

Took the car to the track and it ran in the mid 11s at 122-123 mph with a 1.85 60ft time and an off idle launch. No doubt these guys that can come out of the lights at 4000 rpm and not fry the tires could drive it into the low 11s but I can't and dont care beat on my car that much to improve.

Hope this helps someone.

Eric