Heads, Rockerarms & More Horsepower...

[Tom Welch]

John,

Great Post! Id like to add to it that in Ben's case if he did the headwork first he definately would not have seen that much gain until he freed up the exhaust and intake charges.

Most of us who have bolted on exhaust systems, computer upgrades, air intakes and other items, all the while throwing in dollars from here and there that the wife doesn't know about, do realize that headwork is the next logical step for BOLT ON performance. But for the novice out there who is amazed and somewhat intimidated by the thought of peeling the heads off of his/her viper, headwork is usually left as the final BOLT ON. Actually it works out for the best as the owner has the opportunity to drive the vehicle through the advances in power and is ready when the decision is made to add the 60 or so extra hp that headwork provides.

I look forward to joining in on the cylinder head upgrade market in the near future.......as with nitrous injection, WOW! the gains should be tremendous.

Take care,

Tom
Http://btrviper.com

 

[Tom F&L GoR]

Hi John,
The 77 rwhp from a head upgrade (and header change, rockers, etc) means Ben has greatly improved air consumption. I think air consumption efficiency generally gets worse and worse as the RPM goes up; in other words, at low engine speeds a too-small runner or port doesn't hurt you as much as it does at high speeds.

So back to (lucky) Ben- did the peak power RPM go up? Does the better head combination let the engine breathe better and run to higher speeds to help get the power?

And part II: If so, why should this engine be low speed only? Seems like if Ben keeps going, the peak power RPM would get to the stock 6200 RPM cutoff pretty quick. What's the real limitation; other Mopar engines with similar bore/stroke ratios have run and raced at higher speeds?

 

[treynor]

I believe many of your questions will be answered by this graph, which compares the dyno results with intake/headers/exhaust and heads/rockers/intake/headers/exhaust:

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[Jay Herbert]

The (eventual) combination of items is important, a cam W/O heads, or exhaust W/O Cam and Heads, etc, etc, does not lead getting all you can get. If you know where you are going from the beginning, you should buy the appropriate bolt on pieces such that no money will be wasted. As an example, buy headers for the head and cam you plan in the future, it may not give you optimum gains now, but when thinking forward, it's the right thing to do.

I was at a big Cobra Event this past weekend and had a chance to see a basically "bolt-on" upgraded Viper powered Cobra. It had the TNT package similar to the one covered here, Heads (flowed, rockers, etc.), Throttle bodies, Cam, Headers (custom fabbed to fit the Cobra), and a baffled pan. It dynoed at 600+, but it was the complete combination that mattered, not an individual component. I'm sure we'll hear more about this V-10 powered Cobra as it is set up for road racing, and it is planning on being at St. Louis for an event called the "run and gun" this fall.

As a side note, the event raised over $35,000 for Cystic Fibrosis. The "Cobra" bunch are pretty great folks.

 

[treynor]

Dan,
The graph's confusing because it has HP on one scale and Tq on another -- the joy of Dynojet's newest software. Look closely at the left & right edges of the chart, and note that the HP scale goes from 150 to 550, while the Tq scale goes from 350 to 550. Notwithstanding that, you definitely can compare the two runs because they're both charted on the same dual scale.

 

[HouseofSpeed]

While from a mathematical standpoint torque and horsepower are always equal at 5252....in the world of the chassis dyno, that is not a given. In fact, in the setup section for the graph with the Winpep software...you can choose to "force scale" the graph and it will shift the curves to cross at 5252.

The equation, for those that are wondering, is:

HP = TQ(RPM)/5252 OR TQ = HP(RPM)/5252

 

[treynor]

To be precise -- using US HP and ft/lbs for Tq, the two are always equal at 5252 RPM. However, a dyno chart will only show the HP and Tq curves crossing at 5252 RPM if the chart has the same vertical displacement for both at the the value they achieve at 5252 RPM. The degenerate case is thus where the vertical displacement for HP and Tq is the same for the entire chart, and there is just a single scale used for both.

Also, since math IS one of my areas of relative expertise (and, FWIW, engines are not), I must point out that the mathematical relationship for US HP and Tq expressed in ft/lbs is actually:

Tq = (HP / RPM) * 5252, or HP = (Tq * RPM) / 5252

As you can see, if RPM = 5252 then it cancels with the 5252 in both equations, leaving HP = Tq.

ObModerator note: we need a "geek" smiley.

 

[MES]

Has anyone tried a bigger cam in the Viper or have experience with it? It seems to me that a cam with peak HP around 5600-5800 would be the ideal for the Viper. Most people run the engine up a little above that range when shifting. I thought you should shift 300-400 rpm above the peak HP to get the best acceleration.

BTW that is an impressive gain in HP with just the head replacement. How does the performance head from mopar compare, I assume not very well as nobody seems to use them.