Compression ratio with Hennessey heads

[Bill/APEX Motorsports]

(I decided to start a new thread, as it was--ahem--going astray.)
The following quote is from Ben Treynor:
"Compression ratio unknown; compression test went from 165 to 195-200, which is about 10:1 per APEX. Car runs geat on CA pump gas, no detectable detonation during dyno runs (and we were listening for it!)"
We did, indeed, check the compression on Ben's Hennessey-modified cylinder heads. First of all, let me say that 165psi, which is what we usually see on stock heads, is pretty low for the supposed 9.6:1 compression ratio. 9:1 5.0 Mustangs are typically 160psi, and 9.85:1 DOHC Cobras are between 195-210psi, really consistently. It seems to us that the ratio from Dodge is overstated. No worries, though, as the cars make every bit of their stated hp.
Therefore, it leads us to believe that the Hennessey heads are around 9.8-10:1. Again, that doesn't worry me, as they made the impressive hp numbers that John promises. He said they took off .050" from the deck surface to increase the compression ratio. The supplied pushrods were too long, so, using our adjustable pushrod length checker, we determined the correct length and procured new pushrods so the T&D rocker tip resided on the proper portion of the valve tip. (John had no problem crediting Ben for the pushrods once he receives them.)
So, it appears to us that the stock compression ratio might not be 9.6:1. Oh well. Ever hear of the '99 Mustang Cobra debacle? That cost Ford millions of dollars because the Cobras were about 20hp shy of their "new" rating of 320hp. At least Dodge's hp numbers are on the money, and Hennessey's products again performed exactly as stated.

 

[Fred(DrivingSchool)Kinder]

Hi Bill, if possible join us this Sat in Monterey for our Zone Event. Tuners are welcome to display their products and services. The best way to show your value added is to have a project car on display with mods detailed. Dan Cragin of Santa Monica Dodge will be there and Ted May will also be on hand. If interested send me an e-mail [email protected]. Ben's car would be perfect to put on display.

 

[Marc Lublin]

Bill,
I was unaware that you can check compression ratio's by doing a compression test. I thought there are too many variables like blow by, especially in a used motor. Are you sure you can get an accurate reading that way?
Shouldn't Hennessey have known that you can't just send pushrods when using T & D's because they have to be measured to each individual motor? T & D will give a free pushrod length checker with each order for just that reason. It is virtually impossible and amounts to a guess to supply them before measuring. I'm glad you caught that or Treynor's motor wouldn't be around for all that long. For anyone reading this thread, please never install T & D shaft rockers without measuring pushrod length, this can severely damage your motor. I'm suprised HMS didn't know that since I posted it in another thread concerning them.

 

[Marc Lublin]

John,
My check engine light comes and goes like most 00's with modifications. As soon as I find a fix I will everyone know. If someone else does, please let me know (with the exception of you John, you know I don't trust you for the obvious reasons).
Maybe you can enlighten me as to why you would send a set of pushrods out when T&D says they must be measured first after the motor is put together? This would be fine if you told Ben "I'm sending these in the hopes that they fit, if not send them back" I know when you sent mine to me, I had specifically asked you if they needed to be measured first and your response was that you do this all the time and you know the size I need. The T&D representative got a good chuckle over that.

 

[Tom Welch]

WOW!!

This thread is getting intresting.

Concerning compression ratio calibration with regards to cranking compression, is not much more than an educated guess.

Change the cam to one with a wider lobe seperation or different duration and lift at .050 and watch the cranking compression change.

Just my $.02

Tom
Http://btrviper.com

 

[HouseofSpeed]

Hmmmmm....being the stickler for detail (and all-around skeptic) that I am, I notice several flaws in reasoning here.

First and foremost, as another poster mentions, it is virtually impossible to gauge compression ratio via a compression test. The two are not related in the least. The compression ratio of a given cylinder anywhere in the known universe is a comparison of volumes. The volume of the cylinder in question at both top and bottom dead center...that is where we get the term ratio. IF the Apex theory were viable....I could have an engine with a bent valve (the valve is off the seat) and it would give a low reading...therefore I would have to assume that I have a low compression engine on my hands. This presumption would be false 10 out of 10 times. Perhaps I am being too picky, but never doubt the presence of false logic in this business.

Second point....directed at the great and powerful Mr. Lublin, to say that every set of T&Ds installed on a Viper head requires a different length pushrod is absurd, and honestly..the geniuses at T&D know not of what they speak. IF a uniform amount is milled from the deck surface of a cylinder head, valve lengths stay the same, and the installed dimensions of the valvetrain do not change....the likelihood of needing a different pushrod in every example is ZERO. T&D supplies a jinky setup tool with the rockers that is about as useful as the box it is shipped in. There are many variables with a shaft mounted rocker setup...including shims for the stands, pushrod cup placement on the rocker (when changing ratios), and finally pushrod length.
Bottom line....trust your engine builder, not the goobers that make the product (they manufacture the part...they do not install the part).

 

[Martin D]

Amen Kyle!!!!!

Well Said. I had a conversation with David McIntosh today of McIntosh performance... He said almost EXACTLY what you did. Good to know you guys are on the ball!

Buh-bye.....John, you are too much.

Regards,

 

[Marc Lublin]

Kyle,
Great and powerful? Thanks, but when I am in the know about something I say it, sorry if that offends you. I did not say that they will ALWAYS need a different length pushrod but many times they do and always should be measured. Yes I do trust the manufacturer on this, you should too. It is their design and I would guess they have done tests that show that when they are adjusted too far in either direction it does impede the flow of oil. T&D does make the best setup so far for the Viper and I don't think that they are just trying to make it harder on people to install. With all that said, why would you assume that a motor would take a specific length rod? Like I believe you said, sometimes they are shimmed, or meat is taken out of the head to get the geometry correct. There are variables here! They are not just recommending this for heads that are milled or different valves installed they recommend it even for a straight swap of rockers. Yes, of course trust your engine builder if you don't do it yourself, you kind of have to, don't you? If they are good, they will follow the proper steps as Apex did.
John, I am pleased that you now respond to some threads. Lets see, you ripped me off, said you would return my money almost a year ago, almost never returned my calls after that, then finally did the right thing in regards to the money after pressure from everywhere and you don't trust me??? What world are you living in? I would be happy to list the reasons again why I don't trust you, but more than anything, and I can't stress this enough, I would love to hear why you don't trust me.

 

[Chuck 98 RT/10]

Getting back on topic here. Clarify this for a shadetree mechanic...if I purchase T&D rockers and pushrods, is it possible that the T&D pushrods may be the incorrect length and they will send me the correct ones after I use their measuring tool?

 

[Marc Lublin]

Chuck,
You can speak with Alan at T&D (775)884-2292. He will tell you that first you need to get the geometry correctly on the rockers and the instructions show you how. After that is done and the heads are put on the car, you need to insert and adjustable pushrod length checker. As per instructions you will then be able to find the correct length. After you determine the correct length, purchase a good set of pushrods in that length. It's not as complicated as it sounds. Alan has told me that they will always send you a adjustable pushrod for measuring, when you order a shaft rocker set from them (if you ask for it). If you have had any head work done on the heads you will need to make sure that the valve stem tips are all at the same height. A good machine shop shouldn't give you a problem in that area. If the heights are not all equal, it is conceivable that you will need a bunch of different length pushrods.
Hope this helps!

 

[Marc Lublin]

Shakedown,
I don't know you and the language is definitely not called for, and to top it all off, you are wrong! Call T&D. Why don't you stop and ask yourself why the pushrods Ben was sent were the wrong size? If what you are saying it true, HMS should have had no problem sending the correct size!

 

[Marc Lublin]

Quick question:
Do either Shakedown or Kyle Kent work at HMS? I know this is a little off topic but a little birdie told me at least one was involved with Hennessey.

Thank,
Marc

 

[getbit]

I don't know about shakedown, but Kyle has NEVER hidden his association with Hennessey. Not a secret. Very knowledgable and helpful person.

 

[Marc Lublin]

I heard Kyle is one of Hennessey's techs, on the payroll. Is this true? It's gotten mysteriously quiet in here. I don't know which question it was: The question to John, the question to Shakedown about the rods, or the general question if they work for HMS. Feel free to respond guys, I don't bite.

 

[Sean Roe]

Irregardless whether or not the every set of cylinder heads leaves a tuners / machine shop the same every time, there will always be other production tolerance "variables" to be dealt with, such as deck height. It's a good idea to check the setup at least once before the final install. What's it going to cost you, a little bit of time to know the setup is right? That's time well spent in my opinion.
Like my grandfather used to say, "measure twice, cut once".

 

[Marc Lublin]

Shakedown,
I have to say that there is no doubt that you did proove who the A$$ is on this board. Probably better for all, if you do just sit back and watch. You are definitely not worth any more of my time.

 

[HouseofSpeed]

Marc....yes, I do work at HMS...as getbit noted, I have made that more than obvious. I also understand that you and John have issues....those I am not interested in, nor were ever a part of, what I am interested in is the technical rep of the shop.

I do a ton of work that is not Viper related at my own shop and as such I can't let my guard down. I call a spade a spade...and there is a ton of misinformation in the performance game. I will tell you that if you talk to 3 different people at the same manufacturer, it is highly probable that you will get 3 very different explanations or answers for the same query.

To simplify things a little here.....if there were actually that many variances...or margins of error....in the valvetrain of a Viper, how does the factory setup work deadnuts every time with the same length pushrod??? Its called a hydraulic lifter and consistency in the machining/assembly process. Which I can duplicate in the shop EVERY TIME.

Sean, your theory of deck differences is a non-sequitur as well....how many Vipers have had a block replaced and/or decked??? For the most part, this thread is discussing cylinder head replacement on the original short block...nothing more, nothing less. I will tell you that deck clearance on a "new" (meaning less than 1K miles) short block can vary quite a bit from hole to hole (as much as 10-14 thou). Which just goes to show that DC's QC ***** on their "handbuilt" pride and joy. Even that would only affect P-V and CR to a small degree. It would not affect plunger travel, stand shims, or pushrod length.

There are other issues with cam design as well if we really wanted to be technical....all of which would take up way too much bandwidth considering the actual focus of this discussion.

For those out there that might not be cozy with the concepts or terminology in this little treatise....to mill a head or deck a block will effectively change the relationship of the head to the centerline of the block (cam/crank) which can, in turn, cause fitment issues with the head/intake/exhaust combination..and can cause valvetrain geometry issues as well. The deck clearance issue I mention above is NOT the same concept...deck clearance is the distance from the top of the piston flat to the deck surface when the piston is at TDC...measured in thousandths of an inch.

I have been in the engine/tuning business for 15 years (coming from a family with over 50 years in the race engine business)...everything from exotics to Pro Stock....and my record speaks for itself. I try not to be the bad guy, but I do get pissed when my work (directly or indirectly) is called out and labeled inferior or short-sighted. I can say that I have only been with HMS for the last year...and as such cannot be the defender of past errors or poor engineering, but I can speak on the topic at hand...and tell you that I have set up more rocker arms than T&D has produced...their info is not the final word.

 

[Marc Lublin]

So Kyle, why did Ben get pushrods that were the wrong size? Why did HMS send me the wrong size pushrods as well? (less than a year ago, I think you were there). I do understand how a hydraulic setup works, but if you want to do the best thing for your customers you should make them aware that they should check.
It sound as if your intentions are good, but it would probably be a good idea to put something down on your posts that shows you work at HMS. I would have never known had someone not emailed me. Intentional or not, I believe you have some bias on issues concerning HMS.
Good day all!

 

[Martin D]

Marc,


How much were your pushrods off???

Thanks,

 

[Marc Lublin]

Martin,
To be honest I don't remember. I do know that they were too long and definitely would not fit.

 

[HouseofSpeed]

Marc....are you sure that the stands were installed correctly??? We have had several mail-outs that allegedly "had the wrong pushrod", when come to find out...they had installed the stand incorrectly. The V-10 lettering faces the bottom of the head....this was also the case for Ben and his installer at Apex. I guarantee that the pushrods we sent are of proper dimension if the rest of the package is installed correctly. Your rods were a 7.700 and will provide the proper geometry with the .120 shims supplied by T&D in the kit. In Ben's case, the pushrods are a little shorter because of a change we made in the head machining process. It amazes me that the 5 guys in our shop can set up T&Ds on Vipers...and there are so many "performance" shops that call us for lifter pre-load specs and some that act like they have never set a rocker for a hydraulic tappet before. I am going to start a 976 number for tech questions...it is apparent that there are a lot of people making money off of the unsuspecting and doing so posing as a speed shop.

As an aside, if you were more in-tune with what goes on here in the VCA BB...you would know that I work at HMS. IT IS NOT A SECRET...NOR HAS IT EVER BEEN.

In closing, Marc I am truly sorry that your experience has been unpleasant...and I realize that you do not trust HMS, but the one thing you can definitely count on....I am giving you the real info on your heads. The truth shall set you free Marc.

 

[Tom Welch]

I've been following this thread for a while now and Id like to make one comment concerning rocker arms, their geometry, maintenance and the such.

I am going to offer very soon a cylinder head package(after testing on my own car, of course)and with 20 years experience racing mopars of every head design to come out of their factory, I can attest to one thing;

For the amount of power, compression and loaded valve spring pressures and rates that these cars have and the type of valve train installed from the factory, to spend an additional 1500 to 2000 dollars is not worth the minimal gain in power. Yes, thats a bold statement but here is some proof to consider.

1. The difference between 1.6 and 1.7 in rocker arm geometry is neglegable.

2. Hydraulic lifters really DO NOT require adjustable rocker arms

3. Adjustable rocker arms are just that, ADJUSTABLE. Adjust them, run them, adjust them again, run them some more, adjust them again.....bla bla bla.

4. Miss align them and all sorts of fun stuff can result. Wear on valve tips from mis-alignment, improper lash will result in a possible loss of torque, pushrod length....which seems to be a major consideration, shaft mount(t&d) vs. stand mount(crower)the comparison between them, and so on.

5. These are not 2000 hp hemi's under high compression with 1000psi spring loads. Your stock rockers are your best bet.

Next month when I bolt new heads on my own car it will have the old stamped steel rockers in place....and I will have piece of mind, not having to constantly wonder about valve lash adjustment(did I get the # 10 exhaust right...i hear a ticking sound...and so on).

To me there is nothing better than pulling to the starting line and not worrying about anything other than beating my opponent. Valve train adjustment on a 600 hp engine with a hydraulic cam should not be at the top of anyones worry list.

Just my $ .02 No flames intended to the rocker arm mfg's. They are fine products and I have used T&D rockers, Jesel Rockers, and others on higher horsepower v-8 applications with Roller lifter camshafts. At those higher spring loads, and with larger, heavier valves and higher compression the factory rockers are not strong enough.

Tom
Http://btrviper.com


"She had long black hair...............hanging from her left nostril, and every time she sneezed it popped like a bullwhip!"

 

[Marc Lublin]

Kyle,
Everything was installed correctly and if my memory serves me I think I used 7.70's in my 2000. Which may show that all setups are not equal. I thought I was pretty in tune with this board. I am not saying that you hide the fact that you are a Hennessey employee, but you may want to put that next to your name. I read plenty here and have never seen that you work there. Probably just missed the posts, but if I have, I'm sure others have as well. Besides the fact that people should know where your advice is coming from, if you work there I would think you would be truly proud and let the community know.

 

[Bill/APEX Motorsports]

The pushrod length we ended up using was 7.500", and the T&D rocker arm geometry was exactly as it should be, with the rocker tip contacting the middle half of the valve tip.