Hmmm....DOHC VS Pushrod...

[donk_316]

http://pennockssucks.saturnet.net/phpBB/viewtopic.php?t=291

==DISCLAIMER==
All the following info is based on theory and numbers. Not actual dyno results.

FACT - DOHC head does and will flow more than a gen3 head.

FACT - PUSHROD block design is superior with cross bolted main caps. Both blocks share a structural oilpan design and re enforced 'timing' covers.

FACT- DOHC motor wieghs more than a PUSHROD. Enough of a wieght difference to make a difference to someone who is making every pound count. I dont have exact numbers but anywhere from 50 to 120 pounds has been qouted.

FACT - The DOHC has 5 "camshafts" VS the PUSHROD having 1. Less rotating mass would (and should) mean less frictional losses and parasitic drag in the PUSHROD. The "wieght" of lifters, pushrods and rockers isnt even close to enough to say they "even out" so dont go there.

FACT - Near limitless camshaft options for the PUSHROD block. Solid or Hydraulic. Roller or non-roller. Mild to Wild.

FACT - The DOHC camshafts are considered the bottle neck and limiting factor of the entire motor. Only regrinds are available and they are... questionable.

I was considering building a DOHC motor instead of this PUSHROD motor due to the "way better" head design especially under boost conditions.

TEST 1
With a DOHC stuck with its factory cams / stock heads and a boosted VS the PUSHROD with custom cams / gen3 heads and the same turbo...

The PUSHROD makes 10 peak hp MORE at the SAME RPM.
The PUSHROD makes 20 peak ft# MORE at the SAME RPM.

Near identical curves. No noticable advantage for either motor.

TEST 2
With a DOHC customs cams / stock heads boosted VS a PUSHROD custom cams / stock gen3 heads same turbo...

The DOHC makes 120 peak hp MORE at 2000 RPM higher. (!!!)
The DOHC makes 40 peak ft# MORE at the SAME RPM.

Should also be noted that the DOHC torque curve is near table flat ( and over 300ft#) from 3000 to 8000rpm now.

Tell me what you think. Which direction would you go if you were building an all out V6?

[pepsi_coke]

Re: Hmmm....DOHC VS Pushrod...

FACT - The DOHC has 5 "camshafts" VS the PUSHROD having 1.

I have one of those weird motors with only 4!

[donk_316]

Re: Hmmm....DOHC VS Pushrod...

FACT - The DOHC has 5 "camshafts" VS the PUSHROD having 1.

I have one of those weird motors with only 4!

Next time your motor guy pulls your motor apart, youll notice the cam blank or balance shaft hence the 5 cams.

Please only respond if you have seen the inside of a motor or your name isnt Aaron.

[Crimson Fury]

RE: Re: Hmmm....DOHC VS Pushrod...

dohc, easier to get more out of it(custom work needed!). some where ben posts what is needed to get a 3.1 or 3100(don't remember) up to like 200-300 hp, and if i iremember right, not easy

[geoffinbc]

Cool comparison. That is one honkin difference in HP between the two at 2000RPM. Whats the rest of the graph look like?

[donk_316]

Cool comparison. That is one honkin difference in HP between the two at 2000RPM. Whats the rest of the graph look like?

The difference was not at 2000 rpm. The DOHC made 100hp more 2000 rpm higher than the Pushrod peaked at. Sorry if its confusing.

In that instance i think it was 6500 vs 8500 rpm.

[geoffinbc]

Ahh gotcha. Well then that is not suprising. The extra 2000RPM it what accounts for such a difference in HP.

[Anonymous]

Well let's make this fair and let us retard or advance our intake cams and exhaust, but leave them stock, just turned. They are still the stock cams. I do not know what's best for boost, but you can get much better gains with moving them around for N/A, so I assume boost would do the same. Also, I hope you used a 96-97 motor for this, you should have since you used a gen 3 pushrod.

Holy crap the curves on the DOHC motor are amazingly higher after the cams.

Another thing you didn't take into account is size of the booster. A 3.4L DOHC needs for sure a bigger unit(whether it be turbo or s/c), than a pushrod 3.1, and probably bigger than a 3400 as well, and I bet the size used was based on the pushrod motor.

I don't think there is any question as to which one I'd choose...lol

And at that link you say that the pushrod heads flow more than the DOHC stock vs stock N/A. Bullshit. I doubt you could get a pair of 60*V6 heads to flow a stock 96-97 head. Even with bigger valves, porting/polishing, etc. 24 valves is FAR superior, even under boost. We just have cam specs holding us back.

About the weight, it does weigh more I'm sure, but nto that much I don't think. People weighed the DOHC as is, compared it to a as is Fiero 2.8. That really isn't fair either. The DOHC still has its power steering pump, and the 2.8's crank weighs less (less stroke). I think a 3.1 as is should be weighed against a 3.4 TDC as is, then we shall see. I'll weigh my built 3.4L TDC with the Fiero 2.8, and we will see.

And there is much more than 350fwhp N/A left in the DOHC 3.4L, and I will prove it.

But thanks for the educated, valid points, even if I argued with most...So far, the pushrod is going faster. I think high 13s are the fastest time posted by a FWD 660 N/A so far. And I believe I am the fastest N/A FWD TDCammer, and all the evidence to support it puts me in the high 13s, but I have yet to actually run it. And I have basic bolt ons (and headers...still bolt on, but custom), and a pretty much stock inside, compared to Colin and them's cars, which go much farther on the insides.

[Anonymous]

The extra 2000RPM it what accounts for such a difference in HP.

Wrong. I can all but guarentee that at the same 6500rpm, the DOHC was still making more power, noticably more. RPM doesn't add horsepower. Paired correctly with intkaes, cams, headers, and such it can, but very minimal amounts of the power increse will come solely form RPM.

[donk_316]

The extra 2000RPM it what accounts for such a difference in HP.

Wrong. I can all but guarentee that at the same 6500rpm, the DOHC was still making more power, noticably more. RPM doesn't add horsepower. Paired correctly with intkaes, cams, headers, and such it can, but very minimal amounts of the power increse will come solely form RPM.

In this scenario. The DOHC and PUSHROD were dead even untill 6500 rpm when the PUSHROD flattens out and dies where the DOHC just keeps climbing to 8500 and stays there till 10,000 rpm. It was really impressive...
Too bad the cams needed to make that happen dont exsist.


Please post how your planning on getting 400hp NA (no boost and no bottle) from a DOHC. Im curious.

[RednBlack]

And there is much more than 350fwhp N/A left in the DOHC 3.4L, and I will prove it.

But thanks for the educated, valid points, even if I argued with most...So far, the pushrod is going faster. I think high 13s are the fastest time posted by a FWD 660 N/A so far. And I believe I am the fastest N/A FWD TDCammer, and all the evidence to support it puts me in the high 13s, but I have yet to actually run it. And I have basic bolt ons (and headers...still bolt on, but custom), and a pretty much stock inside, compared to Colin and them's cars, which go much farther on the insides.

Aaron, I'm calling your bluff. You say you are fast, but can't figure out why a fucking engine is locked up? I gave you the benefit of a doubt, you kept on being a MORON! (At least an idiot just doesn't know) Just bring the bitch to South Bend. It is a mission of mine to put you in the smoke..... You used to make me laugh. I think you are more of a PC racer than a Tracky! Put your rubber to the road! :P (this is gonna hurt)

[Guest]

All I have to say is Aaron, shut the fuck up, based on your replies to this thread alone you are extremely uneducated when it comes to comparing engines, hell even just teh way they work. You don't seem to understand the concept of torque VS RPM to "make" more HP, or turbo sizing at all, most basic turbo applications are selected based on displacment, for a starting point. Very few of us actually take into account other variables.

Mutiple valves are not ALWAYS supperior, do you have any idea how the air flow gets stalled at certain RPM in the cylinder due to two different wave fronts bouncing into one another? No didn't think so.


Anyway....

I'd build a pushrod, less parts, cheaper for custom parts, lighter, physically smaller (more room for turbos ). There is also teh fact that engines have been making gobs of HP with pushrods for years, the basic technology and ideas are out there.

DOHC just has the "OMG!" effect.

[Anonymous]

I'll go in order here...But not in detail cuz I don't have time, or the desire.

I would rather not post it. It is floating over at W-body and PFF, they they can appretiate what might be without bringing it down and doubting it, but I am hoping for over 400hp, and hopefully right at 400 to the wheels. This will all be done at a max of 8,000rpm, and for now stock cams. It probably won't make 400 with factory cams, but that estimate is with custom cams.

I would love to. But I have too many things going on. Both of my Z's are in pieces, and the motor from the white car is going back to stock awaiting my Fiero project. And I have to be in school soon, minus a car. Oh, and I don't have a driver's license...And I knew what caused it to seize, I wanted to know how. No shit water got into the motor...I want to know how it did.

More RPM helps make more hp, but by using all of the same parts, minus valve springs, and just runnign higher, hp won't be increased significantly. RPM doesn't create horsepower, it just helps. As for your air waves, who cares? It certaintly isn't hurting my motor at all."

Sure they've been making "gobs of power for years," but we are trying to make more gobs of power, yet keep weight down (turbos add weight), and still make it efficient and streetable. And let's compare your car and mine. You have .2L less displacement (big deal), and a turbo. Yet I am still running just as fast, if not faster (theoretically, no actual proof yet). And I have basic bolt ons, very few at that. A turbo is not a basic bolt on. So when we can have the same, if not more power, from a N/A DOHC, than that is better. The turbo(s) add weight, in a Fiero intercoolers don't exactly get much air flow, tuning is a bitch, streetability is negatively affected, engine life is shortened, reliability is hurt, and so much more, all for the same, even less, overall power.

Turbo sizing, to the very beginnings, deal with displacement. It isn't all about PSI, its about air flow. Bigger, mandrel bent charge pipes and boost goes down, hp/tq goes up. Hell we added a DOHC head to a friends Merc, and his boost went form 21 to 14. Yet the dyno showed 46 more front wheel horsepower. 4 Valves definately came into play. You get more air into the cylinders, therefor you need a bigger turbo to supply the air, at a given pressure. It is that simple.

I'm done now, more to come...

[RednBlack]

We are all less educated for reading the last post

[donk_316]

You cant go all over the net saying your going to make 400hp but your not even close and with make believe camshafts.

You cant say your faster becuase you think you should be.

Isnt there a law against this sort of thing??

My motor will rev to 8000rpm. See 400hp. Be faster than you. From 400 cc's less also. This is all a fact and the motor is being pieced together as we speak. This "untunable fiero turbo" will be ran by a 7727 ecm and a SAFC-2 and AVC-R

Dont post bullshit claims. I KNEW you cant get 400hp from a NA DOHC...