Why 12-valve makes more power than 24-valve?

[Rob Thomas]

Hey guys,



I'm just wondering why the 12-valves make more power,is it that they have been out longer and more is known about them, or is it somthing else? Just curious I quess,thanks for any comments.





Rob

 

[rspinks]

bigger stronger pump

I think it's the fact that the P7100 pump is way oversized for the 5. 9L engine. I thought I read in Issue 35 that the P7100 is used on the C8. 3 engine, so when used on the 5. 9 it is heavily restricted in stock form. There is way more capacity available in the P7100 than the VP44, so minor pump mods produce big gains.



In theory the 24v head should have better flow characteristics than the 12v, so if you replaced the VP44 with a P7100 on a 24v engine you should be ahead of the 12v engine.



RS

 

[Don M]

The 12 valve has the advantage of the P7100 injection pump. Higher pressures and more quantity of fuel can be pumped with the P7100.

The 24 valve head has the advantage in stock form compared to the 12 valve head, but if you were to port both heads the 12 valve head will have the advantage slightly.

I like the 24 valve engine having the injector centered over the top of the piston though. It is easier or less expensive to make power with the 12 valve engine up to a point and then they both get expensive.



I had my head ported to help build a good foundation for future HP gains and get the EGT reduction.



Don~

 

[TxDieselKid]

I don't really think that the 12v's make for more power, I think they just do it cheaper. The 3 supposed highest horsepower trucks, are 24v's,(in no order) JetPoilet, Cummintstroken, and Lawarence from DD are all 24v. The only difference is the DD truck has a p7100. Wish I had one of those...



Andrew

 

[Rob Thomas]

Yea, I did some checkin' a while back, the P7100 conversion to the 24-valve is REAL expensive,so thats out,maybee a ported head though. My list of "wants" is extreamly long,but I'm sure I'm not alone.





Later ,Rob

 

[Joseph Donnelly]

I feel the ported 12 valve head flows a lot more than the ported 24 valve head. The P7100 also has more fueling potential.



When you compare 12 and 24 valve trucks, it is better to do so as diesel trucks, not bottle babies. Propane and nitrous injection avoid the design parameters you are trying to compare. Air flow doesn't matter much when you add all you can use via nitrous oxide. Fueling similarly, when adding propane. You really don't learn a whole lot about the engine because you are avoiding its nature and characteristics. Additionally, some folks are really pushing the capabilities of the engine for daily, durable performance. They have to change head gaskets frequently. If you blow a gasket almost every time you use the bottles, you are not really making usable, durable power. Soon as that is fixed, we will find the next weak link and it will probably cost more and take longer to fix each time.



Mark's truck (Diesel Dynamics) made 546 hp last week on diesel fuel only, with the VP44. Jetpilot made 511 on diesel--the bottles add a lot on his Ram, but that isn't the 24 valve engine combination talking, it's the bottles. No criticism or denigration of his accomplishment is intended, but you see how you are testing the performance and delivery systems for the additives, when you look at only the top hp with "drugs" not the engine parameters that you are interested in. You also have to consider that some folks use a lot more nitrous, for example, than others. Engine durability (presently, head gaskets are the first concern) may mean more to some than to others.



Sickly with his poor little 12 valves has run from 602-614 depending on injectors etc. on #2 diesel only. Lawrence and I have planned several experiments to sort out the best combinations whether 12 or 24 valve. Since everyone starts with one or the other, and changes get expensive, it is no wonder many Rammers avoid or cover up inherent engine design deficiencies with propane and nitrous oxide as cheap "fixes" and "enhancements. " However, one reason I stick to diesel fuel only is the durability issue. Another is the cost to operate and refill tanks and bottles.



In summary, if you want to compare 12 and 24 valve engines, consideer the drugs separately.

 

[Rob Thomas]

Joe,



Thats what I intended the discussion to be on, no DRUGS, I'm not a fan of them,like you I want reliable,usable HP. After all,these are Cummins, not PSD's.





Later, Rob

 

[KatDiesel]

Like everyone else has said, the P7100 pump is the "ace in the hole" for the 12v trucks.



Personally I like the VP44... . since I can adjust the levels of power and smoke at will. You can sort of do this on the 12v with a valet switch, but not to the same extent.



Yes my truck will have a bottle eventually... ... for the strip. After I get the 12's on #2.

 

[americana]

what's involved in putting a P7100 into a 24V? i know some guy put one on an engine in a hummer, don't know his reasoning behind it, though.

 

[CUMINNTSTRKN]

rob



don't worry you can keep up with just about anyone with a vp-44, and imo it's easier to do. all you need is a big set of injectors and a edge comp box and you can make over 500hp. of couse the 12 and 24 both need a bigger turbo at that level, and you need to add a new lift pump to the 24v. it seems the 24v is more just bolt it on and go. the 12v seems to need a lot of tinkering, to get big #'s



friday will be fun, i guess we will see who's on the porch. i'm sure there will be lots of whining. yeh but he used drugs:{ :{ that's not fair. it's funny i guess most of you guys have never competed in a motorsports type event. i'm not using anything that isn't available to everyone. yes i have blown 3 head gaskets. but 2 of them were on my ho motor. i blew the third one on my current truck when the boost went over 75psi. now that i have fixed the head problem i can make seem decent hp without a headgasket failure.



joe would be hard pressed to find a more drivable truck than mine. i'm driving my truck 2000 miles to go to this event. as i have said before we can hook up to a heavy trailer 12k or more and see who can climb the hill the fastest, without melting there motor down.

are you going to wait until friday to dyno? that way we will be on the same dyno same day.



jim

 

[Vaughn MacKenzie]

12v vs 24v ported headflow

Joe D. that is interesting a 12v head has more flow capability than the 24v when both are ported. Are the ports on the 24v small and restrictive? Is there a limitation on how much they can be hogged out? In pictures the valves on the 24v look a bit small to me but you would think with 2 runners instead of 1 on each side would give the all-out advantage flow-wise to the 24v.



This doesn't seem to be widely known but I know Piers does 3 levels of head porting on the 24V, the most radical (stage 3) involves putting in bigger valves (pretty spendy job). I didn't ask about the 12v but I would assume a radical head job on a 12v would involve bigger valves as well.



Vaughn

 

[Mojo293]

Bigger valves would help alot. When it comes to BIG hp you have to flow the air. I've been helping with diesel tractor pulls for a while and know that air flow makes the difference in RPM. The Pro-Stock tractor guys are putting $25-$30K in just the heads for their tractors.

 

[Joseph Donnelly]

It is hard to get into the intake ports far enough to do a thorough job of enlarging the ports. Both 24 valve intake ports look to be a lot smaller than the single 12 valve intake port, although I haven't measured them. The intake plenum is much more restrictive on the 24 valve head, as well. Bigger valves help but there isn't much room to do this modification without causing other problems on swirl, seat cracking, and airflow. I am running stock valves. As I said back in TDR#23, air+fuel=power. The 12 valve system can give more of both air and fuel, at the current level of development. However, the practical difference isn't great. Both setups can make over 500 hp and 600 is hard to get with the engine acting as designed--air through the turbo, fuel through the injection pump, #2 diesel and ambient air only. But when you do that, you learn a lot, get a lot of satisfaction with your accomplishments, and get to use you head gasket for a while

 

[Roger rodbolt]

Re: Why it isn't entirely so.....

Originally posted by RAMTHIS1

Hey guys,



I'm just wondering why the 12-valves make more power, is it that they have been out longer and more is known about them, or is it somthing else? Just curious I quess,thanks for any comments.





Rob

Rob,



I know that the "true to 12 valve" guys will disagree but up to 500 horsepower the 24 valve trucks have the advantage. I currently own three 12 valve CTD's and one 24 valve truck. I dearly love the old P7100 pump and it is easy and cheap to change or grind the plate for cheap/quick torque and horsepower.

But that advantage quickly ends. Above 300 hp power the 12 valve engines quickly run high egts, especially at higher rpms. While it is true that both engines benefit from larger turbos, exhaust and air intakes, the 24 valve engines will stay cooler with matching componets and the same horsepower. This is very important if you are towing or using your truck for a daily driver. Lots of power for a few seconds doesn't mean much... ... ... to me. The 24V engine will make over 500rwhp on #2 only, without head porting or headgasket trouble and keep egts in check with 50lb's of cool boost.



I believe that the stock 24V head may flow better then a stock 12V but more importantly the injectors are placed for better fuel burn, the VP pump puts out higher pressures and will deliver the fuel in a shorter period of time (assuming correct lift pump pressure, timing, and big injectors) which is why the 24 valve engine will make the same power as a 12valve with less smoke.



A couple of years ago I had a reputable aftermarket/performance supplier tell me that anyone that said their 24 valve made over 400rwhp on diesel only was full of "manure", a year later myself and several others were making 500+hp at the rear wheels. The 12 valve guys have had it easy for years as they can just dump in excess fuel and dyno the power. This is only true if you have a '96 through '98 manual trans with the 215hp pump. If you have an auto or an early 12 valve then you must spend major $$'s for a pump upgrade or mod's to run with the push button 24V electronic marvels.



Now before I get things too stirred :-{} , the 12 valve wins in a max horsepower comparison because the P pump can be upgraded to huge fueling levels while the VP44 has only recently been "tinkered with". JMHO I've learned to appreciate both engines!!

 

[Stefan Kondolay]

The guy that does mine and piers head porting locally doesn't agree with Joe. He said that he could get more from a 24 valve head. He has done both and could probably even verify if with flow #'s. I know that he did Pier's old blue 12 valves head and it did pretty well.

 

[Joseph Donnelly]

Stefan, most flow bench work is done at a vacuum applied to the chamber. The situation is different at high boost, I suspect. However, I am willing to look at and discuss data. As I said, I don't have hard numbers.

 

[Marco]

All,



Undervalved engines better than properly valved???

Nahhhh, c'mon that can't be!



Let me point out only the timing. The 12 valve is fixed, while it is "free" for the 24 Valved engine. In other words that allows to make more hp with less stress on the engine.



The centered injector in the 24 V.....



Well you all know that I like electrons, so let me end this MSG with a question.



How much fuel can the P7100 deliver for each injection stroke,

and how much can the VP 44 deliver?????????



Marco

 

[Rob Thomas]

Okie-dokie,



So they're both pretty close in comparison, that makes me a little happier,but I'm still unclear about one thing, headwork? Do I need it? Would I be better off with a cam change? I had the truck dynoed last week,387Hp and 974lbs torque with the stock turbo,yea STILL, but I'm not complainin' about my 24-valver, just wondering about the next step is. I think I'm just about done with the "bolt on" toys, now it's time to get to the meat-n-potata's of this puppy. I want to be in the neiborhood of 550HP,... ... ... ..... NO DRUGS though!



Thanks guys, you really know your stuff!



Later, Rob

 

[TxDieselKid]

If you want 550, no drugs, then you need some $$$. with that $$$ you should look into getting twin turbos(or one BIG turbo at least), o-ringing the block, a ported head, a cam, and some bigger injectors. 550 is a huge number to shoot for, only about 4 people I can think of off the top of my head can hit that number in a 24v.



Your next step i would say is a turbo for sure though.



Andrew

 

[rspinks]

Why did Cummins go to 24V?

If the 24v head doesn't have some major advantage over the 12v then why did Cummins switch? Maybe the 4 valve combustion chamber design allows for the centered injector, which in turn achieves a better fuel burn with less exhaust emissions but doesn't necessarily flow better than the old design.



RS