So, what is it that makes an engine accelerate?

[Gearhead]

Thanks Steelcomp. I'll take a look at the thread later this evening.
I too don't fully agree with what Darin had to say and have some basic rod ratios we try to achieve in our hi rpm competition eliminator engines.
Has there been any threads on Hot Boat forum dealing with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
Thanks!
Gearhead

[steelcomp]

Thanks Steelcomp. I'll take a look at the thread later this evening.
I too don't fully agree with what Darin had to say and have some basic rod ratios we try to achieve in our hi rpm competition eliminator engines.
Has there been any threads on Hot Boat forum dealing with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
Thanks!
Gearhead
Nope. Haven't heard anyone talk about dome shaping to accelerate swirl, detonation reduction through better piston/chamber relationship, or boundry layer analysys, either.
Those types of topics are what I was hoping to get into with this discussion.
Thanks for joining in!

[Gearhead]

Steelcomp, I just had the chance to go back and scan the thread that included the rod ratio comment copy of DM and apologize for posting some of the same old stuff again. One of the post in the thread from cstraub69 when he was at PRI visiting with a drag race engine builder that was considering building road race engines reminded me of a story from a camshaft development session we attended in Detroit about ten years ago. Prior to looking at the actual cam designs, the sessions spent quite a lot of time in the design and matching all the other related components for the intended rpm use. We studied the wire size, number of coils, materials, etc and the mathematical harmonics of the spring and at what RPM this takes place. Presently a SpinTron is utilized to study these relationships in running engines.
Anyway, after the long study of spring, camshaft rates and rpm relationship where the design desire was maximum power while controlling the valve train for longevity, the question was asked by the instructor, "Do we have any drag race engine developers in the group", to which three of us acknowledged. He then stated, "Well, you guys can throw a lot of our study out the window! We have been studying controlled valve trains and inductions and you guys deal in what we refer to as "CONTROLLED DESTRUCTION!"…".
Now I need to apologize for what I have provoked. I asked you in a previous post if there were any threads along some of the relative lines of engine development with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
I apologize because this can become a very long post, even for general discussion purposes. I think I'll break this up into three related post so that it will be easier to respond. I am going to try and keep these post in as general terms as I can and not get into difficult to understand. These thoughts are not absolutes… just some info to promote discussion. I am not the expert.

[Gearhead]

Mechanical design of bottom end in reference to rod ratios: In maximum performance engines we need to keep the entire engine parameters in mind as the engine is a big air pump and we are trying to control this pump in a particular RPM range. From a mechanical point of view the ratio will affect many areas such as load on the cylinder wall, etc. From an engine rotation point of view the rod ratio will affect where the piston is in relation to valve events in the rotation or timing of events. For me this needs to balance with the cylinder head and port flow characteristics. In elementary terms a limited port for a particular size engine and rpm range may be assisted by a long rod or a short rod may help improve the initial signal or response from and extremely large port during the intake cycle. The longer rod provides a longer burn cycle during the power stroke. A very general statement is in a given engine a long rod may work better in a hi rpm application and a short one may help in a lower rpm application. In basic theory I tend to lean towards Smokey Yunich's theory of putting the longest rod in the engine, but there are exceptions. From a mechanical point of view, I also feel stroke length has a correlation with desired rpm range. Use a shorter stroke for hi rpm and a longer stroke for lower rpm torque and power. I'll step out on a short limb here and say for the RPM range used in a jet boat, I prefer a stroke in the range of 4" to about 4 3/8" for the best native mechanical advantage. In a BBC with a fairly normal induction a shorter stroke will have a higher RPM power curve and a longer stroke will have a lower RPM power curve. Now with the advent of impellers in the AA to AAA range, longer strokes can be used. Bottom line. The power curve of the engine needs to match the actual use be it impeller sizing, gearing, prop, etc.
Back to mechanical bottom end…. Generally, depending on the particular engine and use, I like to see a rod ratio in the 1.5 to 1.9 range. Sometimes the combination forces us to go a little lower. Now, in these maximum effort mountain motors that Kaase and other build that exceed 700 cid, they pretty well have to use these tall block and rods. My gosh… have you looked at the bottom end with a 5" to 6" crank installed? Man, that is a lot of metal moving around in there and just imagine the side load on the cylinder walls that from a time frame is exerted over a long time. (Low RPM, High torque = high pressure for a long period of time) So, yes… for any life we pretty well have to use the tall blocks and long rods and we still are having a hard time reaching… and 8" rod with a 6" stroke will only leave you with a 1.33 rod ratio.
What is the most efficient normally aspirated engines of today? In reference to this discussion I think we can say NHRA Pro Stock engines are quite impressive. Now, one of these would not be a particularly good choice directly out of the race car unless we make some changes to utilize the power. One change would be moving to a gear box or another would be change of components. Why? To utilize the power band (RPM range). As has been mentioned in threads, these things make their peak power over 9000 rpm. Let's observe what is going on in these peak efficiency engines that may not be particularly designed for long service life with their light weight parts and the aggressive cam designs resulting in short valve spring and lifter life, etc. But this thread started out about what accelerates an engine… Look at the parts for a 500" Pro Stock. Now, everyone is not going to tell you what they are using, but just observe the parts that are being sold by Pro Stockers in the back of National Dragster, etc. Now with statements by several major engine builders saying "we don't care about the rod ratio". Well, let's look at their engine… Now these are just out of the air figures for thought… Let's say the deck is short… 9.200 range and the stroke is in the range of 3.625… and with the thin rings and the ring package high in the piston.. lets' say a compression height around 1.265… well, we could just hook up the parts with around a 6.125 rod. This would give us about a 1.69 rod ratio…. Which may not be considered the best from the mechanical point of view, but not particularly bad and look at the other side of the air pump!!! Look what it does for the FLOW PATH!!! A straighter shot at the cylinder and now the intake and cylinder head can be used for maximum efficiency…. The induction system is where a lot of power and acceleration is made. Along with all this comes the shorter piston skirts, light ring package, short rods, small crank counterweights and small bearings which are LIGHT WEIGHT, lower drag, and reduced windage in their own right assist in acceleration. Have you seen the oil pan on a wet sump Comp Eliminator? Big boxes with small amounts of oil in the sumps….. Remember above… we need to keep the entire engine use in mind when considering design. Look at the DRCE III block…. Hmmm… short deck potential, big bore potential, large journal camshaft, additional camshaft support….

[Gearhead]

Induction System…. I'll try to be a little briefer in this post which actually is the one that is the most important. When Grumpy Jenkins published his Chevrolet Racing Engine book back in 1976… he first began with the detail of the block assembly. Then he came to the chapter on cylinder heads, and I am paraphrasing he said… we have spent all this effort on detailing the short block which good to bad may be 15 to 20 hp and now we are working on the heads which good to bad could be 100 hp. Basically…. Don't skimp on the top end!!! Again the overall use is the key in selection. Back in '76 there was little selection and now you can just about order any size head for any size engine and rpm that will work decent right out of the box. Too big a port will kill the velocity of the intake tract and conversely too small will restrict the engine. Now which one is best for you? That is the big question. Dynomation is a technical computer simulation that assist in engine design. There no easy plug and play program that can truly simulate your application, but some of these programs help. One fairly easy to use program that I like is Pipemax by Larry Meaux of MaxRace Software. Larry is an engine builder as well as a programmer. One feature I like is the Peak Demand of the port. Generally the peak demand occurs around 75 degrees after TDC in the induction cycle. This is a critical point on a maximum effort engine. To find where you are, you need to know the point of lift of your valve at this degree of rotation and the flow of your port to see if you may have too large a port or too small. Then you can work with induction and cam timing to reach a goal.
Again, I'm not the expert. Get with a reputable engine builder or cylinder head manufacturer. This stuff is for though stimulation and discussion. What trends have you seen in the cylinder heads over the last 20 years and particularly the last 5? On big blocks we have seen the advent of the Pontiac, Raptor and a few other heads. In NHRA Comp Eliminator using small blocks we have seen the big rage over angle of the valves in the heads. What is the deal? Do you notice the tipping of the valve angles? What is this doing? FLOW PATH…. Some of it is increase in airflow, some increase in the flow under the curve, quality of flow and chamber entry. What is this swirl and tumble all about? Swirl might be great for your low rpm street car trying to get maximum fuel efficiency, but it is not particularly good for high rpm maximum effort racing engines. On a flow bench if you are observing both swirl and flow… you reach a point where the flow stagnates and guess what…. Swirl goes crazy! The tipped angles definitely lower the swirl…. I was visiting with a major Pro Stock cylinder head manufacture/developer at the PRI show some 6 or 8 years ago and he said he had two heads with the same flow rates. One of them had less swirl…. And it ran faster down the track. The engine accelerated better……… I think I have put out plenty of air for awhile… As per Steelcomp's hope… all I want to do is stimulate conversation with open minded boaters.

[cstraub]

Gearhead, excellent posts. Your mention of Flow Path is interesting because just a few weeks ago I was discussing some stuff with someone and he had read some stuff out of Europe that stated the cam was nothing more then a mechanical way to make a Valve Path. An if you think about it. . .it makes sense.
To continue this I will start at the bottom. The oil pan. If you had told me 15 years ago there was power in an oil pan I would have have said "Yeah right". Well it was proved to me during some testing of a 2.0 Liter Ford Engine. While on the dyno this road race engine had a stock type pan on it. It was having some crank case pressure issues. The stock pan was taken off and modified with a large kickout, a scraper, and some screening. With nothing more then this the engine picked up 12HP. Huge gain for this thing.
The windage caused from the movement of the rotating assembly needs area to occupy. Now since the windage creates greater pressure, we need more area so that windage created will equalize; note this picture on the bottom of the page:
http://www.stefs.com/catalog/p02stefsapproach.pdf
The high pressure side is moved to the kickout side creating a low pressure side. By doing so the resistance on the crank to do work is reduced allowing it to work easier.
In Nascar we have strict size rules to oil pan dimensions. If we didn't oil pans would be from frame rail to frame rail in size.
So. . .and let me say this . ..if you are a class racer and every ounce of power is needed this whole thread will be of interest but if you are a pleasure boater it will be just good conversation.. . .So selection of a crankshaft with profiled counterweights to reduce windage is critical. Once chosen a well thought out wet or drysump pan must be utilized to control windage through out the operating range of the engine. By doing so acceraltion will be increased.

[cstraub]

Gearhead touched on weight so I will go there next as we go up the engine. I have spoke about Jager rods before. I may have posted this on hear but they are what is referred to as transformed aluminum into what Jager calls Alumini. A 6" Jager rod can weigh in the 415gm range. Very light. Does light make power, apprently yes;
In an IHRA Prostock engine program Jagers rods replaced the Ti rod being used. Weight reduction was around 110 gms per rod. So 880 grams were taken off the assembly. The engine was rebalanced and put on the dyno. An average gain of 35HP was obtained in the the powerband of the engine with the peak gain being 50HP. Engine quickness was also increased meaning the time to reach the operating range was shorter hence the engine was quicker. Reduction of weight in the RIGHT areas, let me repeat that the RIGHT areas can increase power and the ability to accerate.
In another case a set of rods was replaced in a Quick 8 door car. No dyno testing was done but track results for the combination posted quicker times with just the rod weight reduction change.
It has also been rumored that Jager built a 24 to 26lb aluminum crank for a Pro Stock team that runs the "500" inch class. The crank in addition to 400 gm rods and 380gm pistons ( mind you this is a dome piston in the range of 4.600 ish bore) were used to dominate the class during the spam of 12 months. By mid season of the second year the parts were deamed "illegal" by the sanctioning body. To add some more to the pot, the rod to crank pin clearance for oil was .0005". . . yeah thats right. . . .0005" There was no bearing.
Do you think Lance Armstrong would be competitive if he had another 75lbs on his frame?
Do you think the "Thorpedo" would have done what he did in the pool in Sydney if he had 50lbs on his frame?
Yeah weight reduction in the RIGHT areas does help acceleration.

[steelcomp]

Now we're getting somewhere!! Thanks Gearhead! That was a lot of typing, and a lot of good info. That must have taken you a while. Same goes for you, Chris. I'm going to read these posts a few times, as there's a lot of info. I'm sure there are great discussion points to be found here...I'll do my best!
Class is now in session.

[steelcomp]

Steelcomp, I just had the chance to go back and scan the thread that included the rod ratio comment copy of DM and apologize for posting some of the same old stuff again. One of the post in the thread from cstraub69 when he was at PRI visiting with a drag race engine builder that was considering building road race engines reminded me of a story from a camshaft development session we attended in Detroit about ten years ago. Prior to looking at the actual cam designs, the sessions spent quite a lot of time in the design and matching all the other related components for the intended rpm use. We studied the wire size, number of coils, materials, etc and the mathematical harmonics of the spring and at what RPM this takes place. Presently a SpinTron is utilized to study these relationships in running engines.
Anyway, after the long study of spring, camshaft rates and rpm relationship where the design desire was maximum power while controlling the valve train for longevity, the question was asked by the instructor, "Do we have any drag race engine developers in the group", to which three of us acknowledged. He then stated, "Well, you guys can throw a lot of our study out the window! We have been studying controlled valve trains and inductions and you guys deal in what we refer to as "CONTROLLED DESTRUCTION!"…".
Now I need to apologize for what I have provoked. I asked you in a previous post if there were any threads along some of the relative lines of engine development with port velocities and/or the effects of swirl in the combustion chamber and acceleration on a max performance high rpm (max efficiency) engine? Or the affects on acceleration using lighter weight components in the bottom end?
I apologize because this can become a very long post, even for general discussion purposes. I think I'll break this up into three related post so that it will be easier to respond. I am going to try and keep these post in as general terms as I can and not get into difficult to understand. These thoughts are not absolutes… just some info to promote discussion. I am not the expert.
First, no apology necessary, on any of this suff. I opened this thread hoping to open a "higher level" of discussion, and get a little deeper into what makes an engine work. Your responses are exactly where I was hoping all this would go, and I am greatful to have you here. I can (and do) "parrot" a lot of high tech stuff, with a fiarly good understanding of what's being discussed, but I realy don't "know" much of anything (in comparison), having not had as much hands on experience as someone such as yourself, or Chris, or a lot of the other guys here. I know in the past few years there's been an explosion of super hi tech information in engine development, but there's still the basics that need to be understood before any of that's of any use. I'm hoping these discussions will help myself, and others that might be interested, better understand why different engines do what they do.

[UBFJ #454]

Steve -
You say: "Class is now in session." Shouldn't that be 'Race Engine Building Class is now in session'?
In your initial post you asked the question: "What is it about an engine that makes it accelerate? Why does one engine accelerate better, or faster than another comparable engine from point A to point B?" So far the focus of everything here to date has been engine oriented ..... nothing has been said about drive trains/propulsion systems as engines don't accelerate between points A and B without being hooked to something to move them.
I bring this up because I believe far too often people get caught up with building the 'Best Engine', sometimes very expensive ones, and either totally ignore how it fits into the total scheme of things or don't got into the detail of deriving a comprehensive understanding of the total race vehicle system.
In my mind, the believe that 'Hp Is Everything' is wrong. My belief is that while Hp is certainly an integral component in a competitive racer, it is far more important that the efficient, most effective application of that Hp be accomplished ..... to accomplish that, you have to understand each of the components of the total system and how to build/'tune' each of them Individually & Together.
Having said that why not continue with engines ... then move on to the other components of race boats ... then how the total system of individual components should be made to work together.
Just a suggestion.