Advanced Engine Theory and Design
- Thread starter Alky V6
- Start date
Take notes, these are a pro- engine builders secrets
Also when the valves are redone , a torque plate should be used on the heads, more so with alum. heads. I say TIMING IS EVERYTHING , ENGINE SEAL IS TOO! :wink: I was told that you can feel it by the seat of your pants and not just by et, mph loss , and leak down test.
Also when the valves are redone , a torque plate should be used on the heads, more so with alum. heads. I say TIMING IS EVERYTHING , ENGINE SEAL IS TOO! :wink: I was told that you can feel it by the seat of your pants and not just by et, mph loss , and leak down test.
The valve guides need to be checked to, and will need replacing when all this is being done. Alum heads take a set as they are heat cycled and will toughen up to a point and stop moving. Guide tolerances are a fine line between sticking and just right, a loose guide causes the same affect
Dusty Bradford
Well-Known Member
- Joined
- May 24, 2001
Thanks Jeff. I'll keep all this in mind. I was hoping to make it through the rest of the season without pulling the heads. Might not be able to.
Ok, I'm back, or should I say taking a little breather. I've been busy building a 102mm throttle body for the Stage I engine. I thought I would come on here and explain the theory behind my putting such a large throttle body on a Stage I project. I'm sure most of you are thinking I'm crazy. My response to that is, well, maybe I am. :tongue: Hehe!!! :biggrin:
My crazy theory.
There are three main ways to go with, on plenum size.
1. Just don't care and build any size you want.
2. Properly size the plenum or split plenums to take advantage of resonant pressure pulse tuning. Usually, only helping within a narrow rpm range. That range usually being around the peak torque rpm level of the engine.
3. Build a large plenum that will tend to dampen out pressure pulses in the plenum and in effect cause the engine to think it is running individual runners. IR generally causes a broader, flatter torque curve.
I chose a large plenum setup and I'll explain my decision. I'm running a short stroke, small CID combination with a relatively heavy car setup. Most would say to run a tuned plenum to help the engine at peak torque or earlier and get the turbo spooled up quicker. A tuned plenum will help the car get out of the hole quicker, but will sacrifice a little top end. The plan has always been to inject nitrous to help turbo spool up time, so a tuned plenum did not seem to be so important. Heck, if I needed more 'out of the hole' performance, I would only need to change a few nitrous jets. The decision was then to optimize the upper rpm tune of the engine. That meant IR. A very large plenum will give you that effect.
My crazy theory.
There are three main ways to go with, on plenum size.
1. Just don't care and build any size you want.
2. Properly size the plenum or split plenums to take advantage of resonant pressure pulse tuning. Usually, only helping within a narrow rpm range. That range usually being around the peak torque rpm level of the engine.
3. Build a large plenum that will tend to dampen out pressure pulses in the plenum and in effect cause the engine to think it is running individual runners. IR generally causes a broader, flatter torque curve.
I chose a large plenum setup and I'll explain my decision. I'm running a short stroke, small CID combination with a relatively heavy car setup. Most would say to run a tuned plenum to help the engine at peak torque or earlier and get the turbo spooled up quicker. A tuned plenum will help the car get out of the hole quicker, but will sacrifice a little top end. The plan has always been to inject nitrous to help turbo spool up time, so a tuned plenum did not seem to be so important. Heck, if I needed more 'out of the hole' performance, I would only need to change a few nitrous jets. The decision was then to optimize the upper rpm tune of the engine. That meant IR. A very large plenum will give you that effect.
Now what about the large throttle body?
When you study F1 engine design, you will notice that the plenum intakes are designed to keep turbulence in the plenum to a minimum. Especially, the airflow past the air intake runners. You don't need high pressure and low pressure areas in your plenum. You want as calm an atmosphere as possible for each individual cylinder to draw its air from. Hense my upper plenum section strongly resembles a F1 air intake.
What about the size of the throttle body? Do you need such a large bore?
My calculations have shown that the BHP of my little 236 was a bit over 1,000. With the heads (first run M&A) and turbo size (T76) I'm using, things are pretty maxed out. With more head work (relocating and enlarging the valves) and a larger turbo (T91), there is more. I figure, if I need more, it's time to step up to Stage II heads and not fool around with production style heads. Back to the TB. To supply that level of HP through a 70mm throttle body means the air speed as it leaves the TB into the plenum is higher than optimum. By increasing the air intake plumbing from 3" (at the intercooler exit) to 4" by using a specifically tapered pipe will decrease the air speed exiting the throttle body and hopefully decrease turbulence and the creation of high and low pressure spots in the plenum. That will provide a more equal air distribution to the cylinders, and we know the rest of the story. Optimization of every system of the engine is my goal. Heck, I think I have more fun doing this stuff than I do racing. Yep, I'm crazy.
When you study F1 engine design, you will notice that the plenum intakes are designed to keep turbulence in the plenum to a minimum. Especially, the airflow past the air intake runners. You don't need high pressure and low pressure areas in your plenum. You want as calm an atmosphere as possible for each individual cylinder to draw its air from. Hense my upper plenum section strongly resembles a F1 air intake.
What about the size of the throttle body? Do you need such a large bore?
My calculations have shown that the BHP of my little 236 was a bit over 1,000. With the heads (first run M&A) and turbo size (T76) I'm using, things are pretty maxed out. With more head work (relocating and enlarging the valves) and a larger turbo (T91), there is more. I figure, if I need more, it's time to step up to Stage II heads and not fool around with production style heads. Back to the TB. To supply that level of HP through a 70mm throttle body means the air speed as it leaves the TB into the plenum is higher than optimum. By increasing the air intake plumbing from 3" (at the intercooler exit) to 4" by using a specifically tapered pipe will decrease the air speed exiting the throttle body and hopefully decrease turbulence and the creation of high and low pressure spots in the plenum. That will provide a more equal air distribution to the cylinders, and we know the rest of the story. Optimization of every system of the engine is my goal. Heck, I think I have more fun doing this stuff than I do racing. Yep, I'm crazy.
Airflow is a tricky animal. One case being my y pipe before the turbine housing. I run tuned length exhaust primaries with one size stepup to merge collectors and then to a y connection at the turbine housing. Most ask me about the back pressure that might be caused by the y connection on the other back of cylinders. Pressure pulses directed from one bank to the other bank of cylinders. Actually, if you get the angle of attack and bend right you will get a sucking effect on the other bank of cylinders. When I was designing my y connector, I would take an air gun and shoot air down the collector tube of one bank toward the y and actually got a suction on the other cylinder bank collector tube. The importance of studying physics and fluid dynamics in school. Something I wasn't smart enough to realize in my younger days.
SPEEDSTAR said:
Yikes! Your asking me to do the hard work now. I will do this in several posts. There is a lot to resonance pressure pulse tuning. And keep in mind that exact sizes of intake runners, plenum size, plenum intake size, etc. is theoretical and can be vastly different from one engine to the next.
A small plenum example would be the conversion of a single 4 barrel manifold for EFI use. To me this is a convenient setup that has absolutely no tuning value. A large plenum example would be 200 to 300 percent of engine cylinder displacement. Mine is around the 300 percent mark.
That leaves medium sized plenums, which to me would be something specifically tuned to take advantage of pressure pulse tuning. I will have to get my notes out for this one. The first decision with using intake pressure pulse tuning is single plenum or split plenum? Chance has it that a 3 cylinder engine can get the most advantage from pressure pulse tuning. That is why you see split plenums on V6s. You are separating the engine intake system into two, 3 cylinder setups. If you followed F1 during the turbo era, you would have noticed that many of the V6 setups were split plenums. This helped increase peak torque levels which in turn spooled the turbos quicker. As anti lag routines were incorporated in the later years, you say most teams convert to single plenum designs to concentrate more on the peak HP levels. I'll get into specific intake runner, plenum size, plenum intake size in later posts. I'm biting at the bit to go work on my throttle body. Until next time.
Don, are you going to end your plenum basically at the rear cylinder runners, or are you going to extend the plenum past them? In HVAC design I think the rule of thumb is to extend a duct at least 1 (or is it ...? ) diameter past the last side vent to prevent end effects and to get the same flow out of that last vent as out of other vents further upstream. Dave Williams welded up a stock manifold for Bruce Plecan a few years ago that added all the air gap volume to the plenum, and I think extended it towards the firewall, and Bruce always talked about having to add fuel as a result of the improved VE.
) diameter past the last side vent to prevent end effects and to get the same flow out of that last vent as out of other vents further upstream. Dave Williams welded up a stock manifold for Bruce Plecan a few years ago that added all the air gap volume to the plenum, and I think extended it towards the firewall, and Bruce always talked about having to add fuel as a result of the improved VE.ijames said:Don, are you going to end your plenum basically at the rear cylinder runners, or are you going to extend the plenum past them? In HVAC design I think the rule of thumb is to extend a duct at least 1 (or is it ...?
Some pics of this on Bruce's website~
http://home.woh.rr.com/brucesgn/manifolds
ijames said:Don, are you going to end your plenum basically at the rear cylinder runners, or are you going to extend the plenum past them? In HVAC design I think the rule of thumb is to extend a duct at least 1 (or is it ...?
Very good point. It is better to extend the rear wall of the plenum further than the last runner. I can't remember the exact measurement of my plenum, but it is easily 2". It is also recommended to give the rear of the plenum a spherical shape if possible. Not just a flat wall. My plenum design is such that there is quite a bit of open clearance in all directions from each port opening, except for the siamesed ports of course. Each port entrance incorporates an eliptical flare to aid flow into the port causing the least amount of turbulence.
This configuration causes you to have a dead area below the ports where liquid can accumulate, and it does. If you study pics of my engine, you'll notice a fitting at the rear base of the plenum. A line takes any accumulated liquid and drains it to a small closed catch tank. I've been thinking of having the line circulate back to just after the throttle body with a tube cut to cause a suction on the line, but then I won't be able to monitor what kind of stuff is accumulating in the plenum. If I continue to use the drain tank, I can see what and how much of what is accumulating in the plenum by just draining the small catch tank. Plus I won't be circulating that stuff into my cylinders. The stuff that drains out is pretty nasty looking.
One example of the advantage of being able to monitor what is collecting in the plenum. While doing some testing out in front of the shop with the last engine when it was still pretty fresh, I noticed that the engine was missing more than usual. I pulled the car back into the bay instead of doing the test launch I had planned and proceeded to check things out. One of the things checked was the plenum catch tank. I popped the drain plug and quite a bit of water drained out. Can you guys guess where it came from?
Yes I am. Even when using methanol, there is an advantage by intercooling. With running methanol, intercooling and a 200 shot of nitrous, the intake temp is awfully low. I haven't actually measured it at the port, but you can imagine. It is so low that I can't get too rich when injecting the nitrous. She wants to flame out and miss. An engine analyzing program that I use estimates intake temps around freezing.The Swede said:
Your right to think that the methanol does leave water in the intake. When the engine is cold, ice will build up in the intake. After warm up, I would always drain the intake and get a small amount of water. After the engine has been warmed up, the rest of the day I don't have to worry about water collecting. There is enough heat in the intake system to prevent water from building up.
Tonight I'll try to get started on the Helmholtz resonator (pressure wave tuning) topic. I'll cover some basic theory first. After that I'll give you some specs of my manifold as far as the intake runner dimensions go. As I've explained earlier, I am not using pressure wave tuning with my intake setup. I decided to go the large plenum route. Then we can start designing an intake for our fantasy engine.
