Head porting progress Pics and exhaust port questions

Bobby74 · Post by **Bobby74** » Fri Jan 30, 2004 11:08 am

Just for comparison. Here is a pic of a 2 Liter 914 combustion chamber. Notice the nice plug angle?

73notch · Post by **73notch** » Fri Jan 30, 2004 5:10 pm

newbie question, what does the spark plug angle determine? i mean i hear of people modding their heads for a angle similar to the 2.0 heads. is spark plug angle that important? the only thing i can think of is the angle at which its at determines exactly where the explosion happens/starts in the engine, but i am still unsure about the whole idea.
btw thanks alot bobby and everyone for the pics.

Ryan

Bobby74 · Post by **Bobby74** » Fri Jan 30, 2004 6:32 pm

This is just speculation, but I think it has to do with having the plug being more vertical and more towards the center of the combustion chamber. I like the ramps better than having a 90 degree angle. It seems like the flame kernal wouldn't be blown out as much as a plug that is facing the piston. Kinda like blowing a candle out from the side vs trying to do it from the above. Normally they have less volume (CCs) also, but it looks like someone went overboard unshrouding the valves on this head...

kdanie · Post by **kdanie** » Fri Jan 30, 2004 11:12 pm

Turboteener,

I don't have permission to name names of the fabricators or cars but one specializes in SuperComp, ProComp, and ProStock headers and has his stuff on some of the best cars out there (generally 4-2-1 headers with all the tricks), the other specializes in NASCAR and SCCA TransAm cars.

I've spent hours talking to these guys and a couple of others to learn all I can, they're pretty open once they get to know you a little and realize you are truely interested in learning...

As a side note, one of the old time header builders I talked to wouldn't talk until I had a tape recorder, he had been mis-quoted too often in the past, he get's pretty torqued about that, I don't blame him.

ken

turboteener · Post by **turboteener** » Sat Jan 31, 2004 12:37 am

I understand. Secrets are hard earned. Ask any of them if they are using Anti-reversion headers in any of the stuff they? If they are how is this any different than what I am suggesting. An AR step is much larger than what I am referring to.

Bobby74 · Post by **Bobby74** » Tue Feb 03, 2004 2:22 am

Hello,

I made a Header primary length calculator in Qbasic today (remember this guys??).... DOS...

This is based off a calculation by Header's by Ed.

It works off the equasion: BestHeader = (CID * 1900) / (rpmmax * tubeod * 2)

Where CID is Cubic inch Displacement, rpmmax is your Redline, and tubeod is Tube outside diameter.

Does this calculation look correct?

Here is a copy of the program, let me know what you think!!
http://home.comcast.net/~vwbobby/header.exe

Thanks,
-Bobby

raygreenwood · Post by **raygreenwood** » Tue Feb 03, 2004 5:20 am

You guys are swapping generics here. Be careful. Nothing is generic in head porting. A step ...has a flat bottom 180 degrees from flow direction...correct? That means it faces downward toward the piston...correct? That means that for 100% sure it creates turbulence underneath it.....a rolling motion. That means rolling motion at the bounderies. That's not a tragic thing....but its not a good thing if you are running injection. Its better if you are running carbs. Its useless if you lose flow or atomization because of it. How far is the step? How far is too far?

Also...you have made the assumption that reversion waves follow the walls....(? why?). Considering that 90% of the charge is in the center areas...minus the boundery layer (how thick is it...you have no way of knowing). Also...boundary layer gases WILL have variable speed depeding upon surface area, temeperature, texture and radius of curve...and therefore can have more or less effect on the gases in the center. Also, depending on the cam...and depending on the manifold type...reversion waves may not be a problem at all. Its just a suggestion to make sure what use a given person has for the heads they have...before suggesting something that may or may not be drivable in the range they are using the engine.

Also reversion wave tuning is not an issue on every engine or every manifold. It depends on the configuration...it depends on the valve timing. The stock plenum on fuel injection has instance..has more reversion issues at low rpm than at high rpm. This is because the plenum is cross ventilated diagonally by adjacent valves opening. At higher rpms...like 4000+...it has much less issues even though the valves are slamming shut at a higher rate...because the rateof cross-ventilation in the plenum now happens at a rate as fast as the reversion waves travel rate. Again...it really depends on timing, volume, overlap...etc.

Also...many times the flow bench can show an increase in flow...but an increase in turbulence can actually upset valve entry...which upsets fill efficiency...which upsets atomization. Again..especially in injected engines.

The only way to see this really...is with fiber optic photography.

Unless someone is useing the EXACT configuration and rpm range, the reversion wave practices are only suggestions that may or may not work properly. Just some thoughts. Ray

turboteener · Post by **turboteener** » Tue Feb 03, 2004 9:35 am

Ray you are correct we are indeed talking generics, becuase I do not know the exact specs of the original posters motor.

A step is a 90deg change in direction not 180 unless you are referring to the step used in an Antireversion header. When you create a rolling motion along the boundry layer you tend to break up the friction on the boundary layer. That is a good thing.

As far as anti-reversion techniques go I will limit this to the exhaust side. Anytime there is a change in the cross section of the pipe, ie. muffler, header union, cat, turn, crimp, etc a wave will be reflected back into the oncoming flow. This is part of the reason for using a header (the other is to take advantage of the void created in the collector). The wave frequency changes with RPM, load, temp, pipe length, and diameter. All of these things affect when the wave rebounds and with what force it rebounds towards the exhaust valve. The purpose of my header mismatch is to combat the wave that is headed towards the exhaust valve. "Yes I realize that it has a very minimal effect but we all know that competetive engines are the best series of compromises and special tricks." It is impossible to time the wave for each condition but a generic mismatch will help in all situations.

As far as the intake side goes, we are not reffering to wave tuning or "ram tuning". I am just reffering to trying to minimize the bounce back caused as the intake valve closes and the extra inertia from the mixture changes direction. The closer to the intake valve I can keep this mass of air fuel mixture the better in my opinion.

These are my opinions based on my research. There are obviously more than one approach to the same goal. We are dealing with street motors so these matter are less important though education is very important.

raygreenwood · Post by **raygreenwood** » Tue Feb 03, 2004 9:56 am

I agree with your premises in general. But in intake charge reversion..again.... valve timing totally changes how far the reversion travels when it reaches the plenum. I have seen this visually. I do understand thatbasically you are speaking of the charge at the valve pocket when the valve slams shut. Yes, a step may reverse that charge along the boundary. The reulsting turbulence as it rolls in on itself may cause some of the rest of the charge to roll with it. But...again when the valve is open and high velocity intake air is flowing past the step...it causes turbulence and ossible port entry problems. I guess you have to ascertain which is the lesser of the two evils for your engine. Ray

Also, ys, reduction of friction on boundary layers is a goodthing especially if it increases velocity. But also again, without visual evidence and testing, better flow and velocity can also create turulence if you are not careful. That may degrade atomization. I have seen high flowing heads thatactually have poor atomization. Having a greater charge volume and velocity does no good if part of the fuel charge is left in the valve pocket...or if its poorly mixed. This can be seen when engines cannot seem to burn the entire fuel charge...yet for all other indicators, appear to be running normal or lean.

Bobby74 · Post by **Bobby74** » Tue Feb 03, 2004 2:51 pm

I'll have some more pics to post later this evening hopefully.

This discussion is very interesting guys, I'm listening to both sides. Reversion is a very important factor and I believe it Does exist, and tunning around or tunning to the advantage of reversion is one of the aspects I'm trying to do.

Here is my combo to help you guys out:

AW block, full flowed, plugged, and modified oil passages.

-78.4mm C/w'd Type 1 journal crank
-96mm JE forged pistons, Deves rings
-Web 163/86B on 112 lobe centers cam
-Super Hd Al pushrods
-911 adjusters, solid spacers, 1.7 Rockers
-44 x 36 SI ss Valves. Titainum retainers, SINGLE HD springs (slightly stiffer than Scat HD's), AMC oval port castings.

Dellorto DRLA 40's for breakin custom built Plentum injection (multi-point EFI single throttle body) after first 200 miles or so.

This is going into a '65 Split window Transporter/bus for Daily Driving, believe it or not..

Thanks again,
-Bobby

turboteener · Post by **turboteener** » Tue Feb 03, 2004 7:44 pm

I would seriously rethink the lobe centers on that cam. You should at least be somewhere in the 107-109 range. Keep in mind I don't build bus motors but I would stay away from the 112 unless you are going to go turbo end even then there is the possibility that you could put a little too much heat into the exhaust valve. What kind of compression are you planning on running? I would talk with Jake about some of his bus cam reccomendations.

What size plenum are you planning on running? What volumn and runner length are you shooting at? What size throttle body? Are you running MS or some other standalone FI?

What are you going to run for exhaust?

Bobby74 · Post by **Bobby74** » Tue Feb 03, 2004 9:25 pm

Since I will be putting this into a bus instead of my deceased Super.... I will be dropping the compression to 9:1.

I have some of my own conclusions on how this combo will run but I would like to hear your concerns about the lobe center.

My understanding is; a 112 lobe center will give me less overlap. This will give me higher dynamic compression compared to a cam where the gases are aloud to bleed down. This should give me more bottom end grunt at lower RPM's... Am I off base here? I'd like to understand a little more about lobe centers.

Yes, I am planning on using a turbo in the future..but I will probably be switching to some 42 x 38 heads or 42 x 37 next time. Sticking with something mild like a TO3 or 60-1 trim.

How hot is my exhaust going to be compared to a 108 LC cam?

Thanks,
-Bobby

edit: Forgot to answer some of your questions!!

For plentum I will be running somthing about 1.7-1.9 liters.
For runner length it will equal about 550cc's (achived by either diameter or length or combination of both).
For Injection, I'll be running the Perfect Power MIC3 using the mapable ignition also.
Throttle body is a tad over 2 inches.

For exhaust I will be running a calculated 4 into 1, or Possibly a 4-2-1 if construction allows me to route the exhaust how I want it.
I want to have it exit in front of the driver's rear wheel.

I'm hoping to have a reletivly broad powerband with plenty of power, of course!

turboteener · Post by **turboteener** » Tue Feb 03, 2004 9:50 pm

The lobe centers will give a very smooth Idle with the plenum update and the torque curve will be very flat not very peaky like you would get with a tighter LCA. Yes it will boost your dynamic compression but with a bus I think that may give you problems. Remember a bus is a heavy animal with very poor cooling air flow. I would rather bleed some of that compresion down with something like a 108 LCA, but if you run a lower static compression then that cam will run rich and hot so that is a lousy idea. You are right it will give you more bottom end grunt but that cam with that engine combo is meant more for turning some RPMs. I would keep the lift but drop back to something with a little less duration, maybe in the 235-245 on the intake side and the 86 is probably OK for the exhaust.
Keep in mind I don't build bus motors so a lot of this is speculation. Wider lobe centers generally smooth out torque cuves over a broad range and tend to limit top end power where tighter lobe centers will make it "peakier" with more mid and top end power.

I don't know what size the vents are in the 40s but I know the 40idfs were to small for mild 2056 running that cam. But you will get some pretty good throttle response and low end grunt you may just run out of top end. Then again that may not be such a bad thing.

That is one hell of a turbo you are planning on running I know guys that are running in the low 400s with the 60-1 turbo, full boost doesn't come in till 4000-4500 depending on configuration. Don't know that that is what I would use on a bus. I am a 914 guy so that turbo is a great peice for my car. It all depends on the wheel size.

I would check with jake as he does more bus engines than I ever intend to do. UNless you want a tube frame turbocharged monster that will pull 1.0 on the skip pad and run mid 11s in the quarter!!

Bobby74 · Post by **Bobby74** » Tue Feb 03, 2004 10:06 pm

Hehehe, thanks Turbo...

Yeah, I'm not sure exactly What this thing will do, but its a really expensive experiement

If all else fails, at least I did it and tried some of my ideas.

The turbo choice is because its popular with the RX7 crowd. My engine is 1.3 Liters (13B) and if I take that and double it (2.6) that tells me a 60-1 should be good for a 2.6L engine Roughly... (since rotaries actually fire 3 times per cycle, maybe I should be tripling that.... but oh well). If I build a bottom end screamer with a "high end" turbo, than hopefully this will push me Past my normal 'redline'... since it will build enough pressure to exceed the mechanical pumping limits (hopefully).

Anyone else have any opinions on this?

Bobby74 · Post by **Bobby74** » Tue Feb 03, 2004 10:07 pm

P.S. This is my first Type 4 complete build. I've freshened up Type 4's (top end jobs, heads, etc) but never fully built one, so this is uncharted territory for myself also. Don't think I'm some expert, I'm still learning every few hours. I've been studying about 10 hours a day for the past couple years though so I'd like to think my ideas have some merit...