Performance Cams

[swindler_57]

Hello,
My name is Justin Jackson and I have some questions for you if you aren't too busy. I've found out that you are rather popular on this Opel forum and it seems that you are rather wise too so I have come to you for help. I need help selecting a cam for my 1973 1.9L Opel GT. I am planning on boring the motor out .030 and maybe doing some port matching work but not a whole lot. I was told that I should keep the intake sort of rough as to add some sort of turbulence. I am going to install a Weber 32/36 Carb and I think maybe a much newer ignition. What type of cam should I put into my Opel. I want something mild and not too outrageous but something that will fit nicely with my listed modifications. Thankyou for your time.
~Justin

[RallyBob]

Hi Justin, I just need to ask a few more questions to point you in some kind of direction.

What compression ratio are you planning to run?
Are you going to port the intake manifold?
What exhaust manifold or header are you using?
What exhaust pipe diameter?
4-speed or automatic transmission in your car?
Your driving style? Cruiser, stoplight racer, etc.....
Hydraulic or solid lifters?
Your tolerance for a rough idle? Or do you want it to be very smooth?

Lastly, as a general comment, if you are retaining stock valves in the head, you should be sure to read up on what to do (and what not to do) in terms of porting work. Port matching the head to the intake/exhaust gasket will do nothing for power, and I mean nothing. The stock ports are already too big relative to the valve sizes, and the intake manifold is already larger than the intake port, while the exhaust manifold is larger than the exhaust ports. So there's no issues with reversion. Enlarging the intake manifold runners to match the already-larger stock intake ports will simply increase runner volume, dropping port velocity and losing you precious torque. Not the hot setup!

Of course, if you install larger valves in the head, then everything changes and nothing I've said applies!

Confused yet? Sorry if I have, but I'll do my best to explain anything I've said that's not clear, including detail about the headwork.

Bob

[swindler_57]

Thankyou Rallybob for taking some of your time to help me out. There is so much information on this website that I got confused and just thought it easier to ask you. To answer your questions.

~I plan on running a 9:1 compression ratio if the flat-topped pistons can get me that.
~Now that I think of it I'm probably not going to port the intake manifold or do any porting work. From what you said about the valves that really wouldn't be the thing for me to do since I'm keeping the stock valves.
~As to answer the next question I think I am going to stick with the stock exhaust manifold and header.
~The exhaust pipe diameter is going to be 1 1/2" because I am going to do a true dual straight pipe with two actual pipes coming out the back unless you know of anything that might get me better horsepower than doing that. ~In my car right now is the original 4-speed but I plan on driving with a Getrag 5-speed. I don't have it right now but that's what is going to be in it when I actually start driving it back and forth to college(about a 35 mile interstate drive).
~My driving style really varies with my moods. Sometimes I want to cruise but at other times I do a little stop light racing. I'm really not a racer and I don't plan on racing my Opel. I only want it to have some more get-up-and-go and enough power for the occasional street race. Maybe in about a year I'm planning on making a little run to the bonneville salt flats and that's about it.
~I'm going to put hydraulic lifters onto my Opel or at least I'm pretty sure that I am.
~Now for the last question. The idle really doesn't matter too much to me as long as the car starts up easy and doesn't give me hassle all the time. I want something reliable but if the idle is rough then that's okay with me. I'm really not picky about little things like that. I'm into loud cars, squeelin' tires, and the rough idles of drag cars. Actually I kind of like that sound but I'm sure the Opels would be much different. So yes I would be able to handle a rough idle. Whichever would get me more power.

I think that should answer all of your questions. I really didn't get confused because my dad is a mechanic so I just ask him and he kind of explains to me what everyone is talking about when I've asked questions to opel guys. I hope the answers I've given you will allow you to help me out. Thanks for all your help.

Justin

[RallyBob]

I will work up some cam specs for you in the next day or so then.

I would run a single 2" exhaust pipe out back, and then split it after the axle if I were you, as running twin single pipes on an Opel will lose you power. It is quite drastic in fact.

Bob

[greensmurf20]

"I would run a single 2" exhaust pipe out back, and then split it after the axle if I were you, as running twin single pipes on an Opel will lose you power. It is quite drastic in fact."

i can support this by fresh experience. my exhaust got ripped off in a construction zone and i lost all torque completely, and my top end wasnt near as well as it normally is, i couldnt get over 5K in 3rd gear. fixed my exhaust and i can redline in all 4 gears and i can do 30 or so in 3rd gear without it chugging or bogging down again. need backpressure i assume.

[opeldean]

could I be next after swindler?

my car is running great with all your recommended bolt on upgrades, but I am ungrading more with a fresh shortblock(20 over-1.9) and the cylinder head that you see here.

I am currently using a pertronix ignitor and a weber 32-36. My friend is a mechanic.He told me to bring him a cylinder head..and He would make my car run good. here is a picture of my spare cylinder head that I brought to him last friday.he said he was going to do a street port for me and he wanted to know what you guys would recommend for a cam and valves.

my friend is going to use the gasket as a template for both the intake and exhaust ports. he pointed out to me theinternal roughness and mismatch.I have been a reading many of your posts but i am confused on what tell him to do.

he is very experienced on MG's,Triumphs,Healeys and Jags..but has never worked on an opel besides mine.(he thinks it is pretty cool,he likes how the doors cut into the roof and the rollover lights)

my plan was to order 42mm-2 liter intake valves real soon and a cam....
I heard hydraulic was less fussy.

I want the car "tuned and reliable enough to drive to the OMC meeting in california 2005"..my current engine runs good ... but it was a used engine
77,000 miles ago..I dont know how much longer I can push it.

[opeldean]

Rallybob: are undished intake valves desireable?... my friend said the other dished ares would lower compresion too.

advise us if you can.

thanks

Ps: swindler..sorry i jumped in on your thread..I am getting nervous when my head is in the shop to be polished up and somewhere it says not to polish up

[RallyBob]

Bucky, you have a lot of potentiaL 'issues' there.

Do NOT port the head to match the gasket. Especially the exhaust port, but either way you'll lose. Even on a full-tilt racing head with massive valves and a powerband from 6000-9000 rpms, the intake port will barely get as big as the stock gasket, and even then not in every direction (the floor of the port is barely touched for instance). And even on that same hypothetical racing head, the exhaust ports are barely bigger than stock. I usually make general suggestions to baseline from, but in this instance, I'm outright saying "Don't do it!".

The dished valve you pointed to is in fact the intake valve. Yes, it wil lose compression, but it will also be lighter. Six of one, half dozen of another....
You can gain a lot of compression back by using the larger 2.0 intake valve, and installing hardened exhaust seats. Both these operations will raise the valves higher from the seat, and will boost compression and crucial low-lift airflow. These will both aid torque and response.

RE: polishing ports. It does nothing for airflow, it's just for looks. Reshaping the ports correctly will gain you power.

Bob

[namba209]

Originally Posted by RallyBob RE: polishing ports. It does nothing for airflow, it's just for looks. Reshaping the ports correctly will gain you power. Bob

Bob, as much as I appreciate your knowledge on the Opel engine and admire the work you are doing, I must take issue with the above quote. Maybe it doesn't make a difference in slow turning engines, but it definately made a difference on my racing bike engines turning 14000 RPM on one and 16000 RPM on another. Also on my model racing boat engines turning up into the 30000 RPM range. Two facts that have been known for years and widely distributed are: During WW II, a waxed and polished P-51 gained an increase of 30 knots air speed; and, by reducing the boundary layer air in an engine port an increase of 30% air flow has been achieved. I also know that when 600 lbs of paint was applied to my aircraft while in the USAF, it became the fastest aircraft in the squadron. As I said maybe it doesn't make any difference in slow moving air, but the faster the air flow, the more difference it makes. I hope this doesn't offend, I would sure hate to have that happen.


Ron

[opeldean]

Hello Bob, as your student I need a little tutoring.My notes are enclosed from things you have lectured us on.
I understand #1 now....but this seems to conflict with the article from the auto restorer magazine.the article says to smooth..are opels different due to the large sizes of the runners?
#2-what do you mean? do you mean bowl blending?

#3-in a budget rebuild you once mentioned a split profile with a 405 lift

#4- possibbly later a .426 lift split profile was mentioned..

thanks..your response it allowing me to build my dream!I don't care if I beat anybody..I just want it the best it can be.

[RallyBob]

Originally Posted by namba209 Bob, as much as I appreciate your knowledge on the Opel engine and admire the work you are doing, I must take issue with the above quote. Maybe it doesn't make a difference in slow turning engines, but it definately made a difference on my racing bike engines turning 14000 RPM on one and 16000 RPM on another. Also on my model racing boat engines turning up into the 30000 RPM range. Two facts that have been known for years and widely distributed are: During WW II, a waxed and polished P-51 gained an increase of 30 knots air speed; and, by reducing the boundary layer air in an engine port an increase of 30% air flow has been achieved. I also know that when 600 lbs of paint was applied to my aircraft while in the USAF, it became the fastest aircraft in the squadron. As I said maybe it doesn't make any difference in slow moving air, but the faster the air flow, the more difference it makes. I hope this doesn't offend, I would sure hate to have that happen. Ron

No offense taken Ron. However, I have tested a ported exhaust port, left in its rough 'as ground' condition complete with chatter marks from the carbide, with an 80 grit polished finish, and with an absolute mirror polished finish (80, 180, 320 grit then coloring compound with a felt buff), and there was no difference in measured airflow between the 'rough' and the 80 grit, and only 1.7 cfm difference measured at .525" valve lift when the port was mirror polished. However, in subsequent testing of this head with carbon deposits on the exhaust port, the airflow benefits of the polish were completely eliminated.

On the intake port, it makes more of a difference, but not in airflow, but rather in fuel suspension. Polished intake ports let the air/fuel separate easier, and I have always seen higher fuel consumption, and lousier low-rpm response from polished intake ports. I never go smoother than 36 grit on the intake ports for this reason. The sole exception would be for a fuel injected engine with the injectors mounted close to the valves...they will atomize better than any carburetor due to the higher pressures, and since the intake runners of the intake manifold are therefore 'dry', they can be as shiny and smooth as you want them to be!

So perhaps we're comparing apples to oranges here. I have no doubt that a smoother exterior finish is dead-critical for passage through air (and have seen statistics to show there's a few good mph to be gained in top speed on most cars from a good wax job). But when it comes to air/fuel atomization, normal aerodynamic theories don't necessarily apply!

Hmmm, gonna have to wax the heck out of the Land Speed GT when the time comes.....

[GTJIM]

With carburetted motors in particular the fuel/air mixture is a mixture of air, fuel vapour and suspended fuel droplets of various sizes. A lot of what appears to be "common sense" simply ain't so with mixtures of this nature at varying flow rates at varying rpms.

Particularly in ports that are already at the "almost-to-big-already" end of the scale. Especially in Road engines which spend lots of their time at the, variable, low to mid speed ranges rather than flat out at maximum revs.

Mild valve pocket work and concentration on the "short turn radius" on the floor of the port where it curves around to wards the valve can be beneficial in the ever changing flow conditions of this type of motor. Also the relatively "rough" finish ( rather than polishing ) helps the "wet" portion of the suspended fuel re-enter the flow as it is dumped out at the changes of direction in the inlet tract. A polished port wall would let this fuel form thin layers of liquid on the port walls which would migrate towards the cylinder as liquid and be dumped into the cylinder in unmetered amounts without accompanying air. The theory behind the "rough" port walls is that this allows the wet fuel to be dragged back into the fuel/air flow from the narrow peaks of metal inherent in the rough finish.

So, the Opel ports are already big enough for road engines in quite high states of tune and the only real improvements to be made are in port shape rather than port size - particularly in the short turn radius area and under the valve plus the seat area and on into the valve shrouding area of the combustion chamber. As with all "porting and polishing" it is real easy to end up with something that flows worse than the original. that being said - smoothing the short turn radius and the bowl area along with unshrouding the combustion chamber can produce unbelievable gains in power and smoothness of power delivery if it all comes together.

[RallyBob]

Bravo!

Well said Jim....

[namba209]

Jim, Bob, et.al., I guess because of the long runners and relatively slow air flow you're right. I think from the main jet of my carbs to the intake valve is under 3 inches, and it's a straight shot to the back of the valve, and a shallow bend into the combustion chamber, so what comes out of the main jet, already premixed with a specified air/fuel ratio, and nothing to hang on to in the port walls, it just goes right into the cylinder, by the mirror smooth valve and valve stem. I have to say that on these engines it was full throttle or shut off, going from turn to turn through the gears at the highest attainable RPM. I would guess the same applies to my exhaust, a short dump to the exhaust pipe, so that after a year of racing when I tore down the engines, all I had to do was wipe down the top of the piston, combustion chamber and the exhaust port and all were mirror shiney again. So short straight ports could benefit from a minimal boundary layer. Whatcha think? Oh, one more thing Bob, on the LSR, an orange peel free paint job works too in conjunction with a good coat of wax.

Ron

[RallyBob]

Sounds right on the money Ron. If these Opels only had to operate at a fixed rpm or a narrow power band then you could polish and chrome plate the ports I'd think! But with a mega-short stroke engine like a 1.9, and the relatively low rpms they operate at during 'in town' use the port velocities are very low.

Hence my 'torquer' intake manifold idea, to improve cylinder filling at low and mid rpm ranges by reducing plenum volume, since on its' own the 1.9 does a poor job. Ever pull a Weber carb off a just-run engine? There's always a significant puddle of fuel at the bottom of the plenum.

RE the Land Speed GT. You read my mind! Basecoat/clearcoat paint, wet sanded and buffed, then compounded and waxed repeatedly. Smooth wheel covers, Rain-X'd windows, narrow tires with 50+ psi pressure, no door mirror, no wiper arms, no emblems, etc. It's all in the details...

Bob

[Old Hippie]

Man, I love these in-tie-lect-uall conversations with gentlemen. No name calling, fisticuffs, etc. Does a "old hippies" heart good! That's why it pays to be a member!

[RallyBob]

You bring up a very valid point Old Hippie. I've been on many other car-related forums in the past, and have left almost every one of them.This has to be one of the most mature, well moderated forums out there. Seldom is there a flame that gets out of control, or name-calling, or any of the other dung-slinging so prevalent out there on the internet.

Gary, Keith....a job well done. And of course the members themselves couldn't be more gracious. Makes me look forward to the car shows to meet them in person.

[Gary]

Thanks guys.... We do have a great group here.

It's grown beyond where I can read every post, but if any get out of hand, just click on the "Report this Post" icon in the upper right corner (next to the post number) and that will alert the watch dogs.

[Paul]

Bucky, Swindler and interested others

I've attached some links that will give some background information about heads and porting.

Sorry if this post is long. It is not a flame and is meant as encouragement for those of us that are intrigued by the science of the internal combustion engines to study the subject deeper to in an attempt to learn "WHY" things work.

http://www.sa-motorsports.com/diyguide.shtm
http://www.newcovenant.com/speedcraf...opDefault.aspx
http://www.bmw-m.net/TechData/cylinder.htm
http://www.eaa1000.av.org/technicl/engemp/engemp1.htm
http://www.grapeaperacing.com/GrapeA...tech/index.cfm

Also, I like to add a personal observation. First I like to preface what I'm going to say. ...For the past year or so I've tried to research these very subjects so that I cound apply them to my Engine rebuild / performance enhancement project. I've probably spent 100-200 hours reading every book or internet site I could find. Also, I've asked Bob more than my fair share of questions, right Bob? LOL.

........ Okay, what I've learned, and it should be no great accomplishment, is that ALMOST everything written seems to directly pertain to Small Block Chevys. Okay, you say so what. Well the important thing to keep in mind when reading other articles is that the proportion of flow, intake vs exhaust, for the SBC and the 1.9 Opel head is reversed. So, what does this mean to our group. It means that you just can't let your local engine builder do what comes naturally to him without reguard to what is specifically needed for an Opel engine.

Here's where RallyBob's expertise comes in. He is the closest thing the Opel community has to a Smokey Yunick! He has torn down and rebuilt more Opel CIH engines that most of the rest of us combined. Now the special thing is, he hasn't just simlply rebuilt them. He has done countless hours of testing, calculating, designing, researching, studying, learning and more testing.

Now, for a person to be a student of the subject (Opel engines), one can not simply ask Bob everything. We must do some studying of our own. So, what a person has to do is learn the principles of fluid/gas flow, kinetic energy, inertia, spring harmonics etc. Then use Bob's posted info to figure out when the written info for the SBC and the Opel diverge and to see exactly how the things we are learning apply directly to our engines, since more than likely Bob has had that combo on a flow bench and/or on a dyno.

Case in point, dating back to 1998 when the Classic Opels site was started in E Groups, now Yahoo Groups, Bob has posted countless times flow rates of the various Opel heads in various states of tune. We know that on the stock 1.9 head the intake flows 88-89 cfm and the exhaust about 67. We also know that by using the 42 mm intake (still in the 1.9 head) we can get 102 cfm. With a 1.72 intake valve we can get 112 - 115. But we've learned the stock intake can restrict the flow back to 88 cfm. SO... the information we should carry forward is to perfom the greatest proportion of our work and attention on the intake side of the business and less on the exhaust side... up to a point.

I hope I havent added to the confusion. But, I too have a head that was made less efficient and with less low end torque by some over eager SBC machinest whittling on the Intake ports with stock valves and making the exhaust soo good it was way out flowing the intake.

Folks, don't stop asking questions. Continue searching this and the Yahoo site for background info and then the answers you get to the questions asked will make even more sense. Because you will have a better understanding of the factors that influence the subject.

There's a lot to learn. I have just scratched the surface. I wish I were confident answering some of the hard questions. I can, however help some of you find background info in order to ask better questions or to help understand the answers.

Sorry for dropping your name so much, Bob. I hope I didn't brake it.

Paul

[namba209]

Bob, I don't know what the chemical make up is on Rain-X, I do know some of the model boat racers I associate with have used in on the wetted surfaces of their boats with mixed results. IMHO, a coat of wax on all windows, would possibly have the same affect, although on the windshield it may pose a visibility problem, but you don't plan on doing any driving in the rain, or do you. And thanx for the response on the ports, I really do appreciate the technical expertise you have in that area, and the fact that you have actually flowed the head to back up what you have said. You can't be more factual than that.

Ron

[yiger]

I'm a little out of my league here when talking about polishing engine components, but since I do know a thing or two about boat (sailboat, that is) racing, I'll chime in with the age old arguement on the docks after a long day on the water... There's about a 50/50 split in the boating community as to how to achieve the least friction (best flow)- the debate extends all the way to educated fluid dynamics theorists... One side of the arguement says the smoothest hull possible allows the water to pass by with the minimal amount of turbulence (meaning speed). These people use McLube, RainX, or wax on their wetted surface. The other side says if you leave a bit of roughness (and only a tiny amount... like a 600-800 grit sandpaper fairing job) it will allow a tiny layer of water to attach to the hull. That makes the water passing over the hull rub against water, not fiberglass, aluminum, carbon fibre, or whatever your hull is made of. The arguement here is nothing is better than water against water. So- that's the 'aquatic' side of the debate... I'm not sure if that helps or hinders, but that's my 2 cents.

[opeldean]

I ran down at lunch to show my mechanic "rally bob's " comment "on not to do head gasket matching".my mechanic felt a little surprised on the not gasket matching the intake side, but will respect your knowledge,skill and experience.

question for Rally bob, my mechanic wants to smooth down the "intake boss" found in the intake bowl and smooth out some casting marks..

Do you agree with this?.
I plan to order 2 liter intake valves today.

the exhaust side will remain untouches per your advise.

thanks

[RallyBob]

The safest way I've found to 'clean up' the intake port is to have the machinist mill down the valve guide protrusion in the bowl area by about 1/4" first. Then this area can be reshaped with a die grinder to mimic the shape of a GT hood 'bubble'. Blunt end of the bubble facing the port opening, tapered end facing the valve. There are better ways to make the intake port flow well, but unless you know exactly what you're doing, you'll likely hurt the airflow. This is a safe method, and the way I used to port all my street heads.

The bowl can then be blended to meet the new valve diameter. I have had heads with 2.0 intake valves flow as much as 110 cfm with this method, with the port walls completely untouched....
For reference, this is as much airflow as a stock 2.4 intake port. So in this instance, size does NOT matter!
Even if you conservatively 'only' get 102-104 cfm (I'm sure you will get at least this), it's still 16-19% more airflow than stock on the intake port.

For the exhaust ports, you can blend the bowl areas for improved low-lift flow, but refrain from enlarging those ports at all. Even with simple bowl work, that little 1.37" exhaust valve and tiny port will flow almost as much as a 1.60" valve in a stock 327 Chevy 'camelhump' head.

The Opel exhaust port flows so well in fact, that when I ported a pair of 302 Ford heads some years ago for a friend of mine (small block Fords are notoriously lousy flowing on the exhaust port), I modified the Ford exhaust port shape to match the Opel port shape. I was able to improve the airflow from 63 cfm to 99 cfm. That's a 57% improvement.

HTH,
Bob

[opeldean]

I found in prior notes that the
"intake port protuberence should be ground off"

so this is a dumb question that rallybob doesnt need to answer.

[GTJIM]

Originally Posted by Paul Bucky, Swindler and interested others I've attached some links that will give some background information about heads and porting. Paul

Thanks for the links, Paul. Lots of real good stuff in them.

Thanks to everyone posting on this thread for the pursuit of Opel Knowledge!