Performance Cams

[GTJIM]

Have been doing lots of reading and hands on checking with my cylinder head too.

1 & 4) The distance between the top of the piston and they cylinder head should be minimum .040" (1.0mm) and maximum .060" (1.5mm) With the standard, composite head gasket this is easy as they compress to almost exactly .040" (1.0mm) thick so this means that the piston top (or flat area on dishes or pop-ups) should be level with the top of the block or maximum .020" (0.50mm) "down-the-hole" This allows for the correct "quench" at TDC - just like most any other GM engine ........

This clearance needs to be obtained by using the correctly dimensioned components (or by cutting the tops of the pistons if they stick up too high).
"Hacking" lumps off the block or head faces does horrible things to the cam timing - as Nobody has forcefully pointed out to me, till I am a believer - as does using a gasket of a thickness different to the original. Because of the unique cam shaft position up in the head as the cam centre line drops towards the crank centre line the cam sprocket "walks" down along the drive side of the chain and thus the cam has to turn - upsetting the cam timing.
If you "do-the-numbers" even .010" (0.25mm) of "hacking" has a significant effect on cam timing. This change has to be rectified by altering the angular relationship of the cam wheel to the camshaft - either by using an offset bushing (hit-and-miss) or a vernier cam pulley (UK imports from Kent or Piper which are horribly expensive - GBP90 or more).

Consequently, for the novice Opel CIH engine builder, keeping the top of the block and the cylinder head face "unmolested" is the best course of action.

2) Standard bore and stroke for a 1.9 litre Opel CIH motor is:

93mm bore by 69.8mm stroke (3.661" bore by 2.748" stroke)

So your "20 over" is 3.68" bore or 93.5mm bore - same stroke.

3 & 5) "Other GM" springs can and have been used. The exhaust rotator can be dispensed with but the high milage life of the exhaust valve may be compromised with unleaded petrol - unless a hardened exhaust seat is fitted.

All "intake" springs can be used with extra intake spring retainers and a suitable spacer under them on the "exhaust" valve spring seat where the rotator was to give them all the same installed height which is around 1.650" (check this on an intake one to make sure I have got this correct).

With Opel valves (even the 2.0 litre bigger ones that can be sourced from OGTS) this "stock" intake spring set up will allow the use of cams with lifts up to 0.425" for sure and may be up to 0.450" with careful measuring and checking for spring bind and valve guide interference at full lift. The later 2.4 litre springs can be used in this "modified stock" set up too - they are Pioneer Inc. Automotive Products part number RV-925-4 They are the same for intake and exhaust.

With Chevy V8 valves the sky is the limit for springs using any of the many V8 types - including the old favourite the 400 CID Pontiac ones that I have seen mentioned and I understand were in the C & R Big Valve Kits of yore.

I'm still "digging" for information and welcome verification of the above - or even being told that I don't know what I am talking about ( by more experienced Opelers!).

[Travis]

GTJIM,

Just a few comments

RallyBob has often advocated having the piston .005" or so above the top of the block to improve quench

Any proper rebuild will require decking both the block and head, although minimally. However, I consider 'degreeing the cam' an essential part of any performance engine. Each engine configuration will require a different installed position of the camshaft. Therefore, just leaving the block and head unmolested will not get you where you need to be. When you buy the offset bushings they come as a set with different offsets. Using the right bushing will get you where you need to be.

For moderate to high RPM engines, selecting springs merely by the fact that they don't bind is a hit or miss proposition. Valve float and even harmonics of the system will need to be considered. Your cam supplier will be able to supply info on required spring rates and spring seat pressures based on your cam and intended usage. If not, find another cam supplier.

And remember, cams aren't rated on the 'bumpity' scale....

-Travis

[nobody]

I couple of things to keep in mind when you even start to mention decking anything to anybody is thier knowledge of the entire picture and thier abilities not to mention the money factor. Just as decking it and then leaving it alone looses power the use of the wrong bushing or degreed position can have a big impact on the motor and I do mean impact literally. Having been down both of these roads myself with varying degrees of success I am very stronly on the side of get your design right in the first place and never try to make up for it in other areas. Decking the block or head either is a design problem or a bad part and if you are in a pinch for whatever reason you have to use you own judgement on what you do. I'm not trying to argue or start a debate but merely offering my views on this subject and maybe keep somebody from getting in over thier head.

[Gary]

I changed the name of this thread from "I need RallyBob's help!" in order to help out with future searches.

[Paul]

OpelDean,

It has been posted by RBob that for every .025" milled from either the block or head, the cam timing, wrt the crank, will retard 2 degrees. Also, in his post concerning the best low budget mods, he says decking the block to bring the pistons flush to the deck (or maybe as much as .005" above deck) and milling the head .050" will bring the compression up to a true 9.5:1, using stock valve sizes and new exhaust seats.

To correct for cam timing, there are several ways to do this. Some are easier than others and less expensive.... 1) redrill the dowl hole in the cam gear at the appropriate location; 2) modify the cam gear to accept Chevy offset bushing; 3) purchase an adjustable cam gear from Kent or Piper; 4) make custom offset key to relocate the crank gear by the approproate amount. I'm sure there are other ways someone in the group knows about.

In my big valve head by Roger Wilson (okay moderately big Chevy 1.72/1.5), he used a spring by Isky. The part number is 905-D, and is listed in their catalog as for the Capri. He also used their retainer and lock. I'm sure if you called them, they would be able to specify the appropriate part numbers.

This spring and chevy valve combo had seat pressures of: 95-100# valve closed and 195-200# valve open. Well within the recommended seats pressures recommended by RBob for use with the stock Opel hydraulic lifters and stock rocker arms. I believe the combo will also allow valve lift greater than stock. How much exactly,? I'm sure a call to Isky will produce the answer.

Yes you can toss the rotators and use all Intake springs etc. The late model seat pressure specs were I=93/182 E=97/180 Open/closed.

I measured a used head gasket I have saved. It measures .031-.032" I keep the gasket so I can build up the motor and check for valve to piston clearance without destroying a good/new gasket!

GL

[GTJIM]

Thanks Travis, Your points are well taken. Paul, thanks for expanding the info.
Gary - a good change! I posted mainly because I think we tend to overload Bob from time to time and he may just get exhausted from repeating stuff. His vast Opel experience is one of our Communities major assets. Nobody also has many years of Opel experience that are just as valuable to us. As does Travis.

I have spent years building Flathead V8s; Studebaker 6s and V8s plus a Jaguar or two and some experience with SB Chevy, Isuzu and Holdens. The Opel CIH engine is one of the most interestingly different engines that I have come across. I can appreciate why "molesting" the block/head surface is somehing to be avoided if possible but acknowledge that sometimes; "Needs must - when the Devil drives" and now we have much of the info on what happens and why plus what to do to fix the problems "decking" causes.

Can't understand why normally sane people use rough idling cams on the street - The standard Opel hydraulic camshaft is much under-rated with peak power being delivered about 5,000 rpm. Much of my comment is tempered with this thought and I shall use a new 2.0 litre CIH camshaft as a starting point.

[opelrun21]

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

I'm trying not to go over my rear axles with my exhaust, and just put a muffler with a down angle right before them. Is it going to hurt me to do this? If not should Ileave it 2 1/2 or go down to 2? If it is going to hurt me what should I do and why?

You guys are the reason my opel still gets out on the road.

[RallyBob]

I'm trying not to go over my rear axles with my exhaust, and just put a muffler with a down angle right before them. Is it going to hurt me to do this?

You may get exhaust fumes coming into the car because of this. Carbon
monoxide can kill you, so you be the judge...

If not should Ileave it 2 1/2 or go down to 2? If it is going to hurt me what should I do and why?

You didn't give any info about your engine, but if it's stock or nearly stock, a full 2.5" exhaust will kill your power. Keep it 2", and only use 2.5" over the axle.

[opelrun21]

Right now it is stock and it is killing my power. I put a 38 DGES on it and I'm jetting it to what I have gotten from what I've heared you said. (Bob)
135 Main
170 air corrector
The rest was right on the carb when I bought it.I only put the header on because I had all that torn apart. So if I was going to drive it with the stock motor until I can build the 9:1 motor I should run 2 off the header and no matter what always go over the rear axles? Hoppfully when the other motor is built I can still holla at you guys for the knowledge I don't have.


-------------
it's a 73
yeah way before our time

[RallyBob]

Running a short exhaust (before axle) with that header will definitely favor high rpm power instead of torque.

On the DGAS, did you change the emulsion tubes? That's more important than the jet changes IMO.

Bob

[opelrun21]

No I haven't changed the E-tubes. The carb says it comes with F50's. Are they marked on the tubes? I want to take them out and check them. If I can check them, what size should they be while its stock? Also while its stock would the best exhuast for me be the 2 off the header and just turn over the axle toward the ground and out? I just dont want to see pipes out the back, so I can shave the back panel for a smoother look.


She just wants to roll down the street agian

[RallyBob]

Try the F-66 emulsion tubes, it helps off-idle performance a lot.

[opelrun21]

Does off the idle mean when you go from idle to throttle? Cause that is accually my big problem. When I give it gas it bogs, and almost dies but keeps an idle. Hope that is the problem!

Thanks alot Bob!
I'm always ready to listen.

[greensmurf20]

i've done reading, on and off the forums and asked somebody about the likes of me using this cam. internally stock low compression GT, pertronix, weber, header are the only things done to the engine. is it ok to use a 435 lift/290 duaration cam with hydraulic lifters in this car as a daily driver? i dont want solids as this is a daily driver, about 10,000 miles a year, solids just drive me crazy on long trips. a simple yes or no is all i need, i got plenty of explanations from here, just double checking, i dont want to bother you guys more than i have to.

[greensmurf20]

i'm assuming no problems with using this cam, altho its close to the line of whether stock springs are ok to use. how will the "torquer" intake manifold design of Bob's compliment the cam?

[greensmurf20]

well, turns out i'll be letting you guys know if anybody cares to hear. i'll have the cam and lifters in place before the manifold. i have a weak lifter, knocks off and on, today got really bad for a little bit, and then mysteriousely went away as always, lifters are adjusted right. so the cam and lifters was a "must do", the upgrade was a "want to" so i can say how the cam does on its own and with the torquer intake, probably wont have the intake on before i put it up for the winter.

[GTJIM]

The standard Opel hydraulic cam is no slug on the street with peak power at around 5,200 rpm so do not under rate it as a cam for street use. A "torquer" cam is far more use in a road car - especially one that needs to travel smoothly at 30 mph and less around town in top gear!

[kwilford]

is it ok to use a 435 lift/290 duration cam with hydraulic lifters in this car as a daily driver?

I am NOT the cam expert here, but let me take a stab, and hopefully learn something along the way.

First, it this cam a "hydraulic grind"? As I understand it, a "solid" grind has quite an abrupt ramp on the lobe, while the hydraulic grind has a gentle start to the ramp. I believe you can use a sold lifter on a hydraulic grind cam, but not vice versa.

Here is a quote I got from RB when I was asking about cams a while back:
"Stock Opel is .390" intake/.400" exhaust, 198 degree duration @ .050". Pretty mild then (I run cams with over 245 degrees @ .050" on the street for comparison)"

The lift on your cam doesn't seem too wild, but the duration is starting to get up there. Is the duration measured at 0.050" lift, or for the entire lift? Just as a comparison, OGTS's "Torquer" cam ("Good for street application") has a .407" lift, 256 degree duration. The "Combination" cam I bought from them ("Good for street and autocross") has a 0.430" lift and 268 degree duration (I believe those are total durations). They also sell a "Max Comp" cam, with the same lift, and 284 degree duration (solid grind only), which they describe as "Good for autocross and racing applications. Not for street!" Which sounds more like your cam, or even a bit milder.

Where did you get this cam from? RallyBob, can you help us poor unwashed here?

[nobody]

I'll weigh in on this one, that at .050 it is at 230. The ramp on hydraulics is more abrupt to aid in the preload of the springs and oil pressure. If you use solids on a hudraulic grind you loose about 10 degrees of duration becouse of the valve lash differences. Almost nothing you do will change the at .050 numbers but you can change your duration a few degrees by shortening the lash. I've been all over this recently and I know this cam very well.

[kwilford]

I'll weigh in on this one, that at .050 it is at 230. The ramp on hydraulics is more abrupt to aid in the pre-load of the springs and oil pressure. If you use solids on a hydraulic grind you loose about 10 degrees of duration because of the valve lash differences. Almost nothing you do will change the at .050 numbers but you can change your duration a few degrees by shortening the lash. I've been all over this recently and I know this cam very well.

About TIME we got an answer from somebody who knows what they are talking about

I had thought that a solid grind ramp profile was early and fast for the first 10 thou or so to take up the lash, compared to a later but more gentle opening ramp for the hydraulic grind, and then they were pretty much the same for the rest of the lift. Hmm, live and learn...

Hey, does that mean that hydraulic lifters on a solid cam will INCREASE the duration? How well do hydraulic lifters work (if at all) on a solid grind cam? Was I correct in saying "solid on hydraulic, but NOT hydraulic on solid"?

So David, is it a given that Jared's 290 degree duration is the "full" duration, and that it is a 230 degree duration at fifty thou? Do you know his cam, or can it just be calculated by taking away 30 degrees of duration for the opening and closing of the last 50 thou (as a "rule of thumb")?

Finally, will Jared's cam be OK with hydraulic lifters in a street application?

TIA