Welcome a 'new' Opel racecar.....

[RallyBob]

Not a stupid question.

The adjustable cam gear allows the cam timing to be corrected for various factors....milled block, milled head, stretched timing chain, etc. The cam timing itself is the phasing or relationship between the camshaft and the crankshaft.

It also allows the cam timing to be altered to change the engine's power characteristics. For example, for a given camshaft design, advancing or retarding the cam timing will 'move' the power band up or down the rpm range. Advancing the cam will increase the low-end torque/power but reduce top end. Retarding the cam will reduce low-end torque/power but gain power at higher rpms.

There's no 'SAQ' forum, but if you use the search engine on this site you can find many of the answers to your questions.

Bob

[kwilford]

The "Opel Meister" (aka RallyBob) is IN!

Good to have you officially (or even unofficially) back contributing to this forum. Now I just have to remember that to get a question answered by you, I need to post on the "Racers Forum".

[RallyBob]

Just got a phone call, the GT-4 Manta is being delivered to my house tomorrow. Cool.....I can start on the teardown/inspection, removing the blown engine, plumbing the oil lines, and getting it ready for a fresh coat of paint.

[RallyBob]

Got the GT4 Manta delivered to my house yesterday. All in all it's pretty cool. The rollcage is very nice...all TIG welded DOM tubing. There are a lot of details that need attending to, but it will be a very nice car when all is done. And it won't cost a mint to get it running.

[RallyBob]

Here's the interior of the car. While I like the cage, it's a bitch to crawl in and out of the car due to the high side protection bars. I'd hate to have to get out in a hurry, such as in a fire.

[RallyBob]

Another view of the interior rollcage.

[RallyBob]

A view of the underhood showing the front hoops and cage reinforcements. The inner fenders have been cut away too.

[RallyBob]

Forward view underhood. Radiator is a VW aluminum core with plastic end tanks...very light and cheap.

[RallyBob]

A view of one of the tubular upper a-arms and solid-mounted front crossmember.

[RallyBob]

The supplied flywheel is all aluminum, and weighs about 8 lbs. It doesn't have a steel insert for the friction disc, but rather has a plasma-sprayed hard surface for the friction disc. Other parts include two sets of 44 Mikuni sidedraft carbs, a set of TWM intakes, hundreds of Mikuni jets, and lots of other bits and pieces.

[RallyBob]

Lastly, a nice bonus was a set of 15 x 7 MSW alloy wheels with used Comp T/A R1 racing tires.

[RallyBob]

This response is kinda directed towards Paul, but it also applies to anyone interested in some of the more hard-core aspects of engine development. I just got my latest copy of 'Circle Track' magazine (September 2003 issue), and in it there's a good article on air/fuel mixture distribution. In it they describe using a flowbench and using spray dye to see the patterns on the combustion chambers. This is EXACTLY what I spoke about earlier in this forum about the dimpled pistons. I'm sure I'm not the first person to think about testing this way, but this article is the first one I've ever read that talks about this method of testing.

Bob

[Paul]

I guess that means I need to buy a copy of Circle Track. Now that's a magazine I haven't bought in years. I used to LOVE to read Smokey's Tech Tips!!!!!!!!!

You think maybe RallyBob is somehow ralated to Smokey ????

Thanks Bob

Paul

[davegt27]

hey Bob

what are the dimensions on the stud girdle

i just sent a PIC of the stud girdle to a friend and he said he can make those


davegt27

[Paul]

Bob,

I finally bought the issue of Circle track you recommended. Great article! Also, I dug out a really old article on Wet Flow Science from Circle Track in the mid 80s and tried to cross link the info.

I see what you (and they) are trying to do. I wish some of thier pictures were clearer.

Now some questions and thoughts. I realize I'm asking questions about your ancient Chinese secrets... Sorry, but I can't help myself.

What diameter and depth dimples did you use or does it matter? I guess you just used a drill and drill bit.

Obviously, you had to rebalance the pistons afterwards.

Is your dimple pattern in the combustion chamber similar to the pattern shown in the Circle Track article?

How much compression is lost due to dimpling? Does one need to be careful to keep the chamber volume consistant with the resultant volume changes?

The old article on wet flowing heads mentioned leaving a slight ridge at the valve seat to chamber interface to help break up the fuel droplets. What can you tell me about this?

I believe you've mentioned adding dimples or something on the short side radius on the inlet track, right? Or is it on the long side radius? How did you perform this? Hand drill? What if you wanted/needed to put dimples where you couln't reach with a drill?

Sorry for all the questions, but this kind of stuff really get me fired up.

Paul

[RallyBob]

What diameter and depth dimples did you use or does it matter? I guess you just used a drill and drill bit.

*****I used a tapered carbide with about a 1/8" point...depth was to the outer edge of the bit only, that's it, I only drilled using the taper of the bit. I used a die grinder rather than a drill.

Obviously, you had to rebalance the pistons afterwards.

*****No, material removal is minimal, probably less than 1/4 gram, so it's not really measureable.

Is your dimple pattern in the combustion chamber similar to the pattern shown in the Circle Track article?

*****Not really....different CC designs and piston configurations need different patterns. Have to test on a flow bench to establish the pattern.

How much compression is lost due to dimpling? Does one need to be careful to keep the chamber volume consistant with the resultant volume changes?

*****Negligable, probably not even measureable, and at the very least within a tolerance of 1/4-1/2 cc at MOST.

The old article on wet flowing heads mentioned leaving a slight ridge at the valve seat to chamber interface to help break up the fuel droplets. What can you tell me about this?

*****I can't comment, I don't do this. I backcut my valves, and radius the exhaust seats by hand, but that's it

I believe you've mentioned adding dimples or something on the short side radius on the inlet track, right? Or is it on the long side radius? How did you perform this? Hand drill? What if you wanted/needed to put dimples where you couln't reach with a drill?

*****I dimple the short-side radius, piston tops, and combustion chamber walls. Again, using a die grinder, but for the short radius I use a tapered carbide that comes to a point. You don't need to reach the short radius at a perpendicular point, you can grind the dimples at an angle satisfactorily.

Sorry for all the questions, but this kind of stuff really get me fired up.

*****It used to get me fired up to, but now I'm old and life is boring....

Bob

[Paul]

Bob,

Thanks for the answers. Unfortunately, I'm older than you. But, just now playing this game so this stuff is new to me.

Thanks Again
Paul

[RallyBob]

The GT-4 Manta came with TWM sidedraft intake manifolds. These are arguably the best flowing as-cast intakes for an Opel engine, but there's always room for improvement.

[RallyBob]

I decided it would be beneficial to at least port-match the intakes to the head. Port-match may be a misnomer, as I actually made the intake manifold a little smaller than the head to avoid creating reversion. By the same token, the opening of the intakes where the carburetors bolt on are a bit larger than the carbs themselves.

[RallyBob]

The completed intake manifold, fully ported and painted.