Computer Engine Modelling, (18rg in particular)

[jeffro ra28]

Yer all our titanium valves are from the heads we manufacture tho, they are not regular chev items, custom titanium valves they are. Who machined yor collet grooves phil?

[Mr DOHC]

not sure, some guy in townsville, i can find out tho if u like

[jeffro ra28]

hmm id probly getting away with doing it on the lathe. Any idea how this guy in townsville did them? CNC lathe?

What did it set u back for doing just the grooves?

[Steve M]

steve, what u mean by "more restriction at low lift due to its head being inside the line of the seat for more lift than a larger valve head."

So much easier to explain in picture form,ummm.
Using port size as constant (as interpreted from Jeffro's post.

big valve in Xmm seat will sit farther out, therefore, even the smallest amount of lift (first stages of cam) will see the valve well clear of the valve seat.

smaller valve in Xmm seat will sit farther inside port (so as to achieve mating of small valve with big seat valve must be cut wider), the smallest amount of lift (as above in brackets) will see the valve still further inside the line of the valve seat.

Basically, cam has Ymm lift. If valve starts more ontop of the valve seat, it will be closer to Ymm clear of the valve seat-line.
If valve has to sit farther inside valve seat to mate up, it will be less than Ymm away from the valve seat at full lift, and at less than full lift.
I would expect more turbulence during first degrees of cam lift using a small valve in a Xmm hole, than a big valve on an Xmm hole.

This issue would be magnified by the hemispherical shape of an 18RG head. Big valve more smoothly directs air around the curve of the combustion chamber, whereas small valve allows air to deviate and swirl straight into centre of combustion chamber.

The picture inside my brain explains this very well, hopefully my words can do it some justice.
Which would be better? Any thoughts?

[Mr DOHC]

sweet, makes sense to me

[Steve M]

Yay, of course I wasn't thinking of trying to stop reversion at that point.
The same effect could make reversion of gasses during the engine cycle worse. But I guess having your butterflies (quads) closer to the head would help to stop that making too much of a difference to your idle.

Tricky, what Quads are you using? Silver top, Black top, Custom?

[o_man_ra23]

Umm... On the note of TRD cams... when was TRD formed?? I know that in the early-mid seventies as well as the mid to late sixties, toyotas race gear was made by TMSC-R which is Toyota Motor Sport Club Racing. Just wondering about this, cause incorrect terminology when searching for manufacturing specs could lead you to a wild goose chase. AFAIK the 18RG was the brainchild of TMSCR as was the 2TG and the Celica 1600GT.

Cheers, Owen

[tricky]

Steve, your thinking seems to be along the right lines. I wonder what kind of effect the valves protruding into the combustion chamber has on the squish area?

I am using silver top throttles. The diameter is favourable for intake tuning at 8000-8500rpm, so they should perform well. A race engine with a 9000-9500rpm redline would be better off with 48mm throttles. I have the throttles, and I'll make up a manifold once my engine is back together in a couple of weeks, and it'll be a low budget project this year.

Owen, I'm not 100% sure on the cams, but they've been referred to as TRD cams previously. I think toysport cams are replicas of these cams. Most toysport stuff seems based on race-proven designs.

[SeptemberSquall]

Ooops! What I intend on using is the TRD rally grind cams. All I know is 304in/288ex. I think they are close to stock 10mm lift.

304 adv. inlet, 288 adv. exhaust, .395" lift.

[jeffro ra28]

Has anyone any technical data on the TRD stuff.

Duration@ .050" and lobe seperation etc.

[SeptemberSquall]

Has anyone any technical data on the TRD stuff.

Duration@ .050" and lobe seperation etc.

I'll get back to you on that, pm me again if I forget to post the info.

[Steve M]

Recently Celica RA45 mentioned that he knows someone that has the profile of the 304/288 "TRD" cams.

O_man_ra23 you are probably right there about the vintage of the cams and the names of the organisation at that stage.
I know someone over here with an imported 18RG race engine from a JDM race car and he reckons he's got TOSCO stamped into his cams. It came with eight hole cam gears too, which were the standard for "TRD" or whatever they were called at that stage.