20v Head pro/con

[AceSniper]

This has semi been covered b4 I know but I wanna get straight to the point

whats better to have? and why?

The squish in the silvertop comb-chamber vs blacktop open chamber?

Are the valve sizes the same between them? specs?

Larger blacktop throttle bodys VS smaller silvertop?

Larger ports on blacktop better than silvertop?

How has the VVT solinoid setup been changed (if any) whats better?

what im sorta getting at is... whats the best features on each head compared to the other one, and why does it make it better (for N/A use)?

Im not after "I think this is better"

cheers ppl


[/b]

[RedMist]

You better post your application, and how you intend to modify the engine.

I'll consider this a no money concern post.

I'm a firm believer in a silvertop head for a good mid range rally style engine.
Because it flows almost as much as the blacktop head, can be made to flow similarly, port sizes can be modified up easily, reduction in port size isnt as easy, the Blacktop has some silly flow spikes, which I'm yet to correct (VVEGA!!) I love squish, so love the colsed combustion chamber.
I'm developing a blacktop for an all out screamer atlantic style engine (VVEGA!!) mainly because it flows so well standard, an increase in flow will generally mean a reduction in velocity so you need large RPM to keep fuel in suspension. This engine will have Carillo rods, and in all honesty if if I only had a set of silvertop rods to insert into the blacktop I would seriously reconsider the route I've taken. If I only had blacktop rods I wouldnt have even considered it!

So
1. I like squish, without it you have to rely on swirl and tumble to keep the fuel charge in suspension. But without developing two heads with the only differences being closed and open combustion chambers my answer is only theroy based. If your pulling high RPM this becomes less of an issue.
2. They are identical valves. As an aside we attempted to place 1mm larger and tulip valves in the silvertop development head and gained no sygnificant flow increase. However deshrouding the inlet valve gave good gains.
3. For a standard road application I still believe in the facelift silvertop TB's. Its all about flowing a head to as much HP as you believe you will make with as little restriction and as much velocity as possible. Keep the speed up and you keep fuel in suspension and mixed well. Which is like viagra for your dyno curve. Increase the RPM, displacement or VE (to a very limited extent) of an engine and you can increase the TB/port size.
4. My belief is Silvertop exhaust ports are too small. Toyota have modified them in the blacktop and the ratio for inlet / exhaust flow doesnt adhere to any documentation I've read. This is possibly why some companies push a larger exhuast cam than inlet in aftermarket situations.
Good news though. It can be made the exact same dimetions as the blacktop exhaust port.
Inlet, from memory, and it was a while since we flowed the heads, the standard silvertop flowed enough air to put out approx 200 hp. Clean up the flow (and there is little to do, its a good head) and your probably pushing 210-220.
Keeping the above in mind if you want to run this in a 400kg formula race car then you have a tonne of work to do. It'll need to flow radically more. If you want it for fast street, then you need to tidy up the castings, get a photo of the deshrouding of the inlet valve, do the same, and enlarge the exhaust port to approximately that of the blacktop... and your done.

Personally I'm stuck somewhere between a very light rally car and a very heavy formula car at 770kgs. VVega made up my mind with a blacktop for sale with some very good parts attached.
At the end of the day my blacktop will have the port dividers corrected or removed, will have casting marks removed, some work to correct the flow spike between the TB's and head, some work on the valve guides, and probably just a 3 angle valve job.

[craigt]

Listen to RedMist, this guy really does know what hes talking about!!!!
And yes I agree with him, ST all the way. The closed combustion chamber is a far better design as far as correct combustion goes, the turbulence generated when that piston gets close to TDC is enormous. This leads to better combustion.
As a sideline, have you seen the shape of the combustion area in a direct injection diesel engine. Massive squish area to generate the turbulence required for the engines to burn the fuel correctly.
Trust me, Ive talked to RedMist and been round to his place, he knows his shit. He not only knows it.... hes done it!

[RedMist]

Dude, serious head swell!

But I've never built a full race 20 valve. Our first attempt was stymied by the fact that we found a 16 valve fully built for about half of what I would have paid for parts. I just threw away the webers and created my own manifold based on the silvertop TB's.
We have flowed both the silvertop and blacktop. I chose to develop the silvertop and created a single port that suited our maximum horsepower. But that engine was never built, and I switched my effort to the 16 valve.

I'll post a dyno plot of the new Blacktop 20 valve, once VVega ships it, and its built.

So please take everything posted here, by all members with a grain of salt. Especially considering the HP produced by some engines that I would tell you wouldn't pull back my forskin. Some combinations "just work" and they defy most written or previously experienced logic. What’s with the 4K anyway?