How to choose different intake and exhaust cams? - Page 11 - Alfa Romeo Bulletin Board & Forums
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post #151 of 161 (permalink) Old 02-14-2018, 03:04 PM
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Regards to all, I know this is an old thread, but not for this is less interesting.

I believe that probably the answer to the initial question has not be answered yet or is not so clear, altough nobody can negate is that along this thread we have tried to analize from a technical or scientific point of view the different phenomenae asociated to the opening and closing of the valves of our engines.
It can be found too, although sometimes without analitical argumentation, practical and valuable information gathered by people that have deal with these engines for years.

I think there is argumentation enough to maintain the thread alive, to try to close the circle and get a final conclusion to the initial proposed question.

So, to continue, I'm going to throw a new question, more related to the increase of valve lift:

Has somebody tried to install domed tappets in an Alfa 8v engine?
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- SNO Director, Spain branch, Barcelona
- '90 2.0 Spider -- '93 164 QV -- '93 155 2.0 TS -- '02 156 2.5 V6 -- '?? FMG 3.8 Project
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post #152 of 161 (permalink) Old 02-16-2018, 03:17 AM
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Picture below are the camshafts from a PIPO rallycross 2.0 turbocharged engine (85x88mm), max intake pressure is 4.5 bar absolute, 4 valve head, 32.5mm intake, 28mm exhaust, max rpm 8500. The engine is intake air restricted, and also restricted by regulations is the max intake valve lift (12mm). Tappets are domed, have a diameter of 31mm and weight 18g each, valve springs (2, with a slight interference) have an increased on seat tension to keep valves closed when pressures in manifolds is highest.

Power curve is flat from 5500 to 7000 rpm producing 600HP. Intake pressure at max torque is 4.5 bar @4500rpm absolute, falling to 2.9 bar @7250rpm (due to the intake restrictor).

In the picture can be seen the big difference in angle between intake and exhaust cams even being this a turbocharged sport engine, and the almost flat nose of the intake cam (due to regulations). Also note the little concavity of the cams ramps (because the domed tappets).
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- SNO Director, Spain branch, Barcelona
- '90 2.0 Spider -- '93 164 QV -- '93 155 2.0 TS -- '02 156 2.5 V6 -- '?? FMG 3.8 Project

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post #153 of 161 (permalink) Old 02-16-2018, 08:45 AM Thread Starter
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Welcome back! It's good to see you again. Where we landed after much discussion back and forth is a "received wisdom" that suggests that a "little bit" of difference between intake and exhaust cams. One very experience builder suggested about 10% or a bit less. Admittedly, this is more trial-and-error experimentation than more empirical investigation. Nonetheless, despite being more folkloric than scientific, several pretty good 8V nord engines have been built using mildly dissimilar intake and exhaust cams as opposed to the more customary practice of using the same cam for intake and exhaust. But, what you're talking about is a pretty dramatic departure from selecting off-the-shelf-cams with slightly dissimilar timing. So, that being said, I'll bite: how do you start designing a system like this for an 8 valve nord engine?

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #154 of 161 (permalink) Old 02-16-2018, 03:13 PM
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What seems to be missing from this debate is what Alfa Romeo actually did with its port dimensions and designs over the product range.

As an Example I have a GT-V 1600 head with with the so called "1300" intake port which has an exhaust about the same size.

When compared with the later 1750 head the exhaust to intake relationship is very different.

Here from my previous post on port volumes:

Quote:
1750 Series 2

Chamber volume: 75cc
Intake port volume: 69cc
Exhaust port volume: 47cc
Intake Port opening dimensions
Height 52mm
Width 41mm

1600 cc Gt-V

Intake port volume: 54cc
Exhaust port volume:52cc
Intake Port opening dimensions
Height 45mm
Width 35mm
Unless you know what you have how on earth would you know where to start in regards to choosing different cams.

Pics tell all:

1st pic. Intakes Left side.

2nd/3rd Intakes on the Right.

Just to clarify. The exhaust port on the later series 1750 head is actually smaller than the exhaust port on the 1600 gt-v head.

Hysteric.
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post #155 of 161 (permalink) Old 02-16-2018, 07:37 PM Thread Starter
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Quote:
Unless you know what you have how on earth would you know where to start in regards to choosing different cams.

I surmise that most of the people who are interested in knowing more about this admittedly rather arcane subject, also have fully ported heads. People with stock engines often don't have much interest in making these kinds of camshaft changes and, of course, ported heads are usually a considerable departure from stock. Still, it's interesting to see how Alfa made running changes to their port design. My '67 GTV's head was one of the "small port" heads in period and was quite a bit different from the larger ported Sprint GT heads.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series

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post #156 of 161 (permalink) Old 02-16-2018, 09:36 PM
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Whats a fully ported head?

Last edited by Hysteric; 02-16-2018 at 09:52 PM.
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post #157 of 161 (permalink) Old 02-17-2018, 02:35 PM
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Originally Posted by Hysteric View Post
Whats a fully ported head?

https://en.wikipedia.org/wiki/Cylinder_head_porting

Easier than spending typing it all out.
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post #158 of 161 (permalink) Old 02-17-2018, 03:34 PM
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Oh.....Is that what they do?

Interesting stuff this.

Now back to "what is a Fully Ported head"

Last edited by Hysteric; 02-17-2018 at 03:37 PM.
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post #159 of 161 (permalink) Old 02-17-2018, 04:00 PM
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Porting

You guys can`t seem to follow the thread`s purpose and question......

There`s other places for head modifications/porting.
Start here;
http://www.alfabb.com/bb/forums/engi...ification.html

Richard Jemison
RJR Racing

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post #160 of 161 (permalink) Old 02-17-2018, 04:13 PM
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I can follow it but was my point lost on you too?

I think i'll disappear from this thread before it gets too technical....
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post #161 of 161 (permalink) Old 02-17-2018, 07:34 PM
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Quote:
Originally Posted by Hysteric View Post
What seems to be missing from this debate is what Alfa Romeo actually did with its port dimensions and designs over the product range.

As an Example I have a GT-V 1600 head with with the so called "1300" intake port which has an exhaust about the same size.

When compared with the later 1750 head the exhaust to intake relationship is very different.

Here from my previous post on port volumes:



Unless you know what you have how on earth would you know where to start in regards to choosing different cams.

Pics tell all:

1st pic. Intakes Left side.

2nd/3rd Intakes on the Right.

Just to clarify. The exhaust port on the later series 1750 head is actually smaller than the exhaust port on the 1600 gt-v head.

Hysteric.
awesome post thanks for sharing!
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