Port angle and valve shape

[NeilRoshier]

Just as the topic suggests I am interested in finding more information on the merits of increasing the port angle relative to the valve head and secondly which shape of valves suits which type of ports.
The first part of this query relates to the port angle relative to the valve. In looking at diagrams of various racing engines over time some seem to have paid great attention to this port/valve angle (e.g. Lotus TC) which seems to have paid dividends over other engines that may have been constrained by production issues, though with a similar layout are not able to produce the same amount of power (e.g. Fiat TC). Is the increased port angle thus increasing the discharge coeff't as the valve/port is able to flow more evenly?
Secondly there seems to be some confusion in the media (and I admit in my own mind!) about which valve is best for which situation. The american V8 market seem to like the flat/thin head on the valve, and some tuners of hemi head 4cyl engines also subscribe to this, however others do not. The same issues abound in the later 4v tuning market and without unbiased testing of different valves in the same port/head (not that this is likely as it may shatter a few glass houses that pay for advertising). Can someone provide some guidance from their experience?

 

[patprimmer]

4 valve ports are "fussy" because the factory generally did such a good job in the first place, so it's easy to make them worse, especially by visual assessment only. Pushrod engines often have such inefficent ports, that improvements are often visually obvious.

I would think that tulip shape on 4 valve engines reduces the impact of opposite flow from the edges of the pair of valves where the edge is nearest the other valve. Regards
pat

 

[NeilRoshier]

Thank you for your thoughts. The lotus TC is the lotus developed (actually they just paid an engineer to design one and he did a very good job from the start...can't remember his name at the moment) twin cam head on a ford block. It was used for a very long time in all lotus cars. 100-120bhp/lt has often been reported for well developed lotus engines. The fiat twin cam is a similar design (being twin cam 4 cyl hemi head) designed by Lampredi (I think) which has much lower ports that the lotus and can be made to make 100bhp/lt but it seems to have more difficulty doing so. Valve sizes are interesting in that the fiat seems to have an edge. It does in other aspects of the engines too, but that is not what we are discussing.
Looking at a sectioned head of the fiat TC it would seem possible to increase the angle of the port approx 15deg relative to the valve by cutting away metal and welding in a new port made from thick wall ali tube. I am interested in trying this, but would like to know more before spending the time. Why bother?...well the heads ($10-40USD) and engines are cheap and it would be good to try something new. 4v heads are available but do not quite 'look' right in an old car (plus add more cost e.g. head is $600USD needing work).

 

[evelrod]

I am pretty familiar with the Lotus TC having built and raced them for 28 years. Even did a Fiat 124 TC once.
Colin Chapman used the Cosworth designed cyl head for the little Ford 105E engine (originally for F-2 Europe, F/B SCCA) with such success in the early 60's (World Champions 1964 thru early 70's in WRC and SCCA Trans Am Series Lotus Cortinas, Elans, Ford Cortina/Escorts, etc.) that it has continued into the present as one of the most popular in vintage racing. Comparrisons with the Fiat and Alfa engines of similar size is inevitable. The Fiat suffers from valve angle problems as you suggest but can be modified to come fairly close in hp output to an "average" Lotus TC and of course the GTA Alfa twin plug heads can equal the output of the single plug Lotus. I have built Lotus 1594cc to about 205hp and I have seen one of David Vegher's engines at that level also. (I know about the Vegantune, et al, at 250hp but I class those claims as exagerated???) The best I could get with the Fiat was about 185hp but I gave up early on it. Ultimate hp may not, indeed, is usually not, the ultimate for a race car. The overall power curve needs consideration.
The big difference between the Fiat and the Lotus is the valve angle (you can look straight through a Lotus) and port configuration along with the Fiats 'hemi'. The Lotus is a 'hemi' like shape (eliptical) with good 'squish' and mixture motion in the combustion chamber which the stock Fiat and Alfas seems to lack. The Lotus has used several valve shapes including all you describe. The Tilton modified Datsun L-20 Intake and L-18 Exhaust are very thin and I have had head seperation problems with them, the Vegantune things are thin and sharp and I don't like the flow numbers, the Brian Hart jobs are great and I have had a similar set made up from Jag parts by Dave Bean Engr. for the 205 engine using a Brian Hart modified Vegantune head. It seems the tulip shape works the best.
Modifying a Fiat TC to equal a Lotus or Alfa is probably possible but at a great cost in time and money. With the Lotus TwinCam heads on the market , rebuilt, at $8,000 and up it might be a viable alternative if you are a glutton for punishment. I can email you more if you are interested.

Rod

 

[NeilRoshier]

The fiat does have some advantages, such as interchangeability of parts with other models. The 'reverse port' (intake/ex on the opposite sides) has a much better CC and combats some of the issues you mention. There are always good and bad points with such engines, let alone an interest in a particular marque that might sway a persons choice of which one to run. The lotus was just too expensive for me to play with and a bit fragile for an everyday high mileage engine.
It is interesting to hear your experiences with the valves (I have always admired brian harts work...millington too makes fantastic engines) and what different people are doing. I am wondering if the increased port angle will be worth the effort. I have heard of other people adding to the squish bands in the CC to get better resistance to detonation problems...but one step at a time. In the CCC magazine they also did a twin plug conversion on a pinto with good results reported...a lot of work.
Do you think there is a 'general' rule for valve shape or will it get down to specifics of the ports/cc?