Race Engine Forum UK

Then again, it may just be a gap between the end of the trumpet and the top of the carb because the opening in the airbox floor is in fact bigger instead of smaller.


FWIW the air won't even 'see' that step. To impede the airflow the mismatch actually has to be pretty big. I wrote what one might consider to be the 'chapter and verse' on the influence of mismatch in my new book.

One must be sanguine about these things! It is not sanguine to take 'principle' and attempt to achieve it slavishly in practice in every case. That 'maximum attack' approach to tuning belongs in the Stone Age.

G

Sorry if this was covered earlier in the thread but why not full-radius trumpets? I'm going to start working on an airbox for my car shortly so, whilst a different configuration, it's an interesting read.

Full radius - why not?

Poor Miro does have a day job (as well!)...

G

Ah, day jobs - we'd all get a lot more done if it weren't for those...

I just remember the builder of my first race engine reporting back on testing the full-radius trumpets I'd sent him on his engine dyno. He said that they "only" gave 4bhp improvement over the traditional type (like Miro's). I did feel like responding that, at 65GBP, I'd be very happy if all the BHP improvements came that cheaply. Just seems sensible to design your airbox around them.

I don't doubt the gain for a moment and the improvement in torque distribution can be quite remarkable.

However. I built and supplied that engine, fully-dressed. The carbs come with reasonable rampipes and it was bench-dynoed with them and gave a very creditable result. When the list of parts and ops is as long as it was (and generally is) I baulk at pulling off the rampipes Weber supply (which aren't bad..) and raising another charge for replacements.

I can speak for Miro I am sure that he is quite happy with it the way he is.

To be honest I wish there were rather more detailed projects on display on this site. This thread has generated a lot of enthusiasm (to the extent, regrettably that others might feel a bit 'left out') and that's great but I am a bit disappointed there are not more folk doing things like this & who are prepared to have their vehicle analysed like this.

It is - in my view as the creator of this forum - a sad reflection on the way of things that in the main those who 'recommend improvements' seem to be those doing the least - but seem to have 'read' the most. Or at least posted the least about their own projects.

I say that in the most general terms so no-one (least of all you Richard - as you've been 'thru the mill' with your Alfa) so let's have no-one feeling 'got-at'. Just shape up, that's all!

G

Hi Guy - understand your sentiment entirely - I'm looking to learn and share. I've not actually had my car with me whilst I've been signed up on here so it's been more difficult than normal to share what I'm doing though I hope my website indicates my willingness to share.

Miro's example is great and I've got a good sense of what's expected by way of posts. Hopefully I can at least match the standard. I've got a few things I want to do to get my engine "up to snuff". If I ask a question, it's to learn not to sound clever.

Tom has the blue arrows pointing at the ridges that may be there. As I said, it could be the picture and the angle. If those are edges of the bottom of the air box, protruding in the flow, they probably will have a measurable negative effect. If they are in fact just reflections and nothing is "sticking out", things should be fine.

Regarding locking the trumpets in place, (every time new) nylock bolts should suffice? Maybe threadlock will help? I don't think putting a locking wire through the threads is practical here.

TomLouwrier wrote:A picture helps.
I think Homme means these, aka 'downstream mismatches'.

Then again, it may just be a gap between the end of the trumpet and the top of the carb because the opening in the airbox floor is in fact bigger instead of smaller.

Tom

Sorry , now I see ... ( a picture is worth a thousand words). These edges are not very big and it is questionable in my mind if it is worth removing them. It is for sure these ridges are not helping proper smooth airflow, the question is how much ... Shaving off those ridges will require absolute protection against debris contaminating the carbs (and the inlet manifold !)So it It looks like taking the carbs off. ( Will first verify if the trumpets can be repositioned and or refit to match the carbs opening. It seems the mismatch is asymmetrical but on the first look the bottom openings of the trumpets are under 2 mm larger in diameter (ca.1 mm on each side).

Thanks for helping me to understand, but if I do shave off those ridges ( and the process would not be simple as it takes taking them off) and have to change to new trumpets in the future I may create a bigger problem down the line. For the time being I will stick to possible repositioning of the trumpets by moving them around to find the best match for the carbs opening .

Miro

That may be a solution as well. It's hard to tell from one photo what is actually happening, but it caught my eye so I asked. If Guy says it won't hurt he'll probably know best. He's been flow testing so many setups that he's probably came across this many times.

Leave those ridges alone. They were there when it was dynoed - as well they might be for all the intrusion they present (none).

Indeed, who is to say they don't in fact improve performance by introducing turbulence into the airstream.....?

G

... which is exactly what I want to do !

M

Alternative approach to high coolant temp.

A strike of a genius !

Instead of complaining the coolant temperature is too high , I decided to measure it independently of my on board gauges and got interesting results.

The on board gauges normal operating temperature reading is just above 80 deg C, which would be 5 ( maybe 6 deg too high).

When I checked the temperature with and accurate (though also electronic) measuring tool , the temperature proved to be only 75 deg C.

(WHICH IS WHAT IT SHOULD BE !!!)

I went a step further , and put the engine to the highest temp my on board gauge ever shows (when the car is not moving and the engine has been idling for a long time -before vent brings it down ) this temp is given by my on board gauges as almost 90 deg C.

The actual temperature proved to be only 82,4 deg C.


Which is well within the range determined by the thermostat and radiator vent switch.


I remember Guy recommending capillary gauges. This proves why. The standard gauges are apparently very inaccurate.

The difference in the first and second reading was almost exactly 8%. One would expect the accuracy to be within 5 % , but typically the reading varies from actual value by as much as 10%.

The lesson: Using standard electronic gauges yields inaccurate reading. You really do not know the temp/pressure unless you measure it with an external accurate measuring tool. Capillary gauges are not so available ( especially with vintage look fitting my gr 4 style dash, so i will stick with what I got. What is important is that now I know the level of inaccuracy and now how to interpret the reading.

Anybody had similar/different experience with standard on board gauges ?

Note : These gauges typically work on resistance so this can be corrected. If I have too much time during the off season I might -play with it to achieve correct reading.

PS: Once I am on the temp and gauges subject let me add a little note on additional instruments.

I have a n exhaust temp gauge ( left).
This is to watch for raising temp at full throttle as an indication of improper ( too lean ) mixture which can really hurt the engine.
This proves to be quite a useful gauge to have.

The gauge on the right is connected to a simple electronic thermometer sensor into the K&N filter housing. This is to see what effect I get by closing off the carbs and preventing them from drawing hot air from over the engine and forcing it to draw cool air from under the front grill. With the temp under the hood exceeding 40 deg C. the temperature of the air drawn by the carbs when the car remains stationary and engine is idling is only around 32 deg C and on a stage it drops to the level just above the external air temp. Recent tests showed that temperature of iar drawn dropped top 22 deg C. and was marginally higher than external air temperature. This gave us the temperature difference of difference of 20 degrees which was actually much more than I expected. ( even if the readings were within 10 % accuracy the proportional change is the same). This is really remarkable.

Miro

Update on Interior changes...

I really got sick of my standard roof lining and decided to take it finally off.

Removing it proved a bit harder than expected as the Styrofoam base of the lining was really well mounted fitted the rood quite tight. It had steel tape supports melted into it in two places across the roof - side to side ).
Come to think of it this was not only keeping the inside decibels down but also provided ( some /reasonable ) level protection from hitting the roof with a naked head real hard , should the car flip.

However the artificial fiber external lining created significant fire hazard. If this catches fire you get a very good incinerator over your head. So I pulled it all off. ( took me a coupe of hours).


Once I did that I have installed the FIA standard protective foam in areas of the cage that can ( under crash situation) come in contact with the helmet.

I have restored the original Gr 4 steering wheel. Some idiot painted over the original black varnish making it look brand new . I have removed the black paint and got it to the original look with some wear and tear .
Future plans include changing the interior door panels to gr 4 like black, light weight panels, with strap handle and maybe some pockets for maps, etc. , removal of rear side interior panels, installation of a manual extinguisher system, removal of all floor tar panels (they do irritate me) , change to new bucket seats. The new Cobra seats expected later this month will be positioned correctly. Current seats are too high over the floor positioning the driver's and co-pilot's head too close to the roof. This time we will do it right. The new seats hold the shoulders real well and give great head protection on the sides.
The co-pilot seat was selected to give him as wide visibility to the sides as possible. As the driver (referred in the local rally jargon as the "manual laborer" ( -see note below ) really looks only straight in front and does what the pilot tells him , the co-pilot ( in the local rally jargon called the "intellectual") must have a better view ...

Installation of the new seats will also allow for better rear angle of the safety belts. We will also use this opportunity to make sure the belts mountings meet FIA standards.

The co-pilot will get a foot rest and maybe we will out some aluminum sheets over the floor ?

This should conclude the interior changes making them practically final.

Engine setup is done , the only remaining element is installation of the Speedshift ( rev limiter, etc.) which will be done in few days.

Suspension and braking system is getting very close to done. What remains is:

- installation of the front Abarth hubs and new front brakes,
- final selection of the rear brake setup and getting the right rear disks,
- installation of the hydraulic handbrake,
- installation of front Abarth suspension,
- putting the external kill switch and extinguisher connection
- fitting the the rear tow hook

Body :

- light boot cover
- front disks venting

If and when I get hold of the original doors, we would put them in as well as change the side windows to polycarbonate and install original type mirrors.

If this is all than we are getting awfully close to completion . It looks like by the start of 2012 season the car should be in its final reconstruction stage.

We are getting pretty close to making the reconstruction final ... after only 6 years... not bad at all (LOL).

Maybe this is not a never ending story, after all. We will see soon ...

I am old enough to remember president Lyndon Johnson saying : " I see a light at the end of the tunnel".
His critics used to say: :yes, it is the VC with a flash light" .

Hope that in our 131 Abarth reconstruction project actual prospects will be better than that those of the US in Indochina in 1968 and that we will win by successfully completing the project by beginning of the in 2012season .


Miro

Note : the reason the driver is referred to as "manual laborer" is because he is seen as just a "mechanical a link between the pedals and the steering wheels". All he does is pushes the pedals and turns the wheels according to co-pilot instructions. His only task is to keep the car on the road following co-pilot's commands. He is not there to think - just accurately respond to co-pilot's commands. The the co pilot is the real brains of the crew. It is he who decides when the car turns , when it brakes and accelerates. Thus the jagron nicknames.

Excellent posts.

OE gauges inaccurate? Ho ho ho. Call me Father Xmas.

Better view for the navigator??!

Nah, put him down on the floor where he can't see a thing, maybe concentrate him a bit harder on his pace notes and Halda. Takes some driver/nav trust to do that without crashing, mind...

G

Labourer and Intellectual?
Do I hear echoes of the class struggle here, Miro? ;-)

In these parts when someone says there is light at the end of the tunnel, the answer is it'll be the headlamps of an oncoming express train...

gr
Tom