Rampipes and Inlet Fiat 1608 TC & simulations

[TCSeven]

Hi!
I have a couple of Dellorto DHLA 40 H 9sidedraft) carbs and I intend to install them in a 1608 TC that I am working on. I am having difficulties sourcing a good aluminum inlet manifold to fit them locally around my city (Buenos Aires, Argentina).

A couple of people adviced to just construct one using steel tubing.
Do you know where I could source an aluminum manifold for TCs? They mostly came fitted with IDFs so all I could find was the waffle manifold for them. Another question: what length of velocity stacks (rampipe) would you recommend? Is the velocity stack length significant to improve top BHP or driveability? What's your take?

Thanks!

[Os7213]

Hi

For the lenght of the velocity stack in general shorter stack will help in high rpm range, longer stack will help low and mid rpm.
Yes personally I think velocity stacks can help BHP or at least air delivery at certain rpm's unfortunatly in most of case if the car is a daily drive you will want air filters.

I really suggest you to read about total inlet port lenght from middle of the inlet valve to the end of the inlet trumpet.

Here a start with a link to a previous thread that Mr.Croft should reply soon, I have try to found any other tech documentation about total inlet lenght but unfortunatly I think the pro's hide the secrets!!:
http://guy-croft.com/viewtopic.php?t=1075

Hope that help
Hugo

[Testament]

You should be able to use a Weber DCOE manifold, I think GC sells these, as do a number of other companies. If you have a block mounted distributor you will a need a swept manifold to clear it, if you have a cambox mounted distributor you could use either swept or straight manifolds.

[Guy Croft]

Yes, I do a sidedraft manifold for TCs with right-hand drive, ie no brake booster (servo) in the way.

As for rampipe (velocity stack) length you have to either dyno the thing to death or run advanced software simulation to get an optimisation. The total length rampipe outer face to valve throat centre, exhaust header length, diameters of same, valve sizes, cam lift, timing, CR, bore/stroke and working power band all feature in a reliable simulation and it is beyond most peoples' means to get that. You won't find anything worth having on the internet.

There is certainly truth in the statement that long pipes help lower end and short ones top end (power/rpm) but beyond that the main issue is providing a nicely radiused entry for the air into the carb. Frankly - I wouldn't worry overmuch about the length.

GC

[1NRO]

Most stuff found on the internet is too basic as Guy says but there is what appears to be a good software package available for purchase at a very reasonable price. I'd post it up but not sure if it would be appreciated?

Nik

[Guy Croft]

Only if you have used it and can vouch for the usefulness of the results it offers.


GC

[1NRO]

I'm afraid I haven't used it but many pro's use it as a trusted referance. It was developed by a top American engine builder and from what I can gather is based on years of dyno testing. I really do need to buy it and have a play.

Regards, Nik

[Guy Croft]

Let me give you some hints, as there are quite a number of these systems on the market. To be effective to say, even 10% accurate or better - in terms of predicting the torque curve - the software would certainly call you to put in the following critical input parameters:

1. Inlet and ex cam maps lift by degree
2. Exhaust system configuration as 4-2-1 or 4-1 (if for a 4 cylinder engine)
3. Exact inlet tract configuration (eg: split or linked barrels, injection/carb type, tract chord length, diameter)

If the system gives an instant 'push-button' response to your inputs - however many there be - then it is not calculating the wave action in inlet and exhaust over the operating cycle (the key thing that determines whether the engine is going to be powerful or not), it is simply working off presets that the software designer has put in, gleaned from dyno tests. This won't tell you much unless your setup happens to be exactly the same, which is going to be hard to determine without the above being entered. Thus, in my view, there is little to be gained from such systems other than interest value.

That is just my own perspective, but anyone who has gained useful guidance from a relatively low cost system ( I don't want costs mentioned here but I am talking under ‚£1K) is welcome to comment. I should appreciate only detailed and accurate feedback please.

GC

[TCSeven]

Thank you all for your replies!

I do have a block mounted distributor, so a swept manifold would suit, yet I could relocate the distrib. to cambox mounting if I had the proper adaptors. My cams had the slot at the end done just in case I wanted to do this in the future.

Is there a notieable difference between the two manifold types as to merit distributor relocation?

Also, my car is left hand drive, but it is a Lotus Seven, not a Fiat so I have a different layout (and no brake booster!).

I will have to relocate my brake pump to make the carbs fit, but I think I know how to do that.

Guy, should you have aluminum manifolds (swept?) I am interested, please indicate how should I proceed to have a quote from you.

As a last comment, I plan to fit 45mm. stacks, and a couple of K&N filters. That stack lenght is middle to long, so as to improve my low rpms a bit, being a road-race car.

Thanks again!

[NOSferatu]

About rampipes... Without the brake booster I'd construct servo operated changing intake lenght system. Mechanically it is not even challenging. As Mr Croft said, the fun begins in tuning it properly. Finding the waves.

I have already relocated my brake booster, but there still isn't space enough!