Removal and rebuilding of a Twincam

[rgh0]

Rohan,

Any thoughts about how ITG or Piper foam filters would affect performance? They are made of the same stuff as socks.

JAS

It really depends on how its used as any properly designed filter media will have almost no pressure drop. What I believe is most important is to have enough free space from the end of the trumpet to what ever closing plate you have due to a filter or airbox. With the sock filters the closing plate is effectively the side of the engine bay so it is as big as possible.

cheers
Rohan

[rgh0]

Hi Andy
I have added some of my observations in the areas of your comments below

Rohan,

That's a helpful reply. Just a few comments:

- With the standard design of inlet system, you are picking up cold air from the highest pressure part of the car, where the inrush air through the grill stalls against the radiator.

RH - I believe the cold air flows effectively past the radiator through the gap where the original cold air duct was located and as well as flowing into the carbs it also helps keep them cool by the surplus flowing around and then down and out

- By having a large gap down one side of the rad, you are allowing air to bypass the rad, potentially lowering its cooling ability.

RH - No issue with cooling really with either the narrow or current wide radiator

- A twink in racing trim at WOT produces a lot of standoff - which will soak into your filters creating a fire hazard.

RH - I have worried about this, but I have never seen any fuel build up in the socks, Any stand off is contained inside the socks and the socks are fire resistant foam with a little oil on them to help trap dirt

You clearly have found a solution that works for you, but it would be interesting to compare the performance of the engine in race conditions with the two approaches - Mr Chapman's original (plus a larger airbox) vs. the trumpet mounted filters. I am not sure that a dyno test with a static car fully captures all the differences between the two approaches. When you mention lap times, did you try to compare the two approaches?

RH - I have tried a temporary expansion of the standard air box to similar dimensions to the big air boxes i have seen. I was the same on the dyno as open trumpets or the socks. I have not tried it on the track. yes dyno tests will not pick up all the variables but I think they give good directional information

When I still raced, all the cars I looked at (and I may have missed a few) in the HSCC roadsports series were running standard design of airbox / filter - although the filter can was usually substituted for a K&N or Pipercross cone replacement. This may have been a series requirement to be fair - I can't remember to be honest.

RH - Any sort of fancy filter such as K&N or Pipercross cannot be better than an open pipe and just an open pipe and standard airbox made no difference compared to a standard airbox with standard filter

Andy.

cheers
Rohan

[rgh0]

Rohan,

From the dyno testing I've done on 105 Alfa i raced in Sb the 26R and S1 Elan Group M car that I completed a few years ago, what noted on dyno is a drop off in power when the air is sourced after the radiator, or drawing air from alongside/through radiator, less of issue on days in low to high 20 deg's, the power drop off was especially noticeable on hot 30+ deg days.

When back to back tested ITG (single element for both carbs, and large airbox with trunking and quality filter in front of the radiator and routed the hose to airbox through a blanking panel either side of radiator, this stopped air passing other then via radiator the power drop off showed minimal variation run to run.

The last test was ITG filter with trunking feeding air from nose, using blanking panels and it closely mimicked the top number we achieved with airbox albeit with slightly different torque and power curves.

Another interesting fact we found was, if idle down and stopped for a reasonable period after dyno runs in the hot conditions, the heat sink to the Webers was enough to affect the next power run, if it was not allowed to idle/operate at part throttle cruising speed for a few minutes prior to power runs. We put this down to fuel temps, as I had used steel lines to run front to back then steel braided lines to Webers. I also added fire guard tubing over the flexible fuel lines and steel lines exposed in the engine bay/gearbox area to limit heat sink.

The cold air will flow from the nose to the carbs past the radiator without trunking as well as it will flow with trunking given the layout of the body and radiator in the Elan assuming you leave the same gap where the trunking went. Getting cold air into the carbs is important

Keeping the carb bodies cool from heat sink also important so flowing the cold air around them that does not go into the carbs also help and helps stop the heat soak issues you observed

A deep ITG style filter mounted on the carbs will perform similar to the socks if similarly fed with cool air and be similar to a deep airbox fed cool air. I believe you're tests are consistent with that

cheers
Rohan

[Evante]

Thanks!

JAS

[vstibbard]

They are Rohan. I'm sure you're looking forward to Phillip Is Historics, will that be the first run in anger?

[rgh0]

They are Rohan. I'm sure you're looking forward to Phillip Is Historics, will that be the first run in anger?

Yes Phillip island will be its first run. Hopefully it drives off the track this time in better condition this time

cheers
Rohan

[1owner69Elan]

Responding to comments on my air filter choice ....though I am not sure about the seriousness of the questions ..... always hard on email , easier in the pub

You have a range of choices around intake air when building a developed engine. My assessment of these choices based on lap times and dyno results and user experience are as follows:

1. Standard inlet air box with standard or other style filter .... my dyno tests show the standard box cost you power of about 5 hp in a 150+ hp engine but the standard versus fancy filters on the end of a stand box makes no difference at least up to around 170 hp, have not tried it with 180+ hp engines

2. Bigger air box regardless of filter or open end into nose to pick up cold air .. works better as provides better flow to rear cylinders . Worth 5 HP in a 150+ HP engine and reverses loss seen in 1.

3. Open trumpets .... same as bigger air box appears, no advantage to cold air pickup versus just let the air flow past the radiator to the trumpets where the cold air duct would run

4. Open trumpets with sock foam filters - same as bigger air box.. but less risk of nuts and bolts getting in and less dust and wear. socks same as open trumpets in terms of power

In the end for my purposes I have chosen option 4. This makes access on a race day easy to items below the carbs and appears to have no power loss issues while protecting the engine compared to the big air box approach

Just my logic ... no criticism intended and others may differ in opinions but I have done the dyno and lap time tests to gather the data.... have others more data to bring always happy to listen and learn from people who have done it ????

cheers
Rohan

Just to concur with some of Rohan's conclusions:

1. We found a 7hp loss using the standard airbox. On a 181 hp engine. Similar to the 5hp loss noted by Rohan,

2. Dyno runs were therefore run with open trumpets, as I did not have my extra large airbox at that time. Hopefully, as noted, the large airbox performance should be consistent with open trumpets but with the potential advantage of the feed of cold air when on the road.

3. With or without a conical K&N filter on the end of the trunking had no effect on dyno outputs.

4. I have not bothered to block off the sides of the radiator. Virtually no space anyway with the extra large radiator. Never any cooling problems with this radiator regardless of ambient temperature (California) and/or hard driving. With what gap remains it is probably useful to aid in under bonnet and carburetor body cooling.

5. The large airbox is about as big as will fit. I go through major contortions to remove/install it. Always seems as though it cannot possibly fit. I will say that the small radiator side gap also makes it a challenge to squeeze the trunking through.

[StressCraxx]

@Rohan

"4. Open trumpets with sock foam filters - same as bigger air box.. but less risk of nuts and bolts getting in and less dust and wear. socks same as open trumpets in terms of power."

I had oiled foam air filters on my Elan because it had a pair very poorly made airboxes over the carbs. The foam filters worked ok, but sometimes on cold starts the carbs would spit back flames. The #1 cylinder foam caught fire and spread to two more foam filters. I emptied a fire extinguisher into the engine bay. It made quite the mess. I came close to losing the car.

I use the early airbox and hose to the original filter housing with two large holes drilled in the bottom for more flow.

[baileyman]

...

I use the early airbox and hose to the original filter housing with two large holes drilled in the bottom for more flow.

Sure seems the standard box base plate could be easily deepened to approximate a big box in volume and shape. If I didn't already have a big box I might dive into my spares to do just that. John

[661]

The FIA are not now approving large airboxes for HTPs , if you are applying.