Andrew Posted March 3, 2003 Share Posted March 3, 2003 Does anyone know the minimum distance advised, between weber air horns/ trumpets, and air filter. I've seen it written somewhere but can't find it now. Also does it make any difference if its a K & N set up (solid cover), or a sponge type, (Piper-cross etc) Quote Link to comment Share on other sites More sharing options...
chrisj Posted March 3, 2003 Share Posted March 3, 2003 Andrew I had a similar problem but I needed to fit new trumpets to my car and needed to cut the bonnet to achieve this, attached below is a response I had back. Chris Hi Chris. K & N air filters come in varying heights, not to much information to go on, but I should imagine that you have quite shallow ones fitted. Its merely a case of purchasing some more with a greater depth. If you remove the lids of the air filters, you should find the trumpets inside. If not, buying some should be your first priority. If you have to purchase some, you will notice that they are also sold in an assortment of lengths. When choosing the size that you require, theory says that short ones make more top end power, longer ones hike the bottom end up. In practise, this is not always the case, but either way your engine will make a lot more power than without! Another thing to bear in mind, if sticking to K&N's do not buy trumpets that come close to the lid of the air filter, you want at least 40mm from the lid to the trumpet mouth. As for cutting holes for clearance, careful measurement with the air filters fitted (using masking tape on the body to mark either end of the filter protrusion) and the height of the filters from the upper chassis member. Remove filters, stick bonnet on, and transfer measurements to the bonnet. You now have a base line and the length to work from. For the rest of the shape, you can use the filter lids to draw around. Remember, the resulting holes will have to be slightly bigger than the filters to allow for movement from the engine. One last thing, I dont really know whether it is actually worth the effort! Yes, cold air is definately better than hot for your engine, but in 'real-life' when you are driving, under the bonnet there is a slight positive pressure that *may* be slight turbocharging for free! Also, with the air filter hole, hot air is going to be forced past the filters from the positive pressure under the bonnet. And with the way Mother Nature works, if air is rushed past a hole (your trumpets sticking throught the bonnet) it will actually try and pull air from the hole. Ideally, an air scoop which isolates the filters completely from the engine bay with a foward facing intake outside of the bonnet is the way to go. Most of this is theoretical and I have no figures to prove either way and now I am going to hide under a table..... Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 3, 2003 Author Share Posted March 3, 2003 Cheers Chris, I'm running with no trumpets, and skinny filters at the moment. I do have a set of 60mm trumpets that came with the carbs, so 60mm plus 40mm clearance, means I'm looking for 100mm deep filters (or deeper). And yes, I'll cut a hole in the bonnet. Quote Link to comment Share on other sites More sharing options...
andymcc Posted March 3, 2003 Share Posted March 3, 2003 I have been running open 50mm ish trumpets (on a twin weber pinto) and have finally got round to trying to find some filters that will fit on in the space provided...and have struggled... I really do not want to cut the bonnet and was considering fitting pipercross sponge types over the trumpets - the front carb though is VERY tight so i considered finding a really short trumpets for that one only....mmmm Having read the above about the effects of trumpets on top vs bottom end - do you think it will be noticable/v unwise mixing trumpet lenghts..? The other options I thought might be to modify the front trumpet to allow it to suck through the sides aswell (so it doesn't get totally blocked when the filter is pushed against it) But am now doubting this...... Any advice to save me having to cut the bonnet??? Cheers Andy Quote Link to comment Share on other sites More sharing options...
hilux Posted March 3, 2003 Share Posted March 3, 2003 Why not look around for a slim plenum that fits on the carbs if theres room and remote filter it all. No holes and semi charge cooled air from a suitable point at the front of the car. Quote Link to comment Share on other sites More sharing options...
chazpowerslide Posted March 3, 2003 Share Posted March 3, 2003 You NEED ram pipes (air horns, trumpets whatever) on side draught Weber and Dellorto carbs. They help strengthen and smooth the fuel pickup "signal" at the main venturi (the speed at which the air passes through the venturi/auxillary venturi, how turbulant it is and hence the efficiancy and quality of the fuel pickup and atomisation) Without the ram pipes in place the carbs are not working efficiantly and on the larger webers 45 and 48 and 50 DCOE/SP they help locate the venturi and auxillary venturi. You need to have a minimum of 2/3 of the carb bore as a distance between the ram pipe mouth and the filter top plate. Eg for a 45 DCOE you need a minmum of 30mm (2/3 of 45 is 30) Any less than this may give you a decrease in BHP. Shorter ram pipes generally give a slightly BETTER top end BHP longer ones generally pick up the the LOW and MID-range a little. Better have the carbs working as they were designed with a hole in the bonnet than have crap carburation and no hole IMHO. Chaz. Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 3, 2003 Author Share Posted March 3, 2003 Andymcc, In Des Hammill's book, "How to tune Ford SOHC engines", theres a photo of a Cosworth engine in what looks like a westy, with odd length ram pipes. Sounds better than modifying a trumpet, if you must keep it all under the bonnet. Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 4, 2003 Author Share Posted March 4, 2003 Just been doing some measuring,....100mm deep filters will push the front filter out around 50 to 60mm, and the rear one will be roughly flush with the outside of the bonnet. Not only will it look a bit odd, but the front filter will be in the firing line of the front wheel! getting all sorts of crud shot at it!. Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 4, 2003 Author Share Posted March 4, 2003 Just been doing some measuring,....100mm deep filters will push the front filter out around 50 to 60mm, and the rear one will be roughly flush with the outside of the bonnet. Not only will it look a bit odd, but the front filter will be in the firing line of the front wheel! getting all sorts of crud shot at it!....So I thought what about a shorter filter on the front, so they both poke through the bonnet by the same amount. (using shorter ram pipes) Has anyone done anything along these lines, got any pictures? Its a Pinto installation by the way. Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 4, 2003 Author Share Posted March 4, 2003 Oops ! don't know what happened there!! Quote Link to comment Share on other sites More sharing options...
chazpowerslide Posted March 4, 2003 Share Posted March 4, 2003 I think that you'r worrying too much about this too much IMO. The main thing is that you have a deep enough filter to fit in the ram pipes and they are big enough to flow the air for the BHP you have. If the filters flow enough air for the BHP you have there is nothing wrong with using a more shallow filter on the front carb, but I would not miss-match the ram pipe length. If you look at the se7en type car in general you will see many with the filters exposed through the bonnet with no ill effects. If the front filter sticks out and catches crap front wheel then so what! You have to clean the filter a bit more often. I'd rather have everything "mechanically" correct and compromise the aesthetics, I personally like the look of the filters poking out of the bonnet. My SE has the filters exposed about 45mm with 150mm filters fitted. Chaz. Quote Link to comment Share on other sites More sharing options...
Andrew Posted March 4, 2003 Author Share Posted March 4, 2003 Cheers Chaz, one other thought, the plan is to have the car rolling road tuned after sorting the ram pipes/filters.In the mean time will fitting ram pipes etc upset the present state of tune too much. i.e will it run a weaker mixture due to increased air flow? Quote Link to comment Share on other sites More sharing options...
Mike Posted March 4, 2003 Share Posted March 4, 2003 i run a 1.8 zetec on twin 45's, we use shorter ram pipes and the domed air filter from westfield, think its made by pipercross so that no hole has to be cut in the bonnet. mike Quote Link to comment Share on other sites More sharing options...
andymcc Posted March 4, 2003 Share Posted March 4, 2003 The reason I have ever got round to this (apart from the nagging knowledge that without filters I am risking engine life) is that I was also planing a rolling road session and thought I may aswell have it sorted before then incase later fitting of filters messed everything up........ I now reckon the reason the engine smells so rich (why I wantedthe rr session in the first place) is that there is not enough gap between the ram pipes and the bonnet (est 5mm on front one)..........certainly well short of the 30mm needed even on the second choke Time for the saw...thanks for advice Quote Link to comment Share on other sites More sharing options...
Mike Posted March 4, 2003 Share Posted March 4, 2003 the gap between the pipes and the bonnet is that big a gap in ours, take it down to a rr and ask them to set up the carbs, maybe a quick mess about with the fueling will sort it out. ours was set up on the rolling road and runs fine. mike Quote Link to comment Share on other sites More sharing options...
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