Stevensonjr Posted March 22 Share Posted March 22 I’ve got about 400 miles on my1965 series 2 Lotus 7. The side bonnet scoop is too tight for any air filter. I have 2 choices, run without air filters or cut out my original bonnet scoop where the filters pertrude. I’ve fitted 3 different types of filters but none allows closure of the bonnet. I guess I could fabricate a larger scoop instead of just leaving a larger hole in the bonnet. I hate the idea of cutting into an original car. I drive on hard surface roads that are fairly clean, how would no filters affect engine life? I don’t race so the Pre crossflow Kent 1500 seldom gets wound up. Any suggestions would be appreciated. Thanks, Bill Link to comment Share on other sites More sharing options...
Dave W Posted March 22 Share Posted March 22 Bill If you have air horns, you may be able to fit the small cone shaped type motorcycle filters. The other option is to look at K&N filters that would fit the opening and make your own base and cap. Link to comment Share on other sites More sharing options...
Christopher smith Posted March 22 Share Posted March 22 I have the stainless steel mesh type on my 40 DCOE2 velocity stacks. Not sure they filter out much except nuts,bolts and stones. And the rubber attachment rings seem a bit shaky. So can not recommend this type for higher mileage use particularly in dusty situations. But I see claims of better performance from other mesh air horn units. I recall seeing the oval track sprint car guys running without any filters or mesh and wondered how many rebuilds per season they must do. Link to comment Share on other sites More sharing options...
SCse7en Posted March 22 Share Posted March 22 These fit well Link to comment Share on other sites More sharing options...
MoBoost Posted March 22 Share Posted March 22 It’s pretty important to have some filtration in order to prevent not just large debris but dirt and sand from entering the engine, which will cause premature wear of the cylinder walls. The opening in the hood of my car is somewhat restrictive and I’ve been using a short K&N filter. I’ve experimented with foam filters over trumpets, but they made it difficult to remove the hood. Link to comment Share on other sites More sharing options...
theDreamer Posted March 22 Share Posted March 22 2 hours ago, SCse7en said: These fit well My car has a similar wire mesh set up. It appears in the photos to have something behind the mesh. Perhaps some filter foam or just a wad of panty hose material. I won’t know until I get to see the car, (hopefully later today or Monday). However, if nothing is there I’ll figure out some way to affix foam inside or at the very least over the mouths on the outside. MoBoost, I can see how those big foam pods would interfere with taking the bonnet off and on. With the stock K&N chrome ones you have to physically remove the first one if you have clam shell front fenders. Stevensonjr, you might think about getting some air filter foam and cutting a wedge to fit inside the scoop. Glue or use double sided tape to affix it to the inside of the scoop so that it’ll squish up against the inlets when the bonnet is in place. 1 Link to comment Share on other sites More sharing options...
SENC Posted March 22 Share Posted March 22 I'm in the same boat, Bill. For now, I've opted for the mesh/screen filters that sit on the end of the rams, despite their hit to performance (not a big deal since I don't race) and their inability to filter small stuff. But I feel better knowing I'm keeping big stuff out that might cause an immediate and catastrophic problem. Link to comment Share on other sites More sharing options...
jbcollier Posted March 23 Share Posted March 23 The mesh screens are just that, screens. They significantly restrict airflow by a huge amount. And, all they filter out are rocks and pebbles. I have rebuilt a lot of engines (retired 35 year Euro mechanic) and never once have I had to do one due to rocks or pebbles getting in. Dust and dirt? That's a different story. So, first question: What is the climate like where you drive? Dry or humid? I live in a dry, dusty climate. I do not run without proper air filtration, period. You may live in a humid climate. Not much dust in the air in a moist climate. You could get away with no filtration and not limit your engines life too much. Second question: Exactly how much space do you have between the carb and bonnet? How much if you bin the air horns*? Could you build an air box with a side mounted air filter? I have done this in some tight spaces and it has worked out very well. Finally, I'm not a fan of foam air filters exposed to the carb mouths. One backfire and up goes your car in flames -- that I have seen, not pretty. Carb - air box - then remote foam filter, that's fine. *intake horns with screens give far less air flow than just the plain carb inlet with no horns -- maybe not as cool looking but tuning for cool at the expense of power is pretty dumb. Disclaimer: I write in plain-speak with no intention to insult. 1 Link to comment Share on other sites More sharing options...
JohnCh Posted March 23 Share Posted March 23 1 hour ago, jbcollier said: Exactly how much space do you have between the carb and bonnet? How much if you bin the air horns*? To me, this is the key. Understand what you have to work with, and identify those constraints before spending time on solutions that may or may not apply. Pictures of your bonnet scoop and the carb to frame area like many showed above may also help. Link to comment Share on other sites More sharing options...
IamScotticus Posted March 24 Share Posted March 24 (edited) Cut the bonnet hole and do the K&Ns. Not S2 correct, but the 7 has never been about "correct". IF the Crossflow were available throughout the production range, don't you think most S2s would have been built to the latter S3 spec sooner than they were? Of course they would have. I don't see anything non-Lotus about K&Ns on the left. The reasons Lotus didn't do it on the S2s were probably for economy or the oval filters weren't available. They suit the car well. The other option is bang out another bonnet for large filters. We all know if anyone can do that, you could. Edited March 24 by IamScotticus 1 Link to comment Share on other sites More sharing options...
jbcollier Posted March 24 Share Posted March 24 Most S3s came with a single downdraft crossflow. Link to comment Share on other sites More sharing options...
MV8 Posted March 24 Share Posted March 24 On 3/22/2024 at 9:28 AM, MoBoost said: It’s pretty important to have some filtration in order to prevent not just large debris but dirt and sand from entering the engine, which will cause premature wear of the cylinder walls. The opening in the hood of my car is somewhat restrictive and I’ve been using a short K&N filter. I’ve experimented with foam filters over trumpets, but they made it difficult to remove the hood. Moboost's short K&N pleated gauze looks to be the best compromise short of a custom box for a filter aft of the carbs. Link to comment Share on other sites More sharing options...
IamScotticus Posted March 24 Share Posted March 24 (edited) 2 hours ago, jbcollier said: Most S3s came with a single downdraft crossflow. I don't think the S3 had enough time for someone to make a manifold, or Lotus didn't have any support from ACBC to fund it. But I'm sure everyone, especially Nearn, knew it would be an improvement over the downdraught. Those engines were dropped in just how they arrived from Ford, I understand. Edited March 24 by IamScotticus Link to comment Share on other sites More sharing options...
MoBoost Posted March 24 Share Posted March 24 1 hour ago, MV8 said: Moboost's short K&N pleated gauze looks to be the best compromise short of a custom box for a filter aft of the carbs. Note that the opening in the base plate of the short K&N filter will not allow use of air trumpets. Link to comment Share on other sites More sharing options...
theDreamer Posted March 24 Share Posted March 24 (edited) 16 hours ago, MoBoost said: Note that the opening in the base plate of the short K&N filter will not allow use of air trumpets. Here's a photo of short K&N's in a Birkin. (I didn't realize the engine bay was that much wider than an S2/S3) Also a nifty custom built air box with clear plexy that looks like it'll fit under a Lotus/Caterham bonnet. Edited March 25 by theDreamer Link to comment Share on other sites More sharing options...
inchoate Posted March 24 Share Posted March 24 imho for the few hundred miles per year that you're going to drive it's not really worth going crazy. Link to comment Share on other sites More sharing options...
CBuff Posted March 24 Share Posted March 24 Wait. We aren’t supposed to obsessively overthink every little aspect of these cars and throw needless amounts of money to solve the littlest things. Well I have been going about this all wrong. 1 1 Link to comment Share on other sites More sharing options...
SENC Posted March 24 Share Posted March 24 I didn't want to post an idea I haven't tested, but one idea I've kicked around and just not played with, yet, is creating a aluminum-frame that fits snug within the scoop inlet (flush with or maybe extending slightly forward) that would hold filter foam (backed with mesh). Then fashion an alu surround for the rams that effectively turns the scoop into an airbox. I think with shorter rams it might work. I think you have a similar hood and scoop as I do, but I can't put my hands on a good picture of mine. Link to comment Share on other sites More sharing options...
jbcollier Posted March 25 Share Posted March 25 I must admit that I would get another bonnet and cut that up to suit. Seven engine compartments run HOT. You want outside air for sure. 2 Link to comment Share on other sites More sharing options...
Stevensonjr Posted March 25 Author Share Posted March 25 I thought I would send photos as suggested. As you can see the front air horn is sitting in a cut out where it just barely fits. The fast taper of the air scoop does not allow room for anything added to the air horns. I might try a paper pattern to see if a cutout to fit the air horns would interfere with the bonnet latch. I’m open to any suggestions to move forward on this. Thanks, Bill 1 Link to comment Share on other sites More sharing options...
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