Nitro V8 Posted October 22, 2023 Author Report Share Posted October 22, 2023 Well after some time I have now gathered all the bits together to do the 74mm tb conversion. I will detail all the components and photo all as I go along as it maybe helpful to others. I unfortunately won’t be carrying out the work for some while as I am currently recovering from an op on a ruptured biceps. The areas I’m unsure about is are as follows. 1) I have got hold of a 987 airbox but unsure whether to fit it or not as I know it is difficult. Is the 986 airbox restrictive enough with the 74mm tb to warrant fitting the 987 one? Does anyone have any insight into this? 2) If I go the 987 route should I use the 987 maf holder/tube as I have read here and on the US 986forum that the ECU will require a re map to get fuelling correctly and prevent a cel? Again does anyone have experience of this? If utilising the existing 986 maf holder/tube will this now be restrictive? Thank you. Quote Link to comment Share on other sites More sharing options...
Randeep Posted October 30, 2023 Report Share Posted October 30, 2023 On 10/22/2023 at 1:42 PM, Nitro V8 said: Well after some time I have now gathered all the bits together to do the 74mm tb conversion. I will detail all the components and photo all as I go along as it maybe helpful to others. I unfortunately won’t be carrying out the work for some while as I am currently recovering from an op on a ruptured biceps. The areas I’m unsure about is are as follows. 1) I have got hold of a 987 airbox but unsure whether to fit it or not as I know it is difficult. Is the 986 airbox restrictive enough with the 74mm tb to warrant fitting the 987 one? Does anyone have any insight into this? 2) If I go the 987 route should I use the 987 maf holder/tube as I have read here and on the US 986forum that the ECU will require a re map to get fuelling correctly and prevent a cel? Again does anyone have experience of this? If utilising the existing 986 maf holder/tube will this now be restrictive? Thank you. I've just had a 987 airbox fitted with a 987 MAF and 996 TB and 996 plenum (I got a garage to do it though). There is tolerance in the MAF (I think its within 25%) but switching to a 987 MAF is a big jump in area and the ECU can't handle the change without a map. You can however use a thick pvc pipe to act as a reducer in the 987 MAF that brings it within the tolerance. Seems to be working ok on my car at the moment, although I have some other teething issues with an exhaust leak that throws up the occasional engine light (well I think that's the reason!). You'll need suitable silicone pipework (an elbow) and aluminum tubing to get it all to fit and the 987 airbox needs some trimming to get it into the space. Quote Link to comment Share on other sites More sharing options...
Nitro V8 Posted October 31, 2023 Author Report Share Posted October 31, 2023 Hi @Randeep Thanks for the info. I have the pipe work already and a modified 987 airbox. If you put a reducer in the 987 MAF tube to fool the ECU surely that negates any benefit from using it and you might as well stick with the 986 MAF set up? Quote Link to comment Share on other sites More sharing options...
Randeep Posted October 31, 2023 Report Share Posted October 31, 2023 4 hours ago, Nitro V8 said: Hi @Randeep Thanks for the info. I have the pipe work already and a modified 987 airbox. If you put a reducer in the 987 MAF tube to fool the ECU surely that negates any benefit from using it and you might as well stick with the 986 MAF set up? Depends on what you want to do long term, the 986 MAF is attached to the 986 airbox so needs fettling to work. I'm currently running standard manifolds so I'm going to wait until I change them before getting the car mapped, then its just a case of removing the sleeve from the 987 MAF to get the full benefit with a map. Quote Link to comment Share on other sites More sharing options...
Nitro V8 Posted October 31, 2023 Author Report Share Posted October 31, 2023 I see That makes sense then. Who will you use for the mapping? Quote Link to comment Share on other sites More sharing options...
phazed Posted October 31, 2023 Report Share Posted October 31, 2023 Very interesting video I watched last night on YouTube. They did the airbox swap with a 987, larger intake and larger throttlebody. The outcome on the dyno showed a slight increase in horsepower at the top end, but actually a loss in horsepower and torque in the mid range. Quote Link to comment Share on other sites More sharing options...
Patt Posted October 31, 2023 Report Share Posted October 31, 2023 There are RR plots in my "molly" thread showing the improvement using just the larger TB and 996 t-piece. IIRC it was 5-6 BHP and 9-12 Torques throughout the whole rev range. This was without the 987 airbox or a re-map. It' doesn't sound a lot, but it completely woke up the engine and made the driving much more enjoyable. Best £100 odd quid mod IMHO for the car. Quote Link to comment Share on other sites More sharing options...
edc Posted October 31, 2023 Report Share Posted October 31, 2023 https://imgur.com/gallery/s64cXDC Here's my old plots overlaid. No 987 airbox but increase for each mod from circa 3.5k rpm. Quote Link to comment Share on other sites More sharing options...
ieducs22 Posted October 31, 2023 Report Share Posted October 31, 2023 dont know sorry! Quote Link to comment Share on other sites More sharing options...
½cwt Posted October 31, 2023 Report Share Posted October 31, 2023 When looking at these graphs, remember no two rolling roads will give the same output figure, and even then repeatability depends on atmospheric pressure, temperature and even humidity, so ignore the absolute numbers, only look at the difference between two curves on the same graph, assuming even those runs were done without too much time interval on the same day. Quote Link to comment Share on other sites More sharing options...
edc Posted October 31, 2023 Report Share Posted October 31, 2023 Exactly which is why I did what I could to minimise any variation and used the same rolling road each time. Quote Link to comment Share on other sites More sharing options...
½cwt Posted October 31, 2023 Report Share Posted October 31, 2023 14 minutes ago, edc said: Exactly which is why I did what I could to minimise any variation and used the same rolling road each time. Good to know. It was more a pointer to people looking to do work not to necessarily expect the same output figures as those shown on graphs, more a similar increase i.e. +11bhp, as opposed to 261 to 272 bhp, could be 248 to 259bhp on a different rr. Quote Link to comment Share on other sites More sharing options...
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