Drax240z Posted June 15, 2004 Share Posted June 15, 2004 Well we're building up a 3.1L here for a customer. Specs are as follows: - 240z rods, diesel crank, N42 head, 2mm headgasket, .5mm flycut. ~9.7-- 10.0:1 compression, balanced. - .460/280 Cam, performance valve springs (oops, typo before) - Triple 40mm webers, 36mm chokes - 3.9:1 diff ratio Car is a weekend warrior, the engine is being built specifically for autoX. The problem is right now he is running a stock exhaust manifold, as he found that he lost too much low end with a header on the 2.8L engine. (8.6:1 compression, 32mm chokes, same cam as above) What I am wondering is if anyone here has played around with manifolds/headers on a 3.1L and noted the differences in performance. I'm really thinking this cast manifold is going to be waaaaay too restrictive with the displacement bump and the bigger chokes, and probably a higher redline as well. Looking for some facts to confirm my beliefs. Quote Link to comment Share on other sites More sharing options...
Guest tejas74260 Posted June 16, 2004 Share Posted June 16, 2004 if you dont mind spending some bucks on a header (like 700 or so) you can get one custom built for you from stahl headers, they can design it for you based on your platform, check them out, im having them do mine! Mark Quote Link to comment Share on other sites More sharing options...
Guest NoyZee Posted June 16, 2004 Share Posted June 16, 2004 In my personal experience I built my 3.1 w/close to the same specs except my CR is around 12.5:1 and my cam is 460lift 280exh/270int. I ran the stock manifold for @1.5yrs. I never ran headers on the stock engine, but I could see a loss of lowend if perhaps the rest of the exhaust is 2.5" or bigger. Basically not enough back pressure on a stocker. About a year ago I finally made the decision to go to a 6-2-1 header w/2.5" all the way back. That made a nice increase in performance. I've never dyno'd it, but I could definetly feel the torque and hp increase. Mind you my engine had the 60mm TB and intake manifold had been port-matched. Along with head and exhaust porting. The main fact to take into consideration is that w/that high-lift came there isn't going to be much below 3.5K! However, once you hit 3.5K that beast is going to pull like a raped-ape! I'm running the stock EFI,but your carb set-up should get more out of the engine than mine. I believe you'll be amazed at the output. Good Luck!! Quote Link to comment Share on other sites More sharing options...
johnc Posted June 16, 2004 Share Posted June 16, 2004 Stahl is a good choice or try the Nissan Comp 1 5/8" primaries. Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 16, 2004 Share Posted June 16, 2004 I feel the stock manifold is not all bad. It is almost a header compared to some manifolds I have seen. You could try using more exhaust duration to make up for the lack of a header. A 280/290 cam would help out exhaust flow a bunch. Plus a good 2.5 or 2.75" exhaust pipe and high flow muffler would help. I have seen V8 engine dyno runs using split duration cams produce the same max hp and torque with or without headers. However, mid range torque was be reduced by 10%. Why use a N42 head then a 2mm head gasket? I think it would be better to use a stock gasket (1mm felpro) and a P79 or P90 head. Much better head design in the P series as compared to the N series. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted June 16, 2004 Author Share Posted June 16, 2004 A bit more info first guys... the exhaust on this car (a customers car, some of you missed that point) is a 2.5", fairly unrestrictive exhaust, yet still has streetable noise levels. I know the stock exhaust manifold flows pretty well. This guy has been running his 2.8 setup with the stock manifold for the past 2 years and is consitantly 1st in class and often FTD. Competition is getting more stiff and he's starting to lose a bit of ground when it comes to the faster courses, hence the 3.1L swap. That and he was given the keys to a certain turbo car (ahem) and now he wants more power. (damn is that car ever good for business!) The reason for the N42 head is that he had one that had been ported and polished and was ready to go. Purely $$$ savings on that one. Also the higher compression attainable (at a reasonable deck height) with the N42 will likely make up for any other shortcomings. This setup will yield about .3-.4 more compression points than a similar P90 setup. Also the 2mm headgasket should unshroud the valves a bit more, aiding flow ever so slightly... johnc (or anyone else) do you have a picture of the nissan comp header ferreted away that you could post? Thanks for all the info and keep it coming guys! Quote Link to comment Share on other sites More sharing options...
johnc Posted June 16, 2004 Share Posted June 16, 2004 Here's mine (1 3/4" primaries) on a workbench: The "Y" pipe is next to it. Both have been coated with Jet Hot 2000. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted June 16, 2004 Share Posted June 16, 2004 Ditto John on the 1 5/8 primaries Nismo header. Don't get me started on N42 vs. P79/P90... long-short: The quickest, fastest, most powerful NA L6 engines I know of all have N42 heads. NOT saying the N42 head is better at all, just that I have seen ZERO evidence that the P-heads are inherently superior. I have read/heard a lot of talk about how the P-heads chambers *LOOK* "better" for performance I wouldn't hesitate to use either the N42 or P90, personally. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted June 16, 2004 Author Share Posted June 16, 2004 Pyro, I was under the impression that you needed the HKS gasket for the stroker, as the felpro and nissan gaskets don't have a large enough bore size for the 89mm pistons to clear though. (I believe they are 87mm bore, while the HKS unit is 91mm bore) Incorrect impression maybe? Looks like this guy is going to stick with the stock exhaust manifold to save some $$$. Not sure what to think about that! Quote Link to comment Share on other sites More sharing options...
Doug71zt Posted June 19, 2004 Share Posted June 19, 2004 Drax - The local Nissan parts guy (z-car club member) got a buyout on NISMO headers (not sure what size primaries) $525 CDN. That is probably the lowest price that you will find on them new. If your customer is interested, email him quick - not sure how long the stock will last. We have a bunch of hard-core 6 cyl. guys in the club in Ontario, chances are they will sell out fast. His name is Rick Scott, email parts@brantfordnissan.ca - Tell him that Doug sent you. Quote Link to comment Share on other sites More sharing options...
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