Demo243

I know a few people were following along on this- been a while since I last posted here- but finally all came together! Mounted up and running strong! Still a few details to work out; but runs good, sounds good, feels good on the initial pulls. Super happy it worked out!

Well I decided to go for it - Went with 42's and a TWM manifold. Still lots to sort out, but Ill start another thread on it somewhere and link it back here. Rought calculations hopefully put it in between an OER setup and a Mikuni PHH setup $wise.

Part of running a single shared throttle shaft was for a super clean look- like how datsun_tokyo linked above has it. I also still haven’t decided on the manifold- but was planning on the TWM one- seems to be the cleanest and allows me to run without all the linkages. With that said I’m interested- I’ll shoot you PM.

That car is one of the main reasons I’ve even considered this. I have been in touch with him- unfortunately the language barrier is tough. Might need to recruit an old autox friend who is in Tokyo now to translate. The owner of that car did express that he much preferred the HSRs over OERs and that he was never able to find the right tune with OERs. Looking back through his thread he had PHH 50s on there at some point - but that is a very built engine - 3.1 I think with custom head etc. Did a little more digging and thinking on this last night - I think mechanically the hardest part will be the common throttle shaft - it looks like each carb has 3-5 holes on the shaft. 2 for pins for to hold the throttle stop and accelerator pump levers; at least 1 maybe 2 for the return springs; and the main threaded one for the slide lift. With some patience and precise measurements it’s shouldn’t be to terrible, but not a cheap if you mess one up and have to start over on a new stainless shaft.

For the sake of keeping this in the same thread. I found a little more info on the car in the photo- unfortunately it seems the owner passed away last year. But this post on hybridz says he replaced his Weber 45s and actually saw better gas mileage and great throttle response https://forums.hybridz.org/topic/64666-mikuni-hsr45/?do=findComment&comment=1229737 “I decided to try my own setup with 6 HSR45 Mikunis. I had previously run Weber 45's. I used the original linkage so that I could return to the Webers if I wasn't happy with Mikunis. Because of the shape of my extracters I had to add some extensions as The bowl of carb 4 was hitting the exhaust. Apart from that it was pretty straight forward with the carbs being quite straight forward to tune. The throttle response is very good and although I wasn't looking for it the mpg ismuch improved over the Webers.” This of course does not help my decision process… on one hand it says to me it works! But on the other hand it makes me wonder if I should do 45s? I do believe it was a “built” engine but to what extent I don’t know.

Gave them a try - says they haven’t done a 6 pack on a Z. But need to follow up with a few questions

I’ll definitely keep everyone posted- and if I go with 6 I’ll probably start a thread on it so there is hopefully some long term info on it. really wish I could get in touch with one of the few people who have done it. But I’m thinking 6 42s should do it and hopefully be ok.

First I asked them about Mikuni jet compatibility; since I was considering using their jets instead of Weber and had been told mikuni jets would fit- the answer is no they wont “Mikuni genuine main jet cannot be used for OER products. 2. Only Mikuni genuine Air Jet 40φ can be used for OER 3. All OER Jet can be used for Mikuni” I had better luck with a quick response, responding back to that email asking if they had any jetting recommendations for an L28 as a starting point. To which they gave me the linked their product page and what jets come stock and said “Jetting and other settings will vary depending on your vehicle, engine condition, climate, environment, and the features you require. Please enjoy the setting through trial and error!” I can’t really fault them to their response to the jetting suggestions but I had heard they could help. So they is some communication there. Just not ideal- but also not too surprising considering the language barrier.

Correct Datsun Spirit in VA - I’ve heard he stopped doing them because of cost, but that was when PHHs were more reasonable. I also heard he has an issue with V-Performance the other US HSR person who has a very poor track record per the forum’s… OER issues I’ve heard of have been poor casting in the last few years, machining issues, lots of machining chips throughout the carb (basically requiring a clean and rebuild before install). Their direct correspondence with me has been poor. Sent a few messages and finally got one response today about 2 weeks later. I worry about future parts availability as well. Their price is right - especially right now with the YEN… but all that makes me nervous. Per all the calculators and L28 seems to be right on the edge. Could go either way. And with plans to eventually build another engine I would go 44/45s to future proof it. I also think back to talking with the late Todd Walrich when I got the Mikunis for my L20b in my 510 and he said 44s no questions for the L20b- which is slightly larger cylinder size…- but he was a big fan of choking the bigger carb down and I never had any drivability issues. Choking it down I think is where I’m really I’m really stuck on these HSRs since there is no way to do that… so are 42s better since they are smaller or 45s for for more upper end. I’ve read they do well in single cylinder applications since that’s basically what they were designed for big low rev’ing Harleys. CFMs are pretty close 213 for the 42mm and 237 for the 45mm - @ 12” of water… so trying to convert that to 1.5” of Hg which is what I think a Weber DCOE is typically measured at- I’ve read 418 @ 1.5”Hg I think for both barrels? So divide that by 2 to 209. I lost my calculation but I think I figured that the 45mm was 277 converted to 1.5”Hg. All this is probably way over thinking it and complicating it… And I should just pony up for some PHHs or roll the dice on some OERs with Weber jets. Also I’ve never been one to just do things the easy way… ie in my KA swap in the 510 I had a custom oil pan made instead of the standard crossmember flip and new swaybar. I also decided to run my Mikunis on it which required hunting down and manifold and figuring out ignition and what not. So I’m not opposed to the challenge of HSRs just trying to get some info from people who have ran them.

I am considering PHHs but a think 44s would be better. There is a nice set on eBay right now with a new Harada manifold- but they are $4300 plus shipping and additional jets for tuning. That’s 5k pretty easy. Was just trying to figure out some other options.

Well looks like DSI is not doing them or doesn’t want to. I sent them a note before calling and just got a response that “they are not able to help”

Fuel pump, filters and at least soft lines- will blow out the hard lines- are on the list. I’ve done some basic tuning of the SUs - and the car drives pretty well other then the fuel issue after a prolonged pull- but not super happy with what the afrs and just not stoked on the SUs. That why I am looking at triples or maybe a rack of 6 Mikunis as such.

Definitely a simpler fall back- just trying to find some more info out on running the rack of 6

Sorry- F54/P79 L28 at the moment- stock as far as I know, but gonna pull the valve cover to check the cam and maybe scope the pistons- running SUs. Having some fueling issues after long pulls (or highway on ramp through the gears) It was swapped into my 240 before I bought it- but the Z has a full MSA header and exhaust plus poly bushings all around, and upgraded brakes. So some one at some point did some work to the car so I need to check the engine out further. I have another spare F54/p79 engine I’ll plan on refreshing and maybe bumping the compression a little and street cam later on but not looking for a crazy build. Would love Mikuni 44 phh but they are very expensive now. Thought about OERs but haven’t gotten and response from them and have read mixed reviews on them. Had trouble with webers in the past on my 510. So that where these Mikuni HSRs come in. Easy access to Jets and replacement parts. I know that running 6 is overkill but the siren song of ITBs is calling, and it’s something a little different.

Thanks! I’ve sent DSI a message and will try and call them this week. There is a shop is Australia- MikuniOZ- who I think helped with this set up pictured gonna try and give them a call to. Very hard to determine sizing for these carbs- I’ve seen someone running a hot l24/l28 on two 42s or 45s- and then I’ve seen an A15 running four 45s!