James' Race car build

[gt_james]

Getting the carb modded didn't go too well.

The float bowl is very small on the IDA carb, and the biggest needle valve is small too, so for a decent engine you can end up running the bowl dry after a few pulls. Might get away with it on a road car or a more standard engine, but I was having issues.

There's a space in the casting that isn't normally connected with the float bowl on a weber IDA, but with a bit of machining you can internally open this up for more float bowl volume. My mate did this for me and unfortunately he machined through the external bowl wall.



Let this be a warning, be really careful machining your IDA!



I plugged it up with JB weld


He also machined the top cover of my carb, the fuel inlet into the carb was bored out to 8mm.


and the place where the fuel filter goes drilled to 5mm. The fuel filter could still go on, but I am leaving it out as I have a pre and post pump fuel filter, and the internal one is restrictive.


I changed the needle valve too, webers biggest is a 300 size, and I ordered a 400 size, but received a 350 size.

I also changed from a weber 48 to a much nicer empi 51, which had the internal bowl mod done already, and my intake manifold was actually already ported for a 51mm, but the carb I got with it was a 48.

I also had problems with fuel pressure, everyone says a weber works ok with 3.5-4psi. Might be the difference in calibration from one gauge to the next, but for me this was fine with the engine off, but with the engine running none of my needle valves would stay seated and the float level would sometimes creep up, and generally not stay consistent whilst running, but be ok when trying to check the float level statically and no dripping with engine off. I found this out by buying a float level site glass from empi. Really good bit of kit and I reccomend this site glass over any other way of trying to guestimate whether float level or fuel pressure is set right. On my gauge it like 2.5psi of fuel pressure and no more than 3.

[gt_james]

Had a few issues with the exhaust I made, so re did some of it.
The over axle section wasn't high enough and I was having the axle hit it. I also used some slip joins between the under floor pan section before the merge and axle bend, which were leaking badly.

I re made the axle bend, and changed the slip joins to V bands, and I also assembled with some paste. Seems to have stopped the annoying blowing, should be able to pass track noise limits now.




checking for clearance, the tyre hits the arch before any exhaust/axle ugliness.


spring and bump stopped removed whilst checking this.

I changed the brake master cylinder from a 7/8 MX5 master cylinder to a 13/16 suzuki swift master cylinder, as I wanted a lighter brake pedal.


my lexan windows were bonded in, but kept falling down in the doors, so I added some aluminium angle and bolted them in as well as bonded them in.





I changed my seat mount brackets from steel to aluminium, which also allows the seat position to move a bit further forward as I felt a bit stretched driving it.


I painted my dash in halfords vinyl paint, but its really shiny and the glare was awful, so repainted matt black and re 3d printed my cluster with a few tweeks and changed material to ASA. wasn't very happy with the paint finish, would like to get the dash flocked at some point.




fitted vitaloni mirrors


Bought some more volk wheels and some NS-2R tyres so I have a dry and wet set. tyres not fitted yet but will be soon. the wet set are 13x6 not 13x8, so running 175 width rather than 235.



Also modified my dads old long unused race jack, some old worktop screwed on, now means I can get the wheels off the ground enough to change wheels, without having to drive up on ramps to fit a trolley jack under.




I re did the fan wiring as I had a couple of times it didn't kick in when it should've, and changed some rusty once black cap heads for some stainless ones.


My old Odyssey PC680 which was years old wasn't doing a very good job of holding charge, and I kept forgetting to leave it on trickle charge, so I changed it for a LiFePo4 battery. These are much lighter and don't loose their charge through internal resistance like an AGM type, supposedly will be fully charged still after 18 months, which is handy for a car that doesn't get used day to day.


Then on the test drive to check everything over, the alternator belt snapped


Have ordered a replacement belt, but am going to try a short belt around the E shaft and water pump to stop the slipping water pump syndrome these suffer from without the airpump. Have used dual belt alt pulleys before and wasn't that impressed, and gilmers don't appeal. Would like a serpentine belt set up but the short belt solution is £4 not £400 so that can wait.

Here's how the car sits at the moment.


Dyno session booked to check the tune and general health check, but its something like right after playing with the carb.

Trackday at donnington booked for 20th Feb.

[Casey]

You have been very busy James

[gt_james]

I had the car on the dyno last monday and was fighting fueling issues. It seemed like there was a problem with fuel flow as the float bowl was emptying quickly. I had been experiencing problems with the float bowl emptying on the road, and I enlarged the float bowl and fitted a larger needle valve and thought this had done the trick, but hadn't been able to properly drive the car hard on the road (No Autobahns here, Thomas!).

I left the dyno and went through flow testing into a fuel can and timing it. I started off flowing the hose post regulator, straight to a can, then flow tested the carb top hat and also various needle valves. Didn't find any obvious fuel flow issues, and the needle valves I had to hand all seemed to freely move. I checked the float, and it didn't immediately seem like there were any problems with it, the float height was set OK and it seemed to pivot on its pin OK, but when I swapped floats with a spare carb, the float I had been using definitely didn't pivot nicely on the pin in the other carb, I road tested the car and it seemed to be working fine with the new float, then took to the dyno again on saturday, and observed the float bowl sight glass under load and the flow level didn't drop under load, fueling problem solved! We went through changing the jets and emulsion tubes and aircleaner to get it set up and running happily for trackdays. Very pleased to have ironed the issues out and have the car set up and ready to hit the track.

It made 197BHP at the flywheel at 7300rpm.

For reference for any IDA users.

There are different size needle valves from weber. 175, 200, 250 and 300. The 250 size seems hard to find, and most carbs seem to come with 200 size needle valves. On a rotary I think you want a 250 size on a stock port street driven car, or a 300 or bigger on anything more.

There's a couple of suppliers, one in NZ and one in italy that make larger IDA needle valves, 350 (350R) and 400 size. There's also the choice of brass needle valves, with a sprung or fixed ball, and viton tipped needle valves. I wanted the viton tip, but ended up receiving a brass one.

I thought I needed a larger needle valve to stop the float bowl running empty and currently have a 350 in it, but after flowing both a 300 and 350 needle valve (crudely) on my fuel pump set up, but free flowing, not at pressure, I believe a 300 size needle valve should be enough, by my basic calculations, at free flow, it should be enough fuel delivery for a 250HP rotary, and a 350 needle should be enough fuel delivery for a 300hp rotary. Now I have heard on some set ups needing larger than this, and that's running petrol not ethanol or methanol and I took at guess at the brake specific fuel consumption of an NA rotary on petrol.

I thought I'd post this as although I'm sure people have flowed different needle valves, I couldn't find the results online, and a few people I asked thought that my set up might need the bigger 350 needle valve, but I don't think that's the case after finding my issue and flowing the needle valves I have.

There are also "grose" jet needle valves, I have one and I couldn't get it to stop leaking, some people like them, most seem to hate them.

I also found that the little tea strainer filters/screens cost 10HP over a K&N air cleaner, and I already planned on creating a cold air fed airbox, which would be the most ideal.

Most people say webers like 2.5psi of fuel pressure, although some people seem to think they like more, racing beat recommend 4.5psi, and some people seem to say 6psi. I don't know what the "correct" number is, but I do know that the little fluid filled fuel pressure gauges are not very accurate, and too much fuel pressure causes issues, too little fuel pressure generally is of little consequence.

For some strange reason on my set up, any more than about 0.5psi of fuel pressure and my needle valve wont seat and the carb will begin to flood. I can maintain this low pressure on my regulator, and fuel flow doesn't seem to be an issue under load after watching the float bowl site glass on the dyno, so for now I am going to live with a very low fuel pressure, but It's a bit strange.

[spirit r]

Would you say the weber carb are good and economic for street use? I think 192HP with a fat nikki are possible too.

[gt_james]

Would you say the weber carb are good and economic for street use? I think 192HP with a fat nikki are possible too.

I don’t have a modified Nikki to compare to, but peekay has tuned some IDAs for very Nikki like economy. Mine not so much.

192hp is a lot from a Nikki, I can’t imagine many people would make that out the box first time doing power runs on the dyno, I think you’d need a lot of development and perfecting to get there.

[gt_james]

Finally got out on track!



Did a trackday with CSCC at Donington Park. Car ran well, didn't have any issues, big relief! For February I was really lucky with the weather, no rain and afternoon was actually a bit sunny. Managed to keep the car on the black stuff and pointing the right direction Was lots of fun, will have to get more booked soon!

[gt_james]

After a busy year I found some time recently to do a couple of bits to the car.

Made a pedal spacer on the brake to help with heel and toe, I found the brake pedal pad was below the accelerator when deep into the brakes on track, and I didn't have enough adjustment on the pedals to alter it, so made an aluminium spacer.


After the trackday I spoke to some people more knowledgeable than myself and they told me that although 120C oil temp is fine in a normal engine, we want much cooler oil in our rotaries, so a better oil cooler was ordered from Green Bros in NZ and fitted. Never had issues street driving with the ebay cooler, but hard track use is a different story.




I was having an issue with the front tyres rubbing the strut. I fitted 5mm wider wheel spacers to solve it. The 235 semi slicks really are the limit for what will fit the stock front with stock arches and keeping the wheels from sticking out the arches (which looks crap and is not allowed for road or UK motorsport use).

[gt_james]

I got another trackday in this year, hopefully lots more next year. I was back at Donington again, its a great track. This time on the GP layout rather than the national. Oil temps were much cooler, 85-90C and car ran really well. Had lots of fun in it.








My dad giving it a go.

[Hobbawobba]

Those are some nice shots there bro. The 2 or 3 you sent me on Whatsapp didn't look anywhere near that quality aye