Thank you Zak. Ha, I wouldn't say that NA tuning is more fun than boosted tuning, I appreciate both in their own way. It was neat seeing how different parts and tweaks affected the power band and I see myself doing some more runs in the future to test longer trumpets and the eventual flex fuel.

130-ish is more like it D class requires a car to be above 18 on the weight/power ratio, so Scooter can have up to 134whp at its current racing weight and still be in the class. 130 was the number I was estimating based on virtual dyno and the calculated mass-airflow Link was showing.

Thanks man . Still more to learn and improvements to make.

Thank you for sharing all of this Emilio, your input is greatly appreciated .

I have read through your thread more than I can admit. That engine you built was insanely cool and amazing torque numbers for an NA BP! I hope to one day build something close to that within my means.

As far as velocity stack length, I'm currently limited by the filter inside the airbox. Would it be equivalent if I make extensions that go between the airbox backing plate and the throttles to effectively make a longer stack but still keeping a 50mm "bell mouth" zone inside the filter? Another question if I may. How much open space do you recommend between the tip of the bell mouth and the filter? I've seen 15mm spacing being mentioned, but don't remember if you mentioned it in the thread.

 

I need this tea.

 

I used the recommendations from ITG but I can't find anything on their site now. I think they had some charts and specific dimensions for min clearance from filter element to bell mouth. That dim is critical though. You can really destroy flow by getting the filter wrong.
Overall, I recall that too close was bad. Needs to be a min distance. The baseplate matters too as it affect flow around the bellmouth. The tips of the bellmouths are the highest velocity area.

I had the same limitation on velocity stack. I opted to give them the correct clearance to the filter and just be a few mm too short. I wish I could find the data or source for you, sorry. I just remember that putting the filter element too close to the stacks choked it bad and that it flowed better with a base plate.

In a perfect world, the runners would be an arc that cleared the inner fender. But I was happy with the powerband shape and peak so I know we were at least pretty darn close. If you are using up every mm of space to the shock tower bulge and not blocking the stacks with filter element, you're probably good.

 

Thanks again. I found the page where they mention the spacing requirements. It's within the product description: https://itgfilters.net/products/itg-...lter-jc50-s-75

They specify an absolute minimum of 19mm, and a preferred 32mm spacing between filter and end of the trumpets. On top of that, a 13mm gap on top of the filter for air circulation. The filter for the airbox has 70mm of space inside, so that's 12mm less area around the trumpets compared to the open filter, and it doesn't have 13mm gap around the filter, only at the very top. I think we can guess those two reasons are why the airbox is making less power than the open filter. That's a huge bummer considering the price...

Based on your experience, I'll look for a way to increase the runner length a few mm. Borla sells these extensions, but they're too long, and also expensive: https://www.borlainduction.com/extensions.html
I'll look into sketching my own extensions and asking a friend if he could machine me a set.

I have one more question regarding the airbox vs the open filter. We know the filter has more power potential on the dyno based on the dimensions above, but in a real world scenario where heat soak is present with hood closed, would the open filter eventually start making less power due to heat than the airbox? The main reason I went to the airbox was to lower IATs and it does work well in that regard. What approach would you recommend longterm? Would it be beneficial to start looking at insulation strategies around the filter? Would a hood vent or fender vent help at all?

 

Dunno actually. Cold air is worth a lot. Those ITG setups are not cheap but after looking at all the other options, I realized it was a fire and forget (solved) problem that I was confident would make power. Air box makes sense, I just don't have any guidance on implementation.
Just ducting cold air in reduce cooling efficiency as it pressurizes the entire engine bay. If cooling is good enough and hood is vented, maybe that would be worth the lower IAT's. You'd have to test it to find out though. We never did.

 

Understood. Will have to do some heatsoak testing again and grab some proper data. I'm thinking getting the car up to temp, shutting it off for 15 minutes, driving for 10 minutes at 50-60mph and measuring temps with the open filter. Then repeat with the airbox back to back.

I found one of the calculators you mentioned and if I used the right inputs and measurements, it says the optimum runner length would be 12.65 in, or 321mm. I won't be able to fit that, but with some redoing of vacuum lines I can get closer, around 270mm using the Borla spacers or a custom made spacer. This seems like the next step for now.

I re-read over the Whammy engine thread, and if I understand correctly, it seems you recommend stock VVT cams, or at least close to stock VVT cams for best mid range torque? Is that still your take for a stockish RPM limit? Would definitely save me from spending ungodly amounts in Maruha(haha) cams down the road.

 

Big custom cams in Taxi. You're not hitting 205whp om stock cams even with meth. Medium duration to keep midrange and around 11mm lift IIRC. Midrange was a combo of primary size on header, not too much cam duration, the longest intake runners we could squeeze in there and lots of time on the dyno optimizing VVT table. The MS3 pro we used is only an 8x8 table IIRC which is challenging to get the required granularity. Certain parts of the rev range you need big steps in cam table. So I spend a lot of time moving the set points around in those areas. If you scrunch a few set points closer together, you have to compensate somewhere else. For example, once past the torque peak, the tables don't change much. Just a shallow slope. So I get rid of all the set points past something like 6000 to 8500. But I had maybe 5 set points between 3000-6000. It's easy to have a flat spot somewhere because you're sticking to the default set points in the base map. Sometimes you can get close to what you want, leave the tables unchanged and just slide set points around to uncover a beneficial intake/exhaust resonance somewhere.

 

Good work on the dyno, way to get the data! Was that your first time tuning on a dyno?

 

Noted. Medium duration and high lift. I’m not really hoping to build a 200whp engine due to budget and lack of e85 around. 10.5 CR, rods, a slight head shave + cams will be doable in the future, but that’s still a far future.

Also noted on the VVT. I did adjust the set points while on the dyno and the G4X allows for a 16x11 table, but I only used 12x10 this time, arguably didn’t even need that much. I also didn’t spend as much time finding the small gains as you did since I had already hit the 130+ goal, another time I will. That day was slightly overwhelming already with so much to learn. Again, I greatly appreciate your input with all this.

 

Thank you SimBa. Yes, that was my first time on a dyno!

 

I was just specifying what we did for Taxi with a goal of 200whp, not making a recommendation on your build. Opt for shortest possible duration, max lift and stiff valve springs on yours. The Tomei/Maruha cams are great. They are relatively short and get around the need to trim the cam box and lifter bores by reducing the base circle to 33mm (36mm OEM). This allows around 10.5 lift. Assuming SUBs, you just need thick lash caps. I think we usually just ran 2.0mm on all valves and just tipped to suit. The valve springs are critical to keeping the valve seats alive. Bounce destroys them quickly.

 

Awesome. That's great info regarding cam specs and the valve shims for SUBs. I've been overthinking that for too long as well.

 

I've learned about what NA (and some about turbo) motors like from Garage4ag on YouTube. He dyno test all sorts of variables (often involving ITBs) back-to-back so you can see what the changes effect. I actually used one of his videos to show my tuner what intake cam timing does on turbo motors (we used to reduce power in my GLTC car).

He recently did a video on the effects of clearance to the ITBs based on comments that his setup is too close to the shock tower in his Starlet. I don't recall the results, but here's the video for your viewing.

 

I really like that channel, but had not seen that video. Thanks for sharing. Watched it and it's awesome to see the differences, which verify what Emilio and I had been reading on ITGs site. Based on measurements the airbox isn't horrible, but the filter is ultimately the right choice for power. We'll see how the heat soak tests go once I get around to that.

 

You don't even have to do anything to the bottom end to add 30hp. Two N/A builds I did had stock bottom ends with tomei cams, head work, and square tops. VVT block made 160ish and BP4W made 170ish. The 170 build had an aggressive head shave (~.120"), and I think one more step aggressive cams, I forget. Both had BE pumps and dampers to allow them to rev high enough to utilize the cams. Tach looks really weird, because 7500rpm on a ECU looks like damn near 8000 on the tach.

 

Those are fantastic numbers I would like to achieve some day. Thank you for sharing that, Curly. Do you happen to have the dyno plots for these? I'm just curious to see if there were any mid-range differences between them and how they compare to mine as well.

 

I’ll try to find them. They were on a different dyno and computer before my shop got our own, but I’ll look around

 

Dug through CR.net (RIP) to find it. Tuned this back in 2016, no idea how good of a tune it is. Car never broke aside from a seized BE relief valve, it was fixed quickly and I think has barely made it out in the 10 years since, so not really sure on reliability.




The photo might suck, I’m on my mobile and can’t figure out how to get a better resolution. So here’s the site: https://www.clubroadster.net/threads...&sortby=oldest

 

I somehow missed your response earlier; thank you for finding that. That's a very nice power curve to me and makes more torque than mine all around. This is the way.

 

Good news, that exact head that made 162hp on a MS1pnp is going on a 37k '99, with BE pump, SM damper, and a G4X, so I'll be able to do some more modern tuning and compare on the same dyno with the same engine in the next few weeks. Made 125hp with just I/H/E today.

Edit: oops wrong head. The above graph is a VVT head that made 162hp with the mild cams/MS3. The head I'm putting on has the .120" shave, more aggressive cams, and made 172hp on the MS1pnp. Dunno where that dyno graph is.