Balancing Throttles and Filters – #ITBLife
Spend any time looking into individual throttle bodies or individual Weber carburetors and you’ll inevitably find horror stories of being unable to balance idle and poor driveability.
A lot of these issues can be resolved through proper setup of the throttles themselves and others resolved through tuning.
On Black Friday in 2018 I bought an intake Speedmaster79 which is basically a clone of a Borla/TWM stack injection setup, the same as my Dad has on his Daytona Coupe. An important part of this is the vacuum plenum which connects the individual runners together so the MAP sensor gets a good reading and the IAC works correctly. You can see the plenum in the below picture.
You also might notice in this picture that there’s no connection between the runners and the plenum… Which is why I had no MAP reading when the engine was running! Needless to say, this is a major manufacturing defect. Speedmaster, when I sent them photos, basically said “drill some holes” and “warranty expired”. I was ~30 days past 1 year warranty term and I figured such an egregious issue would be met with a little understanding… Nope. I guess they won’t have anyone to blame but themselves when I post a review on their site.
So, what did I do? Drilled some holes.
Luckily drilling the holes wasn’t too bad, just annoying to have to remove and reinstall the intake (oh and change the oil since you always get coolant in it changing out an intake). While I was at it, I cleaned up a little mismatch on some of the runner to throttle body interfaces.
Next up was dealing with hood clearance. A few weeks earlier I’d designed myself a really slick airbox which was going to use flat-panel K&N airfilters.
Reality ended up sinking in when I started looking at how to tighten the air horn screws and how to fit the box around the fuel pressure regulator… Oh well, it was a cool video.
Hood clearance has been a concern from the beginning. Borla has much shorter air horns on its kits and Speedmaster has shorter ones on some of their other units. So I emailed them. And guess what? “We don’t sell those separately”. After an exhaustive search I found a UK company that sold shorter ones and Inglese Induction. Killed two birds with one stone with these guys, picking up not only shorter horns, but also a snap-in air filter. You can buy the filters from this link. The stacks are available direct from Inglese Induction.
These add up to a good solution that fits under the hood.
Not exactly the look I was going for, but they work. The “Monte Carlo” bar part of my shock tower brace didn’t clear the stacks, so off it went. I’ll be looking at an alternate solution for this soon.
To get the idle right, numerous steps were needed. Thankfully Borla has these helpful instructions (Balancing V8 Throttles). The tool used you can buy through Amazon (STE Synchrometer).
Story isn’t over yet. Dyno time coming up soon, but got to resolve some issues with clutch disengagement first. Wait is almost over!
Great article. I also have a Speedmaster ITB intake and share your views on their customer service. No documentation on their website that I can find. I’ve seen various forum posts and YouTube videos that describe mods required just to get them to fit – like the one that allows enough clearance just to tighten the center intake mounting bolts. Can you share how your mods finally worked out with a follow-up post?
Thanks for the reply! It is very frustrating as some elements of the product are executed really well. Ultimately the car is running and driving. Engine builder commented felt would have probably made another 50HP at the crank with a conventional Victor Jr manifold due to the sharp turn at bottom of the manifold. Still have issues with idle, but it’s driveable and the hanging throttle issue has since been fixed with some ECU work. Stand by earlier post of the QA issues and wouldn’t recommend to anyone who want something that runs out of the box or wants top performance.