Group Buy: 3x8 Throttle Body Mod + Plenum Mod

The measured experience on my Weber 3.2 was about 30hp increase, but it came in much earlier with a surprising amount increase of low-end torque. In my experience, the next 'flow restriction' in the system is the head port, and there is more upper end hp hiding there.

Where I am going with this, is that with stock heads, unblown, a 36+ mm throttle body max flows the stock heads.

 

Caribou (sp?) did a euro 308GT4 engine rebuild and dyno tune in a forza issue a while back. They didnt get close to 255hp and they tuned the crap out of it so using 205hp here and 245hp there doesnt mean a whole lot when the numbers are purely fiction. I would love to dyno a pile of ferrari engines just to know, anyone want to supply me with a bunch for me to test? Ill need a few BB engines, FI and carb, 308's, maybe a daytona.

P.

 

As a start, Tate already posted several dynos on their website at:
http://www.carobu.com/html/dyno_testing.html

 

Based on Dyno Day #'s that have been posted here over the years the 245, 205, and 240 hp #'s are not that unrealistic but would agree that no one could bet their life on them. According to Carobu the 205 # was more like 190 etc.

The issue is that CIS was designed for 1 purpose only and that was to allow automakers to meet newly imposed emission standards and in doing so robbed HP from the engine which was significant. The 4 valve head was the solution to the emissions reducing solution.

As I said before remove the CIS and place it in the Garbage Can, even a Rochester quadrajet would be a +!

Spending money on a throttle body mod is not worth it....just my opinion.

 

Thanks for the link Russ, interesting numbers, the GTSi was pretty low.

 

Here are some comparisons at the rear wheels between carbs and K-jetronic. The 328 graphed has a tubi and were about the best numbers I could find for a 328, with most other stock cars running in the 216 - 217 range at the rear wheels.

So using a 17% drivetrain loss number, this tubi equipped 328 makes about 266 hp at the flywheel, close to the stock stated 260. I took and average number for mine, which was 240 (high was 243) at the rear wheels which calculates to 289, close to 30 over the stock rating of 260.

The second comparison is with a 94 348. The point here is torque.

Yes I am very much aware that between car rear wheel dynos are wildly suspect, so I'm just presenting these numbers for entertainment, may be just mine...

That all said, I think it all DOES make the point that getting more airflow to the engine does make a difference, whether it be a larger single throttle body or 8 smaller ones.
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Now this is getting to where I wanted to go, where did you end up A/F wise with the 70mm TB over the stock one? Where is the "overboard" point? In other words did it lean out the mix or not? How far? Has the ignition map able to handle the increase in flow? Were there other corks in the system, the U turn at the bottom of the fuel distributor? snj5's mixture seemed to get pretty thin in the area 4K but it is hard to tell what it is really doing when it is not WOT, such as day to day street driving. It is a good looking chart though, nice work.

 

Well Chris, The A/F mixture will remain the same, as it is a function of how far the air door is depressed, which is a pretty much linear value. The Control Pressure Regulator (commonly called the WUR, or Warm Up Regulator) usually has a circuit that adds extra fuel in the case of a low manifold vacuum situation, such as getting on the throttle.
This is the circuit that causes the most trouble in adding larger cams, as it reads low manifold vacuum (due to increases in duration/overlap) to be read as increases in throttle opening, and it adds fuel accordingly.
Some CPRs may not have this feature, IME, especially if they may be Euro models, or may not have the correct CPR (other makes will interchange)
This is fed by a small hose from either the plenum itself, or a small hose on the plenum side of the Throttle plate.
The Hose that is on the outer side (fuel distribnutor) of the T Plate is to allow the CPR to adjust for changes in altitude.
All things considered, as the Fuel Distributor is not maxxed out or the air door hitting its limits (it has been verified in tests), the mod is completely safe as far as drivability is concerned.

 

Hope you enjoy your 1 extra HP and 1lb/ft of torque as much as you enjoy the music. Its not my opinion that the dollar:gain ratio is non-existant, its fact. You can lead a horse to water but you cant make him drink I suppose.

 

You know, i thought about what I just posted and it comes across as probably mean and a few other things we cant say in public but you know what, I dont care. What I think is a total waste of time is Steven posting here for input regarding his idea, he gets loads of good input from several different people with different cars all saying the same thing - its not worth it. So, after 60 or so posts, (i didnt check) one, maybe 2 people say different (sort of )and he decides to go for the TB anyway. Why bother asking? This is the kind of thread that makes me throw my hands up and judge someone as a dork who is determined to do it anyway regardless of the responses. So I say go for it, blow your money and learn the hard way rather than take good avice from many different people who tried to help and steer you the right way. I tried to help and now I know I wasted my time as did others with their input. Granted a few things were learned but the end result is the same.

Enjoy the throttle body.

 

Should of just left it at that.

If someone wanted to spend $10k on restoring a Yugo, then go for it. I wouldn't do it, but I admire their passion. I've done things against the majority and sometimes it works and sometimes it doesn't. It's all a learning process and like they say, "the trip is half the fun".

I have a carb'd car so I'm just following this thread for general info. Steven, please report back after the mod and let us all know how it goes.

 

No, I can say what I want, ban me if you like, I dont care. The idea was a group buy that would suck others in expecting something worth while and end up being disappointed with the purchase and Steven would be on the hook for suggesting it. The report will be blank, nothing new to report, we already know the outcome......I think I can feel a difference......hmmmmm......yes, worth every penny.

 

I actually think most of the fun is in the doing and daring to try something different to improve. Everybody thought I was nuts (some still do) for all of my mods, but they were fun to do and I learned a lot, passed on the lessons of things that worked and things that did not. I think it takes some real cajones to try anything in that engine bay!!
Looking forward to photos and and results, however it goes.
Good luck!

best
rt

 

I have one of Kermits first bored 70mm TBs, it was from a 308GTSi so it required a few mods for the QV cars. I was looking for more power from my 328 but got side tracked and bought my carbed 512BB instead so my quest for more power in a 328 type of look/design was solved and then some.

I have never installed it for the simple reason my 328 runs perfect and it would require port matching or boring the plenium so no turning back after its done unless I get a new plenium. Kermit also gave me some stainless heat shields that help keep heat away from the plenium as well which will give cooler air into the motor for more hp.

My Boxer turned into quite a project in itself with new paint, suspension and carb rebuilding/tuning so it was nice to have the 328 to drive as well so again I didn't want any down time or tuning hassles from this experiment.

The 328s a great car so I really don't think I'll install the TB but that may change. I might just sell the bored TB as well.

Keep in mind the 65mm TB bore is the same size through all the 308s/328s which began with the slowest 205 hp 308 the GTSi, then Ferrari added 4 valve heads on the QV then 200 more CCs for the 328, both of these later cars require much more air/fuel with the 4 valves per cylinder. IMO it will work and give some HP the biggest concern with increasing the TB is the low end. Their is also a tuner in a Porsche magazine thet bores TBs for 911 CIS cars as well maybe he has some data to confirm the results, a Ferrari should be similar.

 

Ferrari increased power on the 575 by 30hp by "optimising" the intake assembly. Read increasing throttle body size and flowing the intake assemblies. No where in this thread has anyone demonstrated that this mod will not work on the 3x8 motor, just a load of BS conjecture. I hope Steve's experiment is a success and some of you here are forced to eat some humble pie!

 

Stephens, right on, hope you are correct.

Let's scratch the surface a little deeper however. The intake work that is done to extract a little more horsepower is typically a) analysis and engineering around managing the intake pulses to improve the flow, and b) removing obvious restrictions in flow. Regarding b), a lot of smart people here have commented that the existing 3X8 throttle body is likely not an obvious restriction in flow in the big picture, and, the engineers in Maranello would likely confirm this. Regarding a), frequently, intake plumbing can be fine tuned to improve the pulse frequency and flow, but this is a long and drawn out process involved a boat load of trial and error on the CAD/CNC machine and the dyno. Messing with the throttle body without testing is likely to make things worse in this department rather than better.

Of course, somebody should run some dyno tests on the larger throttle body. I'd bet my money that we'll see results exactly in line with many of the other comments here - some loss of torque, certainly at the low end of rpm with a shift in peak hp towards the top end, potentially outside of the max engine rpm range thereby actually reducing overall power output.

 

Let me clarify, my comment on the 575 was in reference to the Super America. Having modified my 550 and in the process seen first hand the quality of Italian engineering solutions, some of the comments posted in this thread are almost laughable. My car, for example, currently has around 50kw at the rear wheels over the standard 550 and has NO internal mods i.e. this is all from intake and exhaust mods, using good old fashioned hot rodding/trial and error work with plenty of before and after dyno work, much of which is already posted on FChat.

 

I'm sure it won't do any warm, and it might do some good. Kermit says the flow numbers look good and that almost always translates into dyno numbers.

 

Your 575 mods are not a good comparison. Your 575 is an EFI motor with nothing more then the airbox, MAFS, upstream of the TB. You have a completly different system to work with over all. Yes intake mods will indeed show imporvment on an EFI equiped car..or a carbed car. But with CIS you have an entirely different fuel and air dilivery system thats more restrictive then the entire intake system of the 575, BEFORE air even reaches the throttle body!!

 

here is a drawing of a CIS injection system and the VERY VERY restrictive plate
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Well, this tread has forced me to go back and reread the Bosch CIS manual that I have so that I have a better understand of how this system really works. I have no interest in trying to disprove anyones ideas and I am happy to have these "bench racing" discussions in public. I ,for one, would love to add a little bit of "umph" to my QV and if the TB is a path to that I will be happy to travel that road, but I have worked on cars for the past 15 years, briefly for a living, so I am no expert on this topic by any means. It is just my method to do some research before jumping in head first. I would be happy to pay to dyno an enlarged TB against my stock one for anyone who would like to test one but does not have access to a dyno shop, or I will send my stock one to someone who has an enlarged one to dyno at there shop. Lets find out the what works and what does not, together. I ,like Steven, do not have a money tree growing in my back yard and I wish him well with his research, if I can help at all please let me know.

 

I plan to dyno a stock QV setup against a bored out tb and plenum assembly within the next few weeks and will of course provide data here.

 

If you have the time and funds to play with, I would be interested in the throttle body vs flow meter with the trap door.
I would suspect that the flow meter is the rate limiting step, but it would be nice to see data.