The V8 Owners Forum -

Evening all. I am based near Southampton and would like to get my car rolling road tuned. The vehicle is an mgb running a tvr big valve v8 with an edelbrock carb so will just be timing, carb jetting and idle mixture that need attending to.

Can anyone recommend a reputable local company who will not get confused about the lack of obd port?

Many thanks.

I've yet to find any rolling road operators that know anything about how these carbs work! In the end I learnt how to set these carbs up by using an actual road and an Air/Fuel ratio meter (lambda probe).

I guess my post is not all that helpful but all that I will say is watch out for rolling road operators that just thrash your car on the rollers then state that it is all running fine, they then take 50-100 quid off you for doing f-all!

The carb has several circuits that will need checking in order to see what the AFR is, an easy one to setup is the idle circuit, the engine will 'tell' you if its happy with what you are doing to the fuel screws. Other circuits all need differing AFR's, whilst accelerating the ratio wants to be 12-12.5:1, whilst running on cruise you want to be as lean as possible whilst maintaining drivability, this could be around 14.5-15.5:1. At WOT you want around 12.5-13:1, 12.8:1 being ideal.

You also need to know what the vacuum level is on cruise and what the level is whilst accelerating as hard as possible but ONLY on the primary side of the carb, you then need to select suitable rod springs so that the carb goes into 'power mode' at the correct vac level.

If the rolling road operator just pulls a few WOT runs then none of the other circuits will have been checked, I'm not sure that you can even load the engine up correctly to test the cruise circuit on an inertia roller.


What size carb have you got and what inlet manifold are you using?

600cfm and an edelbrock performer manifold.

I didn't put any lambda probe threaded ports in my headers, unfortunately....

Should add, it is a 4.5.

I've never had much luck setting up a 600 on what is really considered to be a small engine (mine is a 4.6, gas flowed big valve head, all the usual stuff!), I spent weeks messing about with a 600 carb, I also modified 500 boosters make them flow the same CFM as a 600 booster whilst retaining the 500 booster emulsion tubes. My engine was OK-ish but I could tell that it was a bit lean on the transition circuit. (just as the throttle is cracked open). This is the one circuit that is not really adjustable. Having said that I have adjusted it on my carb by drilling the slow speed jets. I actually run home made annular boosters which transformed my carb! I made a set for a friend that is currently running a 3.5 in an SD1, whilst setting up the cruise we could not find the point in which the cruise circuit went too lean, his engine runs around 16.5-17:1 on cruise which is very good indeed, he gets over 30 MPG. Edelbrock now do a range of carbs with annular boosters.

You have a decent manifold, some of the low rise or dual port manifolds do not flow well at all!

A probe boss can always be welded into the exhaust, its not too much of a job.

The engine flows well, is was built for the Tuscan challenge series, but I may need to go to a 500, we will see. Getting the headers out is a PITA for boss welding, may be able to get to it well enough in situ. Thanks for the inputs.

You are better off welding the bung in the exhaust down stream of where the individual headers join together, you get a more steady reading on the AFR meter.

If you do find a rolling road operator that you decide to use ask them whether they stock the rods, jets and springs. They might say that you need to buy a calibration kit, in my experiance you are lucky if one set of rods and a pair jets in the kit end up being any use.


You might get the 600 to work, some of it depends on what your expectations are. Does your setup have any bad habits at the moment such as hesitation when just cracking the throttle open, or when booting the throttle? Does the engine stumble when you brake or corner hard? Does it drink fuel and are the plugs black? (Along with the exhaust stinking of fuel).

I ran a 500 and a 600 back to back on the rollers, both carbs made the same peak BHP, the 600 made more torque at very low RPM which at first seemed odd. What I think was happening was that my engine was not pulling enough air to open the air valve on either of the carbs at low RPM but at the same time the engine liked the fact that the primary side of the 600 carb was flowing 100 CFM more than the 500. (The two carbs differ on the primary side only).

I modified the air valve on my 500 carb so that it opens quicker in the hope that this helps at low RPM, I actually went too far with the modification which cause a big lean bog so I had to 'backpedal' the modification a bit. (The mod was to lighten the counter weights on the air valve).

baggers wrote: ↑

Wed Dec 05, 2018 8:59 pm

600cfm and an edelbrock performer manifold.

I didn't put any lambda probe threaded ports in my headers, unfortunately....

On my SD1 running a Megasquirt, I have the wideband sensor situated where the pipes join. But a tuner can use one stuffed up the tailpipe. Beauty of MS is you can do a log of the engine running, and see later what the AFR at various engine load and RPM etc actually is.

IMHO a WB O2 is an essential tuning aid. Without one, it's guesswork.

baggers wrote: ↑

Wed Dec 05, 2018 9:29 pm

The engine flows well, is was built for the Tuscan challenge series, but I may need to go to a 500, we will see. Getting the headers out is a PITA for boss welding, may be able to get to it well enough in situ. Thanks for the inputs.

The only difference between the 500 and 600 apart from the jetting is the size of the primary boosters, they are larger in the 500 which causes them to create a restriction in the primary side of the carb. In the past I have made a sleeve that goes over the 600 boosters in order to make them the same size as the 500 boosters. However they are not quite the same because the emulsion tube hole pattern does differ between the two boosters, this may or may not cause an issue when trying to tune a carb with boosters modified in this way.

The car is only just on the road so i am yet so see / notice any running issues; seems ok on the few miles i have done thus far.

I need to do some winter fetteling so will take the good advice and but in a wide band sensor or two just after the headers. I dispensed with a balance pipe and i have 2 side exits so will pop in one for each bank and get some gauging to monitor. I have an old knock link sensor kicking about also so will install that to aid in monitoring advance pinking issues. Will report back!

I may get distracted and but a 500 cfm edelbrock thunder carb anyway

baggers wrote: ↑

Thu Dec 06, 2018 11:13 am

I may get distracted and but a 500 cfm edelbrock thunder carb anyway

If you are up for fitting another carb check out the 500 AVS2 carb, it uses the annular boosters.


Here is a link to a youtube vid on the carb...




I actually have a big bun fight in the comment section with someone from Edelbrock, I guess he/she was just a sales person because they could not really answer my questions. There are some issues with the booster design but overal the carb does work better than their straight leg/down leg booster carbs.

That design makes more sense, will look into one of these.

Fyi, I invested in an AVS2 500cfm, Roadcraft are doing them at only £350, awesome price. Now fitted and running. Will find a dry unsalted roaded day and feed back.

Nice one! I have found that you can go very lean on the cruise with the annular booster design which is good for MPG! You may have to go very large on the secondary jets in order to get the AFR around 12.8:1 at WOT, I think this is because the signal is poor on the primary side, I am beginning to think that with the smaller Rover engines the primay side side of the carb stops delivering any fuel at WOT! It just delvers air! (Not that yours is a small Rover engine).

Happy Christmas all.

Got some miles in around the New Forest during the last few days, weather has been surprisingly good. Set up the idle mix with easy on this carb assisted with a vac meter and a trusty old tachometer attached in the engine bay, runs well. There is a significant cut down on the pops and bangs over the 600, indicating a reduction in rich overrun. I also fitted an old knocklink sensor I had laying around from a scoob I had about 10 years ago, need to dial it in as the v8 seems noisier than the boxer, should prove useful.

Off to the wheel alignment centre in Southampton tomorrow to get the multi link rear squared off, can then use a bit more throttle with confidence.