MGB GT Sebring look alike with Ford ST 170 power

Added: 2026-05-11

[00:00:00]Welcome back to Walker's Workshop.

[00:00:03]One of the worst aspects of this job is when you spend forever mapping a car and get a really bad result. And then I have to go into grief counseling mode and explain to people you can only get the power out that's in there.

[00:00:18]An example is we had a guy with his head in his hands.

[00:00:22]He spent 6,000 lb to gain 3 horsepower.

[00:00:27]It we did fix it. It was just a question of the cam timing and both cams were two teeth out. So happy happy at the end of it.

[00:00:35]Well, I'm going to hand you over to Chris Flower who's had what I think is a really disappointing result given the amount of money he'd spent having this conversion done on his MGB.

[00:00:47]But well, judge for yourself. I'll introduce you to Chris now.

[00:00:51]Chris Flower, tell me about your car and where's your MGB? MGB cuz that looks suspiciously like a Ford.

[00:01:02]It is. It's an ST170.

[00:01:06]Bought four or five years ago as a standard standard road car and then I started to changing the body work. I always wanted to do what they call a GTS. Some call them Seabrings.

[00:01:20]Like a couple of races that they used to have late '60s.

[00:01:25]Just as a a road car and of course it snowballs. Then fancy a different engine. Thought about V8. I thought I'd I should have at least a medium of fuel economy.

[00:01:39]So I went for an ST. Drives lovely. Master gearbox.

[00:01:44]Yeah, really pleased with it. Just here to uh to get any any little issues ironed out.

[00:01:52]>> Well, that that's what we do. We look for the little issues, try and sort them out and then try and get it mapped.

[00:02:00]Are they motorbike throttle bodies? They are. As you probably see one of the tops of the filters came off of that.

[00:02:07]Yeah, uh that that's we're good at bodging. I mean temporary repairs. Yeah.

[00:02:13]Okay, well I think they're off a Honda those. Off a Honda, yeah. Well, they'll be big enough. I mean they're always big. The problem with motorbike bodies is the the butterfly plate throttle angle is quite severe compared to road ones and you find they're quite sharp when you first open the throttle because you get a big change in air flow. But yeah, on performance cars it's not a problem. It's it's only you might have some issues in traffic. But we'll do our best to map around it.

[00:02:43]Yeah, so that makes the throttle response really sharp. Yeah, it's just I think you know, particularly when you're you are in slow traffic and you and you you've just got to pull away and you to try and pull away without looking a complete idiot. You know, you're going to be very careful with it. But yeah, hopefully you can iron that out.

[00:03:01]>> Yeah, not you don't want every start to drag race, do you?

[00:03:04]>> No, no, just to just be able to pull away. Sometimes it's fine, but others you yeah, it feels a bit awkward. Okay, we'll see what we can do. Okay.

[00:03:12]So regarding the filter problem, just explain again what happened, Chris.

[00:03:17]The the top of this one was being sucked in into the into the carburetor the throttle body and it had ripped around this red this red line here and it was it was about to make its way in. And what the problem is if I just feel there where my thumb is, that's the intake trumpet. So you've only got this little little space here for the air to get into the engine. I'll just press my finger into there. Plus that what's across the surface. So you might find these are restrictive. They really need to be further out, but obviously you can't because they'll be outside the car. So what we'll do is we'll check them. We'll do a we'll do a little bit of initial mapping, check for any problems. And yeah, then we'll pull them off when we start doing the full power stuff. We can test it back to back.

[00:04:07]So the first stage was to pull the filter socks off so we can balance the bodies. But these motorcycle trumpets had been cut away and were just completely the wrong shape to get the balance tool in. So we had to come up with something else.

[00:04:25]You can see here the cutaway section. No idea how that happened, but I guess you get it with second hand throttle bodies.

[00:04:39]There was so little air flow showing on the meters, it's amazing that it run at all.

[00:04:44]750 rpm, but we found the answer to that one.

[00:04:49]The ignition timing was adding 40° just to maintain the idle. So it was time to adjust the throttle stops.

[00:04:57]Right, this throttle linkage just looks all wrong to my eye.

[00:05:04]Um Can't get my finger in here, but this here should Can you just work that um second body down just so we can see it moving.

[00:05:24]This one? Yeah.

[00:05:28]No, it's so it comes away separate.

[00:05:31]Yeah, that's it.

[00:05:32]Again.

[00:05:34]Yeah.

[00:05:35]That's just not right.

[00:05:38]It's supposed to be the other side of that arm so that the spring holds it in firm contact and then when you shut the throttle, it forces that throttle closed.

[00:05:48]It's working cuz it's got really big powerful springs, but it's just it's great cuz it's not right.

[00:05:55]Here you can see the mixture ratio at 16.2 to 1 giving 32 brake horsepower.

[00:06:01]Then it's trimmed to 14.1 to 1 and the power increases to 36 brake. This is the kind of mapping that makes the car much more responsive in the real world.

[00:06:12]For the first full throttle power run, we had to leave this modified trumpet off or repaired trumpet. It was never going to survive a full throttle run on maximum power.

[00:07:03]Oh dear, 152 brake horsepower is not what we were hoping for.

[00:07:09]On throttle bodies these engines normally make a minimum 195 and we've seen over 200.

[00:07:16]To add to our troubles, we seem to have lost a cylinder.

[00:07:21]Yeah, so they're basically what you're saying, too close. Too close, yeah.

[00:07:25]You're trying to suck all the air through this tiny surface area when it should be drawing all of this as well.

[00:07:31]And and it appears to have lost a cylinder. But having said that, I don't know if the light will get down in down the hole.

[00:07:39]Let's let's try.

[00:07:45]I think you just about make it out.

[00:07:47]There's a big lump of sponge jammed up against the butterfly.

[00:07:53]Every day's a school day.

[00:07:55]Let me aim it down the end. Ah, look at that. Superb.

[00:08:00]Yep.

[00:08:02]Hopefully that's why we've lost a cylinder.

[00:08:07]Just do that again.

[00:08:10]Oops. Yeah, not good.

[00:08:13]That might have something to do with the the uneven idling and the misfiring I think. Yeah, I would have thought so.

[00:08:22]All right, just give us a demo then, Ollie.

[00:08:25]>> Yes, we've got our HT lead too. I spun crimp in there. That should be quite tight on there.

[00:08:32]What about this See the one of the bunch.

[00:08:43]Try that first one again.

[00:08:45]Yeah, that one.

[00:08:47]That's there.

[00:08:48]>> seems okay. So we got one out of four.

[00:08:50]Yeah.

[00:08:51]Well, don't be greedy. That's not bad.

[00:08:56]Those HT leads not only cause misfire, but they can damage the coil because the energy has nowhere to go and there's possibility you'll take out a driver in your ECU. So really bad news.

[00:09:52]Suddenly the room filled with smoke because this uh plug had fallen out of the block. So, here's the offending item and at this stage I'm losing the will to live.

[00:10:02]Because the power was so disappointing, we decided to do a compression test.

[00:10:07]Pulled the plugs out. Look at this, cracks on either side of the plug another cause of a potential misfire.

[00:10:17]Yep, running.

[00:10:21]All right.

[00:10:25]Rubbish.

[00:10:27]Given the low compressions, I think the cam timing is out on this engine. Uh there's no more we can do today, so it's time for Chris to road test it. So, you've had a quick test drive. What do you think?

[00:10:38]>> Yep. Brilliant. The uh the the the low speed driving, changing gear that I had a lot of trouble with, um sweet.

[00:10:47]Beautiful. And the the response and pick up, uh much much quicker than than than what it was. Uh much more alive, you know, uh responsive. Great. So, all we need now is another what?

[00:11:01]30 horsepower?

[00:11:02]Yeah, well, and we'll go in search of that, but um yeah, com- compared to what it was when it came in, um beautiful. Well, excellent. Thanks very much. Very pleased. No, thank you.