SOLVED 3.9 (carb) Cam Selection Help Please

[Karma Mechanic]

Hi all,

Newbie here asking for some advice please. I have searched extensively on this and other forums but can't find an answer which suits this particular situation.

I have a 1975 factory MGB GT V8. All standard spec., i.e. manual, twin SU carbs, standard inlet & exhaust system etc.

I just want 'standard' performance commensurate with a good 3.9 (not fast road, racing etc.). Smooth idle & broad spread of torque.

As part of my engine rebuild I have had 3.9 liners fitted by Turner Engineering. I bought standard 9.35:1 compression pistons.

My question is which camshaft should I choose. None of the camshafts listed by the usual suppliers seem to match my engine set up (no camshafts are listed as suitable for a 3.9 with carbs). Turner's didn't have a definitive answer.

The available options seem to be:

1) ERC2003A. This is the standard 3.5 camshaft, listed as suitable for carb & EFI, all CRs. This is what my car has at the moment. How would this perform on a 3.9? It's not listed as suitable for 3.9 engines.

2) ETC6849 Listed for 3.5 Defenders / RR Classic / Discovery 1. How does this differ from the 'standard' camshaft above? Meant for automatics maybe?

3) ERR5924 Listed for 3.9 EFI. As all factory 3.9 engines had EFI how would this perform on my 3.9 carb set-up? Any downside?

4) 'Performance' cams. The most likely option seems to be the Kent H180. But Rimmers say this also requires uprated cam followers and valve springs. I already have new standard followers I bought from Turner's so don't really want to buy uprated followers. Also I don't want to mess about with buying & setting up a vernier cam sprocket & timing gauges etc. I just want a straight swap. So are the uprated followers & springs & vernier cam timing actually necessary?

What would the learned members here suggest for me in these circumstances? Any advice would be much appreciated.

Thank you
Chris

[stevieturbo]

Why not just something like Real Steel's "Hurricane", "stump puller" or "cyclone" cams ?

Holley 390 should be ok ?

Why not speak to the likes of V8 Developments, JE Racing, etc etc ?

And you would need to use suitable springs for whatever camshaft is chosen. As for any need for verniers, a lot depends on how well the cam is ground. If it's on a new blank, it should be spot on. If it's a re-grind which I suspect would be less likely these days, then it would be more important to check cam timing is where they say it should be.

And don't get too fixated on whether they say a cam is for EFI or not, or even 3.5 vs 3.9. But the same camshaft in a larger motor will tend to make it feel slightly milder compared to the smaller motor.

[Karma Mechanic]

Thank you Stevie for your advice & swift response.

So I have learned that if it's a new blank- as I assume a Kent H180 would be for example- then I wouldn't need to time it up on a vernier sprocket.
I'm probably tending towards the standard 3.9 cam (ERR5924) unless someone tells me from experience that it won't work well with carbs, or that something like a Kent H180 is a straight bolt-in with no downsides but significant upsides over one of the standard cams.

Chris

[ChrisJC]

I ran a 'TorqueMax' cam from RPi Engineering for a few years. OK, it was in a 4.6litre engine, but it was on carbs (2" SU's).

I ran it with an autobox (ZF4HP22).

I found it to be excellent. It really pulled well from idle (well, through the torque converter).

I don't know if it was a custom grind, or something they had specially done.

Chris.

[Karma Mechanic]

Thanks Chris, I appreciate the response.
Chris