17 replies to this topic

[LC-GTR-1969]

Gday everyone,

 

I have been curious for a while as to what the cam specs were used in brocks 73 bathurst XU1... Mainly for interest sake as I am a bit of a cam theory nerd

 

I have read a range of stuff, but nothing that I can really say is solid info.

 

I have read these specs- can anyone confirm or deny that he ran a cam with these specs? Its a very late closing degree but would make sense to keep up with the clevelands on conrod.

 

Intake 55/90 

Exhaust 94/51

 

Thoughts?

Edited by LC-GTR-1969, 06 March 2016 - 02:20 PM.

[S pack]

The 1972 (bathurst) XJ cam specs have been quoted as intake 55/91, exh 94/51. Is that the cam you are referring to?

 

Camshafts were free under Group C rules in 1973 so the race teams could use any grind they wanted.

[piquet]

Contact Clive at Clive Cams he will know.

Clive used to be the main man at Wade Camshafts who did all the development work for HDT.

If it was a series production car the cam had to be the same as the homologated camshaft but after it went to Group C camshafts were free.

[LC-GTR-1969]

The 1972 (bathurst) XJ cam specs have been quoted as intake 55/91, exh 94/51. Is that the cam you are referring to?

 

Camshafts were free under Group C rules in 1973 so the race teams could use any grind they wanted.

 

I wasn't aware that was the spec of the XJ cam... (i knew the XJ cam was used as the 72 bathurst spec, but didn't know the intake/ exhaust values). I had read it was the 73 bathurst cam but the '73' that was written then was obviously an error- they probably meant 72 in hindsight. Thats the problem with searching crap on the interwebs.

 

I have spoken to Clive previously (about 2 years ago) and he said brock loved cams with really tight lobe separation and requested his cams in his cars have as tight as 97 LSA- however other drivers started to copy and they couldn't make it work (so Clive says), as Brock had a knack of keeping a punchy cam in the sweet spot. However, Clive did not mention which make/ model or car he did this in, so it may have come later in the L34 years.

 

I would love some data on the 73 race cam that brock used (again, just for interest).

[S pack]

I wasn't aware that was the spec of the XJ cam... (i knew the XJ cam was used as the 72 bathurst spec, but didn't know the intake/ exhaust values). I had read it was the 73 bathurst cam but the '73' that was written then was obviously an error- they probably meant 72 in hindsight. Thats the problem with searching crap on the interwebs.

 

I have spoken to Clive previously (about 2 years ago) and he said brock loved cams with really tight lobe separation and requested his cams in his cars have as tight as 97 LSA- however other drivers started to copy and they couldn't make it work (so Clive says), as Brock had a knack of keeping a punchy cam in the sweet spot. However, Clive did not mention which make/ model or car he did this in, so it may have come later in the L34 years.

 

I would love some data on the 73 race cam that brock used (again, just for interest).

It has been assumed that the 1972 XJ bath cam continued on as the XU1 production cam until the end of XU1 production in 1973 but that is actually a myth.

[S pack]

add 44 deg to each figure for ramps.

[LC-GTR-1969]

The 1972 (bathurst) XJ cam specs have been quoted as intake 55/91, exh 94/51. Is that the cam you are referring to?

55 91 sounds huge . I would check the tappet lift it was measured at as some factory hydraulic cams were measured at 0 lift not the .006 lift that most cams are measured at.

Camshafts were free under Group C rules in 1973 so the race teams could use any grind they wanted.

 

I figured when seeing these figures that it was a slow ramp grind (it would have been back in the day I imagine), which may explain the degree values which are way out there.

[LC-GTR-1969]

Last night I watched the Shannons Legends of Motorsport video on the 1973 race...

 

A great watch, and Ian Tate was interviewed... He was adamant that the best HDT engines had 238hp at the fly. He said other teams had more HP, like 250hp but his engines had great torque at 4500 which helped them get through and out of corners quicker, and hence were quicker around the track. He said with that HP they were still able to do 150mph. They kept revs under 6500rpm. 240km/h in a light LJ would give me the heeby jeebies . He mentioned that the 'duck tail' really worked, they tried removing it and the wheels lifted over the crest.

 

Very interesting as 238hp seems quite modest by todays standard, but I guess the whole package is important. They also mentioned 2400lbs for the weight of the race spec LJ.

[warrenm]

That's 220lb lighter than my setup.   To find 220lb to lose.

[LC-GTR-1969]

That's 220lb lighter than my setup.   To find 220lb to lose.

 

Agree... My setup is 2522lbs without me in it but with liquids (about 20liter fuel), and with me in it with helmet and so forth, about 2740lbs. 

 

I imagine the 2400lb quote was without driver, but still a good whack lighter than mine.

[warrenm]

Yep it could be a bit of both but also these were the figures in the homologation specs.if u were smart you would use t he figures to your advantage

And I'm sure no one took advantage.

[LC-GTR-1969]

Yep it could be a bit of both but also these were the figures in the homologation specs.if u were smart you would use t he figures to your advantage

 

Ah, never thought of that- so they didn't homologate at .050thou as well to verify the cams ramp?

 

Wow, I can imagine how this could have been used to 'massage' what was considered a permissible cam spec. A very good point!

[xu2308]

Harry Firth says that Mike Web of GM design did the camshaft for the V8 LJ, he would of done the camshaft for the L34 as well.

Edited by xu2308, 08 March 2016 - 04:42 PM.