FE-FC Holden Discussion Forum

Guys, I've bought all my bits for my planned rebuild, which is a worked 202 ( XU1 replica ), complete with triple Stromberg CD150's, Roller Rockers, XU1 Cam, Flat tops, larger sized valves ect ect....but I'm keen to run an Auto, for ease of driving in car shows ( no burning clutches in slow driving ) and so the missus can have a drive ( can;t drive a manual ), and in keeping with the classic look of an FC, the auto is on the column.  The auto is a trimatic, that will be recond, and shift kitted to improve it's performance.

MY QUERY IS, I'm hearing stories about not going too lumpy with the cam, because it will kill the vacuum and won;t run the trimatic / brakes ???  Also stories of the car surging whilst in DRIVE and sitting at the lights ???

Will a 2500 stall converter help with the surging ?  and what Cam is recomended to avoid vaccuum problems ???

I though autos changed gears from speed not vacuum, or is the vacuum only needed for kickdown ???

Please help solve my queries if you can ?

Cheers

Mark

Mark,

A smallish cam - say 25/65 or 30/70 - combined with a 2000/2500 RPM stall convertor will do the trick. The convertor will remove the creeping at the lights problem, and you can fit a vacuum tank to overcome the low vacuum at idle.

I think the stock 73 XU1 cam was a 35/75 grind which may be a little bit lumpy unless you want to go to a higher RPM stall convertor.

Cheers,

Craig.

Craig....thanks for your help...
Sorry for sounding so green, but what is and what does a vacuum tank do ?

Also can you explain to me what 30/70 means...obviously it seems the higher the number the lumpier it is.

Sorry to ask so many questions, but I'm still learning, and I'm the sort of guy who likes to nut everything out first, then go about building it, because when it all goes into the car, it will be in show condition, all painted and chromed, so I don't want to be ripping it all out again , just to change a cam or similar.

Thanks for your help !

Mark

G'Day Mark
watch out for going for too high a stall convertor as the more slip the hotter the transmission fluid gets at low speed, as this is the reason you are putting an auto in the car (low speed cruising at shows) you don't want to go the opposite way and overheat the tranny.
A Vacuum tank is fitted in some out of the way place and just stores vacuum for when it is needed, such as when you put the brakes on.
A good cam manufacturer will be able to suggest the correct combination of cam / convertor to do the job. Stall speed is also affected by tyre sizing and not just cams.
Try Crow cams or such as they will help.
John M

Thanks for that John.....I didn;t think about heat with high stall converters.....looks like my next move is to talk to CROW CAMS.......

Cheers
Mark

Hi Guys.

With camshafts you get nothing for free,

The bigger the cam, the more power gain higher in the rev band. Problem is you loose power down low were you need it in traffic, where you want it, not to mention loss of economy in traffic.

It depends on what you want from the car. If you want a nice strong drivable car don't go big in the cam, spend the money on a better head.

I've built plenty of strong 6 cylinders with Tri-Matics & there are a few tricks.

1. Don't muck around with aftermarket high stall converters, use one out of a stock Gemini (Tri-Matic).
2. Don't go bigger than a 28/73 XU-1 cam & get it properly degreed on fitting. That is, these cam are advanced not like your aftermarket 30/70-70/30 stuff, this improves drivability.
3.Get your carby combination properly set-up. I'm not trying to talk anyone out of fitting triples, just get them right. Did you know that Harry Firth (HDT manager & XU-1 inventor) made a genuine XU-1 auto prototype & it blew away the manuals in a straight line.

Regards.

Dr Terry.

Thanks Dr Terry...your advice is taken on board...thanks so much....it's good to hear it from someone who has done it before.    I'm so sick of people telling me to go V8 or ditch the trimatic, "they are shit"....it's good to hear someone vouch for using a trimatic !

Thanks again

mark

Hi Mark
I built up a HR Premier last year for a customer, using a balanced 202 XU-1 engine with a 28/73 XU-1 cam, stage 3 head, extractors and triple Stromberg CD's. It ran a Trimatic with a 1500 hi-stall shift kit and heavy duty clutches. I had to alter the stroke of the Modulator Valve to get it to upshift at the right speeds but other than that it worked perfectly.
A previous car I built was a HT using a highly modified six cylinder with triple webbers, we used a HT Trimatic in that one with a 2500 hi-stall and full manual shift kit. As it was a HT box it used a kickdown cable  and vacuum modulator instead of the solenoid and vacuum modulator and it was relativelly easy to bypass the kickdown system. This box worked effectivelly like a manual gearbox minus the clutch pedal.
Cheers
Jock

Jockster, maybe you used a HG Trimatic.  HTs were Powerglide cars (wistfully remembering two of them: 253 Kingswood Wagon 85mph low then shift and a 350 Monaro 105 mph low then shift)...

Actually you are right Spinner the car was a HG but was fitted with a HT Grille and tail-lights, so I kept referring to it as a HT (looks like I still am LOL)
Cheers
Jock

Spinner and Jockster,
The last of the HTs were available with a Trimatic from May 1970. (Except the 350) ;)
Regards ACE 8)

Ace
Most of the HT's I dealt with back then were manual V8's so I'll take your word on the transmission. The HG I worked on was definately plated as a 7/70 so it would have been one of the very first HG's. The owner swore that it was his uncle's car from new and always had the HT grille and lights, but I doubt that he was correct.
Cheers
Jock

I have 192 with a 35/75 and trimatic with a standard stall convertor, I have always intended to put in a gemini convertor but didnt have enough money to get one the day I did the auto conversion. (the conversion had to be done at a unplanned time as the 4th manual box blew a week before I planned to do the conversion)
I can drive it fine and never notice it to be a problem except for the fact that it doesnt like high diffs like the 3.08 in it now and when I go for pink slips they keep stalling it, I also find I tend to drive it with two feet.
I havent really noticed a change with the brakes but ive heard that you can get the vacuum tanks from many modern cars, I think VN or newer may be one of the cars, some turbo or supercharged cars probably have them as well, you could probably ask at the wreckers