Dail in cams or set for vacuum?

[LumpyVR4]

It's time to do my belts and while I'm there I'm fitting a set of variable gears seeing as I have Kelford 272s and the head has been rebuilt, so I would assume it has been shaved. I was intending to get them professionally dialed in, but I've been doing a little reading and have an alternative to consider.

With the cams straight up at idle I have 10 inches of vacuum. Seeing as I don't rev to 8500 and have FP green pumping 35 psi, I figured that I can tweak the cams timing until I can get 15 inches at idle. This should improve my spool and lowish revs off boost response as well as cruise fuel economy.

So the question is do I need to get the cams dialed in, or just start tweaking the cams a couple of degrees at a time until I get an improvement in the vacuum?

 

[BMGTZ]

before you have a go...have checked the piston to valve clearance? You mention the head may have been shaved...best to check

 

[Benzo4gT]

What he said ↑ A lot of hard work and $ could go down the drain if it's a little out

 

[LumpyVR4]

OK. so I'll get the cams properly dialed in at Meek and have a chat about adding in some intake retard and or exhaust advance to reduce my overlap and get the cams working a bit lower in the RPM range and reduce "turbo chill".

 

[EVO-00X]

Yeah Ive got the same issues with my Kelford TX272's. Very low vac at idle and seems like its going to stall when coming to a stop whilst driving. Have to get it tuned out.

 

[BMGTZ]

Yeah Ive got the same issues with my Kelford TX272's. Very low vac at idle and seems like its going to stall when coming to a stop whilst driving. Have to get it tuned out.

what is you idle speed....I like about 1000/1100 with 272s

 

[MDK87]

I bought the comp cams dial in kit and did the whole 15-5deg exhaust & 5-15deg intake piston to valve clearance check with solid lifters and checker springs on my CA18 but I got confused with it all and couldn't figure out how to relate that to maximum advance/retard on the adjustable cam sprockets.

In the end I threw those comprehensive measurements out, set the crank to TDC and rotated each of the cams through 360deg, changing the advance/retard by small amounts until the valve collided with the piston (softly by hand). I then took note of that advance/retard angle, subtracted 2-3deg considering inertial rod stretch and thermal expansion and set those as my maximum limits.

I'm sure there's a better and more accurate way of doing it that doesn't risk bending a valve (as it wouldn't take much) but it just seemed like less of a head fuck to do it that way lol

IMO I think it is a waste of time dialling a cam in for centreline. I yielded better results sticking to my advance/retard limits and just playing with phasing within that window, although it all really depends on where you wish to make peak torque. I'd suggest doing it on a dyno so that you can obtain some quantifiable data from it all.

I'm probably gonna get raped for this post because of it's 'roughness' but I welcome constructive criticism as I might learn something from it.

 

[LumpyVR4]

I plan to dyno the car eventually after a total change to exhaust manifold, turbine housing and o2 dump. Then DSMlink and some big injectors for E85. I figured that initially if I just got myself a little more vacuum at idle it'd be a good thing seeing as I don't have big turbo pushing big boost at high revs.

 

[MDK87]

I guess low manifold vacuum is a trade-off you'll have to live with for having greater overlap.
Is it causing issues with your brake booster or something?

 

[DOUGMO]

dial them in first and then adjust them on the dyno if need be

 

[LumpyVR4]

I guess low manifold vacuum is a trade-off you'll have to live with for having greater overlap.
Is it causing issues with your brake booster or something?

No. The reality is the cams are too big for the rest of the car (stock engine, 16g, 510 injectors) in its current form, and I daily drive it. Although I do plan on making improvements. I think 264s would be more suitable with the rest of the car as it stands. With that in mind I thought I could improve the cams efficiency as far as the rest of the car goes, and thus the cars performance, by splitting the lobes to reduce the overlap.