VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 27-28 Camshafts

Hi All,
I have been comparing three different camshafts as possible candidates for a higher compression 27 motor I am about to build.

I have a stock 28 cam has a 0.195" max lift on both intake/exhaust.
I also have a stock 27 camshaft that has a 0.220" max lift on both intake/exhaust
Lastly, I have a custom ground 28 cam with a 0.185" max lift on intake and 0.205" exhaust.

I don't have the equipment to measure duration, overlap, etc. so putting that aside for a moment, I understand the difference between the 27/28 max lift is probably attributed to the 1.0 vs 1.5 rocker arm ratio respectively. That said, it would seem that max valve lift would be achieved by putting a putting a 28 cylinder head on a 27 motor with a 27 cam - and I know that has been done many times before. I would say this achieves even more valve lift than the 28 motor.

Given the choice between these options, which cam is the better choice?

Thanks,
Coachman

Hi
You can not put a -28 cam in a 27 block.
The front and middle axle shaft bearing are larger on a -28 cam

Thanks for the comparison Bluezone. Yes, I now see the 28 camshaft would not fit in the 27 motor without grinding the front and center journals but my goal is to achieve the best performance in the 27 block. It seems that the 25-27 motor would benefit more from the 28 cylinder head with 1.5:1 rocker ratio against the stock 25-27 camshaft than the stock 28 configuration.

Thanks!

I was recently chatting with a guy from a different department at work that is a retired mechanic and builds performance engines at home. I asked him if he knew anyone who hardened and reground camshafts as I see this question come up on this site occasionally.

He told me there is no need to mess with anything old as there are companies in the US that can produce a brand new custom camshaft and harden it properly. They can apparently produce any profile, lift and duration you can want for just about any model.

I have no further info on company names but if they are out there, try to find them. They may be able to help design a 27 cam with a different profile if you got the old one into their hands.

When I bought my camshaft a year ago the vendor said almost all camshafts are ground to order and only from a few shops. They stock rough castings only and then grind to the profile ordered. They did not specify the shop they purchased from but I think it was in Michigan or Wisconsin. They can make multiple spec'd cams from one casting and do not stock finished cams .

I think it would be a little difficult to reproduce that beveled gear in the middle of the camshaft that drives the distributor and oil pump.

Hi Coachman.
27 block / 28 top gives about 1 mm more push down on the valves than a 28 block /28 top

Greetings Bluezone.

I find similar values for "push down" on the valves given my own measurements of the camshafts.

28 Camshaft max lift: 0.195 inch = 4.953mm X 1.5 ratio rocker = 7.430mm
27 Camshaft max lift: 0.220 inch = 5.588mm X 1.0 ratio rocker = 5.588mm
Difference: 1.842mm

I still believe that could have a positive impact on performance with a higher compression motor, larger carburetor and exhaust.