Inliners International Forums General Discussion Engines GMC 270 information

Going to rebuild my GMC270 engine, in my 1958 GMC1/2tn truck w 3spd OD. I have : HEI ignition, Fenton Headers , Clifford 4barrel intake with 2barrel adapter plate Weber 2barrrel carb.
wanting a 3/4?cam.Where can I buy a water pump and fuel pump? Wanting to wake it up a bit & enjoy it. Even thinking about ditching the single carb setup for Cliffords dual carb setup.
Any advice would be appreciated

I have fallen in love with dual carbs for inlines, based on my experiences with FORD inlines. Two Webers sounds good and will look good in my opinion.

The term "3/4 cam" is an acronym from the early years of hot rodding and it should be retired. In today's age of specialized engine componentry your cam choices are many and depend on the type of driving and the car's intended use. Cams have evolved for specific uses such as mileage, towing, RV, pulling, circle track (many types), drag race (many types), marine, turbo, nitrous, etc.

Generally speaking, adding lift and duration raises the engine's operating range, often at the expense of fuel economy, driveability and idle quality.
One more parting factoid to help your decision: The single most important event in terms of where your engine makes power is when the intake valve closes.

Thanks

Where can I buy water & fuel pumps?

To come here and in 2015 ask about a 3/4 cam makes me think you have been reading the early books about Chevy and GMC sixes, the last of which is California Bill Fisher's in 1954. The 302 was relatively new then and later 270s had not been produced. I have been expressing the need for a modern book dealing with these engines for years. It is common to use valves from small block Chevys that had not been produced when Fisher published his book. Many parts have been produced that ca be used to improve the performance of the GMC sixes.
As far as water and fuel pumps go I'd start with NAPA and as an absolute last resort try O'Reilly. O'Reilly last not because they may not have the part but because they treat their employes like crap! The worst auto parts outfit at lest in the West. Make sure the water pump has the correct pulley width.

Check with Summit on the fuel pump, they have Carter fuel pumps for the 270 for about $35.

Welcome to the board.

I am with Beater on this one. You will be surprised how much you can get from NAPA and Rock Auto for these old engines. I always look there first before paying specialty store prices. BTW NAPA has all pulley size variations for GMC (3/8, 5/8 and 7/18).

Also, to add to FTF's comments on camshafts - I am old school so I don't mind the language of our fathers when it comes to describing cams. But we need to keep in mind what these terms represented in their day: an off-the-shelf speed part to be used in an overall formula/recipe of upgrades.

A cam re-ground "3 quarters of the way to Full Race" was typically 30-35 degrees longer in duration over stock - with a grind that basically followed the stock cam geometry in terms of Lobe Separation Angle LSA and Lobe Centers LC. Additional lift was limited because the amount of material removed the from the base circle was purposely limited so that the stock push rods could be used (with just the valve adjusters taking up the lash).

These guys were trying to sell speed parts to kids on a budget running daily driven hot rods. The low end modification$ were typically done in stages with the car being down Friday night and all day Saturday - ready for church on Sunday or worse case work on Monday.

With a hobby car being built in today's world one need not build to a formula - unless that is what you are after. One can have a cam ground to one's individual specification with Valve Events, LSA and LCs where you want them (within certain limits imposed by the cam core).

On my personal 216 Chevy build I have chosen a dual-pattern grind with much less duration on the intake then on the exhaust. This creates overlap to promote scavenging - but to FTFs point - closes the Intake Valves early enough to achieve peak power at a lower point in the RPM range.

While I am a fan of the old school hot rod books - they focus to much on the intake side of these engines. And many of the 'porting' recommendations are actually mistaken - as simply 'hogging out' material causes the intake velocity to fall.

The proper focus is in fact volumetric efficiency and ensuring that the camshaft design promotes complete sweeping of exhaust gases from the cylinder.

I find this article useful in understanding camshaft basics:
Austin Community College site
with diagrams from Lunati to help visualize:
Lunati Power

I recommend you spend some time studying and planning what you want from the build before ordering a cam.

regards,
stock49

Thanks for the info.....

Just my own thoughts here, but a single weber 32/36 is a little too small for your 270. I think they are rated at like 220 com (at 3" of mercury which makes them even smaller at 1.5 which is what the 4 bbls are measured at so probably around 170) A pair of 74 pinto 5200 Holley/webers would work pretty good and not a lot of fuss setting them up. I just put a pair on a 261(265 with the bore) that I just built and they ran terrific right out of the box. As for a cam, try calling Schneider cams in San Diego. They are pretty good to deal with. They can re grind your cam or may have a core to grind a new one. You get to talk to the boss, tell him what you think you want and what you are doing to the motor, and a few other details, and you will get a recommendation. My Schneider sounds really great, runs really well, and broke in without any problem what so ever.

Thanks...

Danny, That is good advice fromStock49 and mdonohue. They both have much experience. Something very important and often overlooked was mentioned. "... tell him what you think you want and what you are doing to the motor…" be honest with yourself. Match your mods to your real needs. If it is a driver don't build a race engine, it won't be fun on the street. 12 to 1 compression won't be cheap to feed. Don't do anything just because it looks or sounds cool. After you build it and it is running great you can tell any story you want. Not many will know the difference. If you have to lie, lie to others not yourself.
Careful work on the head and the right cam will do a lot. The small ports on the 270 head are just fine on the street. 1.86 intake and 1.60 exhaust valves, flat top pistons, and .035" off of the head surface. Yours should have the stamped/welded rockers. They are fine for any street engine. Good luck and keep us posted of your progress.

Thanks. Its going to be a street driver; but with some mods. not looking to race the kid next to me. I had my 235 rebuilt with a performance cam , stock head work , fenton headers &intake , with two 2barrels. turned out nice. GMC stuff for the 270/302 is a different animal altogether. shiny /performance external parts are harder to find ...

Thanks 4 all of the advice....

I think you will like your 270. I built mine in 1978 and have been driving the crap out of it ever since. It's bee freshen a couple of times.

Yeah I haven't had the chance to rebuild it like my 235 yet.

Thanks 4 the advice....