C-1 Motor Rebuild-Need Help

[Jerry C.]

About ready to rebuild a 59-270HP for NCRS showing and want a little more low end power. I was thinking of 10 or 10.5 pistons. It will be balanced and use stock heads. I have read the LT-1 cam might be a good one to use. Any advice on my thoughts would be helpful and what else should I be thinking about. Thanks

[Duke W.]

Re: C-1 Motor Rebuild-Need Help

The 270 is an engine between a rock and a hard place. The "medium port" heads with 1.72"/1.5" valves are restrictive. A better torque curve could be had with later big port heads and a milder cam, but the heads can be visually IDed from the original type.

The LT-1 cam won't make more low end torque. It will make more top end power without losing significant low end torque, but that's not what you're looking for. If you want a little more low end torque without sacrificing the top end power the L-79 cam should be considered. One other thing you should consider is installing the base cam and essentially converting it to a 245. This will take away the "edginess" of SHP cams and provide better low end torque, better all around driveability, and a much smoother idle, but you will loose the last 500-1000 revs at the top end and associated power that SHP cams provide.

Another good option would be to stroke it with a 327 crank. This will make it a 305 or 310 with a .030" overbore. If you do decided to go with a solid lifter cam I recommend the LT-1 to replace all Duntov cam applications.

Increasing CR from the original 9.5:1 to the range of 10-10.5:1 with suitable pistons should be okay and operate detonation free on modern unleaded premium with only a little juggling of the timing map.

Duke

[Tom B.]

Re: C-1 Motor Rebuild-Need Help

I wonder if the ports in the original heads would be too small to benefit from 1.94 intakes. A little bowl work and port matching should help too.

Tom

[Duke W.]

Re: C-1 Motor Rebuild-Need Help

Pocket porting and manifold port matching are always a good idea - more top end power without loosing any torque, but remember that your heads were cast with completely different coring than the later 461s. Your ports are much small and I don't think there's any way you could expand the ports to the size of 461s and increase vavle size to 1.94"without hitting, water and it would take forever to remove all that cast iron with a die grinder.

Duke

[Tom B.]

Re: C-1 Motor Rebuild-Need Help

I was thinking that Jerry could pick up some performance without altering the visual ID of the engine.

Tom

[Duke W.]

Re: C-1 Motor Rebuild-Need Help

He's looking for more low end torque. Head work will improve top end power, but not low end torque. Peak torque is a function of displacement and compresson ratio, and the valve timing and head flow determine where peak torque occurs in the rev band. Valve timing has a BIG influence on low end torque and SHP cams provide timing that favors the mid range and high end torque at the cost of low end torque.

Duke

[Joe L.]

Re: C-1 Motor Rebuild-Need Help

Jerry----

As Duke mentions, using your original core engine components leaves you in a pretty tough spot with respect to achieving performance upgrades. Also, presuming that you want to enter the car in NCRS judging including, perhaps, performance verification, you need to stick with a mechanical lifter camshaft. Most available mechanical lifter camshafts just aren't going to be good low end torque and power items. Certainly, the GM #3972178 LT-1 cam will be better for you than the original Duntov cam used for your application. But, as Duke mentions, it's not going to give you increased low end torque and power. For a street driven car, low end torque and power are what produces a lot more driving pleasure than top end power. You don't get to use top end power all that much, but you use low end torque and power all the time.

When you combine a relatively small cubic inch engine with most off-the-shelf mechanical lifter grinds or, even, the Duntov or LT-1 cams, what you get is poor low end torque. There's just no real way around that.

One thing that you can do, though, is switch to a more modern aftermarket grind. Comp Cams makes mechanical flat tappet cams which should improve your low end torque and power and work well with your core engine. Their "XTreme Energy" series offers a few grinds in the 256 to 274 degree advertised intake duration which I think will improve the performance parameters you're seeking. Their "Nostalgia Plus" camshaft will improve overall performance from the Duntov and yet still retain a lot of the Duntov attributes. However, I don't think that this cam will offer you as much of what you're seeking as the above-referenced cams.

[Frank H.]

Re: C-1 Motor Rebuild-Need Help

I would suggest the same or slightly higher lift hydraulic cam with the same or similar valve timing and use Rhodes or variable duration lifters adjusted to zero lash,they sound just like solids but give less lift at lower rpm and more low end torque,thats what I have used on my 62 340 for 25 years now,no ones ever guessed its not the solid lifter duntov.Even compared to one running right next to it.And don't add a high volume/pressure oil pump with these type lifters.

[Doug Flaten]

Re: C-1 Motor Rebuild-Need Help

Gearing may also help. A wide ratio set of gears in the transmission or a different rear end may add some drivability.

[Curt S.]

Re: C-1 Motor Rebuild-Need Help

Regarding increasing the cid of the 283; The later 283 blocks (1958 & up) are thick enough to be overbored by .060 , .090. or possibly even .125" (4" bore) if core shift is checked. However, they can't be stroked. The 283 main saddles and bore bottoms were NOT cast to clear the larger counterweights neccessary on longer stroke cranks (nor the nodular cast cranks) until sometime in 1962, coinciding with the release of the 327 I suspect. The blocks can't be safely "clearance" ground either due to the vacinity of the water jackets. You may be able to achieve 3.25" stroke with a "custom" balanced crank using Mallory metal slugs drilled into the counterweights (does not increase the physical size of the crank counterweight). The early heads can have larger 1.94" valves fitted, but the larger 2.02" valves come too close to the (relatively) small 283's bore wall & produce a "shrouding" effect (hurting performance). The 4" bore blocks can get away with 2.02" valves. The 283 just loves to rev by design. They extracted more power from this mouse by increasing the rpm limit with big solid cams. You can "convert" your 270 hp's peak power into "usable" torque using a smaller cam.

[James F.]

Re: C-1 Motor Rebuild-Need Help-Charles

Charles,
The '56-'57 blocks could stand a .125" bore as well. Regards,