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Camshaft

Dellb

CCCUK Member
Hi All

This one is for all you SBC engine buffs.
My 1980 C3 is now complete after 3 years of toil, and I am loving her.
There is however one minor point.
I have to say I am a little disappointed with the way she drives.
The engine is not the standard 350, but a 400. When it was stripped, I was amazed at its condition.
The bores were standard 4.125, and there was insufficient wear to warrant a rebore.
The cam and hydraulic lifters were in excellent condition and thus not replaced.
The heads are standard and are fed by a 4160 Holley.
My problem is this,
The idle is very lumpy, and there does not appear to much in bottom end grunt when getting off the line. Power comes in at a rush much further up the Rev band, which I found strange for such a large engine.
When I searched my engine notes, I found the cam spec. It is a comp cam magnum 12-211-2 270H grind.
This strikes me as a bit wild for ordinary street use with cruising and the odd blast off the line my main requirement.
Therefore my winter project is a cam swap.
Therein lies my dilemma. It is a minefield.
My thoughts are
Roller cam with hydraulic roller lifters and roller rockers. The reasons being
Super quiet operation
Longevity
Easy on the valve train
Able to use modern oils
Low/zero maintenance
My problem is this, I cannot find a mildish roller cam that will give me power from idle.
It appears that if you are going down the road of roller cam you must be wanting a beast of a cam.

Anybody any thoughts

Dellb
 

Roscobbc

CCCUK Chairman
A 224 / 224 @ 50 thou flat tappet cam should in theory be fine in that vehicle - but only on the presumption that the engine has all the other things done to it that one would typically use with that spec' of cam. It is a bit of an 'old school' cam. Myself, I would have selected a more modern one perhaps with more exhaust duration like a 224 inlet/234 exhaust
Is it an automatic? - if so does it have a stock or high stall converter? - irrespective of whether is an auto or manual, what is the rear axle ratio? has it got stock heads? are they early or late heads off the old 350 cu in? - do you know what the compression ratio is? If it is a typical late 70's engine and stock (other than cam) it will most likely be low compression and totally unsuited to the cam installed.
Could be that the simplest change (as you have said) is a new cam - not a so much a roller cam but possibly a RV type cam - i.e optimised for an 8 - 1 cr engine with low numerical axle ratio and auto transmission. Such a cam will significantly improve low end torque using stock heads, intake system and exhausts with lazy torque converters and axle ratios.
 

Forrest Gump

CCCUK regional rep
I'm worried now. The Magnum 270 is the exact same cam that I've just bought for my 383 stroker build!
I was thinking I've erred on the small side with this cam, not wanting to get drawn into the big numbers cams that certainly would move the power to the upper end of the rev range. Comp Cams spec it for use in a 350ci so should be small in a 400ci
As Ross said, the Magnum is an old school cam. That was another reason I went for it as it's stood the test of time, maybe not pushing performance boundaries, nor reliability boundaries on a flat tappet set-up.
I've read numerous times that single pattern cams (as Magnum) always produce more torque than the split duration.
I'm puzzled why you're lacking low down torque in a 400ci. I would have expected almost big block torque.
What intake do you have? If it's a single plane that could make it less happy in the lower range.
 

Dellb

CCCUK Member
Very many thanks for your help.
I am currently ferreting around trying to establish the heads. When I have got the info I will respond with the info
Gents
Many thanks for your help. I have now done some research that has produced some interesting information, but does not yet give me a steer. So I will bare all to see if you guys can spot any error.

Block casting no 330817 shows the block as a 400 cid block, and this is borne out by the engine number T0924 CTA. This number shows that Ross was correct, it being a low power unit built in either 72 or 74.

Where it gets interesting is the head casting numbers. These are 3947041
Which my research tells me are 302/327/350 heads with a 64cc chamber..

The engine is configured such.
Holley 4160 (with additional valve plate modification) feeding a eldbrook
Dual plane manifold. The heads described above are stock.
The exhaust consists of long pipe headers.
Ignition is by Mallory Unilite and is set
Static (vacuum off) 12 degrees at about 600 rpm
I then get about 10 degrees each of vacuum and mechanical, and end up with about 33 degrees.
Gearbox is stock TH 350 driving into a 3.07 final drive.
Eventually however I plan to convert to a overdrive box.
I would much appreciate your views.
 

Roscobbc

CCCUK Chairman
Actually all is potentially quite good. The heads should work - limitations could be max revs - if you use RV type cam or certainly one designed to maximise torque
Dual plane manifold. The heads described above are stock. The question here will be what is the piston height (and therefor compression ratio)
The exhaust consists of long pipe headers. Good as long as muffler are low restriction and header tubes are not too small for capacity - (unlikely)
Ignition is by Mallory Unilite and is set - advance curve needs to be checked-out - might need to get more timing-in at lower revs to sharpen things up a little
Static (vacuum off) 12 degrees at about 600 rpm - subject to a little bit of experimentation static could be moved to up to 15/16 degrees
I then get about 10 degrees each of vacuum and mechanical, and end up with about 33 degrees. Ignore vacuum - mechanical is actually 20 degrees - add my suggested 15/16 degrees on the distributor and you have 36/36 degrees total - (which is as much as you want with your set-up to start with)
Gearbox is stock TH 350 driving into a 3.07 final drive - this is the killer - needs moving up a 3.50 or 3.70 to liven things up a little - couple that with a aftermarket modified 4 speed overdrive box and you'll have the best of both worlds.
 

Dellb

CCCUK Member
Actually all is potentially quite good. The heads should work - limitations could be max revs - if you use RV type cam or certainly one designed to maximise torque
Dual plane manifold. The heads described above are stock. The question here will be what is the piston height (and therefor compression ratio)
The exhaust consists of long pipe headers. Good as long as muffler are low restriction and header tubes are not too small for capacity - (unlikely)
Ignition is by Mallory Unilite and is set - advance curve needs to be checked-out - might need to get more timing-in at lower revs to sharpen things up a little
Static (vacuum off) 12 degrees at about 600 rpm - subject to a little bit of experimentation static could be moved to up to 15/16 degrees
I then get about 10 degrees each of vacuum and mechanical, and end up with about 33 degrees. Ignore vacuum - mechanical is actually 20 degrees - add my suggested 15/16 degrees on the distributor and you have 36/36 degrees total - (which is as much as you want with your set-up to start with)
Gearbox is stock TH 350 driving into a 3.07 final drive - this is the killer - needs moving up a 3.50 or 3.70 to liven things up a little - couple that with a aftermarket modified 4 speed overdrive box and you'll have the best of both worlds.
Very many thanks. A very interesting exchange from which I have learnt a lot. I am never going to want a high revving power house, so I will move the project forward in increments starting with cam selection.

Once again many thanks Ross
By the way, a pic of what we have been discussing

By the way a pic of what we have been talking about
FC60BC7D-D218-4E37-BF12-8F2078B52F31.jpeg
 
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