Factory High Performance 348's

[RCE1962]

Took a look under the 348-409 Home Page under "Engine Specs" and was curious about the 1958 "Police Special" 1960 and 1961 348's all with high 11.1:1 and 11.25:1 compression.

1. Does any body have the factory cam specs for these engines?

2. Small port 817's OK to interchange? Valves 2.06 /1.72 similar with the Hi-performance 348 heads.

RCE1962

[gearhead409]

RCE, the 817s would be an upgrade for the early engines but are the same as the 1147s used on the mid-year 60 and 61 engines and the 586s used on the late 61 engines. i also would like to know the cam specs. as i will be putting a 61 together before too long and would like to degree the cam.

[models916]

Just curious. Why would you consider using a 40 year old cam design. lots of performance left on the table compared to modern lobe design. Even if you use the same lift and duration, the ramp, overlap, intake centerline, lobe seperation is far superior today. Just wondering?

[gearhead409]

Models, your right, but this is a full-on restoration of a 61 ragtop 350HP 348. we already have a nos cam. if i was building a hotrod, i would agree with you 100%.

[models916]

Are you using Moraine 400 bearings? GM timing chain? GM springs and valves retainers, keepers? Who's looking inside? I know guys that restore 100pt Bloomington Gold Corvettes and won't use dated GM internals. I know the judges count the stiching on the carpet edging but won't go inside the engine. No points lost.

[RCE1962]

I have seen a number of threads that agree with using modern cam grinds and I am convinced as well, however, I would still like to know the lift, duration, lobe separation benchmarks used in these engines. :dunno

RCE1962

[real61ss]

I don't mean to be argumentative but I agree with Gearhead, I went through this same deal as I restored my 61 409 motor. A correct restoration should not only look correct, the car should sound correct. You can't hear Moraine 400 bearings, GM timing chains, GM springs, valves retainers or keepers but you can hear the difference in the sound of the motor and the original cam and solid lifters are a big part of the sound of these old motors.
It also depends on what you are looking for, in my case, I'm building a show car so I want the correct sound, if you are building a car for performance then I could see using a modern cam design. This is off the subject but it's the reason that I went to the expense of an NOS exhaust system with factory mufflers and resonators, not only will it look correct but aftermarket exhaust will never have the correct sound.
Just my thoughts

[models916]

I agree with the sound aspect. Modern cams are smooth sounding. I would still be worried about the quality of the cast iron cams and lifters of yesteryear and todays oil.
Even in the old days guys like smokey and McGurk were doing things to the lobes and bases of the lifters to make them live. I posted a link to a cam break-in service, but I have not checked them out yet. Would seem to take the worry out of startup.

http://www.camresearchcorp.com/

[gearhead409]

does anyone have the answer to the original question? my reasons were to build this engine back stock and see how it compares to my 335HP 60 chevy. i drove a 350HP car back in it's day and it was impressive. i don't want to modify this car after all it's a factory hipo 61 ragtop. when i feel the need for speed, most on here know what i drive to get that done.

[Ronnie Russell]

I know!!!!!!!!!!! B L O W N !!!!! Aint nothing like a blower..... Fun ,Fun,Fun :beerbang :beerbang

[real61ss]

Gearhead,
I'm sorry, as usual, we discussed everything except what you asked.
In 1961, there were only 2 cams listed for the 348. The 250, 280 and 305 horsepower motors were the same and the 340 and 350 horsepower motors were the same. I know very little about motors so I'm just typing what's in my book. This is from information obtained in the Chevrolet passenger car specifications.

inlet valve opens.....49˚37'40" BTC
inlet valve closes.....86˚37'40" ABC
exhaust valve opens......77˚31'38" BBC
exhaust valve closes......32˚31'38"
inlet tappet lift .... .2319
exhaust tappet lift.. .2354

Hopefully, you know what all that means. If there is anything else that you need from my information, just let me know.

[gearhead409]

Ronnie, ya, that thing sure scares the heck out of me but it is FUN,FUN,FUN. sometimes i feel like Wild Willie Borsch! Tommy, thanks for the specs. this will give me some idea as to how to degree that old timer in.

[Gerry]

Gearhead,


I have an old Crane Cams catalog which list a "Blueprinted" replacement cam for a 409/360. It also states its the same cam as a 348/350. Here are their specs:

Intake @.050 Opens 1deg. BTDC, Closes 41 deg. ABDC,
222 deg. dur. Gross lift .403. Valve lash .012


Exhaust@.050 Opens 42.5 deg. BBDC, Closes 2.5 deg. ATDC,
225 deg. dur. Gross lift .412. Valve lash .018


Hope this helps.




Gerry

[MK IISS]

The 1961 409/360 used a different camshaft than the 1961 348/340 & 348/350.

[gearhead409]

Thanks Gerry, it will be interesting to compare these specs to the ones Tommy gave me when i get the cam in the engine.

[RCE1962]

Hi models

In an earlier post you mentiioned that "Modern cams are smooth sounding". I never knew this. There is a kid that lives a few blocks from me and just had a 350 Chevy engine professionally rebuilt and claims it has a 3/4 race cam. Either something is wrong or such cams don't make the engine sound the way I remember. There was no "lopey" idle to this engine at all. I think the rough idle is part of the romance of a high performance engine. This car "sounded" completely harmless...or maybe thats the point I'm missing.

Are most modern cams like this now? I've been away from hot rodding too long I guess. dunno

RCE1962

[rwagon57]

Methinks the youngster has either been lead astray by his engine builder or has listened to some old timer telling stories. I don't think you can find any modern cam or for that matter any SBC aftermarket cam advertised as 3/4 race.

Modern cams generally have better idle qualities due to many things including better spring technology, ramp designs, lobe CL spacing, etc. However if they are more than an RV style grind they will typically exhibit at least a bit of lumpiness in the idle. I run a moderately aggressive hydraulic roller in my Windsor stroker, and it idles at about 750 rpm in drive against the brake. A flat tappet cam with the same lift and duration (.530 I & E, 284 Advertised, 224 @.050) would be very hard to live with on the street. This particular engine is in my daily driver and is easy to drive even in stop and go traffic.

The F*&^ engine has a much smoother idle than a 327 I once had with a Sig Erson Viking 100H cam. I don't remember the lift and duration specs for that cam but that 327 would never have a chance against the Windsor. Of course the 395 ci makes a difference too.:brow

Also more cubic inches help tame a cam as well. For instance the cam in my Windsor would probably be a giant Pain in a 302.

[models916]

3/4 in the old days was 300 duration with 400 lift. Who knows what lobe seperation they had or what intake centerline spec they had. New cams can be very radical and still idle smooth and make tons more HP than the old ones. Look at Crane's nostalgial Muscle cams, ground on the old lobe seperation to get the sound of the originals. I am sure there is a loss of HP and torque involved. All they ever advertise is SOUND. The Crane Extreme in my SBc is 302 with 540 lift and Idles smooth at 850 in drive with a cross ram intake. 510 HP on the dyno.

[SS425HP]

Ever notice how smooth the Pro Stock cars idle these days? I have heard 118-120 Lobe separation angle. They build huge cylinder pressure. And, make huge power.

[RCE1962]

Technology has come along way over the years. I now know that includes cams. Never would have imagined "smooth idle and high performance" would ever be in the same sentence. I learn something new everyday. :coffee:

Thanks.

RCE1962

[dq409]

Also alot of the newer cams have a split duration. That is more duration on the exhaust.
This will make a milder sound . JMO,, dq

[Mr Goodwrench]

I thought the 3/4 race cams went out with the flathead fords :dunno now as for me I dont mess around with that 3/4 stuff in my old tractor haulin truck engine.... I only use full race cams:rofl

[RCE1962]

Just got this from a popular Hot Rodding brief. All it shows is .3987 lift for average/stock 348's and .4058 lift w/special cam. Not much difference to me. :dunno . Duration figures not shown. Jerry's cam info a better resource.

Ron