5,7 tbi roller rockers

[Schurkey]

While the TBI swirl ports only flow about 180 cfm, that is still more than capable of 350 hp. They will stay ahead of most other heads including vortecs until 4,000 rpm.

I can't contradict that, but I'm not saying I agree, either. I just don't have the data.

Won't argue on the camshafts in cars. The cars got the 305 peanut cam unless it was a 9C1 which got the L98 roller cam. The truck cam is the same old generic small block cam GM always used. GM 929 or Melling 274 equivalent. It was used in the 300 hp 350s.

No. The 929 cam was considerably "bigger". I found this on The Internet: 3896929 Hyd. - 195/202 - .390/.410 - 112 - 327/300HP

(I don't have a part number for the TBI cam.)
The cam used in the 5/6 lug LO5 was tiny by comparison. Slightly less lift, the same lobe-separation, about thirty degrees less duration; unless GM was playing games with the duration specs of the 929 cam--rating at .006 instead of .050 perhaps? There is NOTHING you can do to "make power" naturally-aspirated when the cam has 166/175 degrees of duration at .050. 195/202 is mild. The LO5 cam is pathetic.

INTAKE LIFT-.382" * EXHAUST LIFT.402" *
INTAKE DURATION @.050-165.9 * EXHAUST DURATION @.050-174.8
LOBE CENTER SEPERATION -111.9
CAMSHAFT MECHANICAL SPECS:
INTAKE VALVE OPENS @ -30.2 BTDC * INTAKE VALVE CLOSES @ 16.1ATDC * INTAKE LOBE CENTERLINE - 111.8
EXHAUST VALVE OPENS @ 18.1BBDC * EXHAUST VALVE CLOSES @ -23.3 ATDC * EXHAUST LOBE CENTERLINE - 111.8

[Edit] No, apparently the 929 is rated at .050 for duration, so the TBI cam really does have thirty dregrees less duration. Found this:

www.hotrodders.com/threads/350-chevy-rv-cams.414281/
The 929 cam as a comparison times at 319/320 at .006 inch lift and 195/202 at .050 lift. valve lift is .39/.41 with a 1.5 ratio rocker and .416/.438 with 1.6 ratio rockers. The LSA is 113 degrees.[/Edit]

 

[L31MaxExpress]

I can't contradict that, but I'm not saying I agree, either. I just don't have the data.


No. The 929 cam was considerably "bigger". I found this on The Internet: 3896929 Hyd. - 195/202 - .390/.410 - 112 - 327/300HP

(I don't have a part number for the TBI cam.)
The cam used in the 5/6 lug LO5 was tiny by comparison. Slightly less lift, the same lobe-separation, about thirty degrees less duration; unless GM was playing games with the duration specs of the 929 cam--rating at .006 instead of .050 perhaps? There is NOTHING you can do to "make power" naturally-aspirated when the cam has 166/175 degrees of duration at .050. 195/202 is mild. The LO5 cam is pathetic.



[Edit] No, apparently the 929 is rated at .050 for duration, so the TBI cam really does have thirty dregrees less duration. Found this:

www.hotrodders.com/threads/350-chevy-rv-cams.414281/
The 929 cam as a comparison times at 319/320 at .006 inch lift and 195/202 at .050 lift. valve lift is .39/.41 with a 1.5 ratio rocker and .416/.438 with 1.6 ratio rockers. The LSA is 113 degrees.[/Edit]

Except I pulled 929 cams out of two virgin TBI 350s. One was from a 92 C1500 and the 2nd was in my HD TBI crate engine.

 

[Erik the Awful]

Probably because GM found them sitting on a shelf and decided, "Eh, we need to use these up. Stock computer won't care."

 

[Schurkey]

Contrary to popular belief, I don't think GM does that sort of thing.

Given the similarity in the lobe separation and valve lift, I can't rule-out some sort of mistake or measurement trickery in the duration figures between the two camshafts. I admit I was surprised to see 165 degrees of intake duration.

There's also the possibility of cam-timing changes; GM has been known to use cams that had reasonable lift-and-duration figures, but installed retarded for emissions purposes. The engines were gutless until you advanced the camshaft via timing-set modifications.

I don't have data to go any farther than that.

 

[L31MaxExpress]

Contrary to popular belief, I don't think GM does that sort of thing.

Given the similarity in the lobe separation and valve lift, I can't rule-out some sort of mistake or measurement trickery in the duration figures between the two camshafts. I admit I was surprised to see 165 degrees of intake duration.

There's also the possibility of cam-timing changes; GM has been known to use cams that had reasonable lift-and-duration figures, but installed retarded for emissions purposes. The engines were gutless until you advanced the camshaft via timing-set modifications.

I don't have data to go any farther than that.

I think the specs are just flat out wrong! The aftermarket interchanges the stock part number for their stock replacement grinds. Even the smallest 305 cam is 178\194 @ 0.050 and .350/.385 lift on a 109 LSA. Same cam came in the B/D car L05 without police package. With 9.6:1 compression and horrible LG4 exhaust those 350s made 180 hp net. Still better than the dog days 160 hp smog head 350s. I think there was one Corvette year rated at 140 or 150 net hp.

Why did my 10/82 305 have flat top pistons from the factory with 53cc 601 heads if GM did not interchange stuff as needed. Pulled apart the same engine in an 85 C10 and it had dished pistons and 416 heads.

Some of the TBI 350s were rated 210 hp. That is 50 hp more than some of the 882 smog head 350s in the mid 70s. My conclusion is that the swirlies are better than the smog garbage castings.

 

[Schurkey]

I think the swirlies are fine to torque peak at ~2800 rpm. After that, they're turds. Yes, they're probably better than the old "emissions era" heads. Keep in mind, those older engines also had horrible ignition timing, lean carbs, etc. Cylinder heads need to "burn" and they need to "breathe". Swirlies are good for burning, bad for breathing. TBI swirlies don't have the advantage over Vortecs to "4000 rpm".

The Vortec engines were rated for torque peak at the same RPM as the TBI engines--2800; but the Vortec had 30 ft/lbs more torque, and therefore more horsepower at 2800. Whether that's due to better heads. better ignition curve, or better fuel injection I can't answer. The Vortec engines had ~45 peak horsepower more, but at a higher RPM. TBI power peak was 210 at 4K, Vortec power peak 255 at 4600. Again, that doesn't have to be "just" the difference in cylinder heads.

 

[Erik the Awful]

According to Wikipedia, from 1973-1975 the L65 in the Camaros had 145 hp. In 1975 the Corvettes bottomed out with 165 horsepower from the L48.

Chevrolet small-block engine - Wikipedia

en.wikipedia.org

 

[Horntoad]

Great discussion!