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Check my thread from last year titled “Roller Cams”. I changed out stock L79 heads and a Comp Cams 268H cam to the Trick Flow heads and a custom roller cam. I picked up 40 rwhp. The block had flat top pistons. I ran the thin ss head gasket. After tuning on a dyno we ended up with 302 rwhp. That’s puts the crank hp in the 370 range there was a nice bump in the torque as well. The engine pulled strong past 6k and was a blast to drive.
Last summer the engine acted like it had a blown head gasket, we removed the heads and found a cracked block. I replaced the engine with a Blueprint 383/430hp last October. I am still sick about loosing the original engine but life goods on. I have really enjoyed this 383. In my opinion the Trick Flow heads are a great mod for a 327, that’s running flat top pistons. I would run the .40 head gasket if I was doing it again.
What am I missing here? If you started with a 350 h.p. engine with your cam and head change your numbers should be considerably higher. The original factory h.p. ratings at the flywheel were pretty accurate back in the day and with a simple cam change from hydraulic to solids and FI you picked up 25 h.p.
I am thinking about these heads as well as I am looking to build a 327 with 9:1 comp & roller valvetrain. The build that I am looking at used iron 2.20/1.60's so I'm thinking that these might be a nice upgrade. It would be tough to cover those beautiful new shiny cylinder heads with orange paint …
What am I missing here? If you started with a 350 h.p. engine with your cam and head change your numbers should be considerably higher. The original factory h.p. ratings at the flywheel were pretty accurate back in the day and with a simple cam change from hydraulic to solids and FI you picked up 25 h.p.
What you're missing is the fact that sixties vintage gross horsepower ratings were significantly overstated... by up to ten percent or more. The true SAE gross horsepower of a typical Flint-built L-79 is a lot closer to 300 than 350, To get modern SAE net HP take off another 11 percent or so, and you're down to 270, which would be about 230 SAE net RWHP.
You guys keep throwing numbers around, but never state the full context like net, gross, engine or chassis dyno. It's all BS.
Someone mentioned that deck clearance on a Flint machined block is .012". Where do you get that number? If everything on a small block is machined to nominal dimension deck clearance is .025", but most are high because as the broach tools wore the decks "grew". If seen up to .015" high and up to .010" difference between the two banks.
If you want to know what the CR is and understand what the limits are for available fuel octane you have to make actual measurements for all the requisite dimensions volumes and use a compression ratio calculator. Unless you're just plain lucky, guessing will end you up with either a low compression stone or so much compression that you have to retard the spark advance map a ridiculous amount to keep it from detonating to dead, and that will make is a stone, too.
A "simple cam change" MIGHT pick up 25 HP at the top end if you do your homework, but it's also going to loose 10-20 HP in the lower rev range, which his not a good thing for a road engine.
According to their Web site these heads flow, out of the box, about a good as a well massaged set of OE heads, and it may be possible to improve them, but without a close look, I don't know how much. So on an otherwise OE engine, they will improve top end power by about ten percent and allow at least another 500 useable revs, but on a L-79 those extra useable top end revs may not be reachable because they might be beyond valve train limiting speed, and I would not trust OE rods to go beyond the tach redline without the potential of sudden failure not too far down the road.
What you're missing is the fact that sixties vintage gross horsepower ratings were significantly overstated... by up to ten percent or more. The true SAE gross horsepower of a typical Flint-built L-79 is a lot closer to 300 than 350, To get modern SAE net HP take off another 11 percent or so, and you're down to 270, which would be about 230 SAE net RWHP.
You guys keep throwing numbers around, but never state the full context like net, gross, engine or chassis dyno. It's all BS.
Someone mentioned that deck clearance on a Flint machined block is .012". Where do you get that number? If everything on a small block is machined to nominal dimension deck clearance is .025", but most are high because as the broach tools wore the decks "grew". If seen up to .015" high and up to .010" difference between the two banks.
If you want to know what the CR is and understand what the limits are for available fuel octane you have to make actual measurements for all the requisite dimensions volumes and use a compression ratio calculator. Unless you're just plain lucky, guessing will end you up with either a low compression stone or so much compression that you have to retard the spark advance map a ridiculous amount to keep it from detonating to dead, and that will make is a stone, too.
A "simple cam change" MIGHT pick up 25 HP at the top end if you do your homework, but it's also going to loose 10-20 HP in the lower rev range, which his not a good thing for a road engine.
Duke
I agree with you on most all you post Duke but sorry I have to take issue with this. The Mopar camp discussed this years ago with the Hemi which as we all know the factory claimed h.p. had to hold up for the racing classifications. The Hemis factory 425 h.p. rating was right on BUT it was rate as such at 5000 rpms. Boost the rpms and it became a whole other animal. The Mopar boys felt that the Chevy small block were very accurate using the real life rpm rates by Chevrolet and I do too. The Mopar camp agrees that Mopar played with the h.p. and rpm ratings.
I can only go by the seat of my pants feeling and I have driven 283, 327, 350, 427 and Hemis of all the different factory h.p. rating and from the Hemi example I give above I think the h.p. ratings at the flywheel are pretty accurate. I am not so sure about all the claimed calculations between the fly wheel and rear wheel differences.
Below is something else that proves out what I am saying note the differences in the rpms of the "true" h.p. column rather than the factory rating.
Most muscle car enthusiasts know that the horsepower ratings of the engines were deliberately set lower than what they actually made. Usually for insurance reasons and so the cars could run in a more favorable class in drag races.
Noted auto journalist Roger Huntington wrote an article about what these engines actually put out; here is the list: (All are gross hp & torque figures.)
Engine------------------Advertised----Rated----------True
------------------------HP @ RPM---- Torque@ RPM-- HP @ RPM
Buick 455 Stage 1-------360@5000----510@2800------420@5400
Camaro Z/28 302--------290@5800----290@4200------310@6200
Chevelle 396 L-78-------375@5600----415@3600------400@5600
Corvette 427 L-88-------430@5200----450@4400------480@6400
Mopar 340-4 bbl---------275@5000----340@3200------320@5600
Mopar 440-Magnum------375@4600----480@3200------410@5400
Mopar 440 Six-Pack------390@4700----490@3200------430@5600
Mopar 426 Street Hemi---425@5000----490@4000------470@6000
Mustang Boss 302--------290@5800----290@4300------310@6200
Ford 351-4 bbl Cleveland--300@5400----380@3400------340@5600
Mustang Boss 351--------330@5400----370@4000------360@6000
Mustang 428 Cobra-Jet---335@5200----440@3400------410@5600
Mustang Boss 429--------375@5200----450@3400------420@5600
Oldsmobile 455 W-30-----370@5300----500@3600------440@5600
Oldsmobile 350 W-31-----325@5400----360@3600------350@5800
Pontiac Ram Air 400------366@5100----445@3600------410@5600
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Notes:
-The most underrated was probably the 428 Cobra Jet engine... its official rating of 335 hp was a joke, especially considering that the 390-4 bbl engine was also rated at 335 hp.
-The second-most underrated was probaby either the Mopar 426-Hemi or the 340-4 bbl. The 340-Six Pack was not listed, but with an advertised hp of 290@5000 rpm and torque of 340@3200 rpm, I would guess about 335 hp @ 6000 rpm.
-The actual power output of that 455 Olds W-30 is very impressive... 440 hp!
__________________
Duke, I took advantage of the Crower Sportsman Rod group purchase coordinated by forum member Scott Marzal in 2006.
My mission from the get-go was to simply install the Trick Flow heads (painted) and call it a day.
I can't believe that TF would offer a vintage appearing aluminum head that wouldn't work with the HP piston of that era.
The cc has a similar shape, look into it. They are on this board...had an interesting combo they put together, made outstanding power and torque without being radical.
I bet airspeed is better than a set of ported irons it makes a difference People look at flow #s and think its end all/be all (not you op). Nice upgrade thats stealthy
For a real port job, guides, all the extras on a 50 yr old set of heads youll be in them almost 2k and you still got old stuff. Meh...
I agree with you on most all you post Duke but sorry I have to take issue with this. The Mopar camp discussed this years ago with the Hemi which as we all know the factory claimed h.p. had to hold up for the racing classifications. The Hemis factory 425 h.p. rating was right on BUT it was rate as such at 5000 rpms. Boost the rpms and it became a whole other animal. The Mopar boys felt that the Chevy small block were very accurate using the real life rpm rates by Chevrolet and I do too. The Mopar camp agrees that Mopar played with the h.p. and rpm ratings.
I can only go by the seat of my pants feeling and I have driven 283, 327, 350, 427 and Hemis of all the different factory h.p. rating and from the Hemi example I give above I think the h.p. ratings at the flywheel are pretty accurate. I am not so sure about all the claimed calculations between the fly wheel and rear wheel differences.
Below is something else that proves out what I am saying note the differences in the rpms of the "true" h.p. column rather than the factory rating.
Most muscle car enthusiasts know that the horsepower ratings of the engines were deliberately set lower than what they actually made. Usually for insurance reasons and so the cars could run in a more favorable class in drag races.
Noted auto journalist Roger Huntington wrote an article about what these engines actually put out; here is the list: (All are gross hp & torque figures.)
Engine------------------Advertised----Rated----------True
------------------------HP @ RPM---- Torque@ RPM-- HP @ RPM
Buick 455 Stage 1-------360@5000----510@2800------420@5400
Camaro Z/28 302--------290@5800----290@4200------310@6200
Chevelle 396 L-78-------375@5600----415@3600------400@5600
Corvette 427 L-88-------430@5200----450@4400------480@6400
Mopar 340-4 bbl---------275@5000----340@3200------320@5600
Mopar 440-Magnum------375@4600----480@3200------410@5400
Mopar 440 Six-Pack------390@4700----490@3200------430@5600
Mopar 426 Street Hemi---425@5000----490@4000------470@6000
Mustang Boss 302--------290@5800----290@4300------310@6200
Ford 351-4 bbl Cleveland--300@5400----380@3400------340@5600
Mustang Boss 351--------330@5400----370@4000------360@6000
Mustang 428 Cobra-Jet---335@5200----440@3400------410@5600
Mustang Boss 429--------375@5200----450@3400------420@5600
Oldsmobile 455 W-30-----370@5300----500@3600------440@5600
Oldsmobile 350 W-31-----325@5400----360@3600------350@5800
Pontiac Ram Air 400------366@5100----445@3600------410@5600
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Notes:
-The most underrated was probably the 428 Cobra Jet engine... its official rating of 335 hp was a joke, especially considering that the 390-4 bbl engine was also rated at 335 hp.
-The second-most underrated was probaby either the Mopar 426-Hemi or the 340-4 bbl. The 340-Six Pack was not listed, but with an advertised hp of 290@5000 rpm and torque of 340@3200 rpm, I would guess about 335 hp @ 6000 rpm.
-The actual power output of that 455 Olds W-30 is very impressive... 440 hp!
__________________
My post was SPECIFICALLY targeted at the L-79 you previously mentioned, but it applies to all sixties Corvette small blocks. The DZ 302 was likely underrated as was the Boss 302. I don't know why because they were small displacement engines, and a 302 Z-28 with the standard 3.77 axle and Positraction couldn't break 15 seconds in the quarter mile back when the mags tested them. They were just too torque shy to be decent quarter mile runners with the standard gear. Chevrolet big blocks, especially SHP may not have been as overrated - maybe the numbers were just more honest, and maybe some other manufacturers actually underrated, and I can believe that the Hemi was.
I don't know who Roger Huntington is, and I have no idea how he derived his claimed numbers, so I can't put any faith in them. They "prove" nothing!
I know a guy with a '68 Mustang Cobra Jet 428, and I think the engine is a stone. I runs out of breath at 5000 revs. I was very unimpressed with its performance. A 427/390 may be somewhat overrated, but I'm sure it's stronger than a Cobra Jet 428. I think the 335 HP rating is probably more honest than most.
Back in the summer of '69 I raced a 440 Charger on a section of deserted freeway north of Milwaukee. I wanted to go from 40, but he kept slowing down and didn't punch it until about 25. I should have known better. So he got a good jump on me and I figured I'd catch him a about 100, but didn't until 130. It was a hot summer night and our windows were open. When I got even with him his engine was missing. I figured it was hydraulic lifter pump-up, so I shifted into fourth gear and walked away, and I have no doubt he heard me shift because my SWC had glass packs at the time and was LOUD! I wanted to talk to him, but he just ran off with his tail between his legs. People always felt my 327/340 was stronger than most, and with its 3.08 axle I knew that if there was enough open road ahead I could never lose no matter how much power the other guy had because none of those muscle cars had the gears top out at 150+ and probably not enough power even it they did have a real tall gear.
Your calculations are a bit high for a L79 with the 5cc dome (.125" dome) pistons and 60 cc chambers. Speed Pro lists the CR at 11.2 with 58cc chambers, and I get the following with typical stock 0.012 deck height and a FelPro gasket:
The DCR with the L79 cam is under 8:1 and very reasonable.
Your calcs are based on a .051” quench. As I mentioned, mine are based on a .040” quench. Big difference! With a 4.030” bore and a .040” quench with. 4.1” gasket and 5 cc dome, static CR would be 11.74:1.
As as far as a DCR, that’s hard for me to figure. I’ve seen a 30+ degree spread on the IVC specs for the L79 cam. I used 69 degrees. But I’ve seen lower and higher numbers published.
Hemi, I bought the 66 L79 6 1/2 years ago. It was rebuilt with flat tops and the 268 cam. I put it on the dyno twice and the rwhp was 248 the first time and 258 the second. The second dyno was after changing to ported 2 1/2 ported exhaust manifolds and a 69 Z/28 intake was added. To stay the least I was disappointed in the power increase. Then I added the TF heads and roller cam and got a best of 302. These are all rear wheel hp readings. My engine when I got it wasn’t even close to 350 crank hp.
The power increase with the heads a cam was very noticeable. I would love to build a 327 with a better bottom end with ported TF heads with the same roller cam. It would pull hard to 6500 rpm’s.
I did the head swap swap in April last year and in the summer I noticed a lot of moisture coming out of the exhaust pipes on start up. Then I started loosing coolant. I actually drove it to Carlisle in August and it was hard to start but ran fine after it warmed up. When I got home we did a bore scope and the top of number 6 and 8 pistons were bright in color like a new piston. We thought it was a blown head gasket but found the block was cracked between number 6 and 8 cylinders. After talking with Black Magic and others I decided to go with the Blueprint 383/430. I am very happy with that engine. I did a test several weeks ago where I ran down to Hereford, NC, turned around and came back to Virginia Beach. I filled up before I left and filled up when I got back. I made no more than 4 stops and was very easy on the gas. I do have a TKO 600. The mileage was 22.3. I did the math twice as I couldn’t believe it.
Your calcs are based on a .051” quench. As I mentioned, mine are based on a .040” quench. Big difference! With a 4.030” bore and a .040” quench with. 4.1” gasket and 5 cc dome, static CR would be 11.74:1.
As as far as a DCR, that’s hard for me to figure. I’ve seen a 30+ degree spread on the IVC specs for the L79 cam. I used 69 degrees. But I’ve seen lower and higher numbers published.
You clearly point out why it is important to have the block deck height and the chamber cc measured, and adjusted as needed, to work with the selected head gasket to result in the CR and quench you want.
Everyone with a stock GM block can expect a deck height above the piston crown from about 0.020" to .040", and it must be measured before an accurate initial CR calculation can be made. When that is known, then the "best" assembly of parts and machine work can be determined from the known dimensions and desire for originality, and for the parts already at hand (to deck, or not, stock or aftermarket heads/pistons/rods, GM blueprint cam or aftermarket, etc.).
A good machine shop should help and guide the engine owner to an assembly that is better matched than just a bunch of catalog parts, and then machine and assemble what the engine owner is will to pay for.
04-20-2019, 03:06 PM
