| Author |
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TomB
| | Posted on Thursday, February 13, 2003 - 12:17 am: |       |
I have a '93 GMC C1500 with TBI 350. I can't seem to find out any info on the web about the heads on my motor (i.e. combustion chamber volume). I am looking at installing the L98 cam and iron L98 heads on my truck. Do the L98's flow much better than my stock heads? The L98's are 64cc. I don't know for sure, but I think my stock heads are 76cc. If this is true, will the L98's bump my compression to high where I can't run 93 octane pump gas and not detonate with the timing advanced to optimum performance level? I know everyone is going to say forget the L98's and get the Vortec heads. There are several reasons why I'm looking more at the L98 setup over the Vortecs. I can get the L98's used a lot cheaper than the very hot item 906 and 062 Vortecs. I don't have to buy a $300+ intake to use the L98's. I don't have to buy special headers with EGR fitting to use the iron L98's. I am reading where a lot of people are having problems getting the Vortec setup to run right with TBI. Plus I'm not worried about 400+ HP and torque out of my motor. I just want something moderately better than what I've got (i.e. 260-300 HP). |
Cchandlerb
| | Posted on Thursday, February 13, 2003 - 7:55 am: | |
TomB,
The stock TBI350 'swirl-port' heads are 64cc, so the iron L98's won't affect compression. The stock TBI 'swirl-port' heads make great torque (as you know), but run out of flow at 3500 or so, limiting HP.
I'm having the same debate as you, Vortec or L98 iron for my 90 GMC C1500 TBI 350. For the reasons you describe, i'm leaning towards the L98's. The L98's are a great head for this application, they make more HP than the stock ones, but lose little, if any, torque.
I haven't heard first-hand of anyone putting a L98 cam in a TBI engine, but it should be a good choice as well. Anything (withing reason) is better than the stock TBI cam (.350I, .384E lift, with 179/194 duration).
Some people have had great results with the stock LT4 cam (NOT the HOT cam). GM p/n 12551142. It has lift of .476/.488 and duration of 203/210. The 115 LSA keeps torque up nicely. These specs are with 1.6 rockers, which are recommended by GM.
Bottom line is, that the iron L98 heads and either the L98 or LT4 cam will get you right around the 270hp range, with more torque down low where a truck needs it. Get a reputable company to burn you a new chip, some good headers and you'll be happy for another 250K miles. An adjustable fuel pressure regulator is also a great idea for fine tuning.
Tom Sallee will definitely be able to help you...your goals are VERY realistic.
Sorry for the book, I get a bit excited about this stuff. Good luck and God Bless.
Chris Bradford |
Anonymous
| | Posted on Thursday, February 13, 2003 - 10:49 pm: | |
My two cents.... My current project is a former TBI 350 with the swirl-port heads (193 casting). They measured out at 67-68 CC's. My combo includes the LT4 HOT cam and 10.6 compression. Intake is a modified aluminum 4BBL from a LG4 to fit the canted center bolts in the heads. Stock exhaust manifolds with EGR air scoops ground out. Going into an enduro stock car with stock rear gears (2.73?) run between 3000 and 5000 RPM's. After I get everything running I'll post results. |
Bogie
| | Posted on Thursday, February 20, 2003 - 2:21 am: | |
TomB, hee, heee, heee; what a find. Little known to the outside world, swirl port heads feature similar combustion chamber design to the L98 and the Vortec. Now, if you own or have access to a die grinder, you can make these turkeys turn and burn kissing close to L98s and Vortecs. Best of all you don't need to spring for a Vortec manifold and if your running a carburetor or TBI in Alaska, the heads have provision for an exhaust heated hot spot.
Now, I'm going to tell you how with installments. As usual, I'm so impressed with my writing that the thing's moving from epistle to book length. It's late, I'm tired, so be patient a few days and I'll share my street porting secrets. Mean time go to Sears and buy a die grinder and some stones. Get a copy David Vizard's books on the subject, they're very good. You'd be amazed at what you can do to enhance port flow. David gives some fantastic tips; I'm a variation on the theme, like David and others,I learned at a high price of failure at the track and years from my youth. Other fathers we're playing ball with their kids, I was at the garage making little twisty ports into big straight ones. The ports didn't work and the kids grew up and moved away by the time I got home. This only proves the theory (we're back on ports now)that the physics drives convergent engineering. Which is to say that in the end science pushes everybody to the same solution. Which is why the Russian space shuttle looks like ours, it’s not a copy, it's the natural solution. It's why the Soviet/Russian Tu144 SST looks like the Concord, etc, etc, etc.
As long as you don't intend to compete on the pro drag racing circuit, you can make impressive improvements to many of the pre and post "smog" heads. However, forget the open chamber smog heads, without out an annealing furnace, submerged arc welder, vertical mill, and Blanchard grinder there's nothing you can do to fix 'em. Doug Roe was the exception, he had that stuff. As you get closer to modern head design, in the post smog era, non professional results become less noticeable, except on the swirl ports. These guys have lots of potential. Finally Fast Burns and their kin. The only place your going to get any improvement is 1) from a pro with a real sensitive flow bench and 2) in rpm and lift places you can't stand on a street driven engine.
So anyway, will do some exploring and have some fun. |
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