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Old 10-07-2009, 07:36 PM
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93 TBI with Impala ss lt1 cam? Is it worth it?

I have a 1993 gmc 1500 with a tbi 350 that finally needs a timing chain after 211,000 miles. I just happen to have a cam from a 95 impala ss with all the lifters, spider, dog bones, etc with less than 20,000 miles on it. would i gain anything from swapping from a flat stocker to a roller? I know the cam for the impala was designed for moving a heavy car, but i've only heard very few things about swapping the cams. as far as the dist goes, i'll probably replace it at the same time.

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Old 10-07-2009, 08:01 PM
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Can't be done unless you have a roller block - which you won't know until you pull the intake for sure. non-roller blocks won't accept the roller lifters, spider, or the dogbones. You need aftermarket retro-fit rollers. Plus, the block isn't made to accept a cam retainer so you would need to have a custom cam button fabricated.

The snout of the LT1 cam is different also, even throughout the LT1 years.

Not to mention that LT1 cams range from 191 intake duration to about 203. Nothing special. Plus your TBI won't be able to keep up with the cam change without burning a custom chip.

Your cam isn't holding you back, its the combination of cam, compression, terrible head flow, and a small TBI. TBIs are very well-matched engines, so there is no one magic bullet for making more power. It all has to be upgraded.
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Old 10-07-2009, 11:38 PM
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it has provisions for all the roller stuff, even the lifter bores are cut for dogbones and threads for the spider, but it has flat lifters and cam. it's as simple as remove needed stuff from lt1, and swap it into my tbi. everything's ready.
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Old 10-07-2009, 11:42 PM
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now, the real question, as stated above, is... is the swap worth my time if i'm in there to change the timing chain. I'm an a/c tech so the condenser won't be a problem, i'll just suck it out at work.
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Old 10-08-2009, 03:02 AM
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As mentioned, no, it`s not worth it. There are other things to keep in mind also. Some of these blocks, even so they have the provision for a roller cam you have to look at the lifter bores, some have the deeper bores for roller tappets and some don`t. How to tell is with the flat tappet lifters, if you can see the lifter sticking up out of the bore when in it`s lift position it has flat tappet bores, if you can`t see any lifter sticking up out of the bores at lift period it`ll accept roller tappets. You can still install the roller cam and lifters with a flat tappet lifter bore, but it`ll sling oil everywhere and you`ll lose oil pressure. Next why is it not worth it? As already mentioned by Curtis, the TBI engine has swirl port heads, these are the worst flowing small block heads in history. No matter what cam you use, even if using a carb, these heads are dead by 3500 rpm, As the speed of flow increases as the RPM`s go up, the swirl vane disrupts flow past the 3500 RPM range. Even if you decided to do the swap you would also need to swap valve springs, flat tappet springs are not designed or meant to stand up to a roller cam and when the springs can`t keep the valves under control the power loss is immediate as 3000 RPM, as the higher the rev the worse it gets. The TBI heads give a engine killer low end torque, but that`s it. Even so it needs a timing chain, at over 200,000 miles, if you mic the bores you`ll likely find it needs a rebuild.
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Old 10-08-2009, 03:42 PM
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bad spelling day

Quote:
Originally Posted by cusz28
it has provisions for all the roller stuff, even the lifter bores are cut for dogbones and threads for the spider, but it has flat lifters and cam. it's as simple as remove needed stuff from lt1, and swap it into my tbi. everything's ready.
The LT1 cam, even as mild as it is, constitutes a big timing increase compared to the truck cam. It will show more power and wont' be so insane that the TBI Swirl Port heads will be much of a detriment unless you intend to run above 4500 RPM regularly. The LT1 is rated at 300 hp at 5000 RPM which isn't far away from the Swirl Pots typical flop over at 4500 revs. This cam also is rated at 340 pound ft of torque at 4000 RPM which is a lot more than your truck engine delivers and again is inside the flow capacity of the swirl ports. The problem you'll have is giving up compression; the LT1 has a static compression of 10.4, the swirl port heads bolted over GM's deep dish truck pistons probably never squeezed more than 8.5 on their best day. So you're not going to get LT1 numbers, but you will get a noticeable improvement. I'd hazard an educated guess that with the Swirl Port heads you're looking at 260 horses and 290 pound feet of torque, that's compared to your existing engine which has been rated around 190 (Calif) to 207 (49 state) hp with about 275 pound ft of torque.

The rub is the computer and sensors that make TBI go, while the LT1 cam is not a lot different from the Edlebrock 3702 which is supposed to be usable with TBI engines without a new chip, the LT 1 has a bit more duration and lift. 194/.378" and 214/.442" for the 3702 and 205/.447 and 207/.459" both cams with a 1.5:1 rocker for lift at the valve measurement. The Edlebrock runs a 110 degree LSA and the LT1 is 115 and it's ground 1 degree retarded. The issue here is not so much the timing differences against the milk toast truck cam which is about 160 degrees with a lift around .34 inch, but is the effect these other cams have on the ratio of throttle position to Manifold Absolute Pressure (MAP) which you can think of in rough terms as manifold vacuum, and RPMs. As cam timing changes, the ratios of throttle opening to manifold vacuum, to RPMs also changes. As these are the three major functions the computer looks at to find the fuel and ignition timing requirements on a table; when these aren't what the chip is programmed to see, the integration of these values has the computer looking in the wrong place on the lookup tables. A new chip, for which there's a lot of places that make them out there on the web, becomes required to put the ratios back into alignment with the fuel and ignition maps. Chips run around 3-400 dollars.

The LT cam fits your engine with the removal of a pin on its nose used to drive the distributor and water pump mechanism of the LT1/4. This will, also, require the use of the roller cam drive gear and chain set as there isn't space with the longer nosed cam inside the timing cover for a double row chain. Even with the GM single row roller, it may be necessary to run a couple/three gaskets under the timing cover to eliminate contact between the chain and cover. The timing set for the 1996-2002 Vortec works just fine.

If your messing with the chip, then one needs to hazard the possibility of replacing the 400 CFM TBI of the 350 with a 600 cfm unit more in keeping with the engine's new breathing potential. Then your mind gets to thinking about better heads and the budget becomes totally shot out the window. But if you're entertaining these thoughts be aware that the chip needs to reflect all these changes so you should do everything at once and rechip the computer for all of it, otherwise costs get really out of hand.

Keep in mind that GM's V8 roller cam/lifter combination uses a shorter push rod. If you don't have these with the pile of parts you got, you'll have to get a set. 90 degree V6's use a shorter lifter and close to standard length push rods. But these won't work in a V8 roller block, they, however, can be adapted to a non roller V8 block.

The bigger problem is 210 thousand miles, while the engine and transmission may be in good shape relative to their years and miles, there is no doubt that this is on the upper range of life expectancy and suping up the engine will not enhance its or the transmission's life expectancy.

Bogie

Last edited by oldbogie; 10-08-2009 at 03:49 PM.
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Old 10-08-2009, 05:07 PM
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spot on, bogie. thanks. I actually have the entire lt1 form the impala that i purchased for my 83 z28. i can use anything i need for my truck from that engine, as the lt1 is getting rebuilt before it goes in my camaro. despite the high milage, i try to take care of it as much as possible. the trans shifts real nice, and the engine has no major leaks or compression issues. it's actually quite clean, only looks about 30,000 miles. I'm glad to hear the cam can do some good in my truck. i would hate to have it rot in my garage or scrap it. good idea with the vortec timing chain. you say that would be the ticket? i'll take your word on it. i know what i'm doing this weekend the actual cam specs for the impala ss cam are 191/196 0.418/0.430 lift 111 LSA. i hope you might be able to tell me a little more about how well this would work with my 350 tbi.
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Old 10-08-2009, 05:59 PM
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Quote:
Originally Posted by cusz28
spot on, bogie. thanks. I actually have the entire lt1 form the impala that i purchased for my 83 z28. i can use anything i need for my truck from that engine, as the lt1 is getting rebuilt before it goes in my camaro. despite the high milage, i try to take care of it as much as possible. the trans shifts real nice, and the engine has no major leaks or compression issues. it's actually quite clean, only looks about 30,000 miles. I'm glad to hear the cam can do some good in my truck. i would hate to have it rot in my garage or scrap it. good idea with the vortec timing chain. you say that would be the ticket? i'll take your word on it. i know what i'm doing this weekend the actual cam specs for the impala ss cam are 191/196 0.418/0.430 lift 111 LSA. i hope you might be able to tell me a little more about how well this would work with my 350 tbi.
Wow don't know how much more to say, the Impala version is a bit different from the Z-28 and Corvette. A bit less cam timing, less compression and cast iron heads instead of aluminum. Actually the cast iron heads probably flow a bit better that the aluminum ones, but you can't use them on a GEN I block.

Imagine, if you will, a world where an Impala LT1 is in a pick up truck. Oh! "OK", back to reality.

The cam you have is not to far off the specs for the old 300 horse 327 cam, however, like the truck heads versus the LT1,Z28/Corvette heads your installation will be whistling down from the over 10 to 1 world to the 8 and fraction world. So that 300 number would probably come down to maybe 250 instead of my ROM of 260 with the aluminum headed LT1 cam. My thoughts there is the 327 pulled that power at 5500, which a 350 with that cam just doesn't show a power increase above the 327, telling you it just isn't quite enough cam for a 350 to take advantage of the 23 more inches. Something 1.6 rockers are made for if the ports can support more flow which the swirl port heads can't. Flow limited ports will respond to more duration as that relates to more time for the port to do something with, but when the port is maxed out adding lift to the valve isn't of any value.

Bogie
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Old 10-08-2009, 07:57 PM
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cool. i would throw another lt1 from a b body in my truck any day, the only problem would be the intake. the intakes never changed, and they're better for higher end flow. i'd probably slap a good lt1 dual plane on it, weld on injector bungs, and run a 454 tbi throttle body with no guts, only idle controller and tps. run a good truck cam, and maybe a 383 crank. add long tube headers and you have a killer truck motor, muhahaha... Your right about the cast iron heads flowing more. like 15-20cfm more. actually, gm took the design from the cast lt1 head, drilled different bolt holes, and called it a vortec head, lol. with my lt1, i'm tossing a 292xfi cam in, working the exhaust ports a little, and cutting the valves to 2.00, 1.55 ( i don't want to completely kill my velocity, just increase my top end flow a little). 1.6rr's, decking the block for a decent .35 quench, toss the w/p drive so i can run double rollers, and run an electric pump. i'm hoping that with a 10.5-10.6 c/r, i'll be around 4-425hp. As far as my truck goes, it's old, has lots of miles, and it's a "while i'm in there" deal with the cam. if it will help my 93 gmc brick enough to justify the added time involved, i'll do it. i greatly appreciate your help.

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Old 10-09-2009, 10:51 AM
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Quote:
Originally Posted by cusz28
cool. i would throw another lt1 from a b body in my truck any day, the only problem would be the intake. the intakes never changed, and they're better for higher end flow. i'd probably slap a good lt1 dual plane on it, weld on injector bungs, and run a 454 tbi throttle body with no guts, only idle controller and tps. run a good truck cam, and maybe a 383 crank. add long tube headers and you have a killer truck motor, muhahaha... Your right about the cast iron heads flowing more. like 15-20cfm more. actually, gm took the design from the cast lt1 head, drilled different bolt holes, and called it a vortec head, lol. with my lt1, i'm tossing a 292xfi cam in, working the exhaust ports a little, and cutting the valves to 2.00, 1.55 ( i don't want to completely kill my velocity, just increase my top end flow a little). 1.6rr's, decking the block for a decent .35 quench, toss the w/p drive so i can run double rollers, and run an electric pump. i'm hoping that with a 10.5-10.6 c/r, i'll be around 4-425hp. As far as my truck goes, it's old, has lots of miles, and it's a "while i'm in there" deal with the cam. if it will help my 93 gmc brick enough to justify the added time involved, i'll do it. i greatly appreciate your help.
I like your manifold idea, I have such a project on the bench right now. A GMPP carb manifold with a 4 barrel throttle body, the manifold modified with bungs for the port injectors of the original LT1 EFI. Trouble is it's been on the bench a long time and doesn't seem to have enough priority to get done. Hopefully, I can wrap that up this winter but it's buckin' my V-Max project right now and I need Mr. Max worse, it a psychotic thing, my brain works better at a 140 mph with the wind ripping out what little hair I have left and the cops in pursuit to give me a ticket for not wearing a helmet. PAA'lease!

Bogie
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Old 10-13-2009, 08:26 PM
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The F-body cam would gain you a little. It's not a big deal to make work with the TBI engines.

Probably one of the best factory type roller cams to use on a chipped TBI engine would be the ZZ4 cam. Good lift and computer friendly duration.

On a side note.....GM made a great low torque 'truck' EFI intake. It's called the TPI intake. Too bad they never had the sense to use it in the trucks......or even the Monte SS.
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Old 10-16-2009, 01:59 PM
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good idea with the zz4 cam and the tpi intake. i just don't have them eventually, i want to find another b-body lt1 and slap in a torquey cam, 383 crank, and a four barrel intake with a tbi adapter. run a 454 tbi, run my tbi dist/computer, and long tubes. mmm. torque.
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