1997 GMC Jimmy camshaft upgrade
 

Hey all I'm new to this forum site and was wondering if anyone knows of a cam upgrade options for a 1997 Jimmy with a 4.3l. I'm going to be putting new stock cylinder heads on my engine and was looking for a possible upgrade for the cam. Basically everything is stock and I'm wondering if there is a cam that will give a little better performance and fuel efficiency that will work with a stock ECM. I'm not looking for anything crazy just a basic cam upgrade.

Any ideas?


Thanks for your time and help!

I'm in the same search as you right now. i have a 97' 4x4 got some junk yard heads in hopes to refresh them and upgrade the cam to squeeze some hp and torque out of the engine for light/medium towing in the mountains.

so far i've gathered that you cant use a cam that will give more than .450 intake valve lift and .500 exhaust valve lift given your rocker ratio: without modifying the head.

HR-204/286-2S-12 Hydraulic Roller Camshaft for Chevrolet 1992-2002 90 degree V-6, 4.3L

HR-194/271-2-12 Hydraulic Roller Camshaft for Chevrolet 1992-2002 90 degree V-6, 4.3L

these are the two cams i'm considering because of thier lower lift height, im trying to gather information on what all i need to change out aside from cam and valve springs.

i hope someone else that knows more can chime in on your post as well.

You can run .500 intake and exhaust lift without machine work on the heads, as long as you run ls6 valve springs with comp cams 787 retainers. I have even heard of a couple people running .525 lift without machine work, however I can't vouch for .525 personally.

I'm running a comp 266hr grind cam. (.500 lift) with that valve spring set up. I chose the cam because it's effective RPM range is something like 1800-5000 As opposed to many others that are made for a higher RPM range- better used with a higher than factory stall converter.(I believe our factory ones are around 16 - 1800 stall)

It is recommended with any cam upgrade to have your .ecu tuned otherwise you're basically pissing in the wind, spending money for the same or possibly worse performance.

chevyriders advice is the same that I would give.

BTW. What injection are you running on that COMP 266HR?

My marine intake/and injectors are supposed to be here tuesday:icon_mrgreen:

so some springs such as these:
https://www.texas-speed.com/p-1383-l...od-to-550.aspx

and a cam such as the 266 from comp, or a crane cam.

and a tune on the ECU: do you have a suggestion for a place that will do a tune?

that's all that's really required? stock lifters and tappets are fine?

Those should be the ones, but here's the gm part number- i just ordered mine from the dealer.
https://cimg9.ibsrv.net/gimg/blazerf...6c940dc70b.jpg

Comp cams 266hr and 270hr are the ones I know of that have .500 lift. 266 is supposed to keep more of your low end power- but the 270 is supposed to give you more of a performance gain (within it's RPM range.)

You can send your ecu out to wait4me performance or pcm for less for an affordable tune. Most people seem to prefer wait4me out of the two.They are know to do decent tunes, however if you find a reputable local speedshop that can dyno tune it, that will get you the best results. They will probably charge twice what one of the mail order tunes cost, but you get what you pay for- and support local business at the same time.

You can run stock lifter and pushrods, I bought new factory style pushrods just so I had nice clean oil passages- but my lifters were in super nice shape so I kept them.

It would be a good time to replace your timing chain/gears while you're in there. I used a 350 timing chain kit because it's much beefier. The plastic timing chain covers are intended to be one time use. I would replace that as well.

Thanks for all the info, makes it so much easier to just get all of it together like that from someone who has already done it.

have dealt with pcm4less before for work. will pick up a ecu from the junk yard for a whole 23$ and send to them.
will just do the 266 and refresh push rods since I have 105k on motor and timing kit like you said.
don't want the 270 because of the TQ converter stall and the little loss of low end there.

and as far as the valve spring retainers im assuming the GM retainers for the LS springs will work? or do you have to use the comp retainers?

gm retainers: http://www.jegs.com/i/Chevrolet-Perf...66344/10002/-1

Thanks again.

You have to use the 787 comp cams retainers, they're clearanced differently. They're cheaper than the gm ones anyway.

Thanks for all the help and input. Its not every day you get this much info with part numbers by someone who has done this kind of work before. I was also curious if this would also work on TBI heads as well. I have a TBI engine that im hoping to be doing a similar cam swap on this year as well. (1995 4.3l. TBI)

Be sure to report back on your progress and the final results. I don't plan to do this to my Blazer but I for some reason find this fascinating. :)

No problem. I'm unsure about the max lift with TBI heads. The only differance i have heard of is that they flow poorly compared to the CPSI heads, and are commonly replaced with CPSI heads for that reason.

I know that doesn't answer your question, but swapping heads is something you may want to consider if you're trying to gain power from the TBI engine. - and as a bonus, you'd be working with heads that you know the tolerances of

Just about to order my valves, springs, retainers and stuff for the oddball 1994 TBI heads.

Have to measure a couple things this week to determine how to machine the guides. They will need K-Lines and will get a set of valves from Manley or Milodon.

I'm also considering the 1995 upward CPI heads as they have the (heart or kidney) shape combustion chambers. If I can get by a cheap set of heads I'll probably go that road but that could open another can of worms for my build. (Just for thoughts - different knock sensors - manifold from dry to wet flow, retain the TBI manifold and machining for the ports. Headers. Accessory bolt thread locations etc.)

Probably going first with my mild ported OEM heads and see what the COMPCam 260AHR will need on ECU modification of the EPROM.

56-440-8 - Magnum? Computer Controlled

The nice thing is that I have a complete set of two engines including ECU and wiring harness and a vehicle that I can test with the completely stock engine and afterwards the modified one.

Not sure yet if I can come by the engine dyno at a low rate then testing will be done with the factory ECU and with the modified one as I should be able to do a complete ECU rigging to run it on the dyno.

At the moment figuring the proper springs and retainers and locks for the respective valves. Have to take more measurements this coming week to get that right the first time.

I'll let the forum know in my build thread about the parts that finally to into the project as this would be a nice base and know-how for an intermediate build with some machining.

Hey, error 401, j just noticed you're a mod now!

Why would you have to change knock sensors with the head? Don't they thread into the block, or am I mistaken?

I'll be watching your build thread to see what you come up with for springs/retainers. I'm interested to see if there's any differences in that area.

Thanks - just made that additional step.

You are right about how they just thread into the heads or block.

For me the knock-sensors would be a grey area. If changing only the heads that would mean a different head to the ECU. A wild guess on my part would be that the frequency of the knock sensors should be pretty much the same as the heads have a generally similar design.

The "kidney-shape" combustion chambers are from hearsay less prone to detonation than the old LB4 heads. Still modern EFI has some spots in the VE tables where it gets close to knock in part throttle operations where they advance ignition as much as possible to get best power out of the fuel.

If the knock sensors were off because of the different design or the sensor has other characteristics (freqency filter) you could run into trouble.
A careful evaluation may be necessary with such modifications in order for the engine to last as long as the OEM.

Just a word of caution and a nudge to investigate such things in depth.

If I can get a pair of the newer heads I'll see if the knock sensor is "exactly" the same part number. Then you had to make sure you understand the sensors output. Some are "switches" some just deliver the signal to the ECU or an auxiliary box. If it is just the signal and it is compatible between the ECU that is in the truck and the one of where the heads came from - you may just go for it.

I was looking around and I talked to someone that said comp cams makes a kit that would take the place of buying the ls6 springs and the 787 retainers. The part number for it is 982-KIT. It was for an 8cyl engine but it would still work with a 6cyl. Looks like it comes with all the springs, locks, retainers, and seals.

Error 401- I never would have thought of that with the knock sensors, I didn't know about the difference in function of knock sensors. Let me know what you find between the two sensors if you get the opportunity.

You just dropped a whole bunch of knowledge on me, thanks!



Tkos15, that seems like a pretty good deal on that kit, especially since it comes with the seals and locks.

I'm just looking into the compcams kit's as well for my build.

The pockets for the OEM springs in the 94 heads are small but it should fit a beehive springs. Not sure if the LS6 kit (i had a look at that too) will fit. the old heads have quite a bit of a boss around the valve guide. May need machining.

have to download these pics from my phone. I'll post back over the weekend.

what kind of numbers can I expect with a 266 comp, cam and LS springs and 787 retainers.

Can upgrade
 

So if tkos15 and Micmak haven’t found a cam yet and you are looking to stay stock with your motor, Crower Cams has a killer reduced price I just looked up (happen to be a crower fan have used them in most my muscle cars) although I was too late at the machine shop for my 4.3 rebuild a few weeks ago. Anyway cam only price $29.00. 114 degree lobe center grind, duration 240 intake 248 exhaust, lift 386 intake 389 exhaust hydraulic flat tappet cam for enhanced throttle response and low end torque with better gas mileage. Go to crower. com and check it out. You will have buy the other stuff but the other slightly bigger cams are 171.00 and up for cam only

Since you folks know more then me, help me to decide nice camshaft with better torque\hp 1000-5000rpm, but with smooth idle(so i guess no more then 260 duration) i d say most agressive but with smooth idle

Heres what i dug:
Stock 96 n up (L35) 4.3 (vin w)
rocker 1.6(Not sure! could be 1.5 or 1.52)
intake valve lift - 0.444, exhaust valve lift - 0.458
0.470 is max valve lift on the OEM springs and rockers

this all came from a few sources, tryin to determine it also here, in fresh topic