You think they are powerful in a truck, you should see the difference in a 7.4 - 8.1 swap in a boat, night and day difference and a noticeable tick in economy too (if you can really call sub 2 mpg fuel burn economy).
CK5
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L18 8.1L swap resource thread
- Thread starter Larry
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I don’t think this has been discussed in this thread yet, but in regards to the valve covers on the 8.1, I think I remember reading somewhere on the interwebs that the bolt pattern for the valve covers on an 8.1 is slightly different than older 454’s, correct? Something about one of the bolts being off. Any options out there for aftermarket valve cover options?
I think I’m going to covert an extra 8.1 my brother and I have to carb with a Dart carb intake and tall deck HEI (motor already has a raylar 202 cam with a standard rebuild on the motor and ring gap increased to run some nitrous) and I’m going to throw it in a drag truck. Since getting rid of the factory intake will need an oil fill on the valve cover and since it’s a drag truck was hoping to get some nice looking valve covers to spruce up the look. If all else fails I guess I can modify the factory valve covers to add an oil fill port and probably a PCV valve too. But since I won’t need coil pack mounts with the carb conversion, it would be kinda nice to get good looking aftermarket ones…you know, to show off at the drag strip, haha
I think I’m going to covert an extra 8.1 my brother and I have to carb with a Dart carb intake and tall deck HEI (motor already has a raylar 202 cam with a standard rebuild on the motor and ring gap increased to run some nitrous) and I’m going to throw it in a drag truck. Since getting rid of the factory intake will need an oil fill on the valve cover and since it’s a drag truck was hoping to get some nice looking valve covers to spruce up the look. If all else fails I guess I can modify the factory valve covers to add an oil fill port and probably a PCV valve too. But since I won’t need coil pack mounts with the carb conversion, it would be kinda nice to get good looking aftermarket ones…you know, to show off at the drag strip, haha
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I believe older BBC valve covers bolt right on without any modifications as I’ve seen many pictures on the 8.1L Facebook groups where people have done exactly what you’re talking about. If there is any modification to be made it must be pretty minor like drilling and tapping a couple holes, if that. A lot of those guys in the group are adding Dart intakes, HEI dizzys and old school valve covers then drop them into older muscle cars. The 8.1L looks like a pretty legit old school BBC when dressed that way. I've thought about doing the same thing with an extra 8.1L I have to drop into my 68 GMC. It has a bored and whored 396 now but an 8.1 would give it an extra 100 cubic inches from the git go
Go for it!
Same bolt pattern. As standard BBC valve covers. Difference is the 8.1 covers are shallower due to the raised lip on the head. So you can bolt up standard BBC covers to an 8.1 but not the other way around. 8.1 covers are to short to clear the rockers on a regular BBC.
That's where the L21 BBC covers are unique. The L21 was a L29 with LS/8.1 style coil near plug ignition. They look like 8.1 covers with the coil mounts but are deeper to clear the valve train.
That's where the L21 BBC covers are unique. The L21 was a L29 with LS/8.1 style coil near plug ignition. They look like 8.1 covers with the coil mounts but are deeper to clear the valve train.
I believe older BBC valve covers bolt right on without any modifications as I’ve seen many pictures on the 8.1L Facebook groups where people have done exactly what you’re talking about. If there is any modification to be made it must be pretty minor like drilling and tapping a couple holes, if that. A lot of those guys in the group are adding Dart intakes, HEI dizzys and old school valve covers then drop them into older muscle cars. The 8.1L looks like a pretty legit old school BBC when dressed that way. I've thought about doing the same thing with an extra 8.1L I have to drop into my 68 GMC. It has a bored and whored 396 now but an 8.1 would give it an extra 100 cubic inches from the git go
Go for it!
Yeah, I heard of guys saying they just drilled and tapped one bolt on each side and then the old school valve covers bolt up just fine. I think I'll try to go that route. I just think it would be kinda cool and throw people off when they look under the hood and they'll think, "Nice, you got a big block in there", but then get confused seeing the crossover coolant pipe on the front and realize it's not a 454
. Plus, it should run really good with the 202 cam in it already, and if I throw a 100 shot of nitrous at it, it should be pretty legit. I basically want to build a fast street truck that I can take to the drag strip and run hopefully mid 12's N/A, and possible get into high 11's on spray (have no desire to run faster than 11.5 as I don't want to get into the extra safety stuff that goes with that speed). And this 8.1 with the raylar cam in it should get me to that.Thanks Larry!
Ah, gotcha, that makes a lot more sense. I did read a few posts on other forums about guys wanting to convert their older BBC to coil over plug and they were asking if the 8.1 cover would work (then I read the subsequent discussion of the L21 cover).
So sounds like just getting any old BBC valve cover will work. That's great news! Thanks Zoomad75!
so been a while since I started at pg1 and will do soon cuz I gotta find the stock regulator p/n which I recall is listed...
but anyone know where to source the vacuum line on the intake that goes to regulator? mine burned up in the fire...
but anyone know where to source the vacuum line on the intake that goes to regulator? mine burned up in the fire...
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Its just a small piece of bulk vacuum line. I don't recall it being formed or anything
i bought smallest autozone had and it was wrong..
found it..
shaped like drawing.. now it is out of stock...trying to find it somewhere
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Cool. None of my 8.1s came to me with that fancy line that I recall. Bulk hose would be fine. That's what's on mine.
Hi All,
Have a weird one I could sure use some help on -
Vehicle - my 91K5 with the Tilden 8.1l swap
Problem - will not start after fuel sending unit replacement
The fuel level sending unit failed prior to the swap, not registering lower than 1/4 tank and I totally spaced having that replaced during the swap
. I took it to a shop for repair as I have dropped that tank enough over the years for that job to lose all appeal. Well, shop calls me today that the truck will not start. After looking at it they discovered the pump is only getting 6.x volts. They are looking into it and should be able to get it but was wondering if any of you know how this should work - non-started voltage at pump, ideal pump voltage, and if there is multiple signals or voltages from computer for the fuel pump circuit etc.... Any ideas?
Thanks,
Dave
Have a weird one I could sure use some help on -
Vehicle - my 91K5 with the Tilden 8.1l swap
Problem - will not start after fuel sending unit replacement
The fuel level sending unit failed prior to the swap, not registering lower than 1/4 tank and I totally spaced having that replaced during the swap
. I took it to a shop for repair as I have dropped that tank enough over the years for that job to lose all appeal. Well, shop calls me today that the truck will not start. After looking at it they discovered the pump is only getting 6.x volts. They are looking into it and should be able to get it but was wondering if any of you know how this should work - non-started voltage at pump, ideal pump voltage, and if there is multiple signals or voltages from computer for the fuel pump circuit etc.... Any ideas?Thanks,
Dave
It should be getting full battery voltage initially for 3 seconds when the key is first turned on to prime the system.Hi All,
Have a weird one I could sure use some help on -
Vehicle - my 91K5 with the Tilden 8.1l swap
Problem - will not start after fuel sending unit replacement
The fuel level sending unit failed prior to the swap, not registering lower than 1/4 tank and I totally spaced having that replaced during the swap
Thanks,
Dave
If they are checking the key on the engine off after 3 seconds they won't see any voltage. If they have a manual relay or the ability to command the pump on with a scan tool then they can see what can be measured back at the pump.
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So, the truck was actually driven to this shop to have the fuel sending unit replaced because the gauge wouldn’t work and now it won’t start after they replaced it where they claim its only getting 6 volts to the pump? The sudden 6 volt story doesn't make sense if you drove it there. What all did they replace? The fuel pump and sending unit, or just the sending unit and moved the old pump over to the new sending unit?Hi All,
Have a weird one I could sure use some help on -
Vehicle - my 91K5 with the Tilden 8.1l swap
Problem - will not start after fuel sending unit replacement
The fuel level sending unit failed prior to the swap, not registering lower than 1/4 tank and I totally spaced having that replaced during the swap
Thanks,
Dave
Larry,
That is correct. Has me scratching my head also. Jason H from Pac Fab thinks it is the new sendining unit. Monday I will make sure that is on their list or retry the one I drove in with
That is correct. Has me scratching my head also. Jason H from Pac Fab thinks it is the new sendining unit. Monday I will make sure that is on their list or retry the one I drove in with
Only thing changed is sending unit .... tend to be the first thing to start with . Swap old back on it and re test .
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So, they moved the existing pump over to the new sender and the truck ran perfectly fine before? If that’s the case, they need to open it back up and look at the connections where the pump and fuel hoses plugs into the sender. I suppose there could be a defect in the sender where the harness is encased into upper body it but more than likely something with the pump connections to the sender. The 6 volt thing has to be a mistake with their readings somehow. If it drove to them it takes some gull to blame truck wiring when it won't start after they changed a part. Even if this was a loaded sender with a TBI pump (you can buy loaded senders for squarebodies with a TBI pump already on them), it would still run on 12 psi….just not rev up very well. I saw that happen once where I recommended a 87 Spectra Premium sending unit and the person bought a loaded one with a TBI pump hung on it then couldn't get it to rev up. Apparently, they missed the part about the EP381 pump needing to replace the low pressure TBI pump.
Anxious to hear what they eventually figure out
Hi All, some updates -
The shop put in a new sending unit and the rig now starts. But it is not registering to the gauge....
I am keeping it over the break and not thinking about what I do next (back to same shop, new shop, or do it myself). Thank you for the help and Merry XMas y'all!
The shop put in a new sending unit and the rig now starts. But it is not registering to the gauge....
I am keeping it over the break and not thinking about what I do next (back to same shop, new shop, or do it myself). Thank you for the help and Merry XMas y'all!
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They could have missed the ground wire that fastens to the top of the frame near the drivers rear tire when they changed the sending unit again or it just isn’t getting a solid ground. Or, you’ve had an issue with your fuel gauge itself all this time. I’m betting the ground as that one can be easy to miss and finicky to get a good ground once it’s messed with. Pretty much need to clean the frame very well down to bare metal and use a toothed lock washer that bites into the frame as the bolt is tightened. Everyone always looses these things and seldom get replaced. BTW, if the needle is pointing to 3 O'clock, that is a telltale sign of ground issue. What kind of sending units are you buying anyway? Amazon Choice Finest Chinesium?Hi All, some updates -
The shop put in a new sending unit and the rig now starts. But it is not registering to the gauge....
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just bumped into this interesting read on fb.. some may have seen it..
www.drivingline.com
The 8.1L Vortec V8 Was GM's Last-Ever Big Block Engine
The Vortec 8100 represented the final link to Chevrolet's roaring '60s muscle car motors.
www.drivingline.com
