73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: egleaves on June 03, 2015, 11:53:48 am
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Hey all....I'm new here and looking for opinions (or facts if you got 'em) about putting a crate motor in my 74 C-10 Cheyenne.
I've only had the truck a few weeks, so we're still getting to know each other. I pulled my 30' camper a couple of hours down the road for Memorial Day weekend with no issue....except that the rig doesn't care much for hills and the drive home was against an exceptionally strong head wind. I couldn't get it over 50 mph in that wind. It feels to me like I need more torque.
I already know that what I am towing is near the threshold of what the truck is rated for, but it does have beefed up rear springs (RPO 1G50) and I don't tow far/often....yet. I want to spend more time out with the camper, and I want to pull it with this gorgeous truck, so I'm contemplating a torque/HP boost from a crate motor.
One of my big concerns is that I might snap the cam or crank in this 40 year old engine. Or burn up a piston.
My research so far has shown that I'll be lucky to spend anything less than $2K on this operation. I'm always a little wary of the "cheapest" option....I believe you usually get what you pay for .
Is is worth the extra money to spend as much as $3K on the right setup? I'm going camping, not racing.
Is my engine stout enough to simply bolt on some extra torque? I can swap a cam or a head and I can change an intake system, but I'm not equipped or experienced enough to mess with cranks and pistons.
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Welcome from California. Nice truck and trailer! I have a 30 footer myself, no slide outs tho.
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Welcome BTW. If the GCVW is within range it maybe that you need a little lower rear end gear to make it work. You need to access your engines health first to figure out which direction to head. What engine, Trans, and rear end do you currently have? Trailer brakes? Sway control? Weight distributing hitch. LT C rated tires? These are all safety concerns to have.
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If I were in that dilemma I would just find a 6.0 engine
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Welcome BTW. If the GCVW is within range it maybe that you need a little lower rear end gear to make it work. You need to access your engines health first to figure out which direction to head. What engine, Trans, and rear end do you currently have? Trailer brakes? Sway control? Weight distributing hitch. LT C rated tires? These are all safety concerns to have.
This
Can't offer much help without knowing what you're starting with
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Basic stats are in my sig, but I'll rehash and expand.
350 ci
TH400 3 speed auto (unconfirmed)
3.73 rear end (unconfirmed, but pretty sure)
Accelerometer based progressive brake controller
Electric trailer brakes
Weight distributing hitch with sway control
I'd have to check on the tire rating, but they are brand new
Towing stability has been excellent...even in high wind. I just need some more oomph.
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Basic stats are in my sig, but I'll rehash and expand.
350 ci
TH400 3 speed auto (unconfirmed)
3.73 rear end (unconfirmed, but pretty sure)
Accelerometer based progressive brake controller
Electric trailer brakes
Weight distributing hitch with sway control
I'd have to check on the tire rating, but they are brand new
Towing stability has been excellent...even in high wind. I just need some more oomph.
If you are having trouble with that setup, you either have timing issues, a wrong cam choice by previous owner, or your engine is real tired. In stock form you should have zero problem pulling that trailer IMO. I would start by confirming your rear end gear. A 2.56 or 2.76 gear would be a dog but a 3.73 should have no issues at all
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I've been a bit suspicious of the timing, but haven't had an opportunity to check it.
....forgot to mention the GVWR of the trailer is 6900 lbs. Truck weighs 5000 lbs with a full tank of gas and two meat sacks up front (just had it on a scale this morning).
When looking for towing capacity I found this chart (see image), but it's for the second gen trucks. Would these numbers still be the same for third gen? According to this chart I should only be hauling 4500 lbs with the truck. This math is not working out in my favor.
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Whoops....I hit the post button before I attached the image. :P
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From your description, it sounds like it's an original '74. Does the engine still have the points distributor?
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From your description, it sounds like it's an original '74. Does the engine still have the points distributor?
Not sure, but I can check on that tonight. Think I might just need new points, or better yet, an EI conversion?
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Not sure, but I can check on that tonight. Think I might just need new points, or better yet, an EI conversion?
If it still has a points distributor, upgrading to HEI would be a good thing.
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Confirm the axle ratio
A lot of trucks had 2.73
Have the compression and timing checked
It should pull ok unless you have low compression from a worn out engine
Make sure you have a very large high quality auxiliary transmission cooler and maybe a trans temp gauge in the pan
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Here might be some comparison info. I inherited my grandpa’s ’74 k20 that he bought new (stock 350/th350/4:10 gearing). Still had the original untouched motor. It REALLY sucked with very low towing power (drank a LOT of fuel also as I had to keep my foot into the QJ). It still ran real smooth and quiet for 155k miles and didn’t even burn oil, but it felt tired. My 2000 Honda Passport 205 V6 (195k miles) towed nicer than the big truck power wise. I was soooooo slow up hills pulling a simple quad trailer. Original points distributor and probably worn out carb on original intake and exhaust manifolds to dual exhaust, th350 trans. Basically all stock except for the small dia dual exhaust. I never fine-tuned the motor, as goal was to replace anyway.
So I pulled the smooth running tired weak HP motor out last year and replaced with a fresh mild built sb400 that ended up only lasting 1 week (shop installed wrong pistons and WAY too high of CR). Instead of re-installing the original motor back in, I had a low mile 260hp crate motor sitting in my garage. The crate motor has a mild summit CAR type cam, edelbrock performer intake, HEI, and the new sb400 intended QJ carb from SMI (bit to big). Also now has long tube headers and larger dia dual exhaust.
Yea long story – whoops. Point being, I’m NOT really that impressed with the 260hp crate performance in the heavy truck, as it’s currently set up. But that’s the problem…..I’ve got a mild low tech CAR type cam as I planned on putting this motor in the wife’s ’68 Camaro as a mild/dependable driver – NOT intended for a heavy 4x4 truck. However this motor still does MUCH better than the original motor once I get some RPM’s up a little higher. My new replacement SB400 is about done, so the crate motor will be coming back out. If for some reason this motor ends up back in the truck, I WILL BE installing a low grunt Comp Cam.
74k20
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The Gear ratio should be on your SPID sticker.
Gearing is really the key here. i tried towing a chevette and open 16' car trailer with 2.56 gears. You can't.
Truck really struggled up hills and had difficulty maintaining 65mph.
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The Gear ratio should be on your SPID sticker.
Gearing is really the key here. i tried towing a chevette and open 16' car trailer with 2.56 gears. You can't.
Truck really struggled up hills and had difficulty maintaining 65mph.
the ratio it left the factory with will be on the glove box if the glove box is still here and hasn't been swapped and the axle hasn't been swapped at some point
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I've been searching for the axle code to no avail. It seems like everywhere is should be, it's not. I did the "spin the wheel and count the driveshaft rotations" check, but the math is rough. I still want to verify the ratio with some certainty. If I can't find a code, I'm just going to have to pull the diff cover.
Here's my SPID sticker. Does anyone see something I'm missing here?
BTW....I appreciate all of the responses and comments I'm getting here. It's been a big help. Thanks.
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By the shape of the pan, I was able to verify today that I have a TH350, not a 400 as i had previously thought.
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Ok, i guess not all SPID stickers have them.
Another thing you can do is bring your VIN# to a dealer and they can look up exactly what gear ratio you got. 3.07 was standard for your combo. With 3.40, 3.73 and 4.11 optional.
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Assuming It hasn't been swapped at some point in t
he last 40 years
Only way to know for sure is remove the cover and count. Teeth or see if the number is cast into the gears
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How to determine what ratio you have without removing the cover (http://forum.73-87chevytrucks.com/smforum/index.php?topic=30546.0)
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i would bet money it hasn't been swapped.
Since the SPID sticker did not indicate any axle options, then i'm going with 3.07.
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Ok. It's been a while since I brought up this discussion, but now it's real.
I went ahead and had a local GM dealer install a turn key, Vortec 350 crate engine (PN 19210009). I'll try to get some pics posted. I had this done back in September, drove it a couple thousand miles, and then started towing the camper. Keep in mind that every component of this engine is NEW, not rebuilt.
Pulling the camper over the mountains of WV was a challenge. I almost burned up the trans, but the engine ran well enough. I'm now 7 weeks and almost 4000 miles into my cross-country adventure and she's developed a bad stutter under load. With or without the camper, but it's most obvious with.
Here's what I know, and what I think.
The only thing I have done to this engine since it was installed is minor adjustments to the base timing. I don't know exactly where it is since I've been timing it by ear for a couple of weeks. Probably 6-8 BTDC.
The stutter is very pronounced on a hill, in third gear (3spd auto), pulling the camper. Kicking it down into second clears the stutter and pulls fine. If it shifts before the top of the hill, the stutter is right where i left it.
Even without the camper I might pull out into traffic with my foot in it, but I get a hesitation and/or backfire before it springs to life. Once it comes to life it runs like a scalded dog.
Once in a while, under light acceleration, I can feel the stutter quit and the engine comes to life. Briefly. This is leading me to a few possibilities. The cap and/or rotor are shot and I'm just not getting good spark, my vacuum advance isn't working correctly, or I've blown the power valve. Or a combination of any of those. Also, the vacuum advance is connected to a port on the carb. I've read that it would be better to connect it directly to manifold vacuum, but that means I will have to install a port on the manifold.
I don't think it's fuel issue....if I had a fuel delivery problem it still wouldn't run well in second gear at 4000+ RPM. It seems to get plenty of fuel, but can't use it all at certain times. Overall fuel milage doesn't seem to be affected so you'd notice.
My next move is to pull the cap and rotor to see what they look like. If that looks good, i'm going to switch my vacuum advance to a manifold source. Any other ideas?
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Basic tune up first
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one thing you might find is the gas switched from a summers blend to winter. i dont know what you might or might not have to do or even if it can cause your problems but its another option
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Pull and check the spark plugs. Wrong heat range and timing could cause premature failure.
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http://www.gmperformancemotor.com/parts/19210009.html
Are you running the 92 octane gas? Looks like a great engine, but for towing it could probably use an RV cam. Really to bad they didn't use a roller cam.
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I always run high octane gas. I asked when I bought it if I could choose a different cam, but the engine was already built and there weren't options to choose from.
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can you hear any ping or is it just a hesitation?
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Just a hesitation that sometimes feels like a dropped cylinder or bad timing. I had a slight knock a while back after advancing the base timing a bit. Dialed it back a little and it went away as expected. These are the timing adjustments I have been doing "by ear".
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I was going through the paperwork turned over to me by the dealer and found a specifications guide with the following excerpt:
"Set spark timing a 32 degrees BTDC @4000 rpm with the vacuum advance line to the distributor disconnected and plugged...(some other stuff).....This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve."
Does this sound like a good idea? Have I been losing power by having the vacuum advance connected? The dealer connected the vacuum advance module to a port on the carb. Today, I capped off both ends to see if there's a difference. We just set up camp today, so I'll be driving around for a few days without the camper.
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the vacuum advance should only be unplugged while setting it. if youre driving it it should be plugged into ported or manifold vacuum. im going to suggest manifold vacuum but this in my opinion wont fix youre problem
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Maybe your jetting is wrong for the elevation your at? It's possible the float might need adjusting. This is a stretch but, what about vapor lock? Where are your fuel lines routed. When you drop into 2nd and stand on it, you're using a higher volume of fuel and working the pump faster. If your starting to vapor lock, maybe that's flowing enough fuel to stop it for a while?
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You said backfire. Exhaust or intake? If you are at a higher alt than normal carb could be going lean at light to cruise throttle causing stumble or surging.
Vac can on dist blown would cause lack of power but shouldn't cause a stumble like you have.
74 points still?
Carb Quadrajet?
Mechanical advance is all part of the timing. Base+mechanical+ vac advance.
32 & 4k might be a tad low but don't think it's your trouble.
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I found at least part of my problem. The cap and rotor were toasted! A lot of the button was missing and some of the metal had actually transferred to the rotor tang. A hole was melted through the cap large enough that the button (what was left, anyway) fell out when I lifted the cap. See pics attached.
Installed new cap & rotor yesterday. Going to check and probably change the plugs today. I'm doing some research on the correct heat range for my application.
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Now that I'm somewhere i can post pics, here's what we're talking about.
Edit: I have no idea why the pics all posted upside down. :o
Edit: Image orientation corrected - Admin
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I changed the plugs today and went with a slightly cooler plug. The ones I took out didn't look bad....nice light brown color, but when I grabbed the boot on the #5 plug part of it disintegrated in my hand. This boot was cooked also and must have been arcing to the exhaust manifold. At times, I could swear I heard an arc, but could never find it. Found it!
I went with cooler plugs in an attempt to reduce the overall resistance in the ignition system hoping to avoid future meltdowns. I didn't bother checking the plug wire resistance because they're new, but I probably should anyway.
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What plug? R44TSL?
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What plug? R44TSL?
MR44LTS is what was in it. I cross referenced MR43LTS to get the NKG equivalent. I forget the NKG number.
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(http://img.photobucket.com/albums/v189/ironroad9c1/74%20info_zps1cqmlurv.png) (http://smg.photobucket.com/user/ironroad9c1/media/74%20info_zps1cqmlurv.png.html) load on the truck shouldnt be over 3,740 , you can see these truck got 3.07 rear gear unless the optional ratio was selected.
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Sorry, screwed up the suffix. I just wanted to make sure you had the right length plug. Your vortec heads take longer threads, 3/4" I think, than your old heads with 1/2" long threads. I believe the lts means it's the long plug, and the short would be a ts. NGK's are my favorite.
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It's running much better since I replaced all of the components that melted. Tomorrow is moving day again....we'll see how things go with the camper in tow.
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Sorry, screwed up the suffix. I just wanted to make sure you had the right length plug. Your vortec heads take longer threads, 3/4" I think, than your old heads with 1/2" long threads. I believe the lts means it's the long plug, and the short would be a ts. NGK's are my favorite.
Hah! And I screwed up, too! NGK is correct. :P
I did a side by side comparison before buying them to make sure the length was correct. It all looks good.
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(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=31086.0;attach=31730)
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=31086.0;attach=31721)
It's astonishing that the vehicle ran as well as it did, isn't it? I've seen that occur a few times over the years.
I recommend that you replace the ignition coil, as well. Once a spark begins jumping the wide gap between the coil center terminal and rotor contact for an extended period, the coil secondary insulation is often compromised by heat, excess voltage and carbon tracking. Eventually the dielectric breaks down and 30+kv punches a hole through the coil insulation to the grounded coil frame or flashes internally to neighboring windings.
Do the spark plug wires have 90° boots at both ends? The distributor boots generally are not the same material as the spark plug boots and will not cope with exhaust heat as well. Make sure the wires were not installed backwards, end-for-end. Additionally, smear a light coat of dielectric grease (e.g., GM 12345579, Permatex 81150, Loctite 37534, etc) on both metal terminal ends of every spark plug wire and inside the boots at the spark plug ends.
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bd, interesting point on the coil....it looked fine, but that sounds internal. Sounds like a good excuse to get an MSD coil. ;D
I am quite surprised it ran very well at all.
The wires are 90 degree on both ends. I noticed the markings on the replacement wire I bought indicating which end was which, but the other wires don't have them, however, one boot is noticeably thicker than the other. I want to assume the thicker boot is meant to be next to the exhaust, and in this case that's how it was installed. The material looks and feels the same, but there is lettering that says "DEED 13" on the thicker end and "DEED 22" on the other.
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She ran like a dream today and pulled the camper, no problem. I had a tiny bit of knock while running flat out on the highway....retarded the timing just a bit and nothing since.
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Thicker boot usually has a kinda mushroomed end that goes on the cap, HEIs use to have a cap that clipped on top of the wires to hold em on.