[4n6mal]

My son and I are restoring a '72 C20 350 w/4-bolt mains I bought from my uncle in Texas. The engine only has 89,000 miles, but has sat for 15 years. Our goal is to make it a good looking Street truck. Since the gas mpg sucked back when i use to drive it, we thought we would do some easy but moderate improvements under the hood.

We have pulled the engine and tranny for easier access. I did have some small leakage, so we replaced the rear main seal, new timing chain and sprockets, dampener, oil pump/screen, replaced distributor w/ new HEI. Cleaned the block and repainted. Had a new Black Edelbrock EPS Performer I had picked up a couple of years ago. Looking to replace the Quadajet with a FI Tech - Go Street EFI.

Friend stopped by and liked what we had done so far and asked what kind of cam did we use? Since the engine only had 89K, I wasn't thinking of digging that deep into the engine, but he was saying that there are better aftermarket cams vs that original one and we might think about a cam swap since the engine is on a stand. He couldn't recommend which one for my setup since he is a Ford guy. But before I install the Intake, what does the forum suggest for good mpg and overall torque? Is it worth the $$'s or stay with the stock cam?

Kind Regards,

Mike and Philip

 

[jokerZ71]

Would need some more info to give a good recommendation.Do you know for sure the motor is original & never been rebuilt? If it is, you most likely have compression ratio of approx 8:1, so, you would need to stay pretty small on cam choice.Along the lines of an RV type cam.Something like 205* intake [email protected] .050".You will also need to use new springs & choose a cam that doesn't have more lift than your heads have clearance for to avoid head work.Do you know the casting # of the heads?

 

[4n6mal]

Stock Cam vs Aftermarket ????

Thanks for the reply jokerZ71,

Yes it is original and not rebuilt. I bought it in 1977 w/ 46K on it and put a camper on it but had to put it in storage about 15 or so yrs ago when I moved because city would not allow me to park it in front of the house.

About 25 years ago I swapped out the TH350 for a TH400.

Because my son and I promised the wifey we would not go crazy on $$ on the restore and make it a project that she could drive I didn't go into a major overhaul by replacing the heads and lower end, so we could do a good paint job on it.
Block SN#V122TPJ / 3970010

 

[4n6mal]

Opps, gave you block numbers that I had taken on my phone.
Where would I find the head Case #?

 

[4n6mal]

Thanks for the reply jokerZ71,

Yes it is original and not rebuilt. I bought it in 1977 w/ 46K on it and put a camper on it but had to put it in storage about 15 or so yrs ago when I moved because city would not allow me to park it in front of the house.

About 25 years ago I swapped out the TH350 for a TH400.

Because my son and I promised the wifey we would not go crazy on $$ on the restore and make it a project that she could drive I didn't go into a major overhaul by replacing the heads and lower end, so we could do a good paint job on it.
Block SN#V122TPJ / 3970010.

Where would I find Head Case number?

 

[johnsongrass1]

Under the Valve Cover between the rockers.

 

[4n6mal]

Thanks, I will check that out tonight when I get home.

 

[JeffB]

This is a good all around cam that has been suggested on this forum a lot,good torque for a truck and mileage friendly and EZ on the wallet to make Mama happy. https://www.summitracing.com/parts/sum-k1102/overview/ Good Carb for your intake and also good for MPG is this: https://www.summitracing.com/parts/sum-m08600vs/overview/

 

[BuzzLOL]

The 204/214 durations performance truck cams for stock engines mentioned above (and below) are good cams, but bigger than the 194/202 cam you have and will make the MPG problem even worse... The problem is in 1970's, Chevy dropped to early 1950's static compression ratios of high 7's:1, but kept the bigger 1960's cam sizes used for 8.5 - 10:1 compression ratios to keep HP ratings from dropping back so low again... for advertising/competitive reasons... One way for more MPG is going to the heavy truck smaller 184/194 torque cam which will raise the dynamic compression ratio and MPG, but will lower your already tepid HP/RPMs... or maybe Comp Cams has a special truck flat tappet cam with more lift at those same low durations numbers to retain HP... Or could go roller lifters/cam at short durations, but higher lift, like GM did to cure the problem in the 1996 - 2002 Vortec truck engines along with higher compression ratio giving much better MPG and even a boost in power from your current level... but that roller cam setup would cost nearly a $1,000 minimum to do in your engine...

Other solutions:

Change to flat top pistons for a boost in compression ratio to around 9-9.5:1...

https://www.summitracing.com/parts/sum-17350-00/overview/make/chevrolet

Chevy SBC 350 Flat Top Pistons Moly Rings Kit 030 355 | eBay

Swap Vortec heads on for ~8.5:1...

Swap in a new ($2100) or used Vortec engine (9.1:1 and short durations roller lifters/cam)...

Remember, the gas savings will eventually pay for the parts if still driven enough...

The swap from well-tuned Q-Jet carb. to EFI will be expensive and not make a noticeable difference in MPG... the newer engines get vastly better MPG and HP mainly because of internal improvements to the engines as I outlined above... 11:1 compression ratio with aluminum heads is common now... direct extremely high pressure gas injection like a diesel uses is also the top MPG getter now...

Your truck prolly gets about 7 - 9 MPG city and 9 -11 MPG hiway... new trucks are more like 17 city and 23 hiway... simple improvements can prolly get you up to 15 city and 20 hiway... The Q-Jet was the best MPG carb. ever... and can also support a 400+ HP engine...
.

 

[GMC boogie]

Here is another nice camshaft that will fit the application. I have always been really pleased with Isky cams.

https://www.summitracing.com/parts/isk-201256-262/overview/make/chevrolet

I am partial to GM lifters also

https://www.summitracing.com/parts/nal-12371044/overview/

Stick with a camshaft in the 194º-204º intake duration at .050 on a 108-110 LSA.

 

[4n6mal]

The head casing i have is 3986339

 

[327NUT]

Just curious....89 thou and then it sat for 15 years, when you pulled the pan to check the bearings and at least install a new oil pump how did everything look?

 

[4n6mal]

Just curious....89 thou and then it sat for 15 years, when you pulled the pan to check the bearings and at least install a new oil pump how did everything look?

This is the first time I have pulled a pan to take a close look but in my opinion it didn't look bad. The oil was dark when it was drained. All the galleries and passages were clear, no sludge found, just a dark film that would wipe off. Since I had a small evidence of oil weepage from the rear main seal, I decided to replace it and while I was at it, also the oil pump. The inside of the pump had no sludge build up. The only bearing I visually looked at was the rear bearing when I replaced the rear seal. The bearing surface looked clean without any visible scratched so I am making an assumption that the other bearings are the same. The oil ports were clean and clear of any debris.

 

[4n6mal]

The 204/214 durations performance truck cams for stock engines mentioned above (and below) are good cams, but bigger than the 194/202 cam you have and will make the MPG problem even worse... The problem is in 1970's, Chevy dropped to early 1950's static compression ratios of high 7's:1, but kept the bigger 1960's cam sizes used for 8.5 - 10:1 compression ratios to keep HP ratings from dropping back so low again... for advertising/competitive reasons... One way for more MPG is going to the heavy truck smaller 184/194 torque cam which will raise the dynamic compression ratio and MPG, but will lower your already tepid HP/RPMs... or maybe Comp Cams has a special truck flat tappet cam with more lift at those same low durations numbers to retain HP... Or could go roller lifters/cam at short durations, but higher lift, like GM did to cure the problem in the 1996 - 2002 Vortec truck engines along with higher compression ratio giving much better MPG and even a boost in power from your current level... but that roller cam setup would cost nearly a $1,000 minimum to do in your engine...

Other solutions:

Change to flat top pistons for a boost in compression ratio to around 9-9.5:1...

https://www.summitracing.com/parts/sum-17350-00/overview/make/chevrolet

Chevy SBC 350 Flat Top Pistons Moly Rings Kit 030 355 | eBay

Swap Vortec heads on for ~8.5:1...

Swap in a new ($2100) or used Vortec engine (9.1:1 and short durations roller lifters/cam)...

Remember, the gas savings will eventually pay for the parts if still driven enough...

The swap from well-tuned Q-Jet carb. to EFI will be expensive and not make a noticeable difference in MPG... the newer engines get vastly better MPG and HP mainly because of internal improvements to the engines as I outlined above... 11:1 compression ratio with aluminum heads is common now... direct extremely high pressure gas injection like a diesel uses is also the top MPG getter now...

Your truck prolly gets about 7 - 9 MPG city and 9 -11 MPG hiway... new trucks are more like 17 city and 23 hiway... simple improvements can prolly get you up to 15 city and 20 hiway... The Q-Jet was the best MPG carb. ever... and can also support a 400+ HP engine...
.

Thanks for the very informative reply. I was surprise to here you that the Quadajet was a very good mpg carb.

You were right on regarding my mileage, 10mpg with an 11ft cabover camper and @ 11-12 w/o the camper. I had forgot to mention that I had removed the stock exhaust manifold and install a set for Doug Thorley headers that had given me noticeable improved power when I drove with the camper.

Replacing the heads would be great but an extra $1k-$1.2K would put me way over my budget and Mama would not be happy with that extra cost, but @ $200 for a cam and lifters would work if I saw a modest improvement in performance and mpg.

I going to have to rethink the EFI vs Carb. I have a contact with FI Tech EFI, Riverside, CA and have read and heard a lot of good thinks about their product. A complete system @ $700 including EFI, pump, ECU and handheld programmer. Just about turn-key. But I am going to take your comments into consideration since that will be that last item on the engine to install. I'll have to check out rebuilding the Quad or one of the other suggested carbs from previous posts. Luckily for me the FI Tech Facility is just 30 mins away and are very open answering questions on performance of their products.

I guess I now need to determine the right cam to choose.

Thanks for your feedback

 

[RWENUTS]

Info I get from reading between the lines in your posts tells me you should just leave the motor alone. Run what ya brung sorta thing. And the 'boss' (aka the wife) needs to drive it with no problems.
Rebuild the quadrajet or get Sean Murphy to build one for you. He's also just down the road from you. Excellent carbs.
https://www.smicarburetor.com/

 

[jokerZ71]

The #339 heads are small valve heads(1.72/1.5), so, you may not see a big improvement. A good budget choice for you would be a set of later model (87/95) #193 swirl port heads.These heads can easily be found cheap.They were used on the 87/95 tbi equipped trucks.They are not by any means a performance head.They are designed for good low rpm torque & great milage below 4500 rpm.Combined with a modern profiled cam, they work pretty well in your situation.
I also think the FI Tech system is a great idea.You will see some milage gains & alot of other benefits over your current carb setup.

 

[BuzzLOL]

I had forgot to mention that I had removed the stock exhaust manifold and install a set for Doug Thorley headers that had given me noticeable improved power when I drove with the camper.

Replacing the heads would be great but an extra $1k-$1.2K would put me way over my budget and Mama would not be happy with that extra cost, but @ $200 for a cam and lifters would work if I saw a modest improvement in performance and mpg.

I going to have to rethink the EFI vs Carb.

Yes, the engine you have is about 225 grossHP... stock iron manifolds/single exhaust knocks that down to about 175 HP or lower... headers and dual exhaust brings that back up to about 225 HP again... so a noticeable difference... as is usually said, (budget)headers give about the most power per dollar spent...

My old '86 Monte Carlo 305" V8 Q-Jet carb. was rated 17 MPG city and 25 MPG hiway... 10 years later a new mustang with 302" V8 and EFI had the exact same ratings... so that tells you the 'magic' of EFI...

A smaller cam would prolly get you 1 or 2 more MPG... but, as I mentioned above, NO "performance" increase, a drop in HP... but prolly a little increase in off idle and lower RPMs torque which would help cruising a camper... Depends on what your plans are for the truck...

Lowest cost option giving the biggest boost in MPG and also more power would be swap pistons... and keep cam, intake, carb... (inspect the cam closely to make sure no wiped out lobes)... that gives about 275 HP...

Domed pistons (not linked above), mild performance cam, and high rise intake manifold (trucks usually have room) can give around 325 - 375 HP with still much better MPG... the higher number assuming your stock heads have the car/light truck valves (1.94"/1.5") and not the smaller heavy truck (1.84"/1.44") valves and smaller ports... Like I said, depends on your plans for the truck...
.

 

[jokerZ71]

In a comparison of a carb vs EFI, with a perfectly tuned carb & motor, EFI milage would similar, but, in the real world, that very seldom the case.The EFI offers alot more benefits.Better, quicker starts, especially in cold weather without running excessively rich & washing the cylinders until warmed up.Better throttle response.Better fuel atomization. Self adjusting for weather/altitude changes.The FI Tech system is very affordable & an easy install.Unless you go too big on the cam, you will see some milage gains over the stock cam you have now.

 

[BuzzLOL]

The #339 heads are small valve heads(1.72/1.5), so, you may not see a big improvement. A good budget choice for you would be a set of later model (87/95) #193 swirl port heads.

OK, I hadn't seen Eric's posting when I posted the above... the HP numbers are going to be quite a bit lower than what I posted above and these heads are prolly going to be limited to about a 200 HP max build no matter what you do...

However, changing pistons can still give a good bump up in MPG since they are still big chamber heads giving too low compression ratio...

Too bad you aren't closer to this member who just inherited a brand new Vortec 350" engine... don't know if he has any plans for it or wants it:

http://www.hotrodders.com/forum/motor-448730.html
.

 

[techinspector1]

Info I get from reading between the lines in your posts tells me you should just leave the motor alone. Run what ya brung sorta thing. And the 'boss' (aka the wife) needs to drive it with no problems.
Rebuild the quadrajet or get Sean Murphy to build one for you. He's also just down the road from you. Excellent carbs.
https://www.smicarburetor.com/

This is excellent advice. It's what I was thinking too.