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Old 01-04-2017, 11:46 AM   #1
BrianG
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Lets talk Small Block

So, I'm trying to either embrace or resist a motor change in my truck. A quick history on the truck is. I bought it somewhat restored 25 years ago or so. It had a new or rebuilt one piece rear main seal 350 in it. It is a short bed 4x4 with 33's and 373 gears (those won't change) and a 350 turbo transmission. I drove the truck for about ten years and then sold it when I got married. Then ten years later, my wife tracked it down and we bought it back as a 10 year wedding anniversary present. During the time that the previous owner had it. He rebuilt the engine (recently). He was friends with a guy who drag races. They had the blocked checked and the bore was good, straight, and didn't need boring. They put higher compression pistons in it, different cast iron heads by World Products, a cam (of unknows specs) Holley intake and carb. The only thing I did to it was change from the 750 double pumper he had on it to a 670 Street Avenger. He went on about how great the motor was and who built it. When I drove it home it really ran great and had good power, so I decided not to touch it. The truck was so rough though at this time, and I was so happy to get my truck back, that I probably wasn't really judging thing correctly.

So getting caught up to current. Last year, I finally finished the truck (I know they are never really finished, but I could now drive it). The motor seems just okay. It has decent power, idles like a hopped up Harley (sounds cool), but is very low on vacuum. My power brakes are horrible. I've done everything seemingly possible to tune it to give me the best vacuum I can get but if memory serves me correctly it is only around 10 inches of vacuum at idle.

So.... I'm debating either swapping the motor for a 383 stroker or doing something with the one I have now. I'm sure I need torque at low rpm more than I need horsepower at high rpm. I've always wanted a stroker, but the prices are kind of scaring me. I really like this GM crate stroker http://www.chevrolet.com/performance...nes/sp383.html
but it is around $7000. I thought about a Blue Print motor like this from Summit, https://www.summitracing.com/parts/m...3ct1/overview/
but I hear bad things about Blue Print.

I suppose I could send my block and have it prepped for one, but would rather not do a complete rebuild.

Other options would be to just recam my 350 but I don't really know which to go with. How big can I go and still have decent power brakes? What kind of power could I expect to be able to get from a 350. I've read that my heads are decent heads, but nothing really spectacular. Supposedly comparable to the old GM camel hump heads. My luck with junk yards is not good, so if replacing the heads is essential then I'd look for something available new and they would have to be compatible with my headers that are new Headman Longtube.

I definitely will be staying with a small block. Nothing against the LS swaps, I know those motors make awesome power, but I'm sticking with a small block in this truck. I feel like my best options are between a new cam and possibly new heads, or swapping in a 383.

I think it all comes down to will I be happy with a 350 if I go with the right cam or should I hold off for the 383. I'd love to hear some feedback on this. Remember though.... this is a 4x4 with 33's and 373 gears. I assume what works great for a lowered 2 wheel drive will not necessarily work great for me. So, I'd especially like to hear from anyone who has put together a power plant for a similar truck. Thanks for reading such a LONGGGGG post.
Brian
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Old 01-04-2017, 12:08 PM   #2
James the III
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Re: Lets talk Small Block

Why not get a vacuum pump off a late model car /truck and add that, so your p/b work correctly.. instead of replacing the engine..
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Old 01-04-2017, 12:30 PM   #3
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Re: Lets talk Small Block

My opinion, FWIW, you will really like the GMPP engine you picked. Stay away from blue print. Sounds like your current engine is over cammed. A cam change may get you right where you want to be. Without knowing what cam you have we're just guessing. I would start by swapping cams, if I'm still not happy, throw in the GM crate motor!
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Old 01-04-2017, 12:45 PM   #4
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Re: Lets talk Small Block

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Originally Posted by B. W. View Post
My opinion, FWIW, you will really like the GMPP engine you picked. Stay away from blue print. Sounds like your current engine is over cammed. A cam change may get you right where you want to be. Without knowing what cam you have we're just guessing. I would start by swapping cams, if I'm still not happy, throw in the GM crate motor!
Thanks for the reply. I agree, I also believe that I am over cammed. the motor just keeps making more and more power the higher you let it rev. But it's not a race car, so that's not really ideal for a 4x4. It used to be strictly an off road vehicle, so, maybe that worked great for him. Now its pretty much a road vehicle. If money were no object, I would for sure get the GM 383. I guess, I'm sort of hoping that someone will chime in and say.. hey, I have the same setup as you and went with this cam and these heads and it made really good power.

Just curious do you have that GM383, or know of someone who does?
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Old 01-04-2017, 02:23 PM   #5
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Re: Lets talk Small Block

Only thing that motor will do is lighten your wallet a bunch.
And likely not perform any better down low where you need it.
And likely not produce any more vacuum for your booster.
You something milder than can be swapped easily and be upgraded in the cam selection later if you need it.
Your tire/gear combo needs a low rpm grunt motor.
This will fit the bill.
http://www.jegs.com/i/Chevrolet+Perf...30283/10002/-1

Or this.
http://www.jegs.com/i/Chevrolet-Perf...30282/10002/-1

And only 5 grand cheaper.
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Old 01-04-2017, 03:22 PM   #6
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Re: Lets talk Small Block

Not to insult your intelligence or anything, but have you checked how the booster is plumbed for vacuum? On my truck, I currently have both the pcv and booster pulling vacuum from the port on my fuel injection and the brakes are horrible at low rpm. If I cap the pcv and just run the booster they are great. I am waiting on a fitting to correct this issue on mine so they wont be tied together with a "t" anymore.

Just making sure you have covered all of your bases.

Another idea for a motor is a gmpp 350 ho. That's what I am running and it works great in my truck. Plenty of low end power and they are a decent price.
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Old 01-04-2017, 03:28 PM   #7
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Re: Lets talk Small Block

Quote:
Originally Posted by geezer#99 View Post
Only thing that motor will do is lighten your wallet a bunch.
And likely not perform any better down low where you need it.
And likely not produce any more vacuum for your booster.
You something milder than can be swapped easily and be upgraded in the cam selection later if you need it.
Your tire/gear combo needs a low rpm grunt motor.
This will fit the bill.
http://www.jegs.com/i/Chevrolet+Perf...30283/10002/-1

Or this.
http://www.jegs.com/i/Chevrolet-Perf...30282/10002/-1

And only 5 grand cheaper.
Excellent choices , the l31 is a great engine
Ill add this gm engine with excellent low end torque ,would be my choice for a big tire truck like yours , http://www.jegs.com/i/Chevrolet-Perf...32529/10002/-1
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Old 01-04-2017, 03:39 PM   #8
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Re: Lets talk Small Block

Do you know how much compression your motor has? I ask because I've seen people but big cams in motors in order to bleed off compression and keep them on pump gas. Might be something to check before doing a cam swap.
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Old 01-04-2017, 03:53 PM   #9
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Re: Lets talk Small Block

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Originally Posted by Camaroguy View Post
Not to insult your intelligence or anything, but have you checked how the booster is plumbed for vacuum? On my truck, I currently have both the pcv and booster pulling vacuum from the port on my fuel injection and the brakes are horrible at low rpm. If I cap the pcv and just run the booster they are great. I am waiting on a fitting to correct this issue on mine so they wont be tied together with a "t" anymore.

Just making sure you have covered all of your bases.

Another idea for a motor is a gmpp 350 ho. That's what I am running and it works great in my truck. Plenty of low end power and they are a decent price.
That is a good question. I have tried a few different things with the PCV. From everything I read, it's pretty much a necessity. I have tried manifold vacuum and the port on the bottom of my Carb, which is also essentially manifold vacuum. No real difference since they were both manifold vacuum. The PCV does eat quite a lot of the vacuum. I switched to the PCV from a 302 Camaro since that was supposedly a low vacuum engine. It didn't really make that much difference if any
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Old 01-04-2017, 03:56 PM   #10
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Re: Lets talk Small Block

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That is a good question. I have tried a few different things with the PCV. From everything I read, it's pretty much a necessity. I have tried manifold vacuum and the port on the bottom of my Carb, which is also essentially manifold vacuum. No real difference since they were both manifold vacuum. The PCV does eat quite a lot of the vacuum. I switched to the PCV from a 302 Camaro since that was supposedly a low vacuum engine. It didn't really make that much difference if any
Sounds like you're on top of it then. Good luck on your choices.
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Old 01-04-2017, 03:58 PM   #11
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Re: Lets talk Small Block

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Do you know how much compression your motor has? I ask because I've seen people but big cams in motors in order to bleed off compression and keep them on pump gas. Might be something to check before doing a cam swap.
I don't personally know or have a tool to check. I don't know what the chamber size is or the thickness of the head gasket or the piston to deck height neither, so I have no way to figure it out. The guy who I bought it from said 10 or 10.5 I believe. I don't think he really knew for sure though. He said that he was told by the engine builder to run it on 94 octane or mix in some race gas. I run the highest I can find which is usually 93. I don't get any spark knock what so ever. Timing seems to like a lot of advance.
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Old 01-04-2017, 04:07 PM   #12
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Re: Lets talk Small Block

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Excellent choices , the l31 is a great engine
Ill add this gm engine with excellent low end torque ,would be my choice for a big tire truck like yours , http://www.jegs.com/i/Chevrolet-Perf...32529/10002/-1
I had considered that 383 from GM except I was looking for something with a little more compression I guess. It seems like the two they offer are on the complete opposite ends of the spectrum. A basically stockish replacement that runs on pump gas (boring) or the ultimate high performance unit.

I wonder if the compression could be raised on that motor by changing out the head gaskets... but that seems silly on an assembled engine.
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Old 01-04-2017, 04:11 PM   #13
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Re: Lets talk Small Block

Quote:
Originally Posted by geezer#99 View Post
Only thing that motor will do is lighten your wallet a bunch.
And likely not perform any better down low where you need it.
And likely not produce any more vacuum for your booster.
You something milder than can be swapped easily and be upgraded in the cam selection later if you need it.
Your tire/gear combo needs a low rpm grunt motor.
This will fit the bill.
http://www.jegs.com/i/Chevrolet+Perf...30283/10002/-1

Or this.
http://www.jegs.com/i/Chevrolet-Perf...30282/10002/-1

And only 5 grand cheaper.
Those will not work because they are made for fuel injected vehicles. They won't run a fuel pump. I definitely like the price though. Still a 350 though, and I have that. I'm more trying to decide between a cam and maybe heads on my 350 or a 383.
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Old 01-04-2017, 04:20 PM   #14
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Re: Lets talk Small Block

The L31 is the hot setup for a 4x4. Need to run an electric fuel pump though. I'd recommend that as a second option to changing to an RV cam in your current motor - like an Edelbrock performer cam.

That 383 would be a monster off idle though
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Old 01-04-2017, 04:27 PM   #15
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Re: Lets talk Small Block

I have an 84 Monte SS with a 406 small block that barely makes 10 inches of vacuum at idle and have no problem with the power brakes. You may want to check the check valve on the brake booster as well make sure that isn't leaking. I would also make sure that the vacuum line goes right from the manifold directly to the booster with not Tee's or any other connections.

Now as far as what to do with your motor. If you have a good 350 with decent heads, I would say get a milder cam and torque converter to match it. Most likely that would solve your issue and not cost a ton of money. If you don't like the results you could always get a different short block swap the heads and most likely you would have needed the converter anyways to match the new motor. If you still don't like it you could then spring for a nice set of heads. Although if your looking for low end grunt I doubt you would need some crazy high flowing heads.

That's my suggestion.
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Old 01-04-2017, 04:33 PM   #16
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Re: Lets talk Small Block

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I had considered that 383 from GM except I was looking for something with a little more compression I guess. It seems like the two they offer are on the complete opposite ends of the spectrum. A basically stockish replacement that runs on pump gas (boring) or the ultimate high performance unit.

I wonder if the compression could be raised on that motor by changing out the head gaskets... but that seems silly on an assembled engine.
450 ft pounds is anything but boring , the problem with many engines built by "race shops" is many times they are mismatched junk , that do nothing well , gm crate engines usually run very well in my experience , and their parts are matched for each other , not some "mechanics" wet dream .
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Old 01-04-2017, 04:51 PM   #17
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Re: Lets talk Small Block

You might want to consider a hydroboost brake conversion and leave everything else as is. Eng sounds more than sufficient. Lots of threads on here - recommend chat up Captainfab on the subj.
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Old 01-04-2017, 05:26 PM   #18
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Re: Lets talk Small Block

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450 ft pounds is anything but boring , the problem with many engines built by "race shops" is many times they are mismatched junk , that do nothing well , gm crate engines usually run very well in my experience , and their parts are matched for each other , not some "mechanics" wet dream .
Two very good points! I don't disagree at all with either actually. And I think what I currently have is the second of those. Maybe even worse. I think it was what the engine builder who was/is a drag racer had laying around. I'm sure not matched together correctly, especially for a 4x4 truck.
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Old 01-04-2017, 05:28 PM   #19
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Re: Lets talk Small Block

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You might want to consider a hydroboost brake conversion and leave everything else as is. Eng sounds more than sufficient. Lots of threads on here - recommend chat up Captainfab on the subj.
That was/is sort of my third option that I have been considering. I guess I've been thinking more strongly about going after the motor because I just feel that it isn't really put together for a 4x4 and probably more for a race car.
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Old 01-04-2017, 08:46 PM   #20
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Re: Lets talk Small Block

It would be worth pulling a valve cover and putting a dial indicator on your rocker arms to figure out your current cam valve lift specs, just to have a baseline to compare what cam you may want to change to.

Since it's a one piece seal block, look thru the pushrod and drainback holes and see if it's a block made for the factory roller setup (lots of them are). If you have a flat tappet cam in a block that has the provisions for roller it's a cheap upgrade to put the factory roller lifters in it. You could run a factory Vortec cam or HT383 cam, that would get you in a better power band for your use.

What's the chamber volume on the World heads you have? See if you can find that out and borrow/rent/buy a borescope to look at the piston tops. A lot of the new ones are video capable so you cold post a pic here and figure out what you have. Then you'll have a fair guess on CR and whether you need to do anything about it.
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Old 01-04-2017, 09:35 PM   #21
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Re: Lets talk Small Block

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That 383 would be a monster off idle though


You've never had a big block, have you?

My $.02:

If the engine was built to run on 94 or better, you are going to need to lower the compression. If it were me, I would figure out what thickness headgaskets you have and get a set of gaskets that are a fair bit thicker to drop the compression a touch. Then swap in milder low-end oriented cam while you have the intake off and be done with it.
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Old 01-04-2017, 09:43 PM   #22
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Re: Lets talk Small Block

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You've never had a big block, have you?

My $.02:

If the engine was built to run on 94 or better, you are going to need to lower the compression. If it were me, I would figure out what thickness headgaskets you have and get a set of gaskets that are a fair bit thicker to drop the compression a touch. Then swap in milder low-end oriented cam while you have the intake off and be done with it.
I've put some miles on a couple different 427s. I have made questionable choices whilst driving it,

I think that Vortec 383 with a peanut cam would be a real torquer from idle rpm.
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Old 01-04-2017, 09:53 PM   #23
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Re: Lets talk Small Block

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I have made questionable choices whilst driving it,
Excellent way of putting it. I like that.
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Old 01-04-2017, 10:09 PM   #24
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Re: Lets talk Small Block

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Originally Posted by 1972RedNeck View Post


You've never had a big block, have you?

My $.02:

If the engine was built to run on 94 or better, you are going to need to lower the compression. If it were me, I would figure out what thickness headgaskets you have and get a set of gaskets that are a fair bit thicker to drop the compression a touch. Then swap in milder low-end oriented cam while you have the intake off and be done with it.
Why does the compression ratio need to be lower? I'm not questioning you, I just am trying to learn. I know that I said the guy told me that, and it may be true as far as optimum performance, but I do not get any spark nock what so ever and my timing is not retarted. Will I make more torque, or change the torque curve some how if the compression is lower? Thanks for explaining
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Old 01-04-2017, 10:46 PM   #25
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Re: Lets talk Small Block

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Why does the compression ratio need to be lower?
Your compression ratio needs to be lower because of the effect of dynamic compression ratio. You can read up on it several places on the net, but briefly, here's how it works.

Let's assume that you have a 10:1 engine with an Edelbrock Performer RPM cam. That cam closes the intake valve 44 after bottom dead center (ABDC). Plugging your 5.7" rods, 3.48" stroke, 10:1 compression ratio, and no boost into a dynamic compression ratio calculator (I used Wallace Racing's free one), you end up with a dynamic compression ratio of 9.0.

Now, substitute an Performer cam that closes the intake valve at 29 ABDC, and the dynamic compression ratio is 9.6. You will end up with a much more detonation-prone engine, all else being equal.

That is why you will occasionally see people over-cam an engine that has too much compression; it scrubs off some dynamic compression. It's not the ideal solution, but it "kinda" works.
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