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

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..

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!

Re: Lets talk Small Block
 

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?

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.

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.

Re: Lets talk Small Block
 

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

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.

Re: Lets talk Small Block
 

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

Re: Lets talk Small Block
 

Sounds like you're on top of it then. Good luck on your choices.

Re: Lets talk Small Block
 

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.

Re: Lets talk Small Block
 

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.

Re: Lets talk Small Block
 

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.

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

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.

Re: Lets talk Small Block
 

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 .

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.

Re: Lets talk Small Block
 

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.

Re: Lets talk Small Block
 

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.

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.

Re: Lets talk Small Block
 

:lol:

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.

Re: Lets talk Small Block
 

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.

Re: Lets talk Small Block
 

Excellent way of putting it. I like that. ;)

Re: Lets talk Small Block
 

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

Re: Lets talk Small Block
 

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 44º 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 29º 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.

Re: Lets talk Small Block
 

I know that the heads are the S/R or the Stock Replacement heads. They have a 170cc intake runner and either a 67 or 76cc compression chamber. I don't have a dial indicator but it is something I should probably add to the tool box.

Re: Lets talk Small Block
 

Another thing that I remember is that it is supposed to have higher compression pistons. Flat Top I presume, but I'm sure there are many differences. The guy I bought it back from told me that they actually had a harder time finding the pistons because they did not bore it, than if there were to bore it. Seems as though most of the company's had plenty of oversized in stock but not the stock bore size.

Re: Lets talk Small Block
 

It would be worth finding out which version head you have, flat tops with the big chambers might be workable with a smaller cam. The small chambers may have too much compression for a smaller cam.
Are there casting or model numbers on those?

Re: Lets talk Small Block
 

I had a 69 K10 with a manual transmission (SM465) and 4.11 gears, 33x12.50x15 MT tires on steelies

The engine:
350, bored 0.060" over (=360)
Weiand 180* dual plane intake
Holley 650 Double pumper
Cam was Crane 113901 for towing, off road, and low-end torque
Pistons were 8.5:1 compression flat top.
Heads: 1.92 Truck heads ported, polished, and gasket holes matched
Exhaust Manifolds: rams horn cast iron manifolds (also ported, polished and matched)
Exhaust was 2-1/2" duals with DynoMax turbo mufflers

The engine was ported, polished, and balanced to 10,000 RPM. It was VERY smooth running.

I was pulling around 350 HP and this truck did VERY well for towing and would get no less than 12 MPG no matter what I was pulling. On the open highway, treating it nice, I would get 14 MPG.

Over time, I did a rebuild and the machine shop junked my heads, so I installed a set of STOCK (not ported, polished or matched) 1.92 truck heads. I lost at least 75 HP, the truck dropped to 8-10 MPG, and the carb was way over-jetted. I was starting a family so I sold it.

Anyway, the biggest difference you have here is that if you are actually at 10 or 10.5:1 compression, you COULD install a less radical cam, but you will have to run premium or above fuel. I agree that the engine the way it is currently set up would not be much fun to drive unless it is at WOT.

I set up my truck for driving and being a workhorse and it did that VERY well.

Good luck! I was first thinking a simple cam swap until I read the compression ratio. that combination would push me more toward one of the crate engines. Make sure you get it cammed appropriately for an automatic or manual transmission. (It can affect shift points)

http://www.cranecams.com/56-67.pdf

Re: Lets talk Small Block
 

I was able to find some casting information under the valve covers. I could not find any exact number when I had it out when the truck was getting painted. The general casting information just tells me that it is their base S/R head and according to the website they come in two different chamber sizes.


A question though... Regardless of the chamber size (which if I understand you will be important in determining which cam I can successfully run) If these World Products Stock Replacement heads are just as they claim, a decent stock replacement head. Then what can really be expected out of them? Is for example, 400 ft lbs of torque at say 2500 to 3500 rpm realistic? An open question to anyone...

Re: Lets talk Small Block
 

The truck runs nice now, right? I thought that's how you started out. You don't need an engine or any changes, you need more vacuum or brakes that don't use vacuum (hydro-boost). Diesels make virtually no vacuum, they come in heavy trucks, and they stop.

Re: Lets talk Small Block
 

The motor runs good, but I can't help but feel that it could definitely be better, especially at lower rpm. When I bought the truck back almost six years ago and drove it home, it seemed great. But I think that I was probably overly excited about the prospect of getting my truck back. It had been rebuilt not too long before I bought it back so I didn't tear into it. Now that the truck is done, I wish I would have opened it up and at least figured out what it was put together with. I've tried to ask the guy but he doesn't seem to know what was put in it.

I have definitely thought about a hydroboost system. But after thinking about it for quite some time I'm now considering tackling the issue through the engine rather than the braking system. There's really no reason that the current power brakes shouldn't stop it if it had the correct vacuum.

I know you run 4x4's. Do you run small blocks or big blocks? 350's or 383's just curious.

I've rebuilt a few small blocks and other motors but don't know enough about them to know what combination of heads and cam and pistons work best together. I don't really know of the correct resources other than to ask here on this forum, that can help give me an idea of what kind of power potential there is for my 350 vs buying a 383 and yet keeping it at a range that will still allow it to make enough vacuum to be streetable.

Honest real world feedback is sometimes the most valuable. That's why I really appreciate your feedback and that of the others on this forum.

Re: Lets talk Small Block
 

I think someone mentioned it but a vacuum reserve canister would be something to check out before tearing into the motor. If the brakes are your biggest issue and you don't want to convert to hydroboost then it seems like it'd be the way to go. That is if its really about the brakes and not about you just wanting a new motor. Let me be clear, I don't mean to imply theres anything wrong if you do want a new motor but a new motor is not at all necessary in order to get your power brakes to work correctly.

Re: Lets talk Small Block
 

There is a lot of speculation here about your engine specs. You won't really know what's in it unless you tear into it and see for your self what pistons, cam lift, duration etc it really has. It sounds like a fun engine for off road adventures but maybe not so good for the street.
So far no one has asked just what shape your brake system is in. Have you rebuilt the complete system or just know it doesn't feel right? If the truck once stopped good but now doesn't I would pull the wheels and inspect the whole system. Low vacumn will diminish power brake performance. If I recall correctly the factory system needs a minimum of 9 or 10" of vacumn to operate right. There could be a small vacumn leak in the brake booster reducing it's effectiveness. If it is an original brake booster it would be suspect due to age. There is a coil spring inside the booster that can break and rub a small hole in the diaphram bleeding off vacumn. I've had that very thing happen on an 82 pkup. That truck had a stock exhaust and I could not hear the vacumn leak. You could remove the vacumn line from engine to booster and plug it and see if the vacumn signal goes up at the engine. If so it can indicate a vacumn leak in the booster.
A vacumn reserve can from the salvage yard could be a good tool to narrow the cause to either just a low engine vacumn or worn/weak vehicle brake system.

Re: Lets talk Small Block
 

I've never run a big block in these 4wds. Mostly 350s, built a couple 383s, and had some with a 400. I have no use for a big block in a 4wd. I look at them like tractors, where power comes through gearing more than HP. I like the 400 SBC in a 4wd. That's why I like 383s. It's about that stroke.

I wish I could tell you the specs on my '72 350 I built in '91. I believe I used an RV range cam and bumped the compression a bit. It's no monster but runs out nice. I had a cracked head this summer and put a fairly fresh pair of 1.94s on and it runs better yet. I was concerned the bigger valves would mess up the combination, but they were cheap. Turns out it runs better.

I was about to build a 383 before I found those heads. That is still the plan for some day. I have another engine for that.

Re: Lets talk Small Block
 

The brake system has been completely gone through. The booster and reservoir are new along with most everything else. No leaks anywhere, everything bled properly, check valve checked. Etc.

I get onc good pedal than very hard pedal because I'm not getting any help from my the booster. It's pretty scary in town.

You are right it would be great for wide open fun. It needs a lot more power between 2000 and 3500 is my guess. I think more vacuum would help the idle and trans kick down also. I realize I need more info from what I currently have to really make the best decision. I guess I didn't realize the puzzle would be so complicated and that's why I appreciate all the feedback so far. It doesn't seem as easy as saying ...oh put this cam or this cam and change to these heads and you'll be happy with it. Or even ...I doubt you'll be happy with anything but a 383.

Assuming that I do have flat top pistons and going up from there. Is it ignorant to asuume that I can get a close idea of what a good cam would be for my stock replacement heads. And what more potential I could get with cam and heads? And what I might be able to expect in tourque from either of those combinations. The drop in 383s I was looking at advertise their specs so I could then compare to that.

Re: Lets talk Small Block
 

I'd junkyard crawl for a vac pump and can.. and be done with it..

Unless you are just looking to rebuild or replace the engine.. just because.. then go for it.
But even the vac pump won't fix a bad booster..
new does not = good put a hand held vac pump on it and see if it holds vacuum..
Many oem pumps
ford trucks mod motors (most)
all non hydro boost oil burning trucks
caddy's
g.m. small cars sunbird/sunfire/cav/ colbalt

Re: Lets talk Small Block
 

Good info! Thank you. From how I read this, I read that with the right cam even stock heads can make good 4x4 power. However, the 383 would really put a smile on my face. I need to figure out which cam I have I guess. I don't want to end up with a situation where I drop in a cam and end up not being happy and then go heads and bigger cam or whatever. Not like test driving a car where you know what you are getting. The more information I can get from others like you will definitely help.

Re: Lets talk Small Block
 

Sounds to me like a set of vortec heads and a mild cam is what you are looking for.

Re: Lets talk Small Block
 

I agree, Vortecs and a mild cam would probably be a great solution. It really depends on the current pistons, the Vortecs have a 64cc chamber so it's easy to get too much compression with no-dish flat tops made for 76cc chambers.

It would be nice if it's a roller cam compatible block. Google images can help with the ID, it's pretty easy to see the difference with side by side pics. Easy enough that you can tell by looking thru the head casting holes with just a valve cover off.