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Discussion Starter · #1 ·
I have a 89 suburban chevy 350 638 casting block. I want to change the camshaft out for a comp cams 230/236 cam (XR282HR). Im not sure what cylinder heads are best for this set up. Any help is greatly appreciated. Im pretty lost trying to figure out what heads to go with.
615642
 

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Looks like you already swapped some stuff. What heads are on it now. That will help us figure out what the intake fits.
89 should be a TBI from the factory, so was it swapped with older heads? Carb intake configured for TBI heads? Need a few million more points of info.

How will it be driven? Towing? Street? What is the rear axle ratio? What transmission? That cam is HUGE for a big heavy truck. Unless you plan on really expensive heads and a ton of modifications, that cam might be a terrible match for the truck.
 

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Discussion Starter · #3 ·
So heres what i know. Its a 89 suburban 350 motor put into an 84 k10 with 373 gears front and rear on a 700r4 tranny. The carb is a 750 cfm edlebrock. The intake is unknown to me. The heads say Mexico on the outside. I dont know the casting numbers on the heads. The cylinders might be flat top but for the sake of this discussion im going to assume they are stock. I plan on mostly street for this truck but i will occasionally put something in the bed or possibly tow. But i dont imagine anything more than 3-5 thousand pounds max. All i know about the block is that it will accept hydraulic roller cams because it shares specs from perforbloack of that time. Thats is what im going for it to turn it into a roller. What kind of modifications are you thinking i would need to make this happen. So far on my list is roller cam kit, heads, intake, and a stall converter, probably roller rockers as well
 

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638 block in a Suburban is cast to be a roller block, but the machining isn't done to accept a roller cam as-is. The bosses and things are cast into the block, but they aren't drilled/tapped. Not hard to do, just be prepared for a little machine work.

Head casting numbers are under the valve covers between two sets of the valves. It would be helpful to be sure. If they are the heads that came with the 89 motor, they are TBI heads which have a specific intake bolt pattern. TBI heads are not good for anything but under 4500 rpms. The good news is that any SBC head will bolt on, but you'll just have to be careful which intake you buy to go with it.

The cam you mentioned would be great in a 10.5:1 compression 350 in a car that weighed 2600 lbs and only every saw life at 1/4 mile at a time. Terrible truck cam. Really hairy idle.
 

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Discussion Starter · #5 ·
638 block in a Suburban is cast to be a roller block, but the machining isn't done to accept a roller cam as-is. The bosses and things are cast into the block, but they aren't drilled/tapped. Not hard to do, just be prepared for a little machine work.

Head casting numbers are under the valve covers between two sets of the valves. It would be helpful to be sure. If they are the heads that came with the 89 motor, they are TBI heads which have a specific intake bolt pattern. TBI heads are not good for anything but under 4500 rpms. The good news is that any SBC head will bolt on, but you'll just have to be careful which intake you buy to go with it.

The cam you mentioned would be great in a 10.5:1 compression 350 in a car that weighed 2600 lbs and only every saw life at 1/4 mile at a time. Terrible truck cam. Really hairy idle.
Thanks so much! This helps me out a ton. Do you know if i need to do anything else to accept a roller other than tapping those holes under the intake? Do i need anything to keep the camshaft from moving forward at all?
I planned on getting a new intake anyways so i imagine i will match it up with the new heads.
i really dont plan on doing any “heavy lifting” with this truck but im curious as to what you would suggest for a cam in this thing. Are yousaying its better to have the mid range power and low end torque or is there a better cam for big power all together on this motor?
 

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Thanks so much! This helps me out a ton. Do you know if i need to do anything else to accept a roller other than tapping those holes under the intake? Do i need anything to keep the camshaft from moving forward at all?
I planned on getting a new intake anyways so i imagine i will match it up with the new heads.
i really dont plan on doing any “heavy lifting” with this truck but im curious as to what you would suggest for a cam in this thing. Are yousaying its better to have the mid range power and low end torque or is there a better cam for big power all together on this motor?
If you run your truck across the scales today you will find you are already doing heavy lifting with only you in it.
Probably over 4400, or somewhere pretty close to that.
Trucks are heavy.

Depending on what size tires you will need alot more gear. Also the 700R4 will allow this, but its not going to like all the torque, and high RPM shifting.
And a quality stall converter is going to cost more than $500. Not much more, but anything less will be a difference you can feel.

It sounds like you want a good running truck. But nobody can help you, until you state your exact goals.

My truck ran 13.60s with a Vortec 350. It was very strong all around for the small motor in a heavy truck.
Now goes 12.60s with a 406. It looks the same, sounds the same, and drives the same, just gets to the finish line a second quicker than it did before.
I take it on 6 hour round trips to get stuff, and my wife can hop in it and drive it, no problem. But it took lots of planning, and some good advice from guys on here to get where im at today.
 

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[QUOTE="Reidp84k10, post: 4793275, member: 436143" Are you saying its better to have the mid range power and low end torque or is there a better cam for big power all together on this motor?
[/QUOTE]

I was thinking. (Dangerous!)

You will have to be brutally honest with yourself, and have a healthy budget.
Good heads, and a cam that makes some power are not cheap. Is your short block up to it?
$699 converter
$2500 tranny
Gear swap w/posi
This is a starting point.

How does the truck run now?
What do want it to do differently?
What is your all in budget?
You can change gear ratio first, and see a huge difference if your tires are over 26 inches tall.

You might want to leave the engine alone for now...
 

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Yes, you will need a thrust plate or thrust button. I prefer the plate, as the button often dictates what timing cover you use.

I strongly suggest pulling a valve cover and checking head castings. If they are the stock 89 TBI heads, they are the worst-flowing head chevy ever put on a production motor. Worse than 265 and 283 heads from the 50s. Quality power AND torque needs two very important things; head flow (both quality and quantity), and proper cam selection.

With heads, there are two things you're looking for: enough peak flow cfms to support the hp you want, and enough velocity to make good torque happen. You can have both, but it's not usually easy or cheap. Look at head port volume. Using random, round numbers, let's say you have two heads that flow the same 200 cfm. That flow suggests you can get X hp. One of the heads has 175cc ports, the other has 190cc ports. Every time, I would choose the 175cc ports. This means that the velocity of the intake charge is much higher which (along with other factors) means that low end torque will be helped. Airflow through an engine is partly about inertia and harmonics. A small, fast-moving column of air generates inertia, which means in a certain RPM range, the inertia will keep filling the cylinder even after the piston stops moving at BDC. The whole thing is a dance. You get the right volume of air moving at the right speed, then select a cam that closes the intake valve at the right time. Close the valve too early, (cam too small) and you miss out on that extra air. Close it too late (cam too big) and the air starts bouncing back out. (which, incidentally is why big cams have a lumpy idle). As you can imagine, this is why cam "size" reflects the RPM range. The physical properties of the moving air don't change, but as piston speeds increase, that intake valve closing point needs to happen later and later as RPMs rise. So a bigger cam matches the intake valve events to trap the most air during higher RPMs.

Big ports means slower air, which means you have to rev it higher to achieve that peak air-trapping. The holy grail is smaller ports that flow a lot of air so you can have the best of both worlds. Adequate velocity during low RPM, and adequate mass flow at higher RPMs.

The TBI heads (if that's what's on there) have small ports with a big swirl vane cast into them like a bent shark fin. It's designed as an MPG/emissions thing to keep the air and fuel mixed well. They are an example of great velocity, but terrible flow. They make pretty good torque in the low RPMs, but they are running out of breath by 4000 rpms.

For a street/truck/light towing vehicle, I can't imagine a better head than stock Vortecs. Aftermarket castings are cheap and less crack-prone. This assumes you have flat-top pistons. If you have dished pistons you'll get about 8.5:1 compression. Flat tops will give you 9.5:1 or so and a great platform. Pair that with something like a Melling 22135 cam (206/213 duration) and you have a recipe for around 300 hp with a torque peak at around 2600 rpms.

The Vortec heads have a specific intake bolt pattern and slightly higher ports, so you need a Vortec intake. You'll find that vortec carburetor intakes tend to be expensive because they're a "specialty performance" item. Easy solution: Find a marine junkyard. Marine engines used carburetors on Vortec engines for many years, so dead boats have lots of them. You can usually get them for $50 plus shipping instead of $300 from Edelbrock. Many of them on Volvo Penta and Mercruiser engines were actually the ZZ4 intake which is a great piece.

If, on the other hand, you pull the heads and notice dished pistons, we'll need to have a whole different conversation.
 

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Discussion Starter · #9 ·
If you run your truck across the scales today you will find you are already doing heavy lifting with only you in it.
Probably over 4400, or somewhere pretty close to that.
Trucks are heavy.

Depending on what size tires you will need alot more gear. Also the 700R4 will allow this, but its not going to like all the torque, and high RPM shifting.
And a quality stall converter is going to cost more than $500. Not much more, but anything less will be a difference you can feel.

It sounds like you want a good running truck. But nobody can help you, until you state your exact goals.

My truck ran 13.60s with a Vortec 350. It was very strong all around for the small motor in a heavy truck.
Now goes 12.60s with a 406. It looks the same, sounds the same, and drives the same, just gets to the finish line a second quicker than it did before.
I take it on 6 hour round trips to get stuff, and my wife can hop in it and drive it, no problem. But it took lots of planning, and some good advice from guys on here to get where im at today.
If im brutally honest with myself. What i really want is 430hp without too much torque loss down low. And a good sounding idle. Everyone loves a choppy idle but i dont know if im allowed to have that with a 4500 pound truck. I see trucks online that sound like that and seem to have a lot of power but is it all for show?? I dont know. My transmission has 4 extra clutches between gears. 9 in total and the man that built it recommended it would be good for about 500-600 hp. I figured i would be ok keeping it just below 450. My tire size is 35 inch. And 373 gears in the rear and front. I dont know what ratio that comes out too. After talking to a friend they suggested i get some edelbrock performer heads and a good valvetrain and then match it up with a better intake. Possibly an air gapper.
i dont care to put a trailer behind this thing so my biggest hurdle seems to be just the sheer weight of the truck. But how do i get that great sounding idle without overworking everything just because of the weight?
 

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Discussion Starter · #10 ·
Yes, you will need a thrust plate or thrust button. I prefer the plate, as the button often dictates what timing cover you use.

I strongly suggest pulling a valve cover and checking head castings. If they are the stock 89 TBI heads, they are the worst-flowing head chevy ever put on a production motor. Worse than 265 and 283 heads from the 50s. Quality power AND torque needs two very important things; head flow (both quality and quantity), and proper cam selection.

With heads, there are two things you're looking for: enough peak flow cfms to support the hp you want, and enough velocity to make good torque happen. You can have both, but it's not usually easy or cheap. Look at head port volume. Using random, round numbers, let's say you have two heads that flow the same 200 cfm. That flow suggests you can get X hp. One of the heads has 175cc ports, the other has 190cc ports. Every time, I would choose the 175cc ports. This means that the velocity of the intake charge is much higher which (along with other factors) means that low end torque will be helped. Airflow through an engine is partly about inertia and harmonics. A small, fast-moving column of air generates inertia, which means in a certain RPM range, the inertia will keep filling the cylinder even after the piston stops moving at BDC. The whole thing is a dance. You get the right volume of air moving at the right speed, then select a cam that closes the intake valve at the right time. Close the valve too early, (cam too small) and you miss out on that extra air. Close it too late (cam too big) and the air starts bouncing back out. (which, incidentally is why big cams have a lumpy idle). As you can imagine, this is why cam "size" reflects the RPM range. The physical properties of the moving air don't change, but as piston speeds increase, that intake valve closing point needs to happen later and later as RPMs rise. So a bigger cam matches the intake valve events to trap the most air during higher RPMs.

Big ports means slower air, which means you have to rev it higher to achieve that peak air-trapping. The holy grail is smaller ports that flow a lot of air so you can have the best of both worlds. Adequate velocity during low RPM, and adequate mass flow at higher RPMs.

The TBI heads (if that's what's on there) have small ports with a big swirl vane cast into them like a bent shark fin. It's designed as an MPG/emissions thing to keep the air and fuel mixed well. They are an example of great velocity, but terrible flow. They make pretty good torque in the low RPMs, but they are running out of breath by 4000 rpms.

For a street/truck/light towing vehicle, I can't imagine a better head than stock Vortecs. Aftermarket castings are cheap and less crack-prone. This assumes you have flat-top pistons. If you have dished pistons you'll get about 8.5:1 compression. Flat tops will give you 9.5:1 or so and a great platform. Pair that with something like a Melling 22135 cam (206/213 duration) and you have a recipe for around 300 hp with a torque peak at around 2600 rpms.

The Vortec heads have a specific intake bolt pattern and slightly higher ports, so you need a Vortec intake. You'll find that vortec carburetor intakes tend to be expensive because they're a "specialty performance" item. Easy solution: Find a marine junkyard. Marine engines used carburetors on Vortec engines for many years, so dead boats have lots of them. You can usually get them for $50 plus shipping instead of $300 from Edelbrock. Many of them on Volvo Penta and Mercruiser engines were actually the ZZ4 intake which is a great piece.

If, on the other hand, you pull the heads and notice dished pistons, we'll need to have a whole different conversation.
I will pull the covers on it tomorrow or wednesday and find out what i have. I honestly thought it wouldve been more simple to match something up for my truck but you guys are awesome. Thanks for being patient with me and helping me out through this. Ill get that info on the heads asap. Anything else i should bring to the table about the truck to help out the conversation?
 

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I like the way you talk. Couple of guys will chime in with a good head and cam suggestion.
450 should be easy for you to attain.

As far as gear selection, those 35s are killing you right now. Let me get on a gear ratio selector and figure something out for you. I think if you're 80 mile-per-hour RPMs on the highway in 4th gear is around 3500 RPM you will be good. Others can give more suggestions.
 

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Discussion Starter · #12 ·
I like the way you talk. Couple of guys will chime in with a good head and cam suggestion.
450 should be easy for you to attain.

As far as gear selection, those 35s are killing you right now. Let me get on a gear ratio selector and figure something out for you. I think if you're 80 mile-per-hour RPMs on the highway in 4th gear is around 3500 RPM you will be good. Others can give more suggestions.
I thought I was doing good ha ha. There were 38’s on there before. It’s good to know that 450 hp seems obtainable though.
 
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