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Old 06-17-2013, 09:32 PM
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smog 350, more power?

Hi guys, first up let me say that im not real familiar with carby v8s, I havent owned one since highschool more than 12 years a go, so some of my questions / responses might seem a bit stupid.
I do however have a decent mechanical skill-set, I can weld, I have build roll cages for race cars, have an electronics background and have done engine conversions.

ok so I have a 70s truck smog sbc 350 (TJA code). with the 3998993 smog heads (75cc), at some stage its been rebuilt by a previous owner, but the motor is real slow and sluggish so id say its only been built to factory spec (which was 160hp!) and still has a low comp ratio.


I was wondering what the best route to get good (and sort of cheap) power (looking for about 300-350hp) out of this would be? I was thinking of swapping the heads to some decent aluminium heads? with a smaller chamber. ie 64cc. would I need to change the cam to get a bit more lift also?

Im not sure yet if it has dished pistons, I'll borrow a bore-o-scope and have a look in the cylinder soon.
but at the moment im just trying to work out if this would be worthwhile? and If im deluded in thinking I can get some decent power by simply swapping the heads, and basically leaving the bottom end alone?
or should I just go straight for a stock GM crate 290hp 350.

thanks in advance.

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Old 06-17-2013, 09:58 PM
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350 hp is a strong engine,

If you are serious then the engine comes out. guessing is the worst thing to do
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Old 06-17-2013, 10:23 PM
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Like Vinnie said, 350 hp is pretty healthy, but easy enough to get. Do you know any history on this '70's motor? Mileage?

If you want to build reliable 350 or so hp, you should consider at least a freshen, if not a full DIY rebuild.
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Old 06-17-2013, 10:40 PM
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The cam and heads work together. Swapping on some small chamber heads will raise the compression, but with a factory cam (low duration, the intake valve closes sooner), you will build more dynamic compression, which can lead to detonation issues. So, higher compression ratios dictate that you use a cam with more duration (the intake valve closes later, allowing some of the intake charge to reverse during the compression stroke) so there is less dynamic compression ratio.

Even if you bolt on some nice heads, you don't have enough cam to make use of the CFM they are capable of flowing.

The other problem is that you have a flat tappet hydraulic cam shaft in there now. With today's oils it is difficult to get them to last. You need to buy old school dino oil and add plenty of zinc to supplement it (just search for wiped cam lobe to see the horror stories). When you go to a high performance cam with more duration and more lift, you also need stronger springs, all of which adds more stress to the cam/lifter interface and thus a greater chance to wipe a cam lobe. Most guys say screw it, and go to a roller cam. If you have enough dollars, you can get a retrofit kit to work in your old block.

I am not trying to scare you, but give you a dose of reality. I am agreeing with vinniekq2, you really need to pull the engine and do this right (of course would you expect a different answer from hot rodders? ). 350hp is an easy goal to achieve.

What is your budget? Depending on which GM350 290hp your looking at, that ranges from $2000-$2500 depending on options. That is a pretty good budget if you want to do the work yourself.

You could always get some long tube headers, nice exhaust, new intake...probably add another 50 hp to what you have now, even a set of full roller rockers could add another 20 hp on top of that. Now you have more performance in the meantime while you research what you want, and a pile of parts to use on the next iteration of the motor.
==
Of course what I would do...
Buy this nice ready to go roller cam block which is already clearanced for a 383 stroker kit and start building it up, then drop it in the car.
http://www.summitracing.com/parts/sum-150100
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Old 06-18-2013, 05:15 AM
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thanks, that's the sort of answer I was looking for. I understand that I don't know much about v8s so the knowledge is welcomed.

I guess ill just stick to me original plan and sell this motor for whatever little money I can get and buy a crate motor or do like you said and build one from scratch.
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Old 06-18-2013, 09:26 AM
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Crate motors are nice if you want to get up and running quick. But man, I tell you what, you learn SO much from doing it yourself (how to work on your engine, and how engines work)! If you get a crate you motor you will never have an appreciation for the work in the motor and the quality of the parts. I recently built my first SBC350 and it was a great and also frustrating experience. My appreciation for quality American made parts is at an all time high.
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Old 06-18-2013, 09:56 AM
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I have a 350 sbc with a lunati voodoo roller cam 219/227 @ 50 515/530 lift with 1.5 roller rockers and dart shp 180cc aluminum heads on my mild s10 truck with a 600 holley and this thing is a very strong motor that should be making way over 350hp and 400 ftlbs and running a stock type bottom end with a scat 3.480 cast crank and scat 5.7 rods with 4 valve relief hyper pistons and it runs very strong from off idle all the way to 6 grand with a 2200 stall and 3.42 rear gear with 350 turbo. Whole motor was not too much more then what a decent crate motor cost. I know a roller cost more but in the end its worth it you don't have to worry about loosing a lobe etc. The dart shp aluminum heads are usa made and they are very good quality and come with everything assembled for less then a grand.
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Old 06-18-2013, 10:24 AM
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You are not going to solve your power problem with a 350-290hp crate motor swap.
This lame low cr no power no torque engine is as bad as the engine you got.
It has same crappy smog heads, lower compression and a cam that is a totoa mismatch to that.
329ft plbs of torque is pityful.

Fix the 350 you got.

A low cost effective boost is a ported 305 head swap. using the common 4416 head casting (58cc) and generous hand home porting. Add 1.94x 1.60 valves and a new valve job, install with a .015" shim head gasket.
Now you can cam it for power. with more compression and port flow.
Don't be shy with the porting, more is better.

If you are not up for that install new aftermarket 58-64cc high perf heads.
There are many to choose from.

keep the cam duration 222@.050" or less for a truck.
Add a performer rpm manifold and 750carb and headers and you ahve a respectable truck motor...

Another real good path to power on a low cr truck motor is to supercharge it.

Keep the desirable low compression ratio fully hand home port your 993 heads and add a 177 weiand or 142 weiand blower and a off the shelf cam that is blower friendly ( eg: Crane HMV278-2) and a 750carb.
adds a ton of power and torque to get the truck going. no disapointment here.

Start by determining the health of your engine with a simple compression test.

Last edited by F-BIRD'88; 06-18-2013 at 10:31 AM.
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Old 06-18-2013, 11:51 AM
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Get some better heads http://www.summitracing.com/parts/su...make/chevrolet and this: Stage II Turbo Charger Upgrade T3 T4 turbocharger Kit 300HP Boost Intercooler | eBay

Last edited by JeffB; 06-18-2013 at 12:03 PM.
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Old 06-18-2013, 01:17 PM
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Quote:
Originally Posted by Daedalus View Post
thanks, that's the sort of answer I was looking for. I understand that I don't know much about v8s so the knowledge is welcomed.

I guess ill just stick to me original plan and sell this motor for whatever little money I can get and buy a crate motor or do like you said and build one from scratch.
You've got to really study GM crate motors several have good looking power numbers but are not well laid out which makes them gas guzzling and detonation prone for the power they deliver these tend to have aggressive cams with low compression heads and pistons. While the bottom end looks strong with 4 bolt mains, the pistons are low compresson deep dish types under heads with large low compression chambers, this nets some decent looking dyno numbers but it gets there by taking inefficient combustion and beating on it with a big stick. Specifically I'm talking the 12499529 engine. It's a good engine and will add a hundred horsepower over what you currently have, it just burns a lot of gas getting there. With better heads like L31's that engine would deliver more like 330 horses with the cam that it comes with.

The L31-R Vortec crate number 1250283 for about 300 dollars more than the basic 12499529 brings almost the same cam timing but uses a roller cam with the better and higher compression L31 Vortec head, it uses a four bolt block, it does require an electric fuel pump as it isn't machined for a cam driven pump. It uses hyper-eitectic pistons on powder forged rods. It uses a one piece rear seal that requires you change the flexplate you've got for the newer model. I think this engine is a better deal for that 300 hundred bucks. More power, better efficiency, a roller cam you don't have to worry about going flat, less rear seal oil leakage,,,, just a lot of good stuff in that small delta cost.

Bogie
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Old 06-18-2013, 06:26 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
You are not going to solve your power problem with a 350-290hp crate motor swap.
This lame low cr no power no torque engine is as bad as the engine you got.
It has same crappy smog heads, lower compression and a cam that is a totoa mismatch to that.
329ft plbs of torque is pityful.

Fix the 350 you got.

A low cost effective boost is a ported 305 head swap. using the common 4416 head casting (58cc) and generous hand home porting. Add 1.94x 1.60 valves and a new valve job, install with a .015" shim head gasket.
Now you can cam it for power. with more compression and port flow.
Don't be shy with the porting, more is better.

If you are not up for that install new aftermarket 58-64cc high perf heads.
There are many to choose from.

keep the cam duration 222@.050" or less for a truck.
Add a performer rpm manifold and 750carb and headers and you ahve a respectable truck motor...

Another real good path to power on a low cr truck motor is to supercharge it.

Keep the desirable low compression ratio fully hand home port your 993 heads and add a 177 weiand or 142 weiand blower and a off the shelf cam that is blower friendly ( eg: Crane HMV278-2) and a 750carb.
adds a ton of power and torque to get the truck going. no disapointment here.

Start by determining the health of your engine with a simple compression test.
thanks,
I would be keen to install performance heads, I was looking at patriot (now promaxx) as they seem like an ok budget option?
but im not afraid to get my hands dirty so the 4416s seem like a nice option, but itd be harder to find over here in Australia, we dont really have any GM wreckers. so id have to find online and get them shipped.

I should mention that even tho its a truck motor its not actually in a truck, its in a 68 camaro. (dont ask, but I got it real cheap because of the fact, so i do have room to spend a bit on an engine/build)

I actually have a 144 weiand kit here that I bought recently, but in Australia we have strict laws on modifications and there have been a lot of recent crackdowns so converting from N/A to forced induction, so it would cost too much to get the proper certification, so I was going to resell and use the money for a motor or build.

I have done a compression test and it was approx 160psi (within a few psi) across all 8. the head has evidence of being decked recently, so combined with this its a fair assumption the motor is healthly and not too old since being rebuilt.
I will however do a combustion chamber inspection once my borescope arrives.

and oldbogie thanks ill look into that motor.

Last edited by Daedalus; 06-18-2013 at 06:44 PM.
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Old 06-18-2013, 07:40 PM
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Why would a 1968 Camaro need emissions certification?
If the car needs mechanical inspection take it in without the blower.

The blower fits under a 3" cowl hood or a small hood scoop.


4416 heads are very common on 305 engines.
others to look for 062 906 vortec 083 350 TPI 081 305 TPI.
anything with a 64cc or smaller chamber.
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Old 06-18-2013, 08:34 PM
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Originally Posted by F-BIRD'88 View Post
Why would a 1968 Camaro need emissions certification?
If the car needs mechanical inspection take it in without the blower.

The blower fits under a 3" cowl hood or a small hood scoop.


4416 heads are very common on 305 engines.
others to look for 062 906 vortec 083 350 TPI 081 305 TPI.
anything with a 64cc or smaller chamber.
it doesn't need emmisions but to be legal it would have to have an engineers certificate, stating that the conversion is safe and it has sufficient brakes to match the increased power output, regardless of how much power its actually making. which will cost between $1000 to $2000 and the engineer will check every other aspect of the car to make sure its all up to scratch before signing off.

we have police randomly setup "defect stations" ( there was one in my area 2 days a go) with patrol cars out looking for modified / suspect cars in the area, and they make you go to the station, check over your whole car, then issue you an immediate fine for anything defective / without paperwork, you also cannot drive your car after receiving the defect notice, until it is reinspected and passed, so you have to get towed home as well.

If we didnt have these id be all for it, theres also the matter of if you cause an accident, and your car is illegally modified, the insurance company may not provide cover.

its a nightmare to have a legally modified car here in Australia now, even with all correct paperwork you still get hassled and delayed by police, ive sat there for half an hour while they were checking over my certificate and hence the reason my other car is race only now and not road registered.

It could be done, but if I can get similar power for similar price naturally aspirated, its less of a headache in the future

thanks, ill keep an eye out for any of those heads, it looks like the best option, im sure with a new cam, lifters, etc as well as the heads ill still come out better off than with a crate motor.
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Old 06-19-2013, 10:54 AM
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Originally Posted by Daedalus View Post
thanks,
I would be keen to install performance heads, I was looking at patriot (now promaxx) as they seem like an ok budget option?
but im not afraid to get my hands dirty so the 4416s seem like a nice option, but itd be harder to find over here in Australia, we dont really have any GM wreckers. so id have to find online and get them shipped.

I should mention that even tho its a truck motor its not actually in a truck, its in a 68 camaro. (dont ask, but I got it real cheap because of the fact, so i do have room to spend a bit on an engine/build)

I actually have a 144 weiand kit here that I bought recently, but in Australia we have strict laws on modifications and there have been a lot of recent crackdowns so converting from N/A to forced induction, so it would cost too much to get the proper certification, so I was going to resell and use the money for a motor or build.

I have done a compression test and it was approx 160psi (within a few psi) across all 8. the head has evidence of being decked recently, so combined with this its a fair assumption the motor is healthly and not too old since being rebuilt.
I will however do a combustion chamber inspection once my borescope arrives.

and oldbogie thanks ill look into that motor.
Then again you could move to Texas.

Bogie
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Old 06-19-2013, 06:09 PM
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ok so Im leaning towards this cam, its a hydraulic roller retrofit.

12-422-8 - XTREME Energy

and these heads. I know they're cheap but Ive read quite a few good things about patriot (now promaxx) so im willing to take the risk.

http://www.summitracing.com/parts/pmx-2169/overview/

do they seem like they will play well together?

one thing i've noticed is the cam says stock springs cannot be used.
I guess ill try and email promaxx for spring specs then confirm with compcams whether they will be ok.
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