Building sbc for boost

[BR3W CITY]

So I have dealt with forced induction before; but only on vehicles already designed for it (previously owned srt4's, RX7's etc). And I'm fairly comfortable with the regular mechanics of the sbc.

My issue comes in when creating a sbc to handle boost. Currently I have a 355 built by the previous owner (around 12k miles on it). 4 bolt mains, scat crank (i believe its just the regular cast steel replacement), stock type pistons and rods, 2.02 heads (have to check casting #) and some other stuff.

I'd like to build a motor to handle a moderate amount of boost, however the source (turbo or s/c) is yet to be determined. I have spent countless hours on turboforums but since its a heavily mustang site I havn't come up with too much relating to what I want to do.
What do I REALLY need to build a mild motor for boost? I have been looking at forged rotating assemblies etc, but my power goals are in the 500's so I'm not sure if thats needed or overkill. I know compression needs to be lower (8-8.5?), any other recommendations? Fuel system etc? It will be carbed no matter what.

I can provide you with more specs on what I've got, and about what I want to do....but this post is long enough already. ANY help is appreciated!

[swb85]

At a minimum you're going to want a good set of pistons/rods. That scat cast crank is very stout and will handle the power level you're looking for....but you know how addicting boost can be----so a forged crank is probably a smart upgrade just in case you end up going nuts on it. I would also run some ARP head studs and MLS head gaskets. There's plenty of other things to think about depending on the boost level and rpm it will see (bearing type & clearances, ring material & gaps etc etc). I'm not very up on blow through carb setups, I'm sure some here have experience with them and will chime in......

[BR3W CITY]

Budget may rule against a full forged assembly; I was thinking the scat crank I have maybe with some h-beams, and forged pistons. ARP studs and a good gasket is a good idea, I tend to forget the small stuff like that can make a big difference in longevity.

It will be a mostly street machine, but I do plan the occasional track romp. Shooting for the 500's or so in power; hoping to keep the rpm's in a streetable (sub 6500 ish) range.

[Alex1]

Bascally buy the best stuff you can afford because we all know that boost is addictive and that you will be wanting more.

Forged pistons are a necessity in this case.

[Wild83C10]

If you are searching for 500hp and don't have the money to build an all forged rotating assembly how do you plan to come up with the funds to buy the SC or do you have that budgeted already?
A decent turbo kit, if you can piece it together yourself, will run $1500 to $2k. A SC whether it's roots, screw or centrifugal will most likely be more, unless you find a used kit.

No reason you can't get 500 hp out of a stout N/A sbc. You could have a high 12 sec truck with the short block you already have.

[BR3W CITY]

i could afford the full assembly. but it in the longrun of the build, is it really needed? I understand the need for the good rods and forged pistons, but alot of folks have said a forged crank only starts to come into play at even higher power levels, or when using a bigger s/c (something about the snout snapping?).

I have a rough number set aside for the motor, but im trying to build as smart as i can. (I have budgeted around $2500 for a diy turbo setup, and im lucky enuough to have a large fab shop at work for piping/welding etc). Right now, the motor itself is step 1, and i want to make a good foundation, but no reason to throw money at it.

I COULD build a stout NA motor, but I really would like to do a FI build.

[Wild83C10]

Ok just want to make sure everything was thought of.

The forged stuff is a bit more forgiving that is why it's recommended. If you have a good tune then you can run cast crank and rods, even pistons, but probably not worth the chance.

Once you get into quality forged stuff the OE block then becomes the weak point on a FI motor. You should be able to run 600 hp/lb-ft without a problem.

I would shoot for 9:1 CR it will provide a bit more driveability for the low end.

[BR3W CITY]

Ok, thats what I'm looking for! If I can find a deal on a forged crank, I'd love to have that peice of mind...but if i could retain my scat crank, and use some nice forged pistons and rods that would be ideal. I'm not looking to build an all out race motor, and its really not in the budget to buy a dart block or anything like that right now.

Why do u suggest 9:1? Just so shes not a dog before spooling? I assume if i were to go lower, I would sacrifice some of my part throttle/low rpm driveability?

(anywhere else to look on this topic? I can't find any sites dedicated to boosted small blocks!)

Thanks!

[swb85]

Don't forget that you'll need to have your current crank re-balanced if you replace the pistons/rods.....that's going to run you $150-250 depending on your location. Might be close to a wash by picking up a balanced rotating assembly with a forged crank and selling your cast crank to offset some of the cost......just something else to consider.

[Wild83C10]

Originally Posted by BR3W CITY

Ok, thats what I'm looking for! If I can find a deal on a forged crank, I'd love to have that peice of mind...but if i could retain my scat crank, and use some nice forged pistons and rods that would be ideal. I'm not looking to build an all out race motor, and its really not in the budget to buy a dart block or anything like that right now.

Why do u suggest 9:1? Just so shes not a dog before spooling? I assume if i were to go lower, I would sacrifice some of my part throttle/low rpm driveability?

(anywhere else to look on this topic? I can't find any sites dedicated to boosted small blocks!)

Thanks!

I suggested 9:1 because of the part throttle/low rpm driveability. However I didn't state that thinking that aluminum heads would be used. Iron head you may want to drop it down a bit.

I don't see any reason why you just couldn't swap your pistons and leave everything else. That is provided you don't get greedy. Once the power bits it doesn't let go and you will want more. If you can be happy with your current goal until you have the money to build something better then just go with new pistons.

You can pick up a complete short block with all forged assembly and new 4 bolt block for like just over $2500 these days. M & R Engines. SpeedOMotive is a good place for complete rotating kits.

[BR3W CITY]

thats a good thought, i didn't condisder that!

I have seen some of the assemblies on jegs/summit etc; but it seems i might have better luck peicing one together with the pistons/rods I want. The balancing on some of those from Eagle etc has come into question, as being only weight matched. Thanks for the help, we'll hear more on this!

[1FAST68]

I built a basic 350 with a procharger along time ago that was screamer on pump gas. I used the trick flow heads when they 1rst came out, stock crank and stock rods with arp bolts, trw dished pistons, and a solid flat tappett cam.
At 10lbs of boost is made 630 on a chassis dyno and run mid 10's in a 70 camaro.

Your goal is pretty easy to do.

[BR3W CITY]

thats not bad for everything in the assembly

1fast68. would you mind telling me more about your setup? it sounds like you made hella power on a pretty stock setup.

[1FAST68]

It was very basic. It was a blowthru setup with a 650 holley dp, performer rpm intake, and I would have to do some thinking to figure out what the cam was its been a good while ago.

[BR3W CITY]

any issues with longevity? (and how much boost?)

[1FAST68]

I never hurt anything and the boost was 10lbs I think. Those Trw dished pistons are tough. The cr was in the 8's.

You can use 9:1 as Wild83 suggested, but I don't know if pump gas will work at 10lbs or above.

If you have E85 in your area you can go higher on the cr and boost but then you get into more expensive fuel system and carb.

[cgav8tor]

http://67-72chevytrucks.com/vboard/s...d.php?t=310179

If interested, here's my thread from the summer using a 355/Wieand 144 w/ 9:1, 93 octane, and NOS/104 (?) additive. Running through an M21 4 spd to a 3:73 Posi. Producing @500HP+ and assisted by Burkart Automotive (NHRA driver) in the tuning. I don't go above 5 on the boost. Too much money and time to blow it all away. Maybe a little scared too!

Still runs tall but have a small leak from the timing cover. The thread ended re the guage that I bought from Summit. It was repaced for free.

Good Luck

[BR3W CITY]

hey thanks! your 355 is a little more like what ive got sitting in my truck right now, but damn! it seems like you had trouble with the 144 manifold.

I have spoken to some of my welders at work, they agreed to do all the finish welding on turbo headers for pretty much nothing, which is a big plus! Now it looks like I just need to dial in the motor setup and get the beoth peiced together. So much to do, so little time and even less money (and probably even less talent)

[71/454]

fuel system you will need mallory 4309 regulator, a high psi pump capable of delivering 7 psi on top of your boost psi ( I prefer the walbro ones). You can use your current engine provided you are diligent with your tune and don't get boost happy. I run 10.5 to 1 and 12 lbs of boost on this setup, but I am at a high altitude. Are you going to run an intercooler?

[BR3W CITY]

not planning an intercooler, may consider a meth setup but trying to keep things pretty low-tech.

I have a chance to pick up a pair of 60AR comp and 67AR exhaust garrett's for $100 so that may be the beginning (seems like a good deal, and the guy is local with a good rep).

[Ryan Hubbard]

I have been running a 2 bolt main block with a scat cast steel crank, forged rods and forged TRW blower pistons. I ceramic coated the piston tops and had the sides of the pistons coated also for lubrication. I am running 8.5:1 with the Edelbrock Performer RPM heads with the small chambers. I am running a B&M 144 blower with the smallest pulley. I have been running this engine for 30,000 miles in my truck and opened it up and inspected everything last year and it all looked fine and just closed everything up. The only trick with putting turbos on is make sure you use a turbo cam and not a blower cam, they are two totally different specs.