So I have looked into posts and stickies and did my fair share of searches.. With that out of the way I have a few questions about building my motor to take turbo well and the turbo its self. I plan to run a single turbo on my 355 build and am wondering a few things. I want to keep street compression of 10:1 for 92 octane gas. That being said I'll shoot.

1) What psi should I run for the following gain? Answered
2) Is a 350hp w/o turbo relevant to boosting to 450hp? Answered
3) If so will I need my engine forged or is aftermarket cast good enough for low boost? Answered
4) What compression should I build then engine for this gain? Answered
5) What j/y turbo would you suggest from expierience to use with a 5.7 carbed sbc?
6) I know you can turbo a carbd car is there anything that needs to be done to the carb aside from creating a turbo pip to carb type intake for it? Answered


I know I am probably gonna get my butt reemed by the seasoned guys here but I am brand new to turbo and having trouble finding the info i need. Any articles/ guides would be most appreciated as I am interested in learning for my self.

Since you are building a motor instead of putting a turbo on an existing sbc, why not have it 8:1 comp with forged internals. So you can boost it somewhere around 30psi.

Cost and its a daily driver... sorry if I forgot to put that. I am aiming for 450-500hp and trying to keep a daily driver around 12+ mpg. 400hp 355 can keep 15mpg driving like an old lady so I've done enough research to learnt hat power adders make your power more streetable and efficient. Therefor I am looking into turbo since its the cheapest application with a j/y turbo. I take it if I can run 30psi on forged internals that 6psi on cast is no problem?

You have pretty much the same plan/goals for my next turbo build.

I'd shoot for 5-6psi of boost and see where that gets you. The nice thing about a turbo is that it's easy to vary the amount of boost.

For low boost, aftermarket cast internals should hold up providing you can keep detonation out of the picture. Going forged allows for a little more room for error or if you plan on increasing the amount of boost in the future.

The turbo is going to make the gain, not the compression ratio, so with low boost, 8.X:1 should be fine.

I found it almost impossible to find a large turbo at a junkyard. If you can, that's great, but I ended up using eBay. The ideal way to size a turbo is by using compressor maps, but I still can't read them. Probably something around a T62-1 with a .86a/r should be close.

Yes. Visit Blowthrough Carb How-To to see how to setup a carb for blowthrough.

Also, turbo books like Turbochargers by Hugh Macinnes and Maximum Boost by Corky Bell are very good references.

Ahhh excellent help thank you very much! Basically now I just need to finger the right size turbo for my engine correct?I figured detonation wouldnt be a problem how do you judge the compression a turbo adds if it isnt based on the amount of boost? And is 350hp a good base to turbo? Most little ricers I see take 200hp engines and squeeze 400hp out with a turbo wouldnt that make my 350hp to 450hp an easy acomplishment if I match everything correctly?

Yeah, sizing the turbo can be hard to do b/c it depends on what matches the engine the best and what you can afford. Sorry if I was confusing about compression .. boost will increase the compression of the engine, but if you start at a low base compression, the increase from the low boost shouldn't be a problem. There are too many variables to say how much the turbo will raise the compression, like whether or not the system will be intercooled.

A 100hp increase is very obtainable with a turbo. I more than doubled my hp when I turboed my lg4 (10psi).

Also, if you end up needing to change the compression ratio, that would be a good time to go to forged pistons if nothing else, since they take the most abuse from heat and detonation.

Hmm alright so opt for forged pistons to take the abuse incase anything does detonate. I'm gonna do some research and match a turbo to my engine but with the small gain i am looking for I think that anything I put on there with a reasonable psi will yeild me a 100hp boost on a 350hp base. Plus I do plan on doing an intercooler which I'm not even sure if I not for that little of an increase.

I would shoot for around 8.5 to 9 to 1 compression ratio if 450hp is your goal. It will not be a dog off boost but when the small amount of boost creeps in it will get really fun (and not as dangerous as say 10 to 1 compression like you previously said you wanted). Be carefull when figuring out the compression ratio of a motor, most people contrary to popular belief dont know how to figure out compression properly (they dont take all the variables into account, include in this variable quench). You can pick up some good information from books on this, David Vizard books come to mind.

I would use forged pistons and keep the rotating assembly stock to save some money. Use ARP bolts on the rods and it should be more then fine. Dont worry you can slap almost any decent sized turbo on with a relatively stock 350 and get your 450hp at the crank.

Remember boost is addictive! I swore I woulnt go up from running 10% underdriven on the street, at 10% underdriven it felt nasty, then I quickly went up to straight up and I laughed like an idiot after I felt the difference on a street car, then I procedeed to overdrive it 10% over and that got scary quickly on the street......... I might try 15% over for kicks.....Hopefully I wont granade it.

Take care and good luck with everything.

What do I want for pistons on a daily driver? Flats, Dish, or Dome? How many valve reliefs too? Yeah as far as the compression goes I am going to build the motor 8:1 n/a and hope its 9:1 or 9.5:1. Should be plenty safe for 92 octane right? or does boost change things?

I'm going to go with cast steel except pistons I'm going forged to take the extra load. This sounding good so far?

PS: Does my valve train need any major upgrade besides the obvious for the hp? BTW has anyone ever rebuilt with a summit 355 kit with forged rods and pistons and cast steel crank? I'm questioning the quality of it just because its summits brand but it would save me a clean 300$ in gaskets and timing ect.

Your piston descision aside from being forged depends on the heads you wish to get, and how big the chambers are. Boost will definately affect your final compression ratio. But shoot for 8 to 1 NA regardles, trust me you will be happy and pretty safe. On a boosted motor nothing(including forged anything) will save it if detonation is present, it will only slow its death so keep it rich at first and tune from there and you will be fine.

Summit equipment sells rebranded good quality parts, most of my car has been built up around summit parts.(They usually turn out to be some big name companies parts without the branding) No worries there...... But before you shop for this make sure you know what kind of heads you are putting on (chamber ccs etc) so that you can make an informed purchase on your other parts.

I'm think of going some cast vortecs and getting em ported and polish and throwing roller rockers ontop. Stock they are suppose to be good to 420hp (seen the dyno sheets on that) so I am asuming with some porting and roller rockers they'll be good to atleast 480hp.

I'll be going with these stocker vortecs
http://store.summitracing.com/partdetail.asp?CP=1∂=NAL-12558060&N=700%200&Ntt=NAL-12558060%20or%20NAL-VORTECZZ5%20or%20SUM-151124&Ntk=KeywordSearch&rsview=sku&Ns=

The only problem is how do you tell your est compression of pistons? Theres nothing listed as 10:1 pistons obviously because of the other factors but how do you tell?

If you are going with a set of vortec heads make sure you polish the chambers well to get an extra one or two CC or so of volume on the chambers, they are around 60-63ccs depending on how the caster felt that day. Get around a 22cc forged dish pistons for a 350 (your overbore of course). This with a 64cc or so head with composition head gaskets will give you around 8.5-1 compression maybe a touch lower depending on gaskets, which should be fine for your goal. If you want a lower compression (youll be fine at 8.5) you will need to go to a larger chamber head (or bigger dish piston) say 72-76cc which will yeild around 7.8-8.5 compression ratio. These are very general guidelines of course but should get you in the right direction.

Anyways as long as you go with my first suggestion or larger on volume of dish or chamber you will be ok.

Hint:TRW-L244 what i always use!

Awsome thanks!

cam chosen yet?

I'd do that absolutely last. After heads, after piston, after CR is calculated, heck, after the shortblock is built There's a lot of choices in that. Make the right one, it'll be the difference between hard to drive, hard on gas etc, and VRRRRROOOOOOOOOOOOMMMMMMM, and easy to drive. Wider LSA and more exhaust duration usually. Comp cams take the "fun" out of finding the "right" cam for a turbo application... They call them "camshafts for turbocharged applications" go figure eh? Call 'em up and ask for a recommendation for your setup. You'll be glad you did.

Isn't it for a turbo that you want less exhaust duration?

yeah I'm callin up crane thats why I had no questions on cams

hmm, I don't think so. I think more exhaust duration gives more volume of air being pumped into the turbo, spinning it more.
At least that's my random guess, I think all the "turbo" cams i've seen have 10* more exhaust duration then intake, compared to 4-6* for a "normal" split pattern cam.

Yeah thats how I always interpreted it. I dont know what purpose the wide lobe seperation serves but I always asumed the increase exhaust lift/dur feeds your turbo more power.

The theory at least, from a pressure comparison perspective is that with a turbo setup you’ll have more exhaust pressure than intake, so you want to prevent overlap as much as possible to prevent reversion/exhaust pressure from forcing exhaust through the chamber and into the intake.

You do that by decreasing overlap 2 ways, the traditional increasing LSA and since there is a lot more pressure on both sides of the exhaust valve you can also get away with less duration on the exhaust.

That appears to be about as far as cammotion gets with their recommendations.

Crain tends to do this also, sort of but goes aggressive in the wrong places.

Comp… well, they’re totally random, call them 3x far enough apart so they don’t remember and you’ll get 3 completely, and I mean COMPLETELY different recommendations.

Real world, the dynamic picture is not quite that simple… those basic rules regarding pressure will work but there is more going on and some have found better results experimenting some. For example, the better your exhaust is the more you should consider something more like an NA cam for the same engine, and another interesting example, that exhaust blowing back into the intake thing… Ford did some studies and found that it helped fuel atomization…

you also have to remember that when choosing lobes for a powerband, increasing LSA will extend the power band and decrease midrange so you may want to choose lobes slightly differently.

I'd really like to know more about your turbo lg4. I've got a carbed lg4 parked in my driveway and my friend says he can hook me up with pretty much any turbo I want. I'd like 400 hp if I can because I think that's about as much as the drivetrain will handle. I'm thinking blowthrough and I really don't know anything about what size turbo. I'm also thinking of a remote mounted turbo like sts. What's your advice?

No problem. I did a pretty thorough write-up on my cardomain page, if you want to check it out. You should be able to get to your hp goals with the right tune. As far as turbo selection, I'm not a good person to ask. I just went off what other people picked for turbos with similar engine combos and goals. I also don't know much about the remote mount turbo. It seems like it would be more expensive and harder to install than an engine mount system. They do look pretty cool though.

My advice is to make sure the engine will be able to handle the extra hp, b/c the pistons/rings didn't last too long on my lg4.