I am trying to build a pump gas 650hp 350 sbc for my 86 camaro. I want to put either a holley powercharger 250 roots blower, 6-71, or 8-71. I am wondering if this is possible with 91 octane? What do you guys recomend for cam, or suggestions on a different power adder? I am starting from scratch, let me know what you think.

Dan

 

you mite need to go turbo to do that

 

Sounds good on paper, but $$$$

Turbo or a mean n/a set up for heavy dose of nitrous

You have the funds to back up that motor with a rearend, tranny, and suspension mods?

Not saying it isn't possible with a roots, but geez...a lot more efficient ways to go at it

If I had unlimited funds I would build a LS1 with a vortec....

 

What heads do you plan on using?

Do any parts exist for this thing already?

and yes, it can be done with pump gas and a positive displacement blower, if that's what you want.

 

I have edelbrock's vic jr heads, and a 8.2 compression bottom end. Other than that, that is it. I dont have an unlimited budget, but dont mind spending some money to make the HP. I have a 69 firebird that runs on the bottle, and I hate having to fill it up all the time, and run high octane fuel. I am looking into building a bracket car that will run low 10s or 10.0s. I can get a new holley 250 for 1,700, and either a 6 or 8 for around 2,000. That is why I was leaning that way, but let me know of any other alternatives.

Dan

 

read my sig and go to town!

 

Is the compression actually 8.2 or is it 8.2:1 pistons with who knows what compression.

If your quench distance at that compression is decent then you’re in a pretty decent place.

I don’t know what your bottom end looks like, but cam it to make max power somewhere in the 6000-6700rpm range (probably something in the high .23x to low .24x on the intake, 5-10* more on the exhaust, preferably some fairly aggressive lobes to keep the advertised duration down and an LSA of 113-114) add appropriate headers/exhaust and pulley the blower to move enough air for your 650 hp and you should be running somewhere in the 6-7 psi range and making that kind of power without detonation.

I’d be tempted to go slightly more streetable with the cam (say high 22x or low 23x on the intake…) a more careful tune, and about 9-10 psi and keep the rest the same, and again, you’ll be right in the range you want to be.

Of course, these are absolute optimum, “if you get everything right” recommendations… If you’re not into fully tweaking things till they’re “right” then I would suggest going a little bigger all around just to be safe.

 

I am thinking aboutrunning comp cams 12-704-8. 255/262 at .050", and .575 lift intake and exhaust. 114 degree LSA. Looks like I will probably run a 8-71 with 8 psi. On DD2000 I go peak power in the 7,000-7500 rpm range. shows 618 hp at 6,500 and peaks at 652 at 7500 rpms. Peak torque at 511 at 6,000 rpms. As for compression, it should be almost right on with the heads and head gasket. Its not any higher than 8.5 for sure. I can always run thicker head gaskets to be safe.

leeperryracing, I was thinking about a ATI. I use to install their blowers on alot of mustangs, and they are awsome blowers, but I have never set one up for a carb. Also I was thinking it would be cool to have the big blower sticking out of the hood. Plus I can get the 8-71 for less money than the ATI, and I have 2 750s laying around, so I would be set on carbs.

Dan

 

leeperryracing, what cam are you running?

Dan

 

I didn’t want to suggest anything that big because I wasn’t sure that you were building up a short block and rest of the drivetrain to work with something like that. I suspect that unless those heads have been worked some that they’re going to run out of breath somewhere in the mid to high 6K range, so I don’t think that you’ll ever see 7500 and I think that cam would be slightly overkill, but otherwise…

Thicker head gaskets won’t help if you don’t maintain some reasonable quench. If you really end up in the low 8’s you should be fine anyway, my brother’s car runs 9-10psi with a positive displacement blower, no intercooling (it’s port fuel injected so not even any fuel going through the thing to cool it), 8.6:1 compression, 218/226/112 cam and aluminum heads, the thing is even happy on 87 octane with the timing locked out at 33*.

Actually, I suspect that will be your biggest issue, with that big cam and low compression your idle will be iffy, locked out timing at a higher setting like that will help.

 

ModifierRacing, you are definitely right....your roots set up will cost considerably less than my blow-thru set up. My cam is a custom grind from compcams(cost me $110 more than an off the shelf one). It is .512/.532 and 226/238 dur. @.050 with a 116 lsa...it is a KILLER cam, idles real smooth and I still have a lot of vacuum for my brakes and such. I wouldn't be surprise if that cam is responsible for close to 100hp

 

Thanks leeperryracing for the cam specs.

Dan