My boss is building a Weiand roots blown 383 for his 67 camaro. Its the 177 model. His engine is going to be built with all forged components and 8.5:1 compression. The techline at weiand stated that with 8.5:1 on 93 octane the most boost he can run is 6-7psi with a total timing of 28-34 degrees. Why is it plenty of FI guys here an on other sites can run 12-15psi on pump with LT1's and LS1's with centrifigals and turbos, but a roots blown forged 383 shouldnt go over 6-7psi?? Seems odd. I think they said his dynamic compression shouldnt be above 12:1 according to weiand.

I also told my boss to run lower timing (like 18-20 degrees) and just run more boost.

Does the weiand guy know what he is talking about?

 

I think the main differences are going to be the fact that our ECM has the ability to constantly tune the fuel ratio and timing, and the roots blowers generate alot more heat which increases the chances of detonation. I'm not sure how much he could run with the roots, but I bet the recommendations from Wieand have a thick safety cushion .

 

I assume its because there is no charge cooling, thats why they say 6-7psi max. He will follow their recommendations too. Here is the million dollar question:

Which car will be faster down the track assuming nothing changes except FI:

1. 383ci roots blower @ 6psi
2. 383ci centrifugal @ 12psi intercooled

I assume the centrifugal will murder it since your only under 4k at the launch (it depends on the person ), other than that every shift will be right up there rpm wise.

 

Taking into account the size of his engine, the heat issue with Roots type blowers and how that is affected by blower size; I can't help but wonder if he might not be better off with the 250 Blower. (As opposed to the 177.)


Just a thought...
Perhaps he's already considered and rejected the idea.

 

Good thought...I believe he only wants to step up to the 177 because height of the unit starts to be come a problem. He actually liked the 142 unit, but it wont flow enough for a 383, so he said 177 may be doable, but he needs a new hood for that. He doesnt like the huge 4" cowl type hoods, so height will be a limiting factor.

I guess it comes down to 6psi roots blown 177 versus 12psi intercooled S/T trim. Which one will make the faster car down the track? I assume the centrifugal.

 

You are correct, The centrifugal woould kill the roots, the roots would provide more low end torque and throttle response, but the centrifugal is more efficient and would provide a cooler charge even without the intercooler. plus with the levels of boost mentioned, there is no comparison between 6 and 12 psi.

 

Well, there are several variables and you have to consider the vehicle as a package.

A lot of people like the Centrifugal blower specifically because it makes it's boost slowly at first, coming up to full boost as your engine's RPMs climb. This tends to reduce the tendency that a Roots has to overpower your tires. (Not to mention your drivetrain.) A Roots behaves a lot like a normally aspirated engine of twice the size.

I would say that the most important part of choosing between the two is to decide how you want to use your car ans what your expectations are.

 

Well, his car is a 67 camaro, street car mostly. He is going to have HPE build his 383. He would like to make 600rwhp atleast. I dont think the Weiand 177 @6psi will get him there. I do think the D1SC or T-trim will though (at higher boost obviously). Plus he can run an intercooler with the centrif. I almost got him talked into it

 

LT1's can get away with a bit more boost because their cooling system takes heat out of the heads first, which effectively lowers compression along with the F-Body's aluminum heads. While this lowers thermal efficiency, it allows for more boost.

The draw through arrangement has an aftercooling effect utilizing the evaporation of gasoline to pull heat out of the charge. While not as dramatic as an aftercooler on a centrifugal setup, the benefit is there.

The small displacement underhood blower must be spun pretty tight to make much boost which lowers its efficiency. The multigoove belt , small contact area and spring loaded idler allow for belt slip as the load increases on the blower with higher boost.

While his horsepower goals are most likely out of reach, he should ask himself what his performance goals are. 10 second 1/4 mile times and solid reliability and drivability are easy to obtain with that setup, with virtually no cruise noise.

Engine tune will be determined by the rest of the combination. The advice given by Holley/Weiand was safe and fair and is based on Weiand's (pre Holley buyout) years of servicing/owning the supercharged street performance market. The recommendations are safe and generic.

 

At the risk of asking a silly question, are we talking about a Gen I or a Gen II smallblock?

 

what about a whipple

http://www.whipplesuperchargers.com/...sp?ProdID=1171

 

Most excellent suggestion.....

 

1st gen standard SBC.

 

Good suggestion, but it runs into the same problem as the roots, maxxed out ~7psi on pump gas due to no intercooling. 518hp @ flywheel at 7psi wont cut it. I am guessing they only published the 7psi cuz thats all they will run safely without charge cooling. He is looking for ~600rwhp (680hp @ flywheel). I know the whipple and roots have a flat torque curve, but after 1st gear, it doesnt matter.

 

I'd disagree about the Whipple. The screw compressor's effciency is higher than the roots. The Whipple progressively compresses the intake charge, whereas the roots is a bit more savage, this is the reason for the high helix roots blowers used in racing. The little 177 blower has 2 lobe rotors as well. Just about as bad as the roots gets, and they still work well.