STD Helix vs Hi-Helix Roots

All things being equal, what will be the performance difference between the Std and Hi-Helix roots?

The reason I ask is that I just had the rotors replaced in my old 14-71 SSI "B" Std rotor to "F2" Hi-Helix rotors. I was spinning it 44.4% over and pretty much had the tune up dialed in. I did run it at 50 over before and picked up over a tenth at the 1/8 mile race I was running so I know there was some more left in that combination.

The goal is to make this go quicker but not sure if I need to reduce the overdrive or just leave it and throw more fuel at it. If I left it the same, how much more fuel? Calculated flow to motor now is 12.93 GPM. Working on installing a flow meter.

526 KB Olds AJPE Heads
8600 Shift
11.5" top opening
Full open bottom with pie in setback plate

Thanks.

Tom

 

helix

Try 9000 if you are comfortable.

 

iam with don 9000 what trans? I run a mert hihelx retro spinning it over 50% with way over 40 # of boost

 

Appreciate the replies but I'm not sure how revving it higher will tell me how much more fuel I'll need to put in this. I can run it higher but what I was wondering is if I keep the same overdrive, will I need to put more fuel in it to keep it safe and how much. The only change I've made so far is the pair of rotors. I figured with the better rotors it'll have more flow and will need more fuel. I was looking for a ballpark area to get me started because I wasn't sure what the difference in flow would be between these two sets of rotors.

I had 38 LBS with the old rotors.

Dave, the trans is a Turbo 400 with a 1.86 1st and 1.31 2nd gear.

 

Call SSI and ask how much more air you will get from that F2. It is way way better than the B.
This will help you figure how much more HP you'll make. Use this to see the increase in % and increase your GPM by that amount.
It won't be perfect but it will get you close enough so you have some confidence.
Good Luck!

 

that dont sound like enough fuel to 12.9 gpm but what do i know i spin mine 57.7 over

 

How did you get the F rotors into the smaller diameter B case , did you bore the case out or have SSI make the rotors a smaller diameter ? . I am pretty sure when they replaced the D rotor with the then new design F rotor they made the rotors a larger dia. to the maximum allowed by the nhra/ihra rule book . Also the "V" angle of the pie opening is different from a std. rotor to a HH rotor in the SSI cases , I know yours is a full open bottom but i figured I would mention it .

 

Does the "B" case have a Delta output? Or are you using hi-helix rotors in a case with a full size rectangular output?

 

The high helix rotors make more air, and push the air towards the front. Hopefully you are running port nozzles, If you are running 55's in the front two cylinders, I would put 65's in, and richen the whole system .020 on the main jet. Just a rough guess, maybe someone has an exact setup for you.

 

Yes the F rotors are larger. I assumed SSI bored his cases.

 

Its my understanding that a hh moves the air to the front slower thus angles the air more into plenum and away from the panel. With your full bottom and 11 inch top I can see a lot of leakage. But should run somewhat cooler.

 

Called and they weren’t quite sure of the difference. Probably have to get it on the blower dyno to compare. We talked about adding 10% more fuel as a start.

Yeah, have the pulleys to go 57.7 and SSI said the top opening would work just fine for that. Will have to sneak up on it, may be looking for a bigger pump.

The rotors were turned down on the edges by .045" so it was a total of .090" taken off. The "B" case is .090 smaller inside than the "F" series.

The case I have is a full open so I used my setback plate to put the "pie" in. SSI gave me the schematic for the "F" case a few years back and I programmed in the dimensions into a CNC and cut the plate. I was using that all along with the STD/60 degree "B" rotor.

No (in the plate) and yes, full size.

Thanks Ken, have a 59 in 2 and 62 in 1. I'm all for richer now as I can back it down. Just didn't want to start too lean.

I'm hoping it to be cooler. The other rotors had tons of strips in the rotors (more heat), more for a fuel car that alcohol so Rich told me.

You may ask how I got to this concoction. It started out last week when I broke the coast rotor's front shaft on the burnout. I was weighing my options because I was looking for a new blower anyhow to try to get this car down the track faster. I took it apart and with the exception of the rotors being goofed up from banging in to each other, everything else looked pretty good. Was going to have SSI weld up the rotors as they were not that bad and replace the shaft. The shaft broke right at the internal lightening hole and where it registers in the bearing, the thinnest area. Rich said that if this one broke the others would probably follow as all the shafts are machined the same. This design was changed in the newer stuff so this would not happen.

He said he had a pair of F2 rotors that he could machine to fit the "B" case so I took him up on it. I guess you could call this a poor man's Hi-Helix with a delta opening if you use the plate.

It’s a door car that weighs about 2700 LBS with me in it. It has gone a best of 6.64 @ 210 MPH. I’m really looking to shave some off of that time so I can be competitive with the group I’m racing with.

 

I know this is ridiculously old but I’m curious how much difference the rotors made?