Combination help

I have a 527 bbc 10.1 .750 roller,edelbrock performer rpm heads and just recently switched to a high helix 8/71.This in a 1700lb altered,we had a old Bowers 8/71 and went 7.12 192mph.With the new blower we only went 7 45 187moh at 23% overdrive.Im wondering if the heads are too small.We really thought it'd be faster with the new blower so any suggestions I would greatly appreciate.

 

I associate the Performer series with a street head but Edelbrock may have changed name. You have a lot of cylinder to fill. Boost gauge says ?

 

Unfortunately I don't have a gauge.Nothing else in the combo has changed.35 degrees timing ati powerglide and converter.It also has 4.10 gears.But I can't figure out why it's down on power unless the heads are restriction.I was hoping maybe somebody went thru something similar and could lead me in the right direction.

 

I will be a smart ass and say put those heads on your dually and get a race head. Hopefully others will post too. Call Edelbrock. All these companies like to see their parts run well.

 

The blower boost difference may tell the story.

 

Yikes ! Just noticed 35 degrees timing. Very high I think.

 

What fuel pump ? All in the hat ?

 

If you were close in fuel with the Bowers (i.e. not exceptionally fat), the new blower may make enough more air that you're really lean.

 

It's possible at 23%, the Bowers was making more air than the HH at 23%. We had that issue with a straight rotor versus a high helix blower once.

 

Pretty sure if you bump that overdrive up around 35% or more that blower will come alive...

 

Am I missing something? If we have no idea what the blower boost was before and no idea what the new blower boost is,....how can we make suggestions.

 

Your boost number is a critical part of the problem. Peak boost capture kits are less than $ 150 . and could save you serious $$ in burned pistons. Spud Miller at Fuel Injecion Enterprises has the kits

Do you have any motor data collection capability?

Spark plug reading for this issue is critical. You may be seriously lean. How much did you richen the bypass jet for the blower change? It should want more fuel with the high helix.

You did not change the heads.. The blower is the change. The heads may restrict full potential, but you should not loose performance, unless your jetting was way off. Have you verified that you have no piston damage from possibly running lean?

Your timing sounds high. Big block guys need to contribute on that one. May be head or static compression related for timing. What is your static compression.

I would not change over drive until you know the boost and have verified lean or rich.

As far as I have heard , high helix output is very close on the low end and considerable better on the high end. A blower wizard needs to comment on that.

What brand and model high helix blower did you get? Is it brand new? How is it stripped ( how many points of contact....did it feel tight to hand rotation when new? )

What is the high helix blower case configuration.... delta openings on top and bottom ? does the new blower have nozzle provision in the upper rear of the case. Blower inlet dimension compared to old blower. Does your hat and intake manifold match up with the new blower.

The high helix 8-71 unit should increase cubic inch per revolution by about 14 %. over standard helix. ( see Spud Millers work sheet on Fuel injection enterprises web page. )

Your old blower may have been better than you thought. What is it's case configuration, stripping and maintenance status of the old one ?

Wish you the best of luck on a damage free correction.

Ray H.

 

How much fuel did you add?

Regarding timing....

My experience: if you use hemi fuel, you can probably get around 27 degrees in a standard bbc headed motor (115-119 cc chamber) before you start beating up bearings. Add a little more fuel and you can get 30 in it and that’s probably where it will run best. Keep adding fuel and you can get 40’in there if you really want to, but I wouldn’t suggest it.