BEST STREET USE CR FOR 8-71 BLOWER ON HEMI

[K-chai]

Hi
Any suggestion on the CR for street use(MAXIMUM 91OCTANE) should be on 426 hemi with Blower8-71
Thank you
Chang

 

[MiradaMegaCab]

How much boost are you going to run?
Do you plan on W/M injection?
Vehicle weight, rear gear ratio, give us some details and plenty of pics!

 

[K-chai]

Hi
actually this car is not mine, but my friend in thailand(mine is 68 in the restoring process). The spec of the engine is use to be 426 hemi with 11:1CR but since the fuel quality in our country is maximum 91MON. The engine is broke down. Now we set the new engine wit 8-71 blower boots around 5-7. TDI 6X gearbox and the reargear3.5.and we reduce the CR to 7.5 . The car is not pull that hard as we expect. We really dont know what is the problem. Should we increase the CR. Or any other suggestion .help us out plz.

 

[K-chai]

1st pic is before we put the blower

 

[K-chai]

Engine bay of my friend's car

 

[K-chai]

Mine is still Dry

 

[K-chai]

How much boost are you going to run?
Do you plan on W/M injection?
Vehicle weight, rear gear ratio, give us some details and plenty of pics!

K-chaiActive Member
Hi
actually this car is not mine, but my friend in thailand(mine is 68 in the restoring process). The spec of the engine is use to be 426 hemi with 11:1CR but since the fuel quality in our country is maximum 91MON. The engine is broke down. Now we set the new engine wit 8-71 blower boots around 5-7. TDI 6X gearbox and the reargear3.5.and we reduce the CR to 7.5 . The car is not pull that hard as we expect. We really dont know what is the problem. Should we increase the CR. Or any other suggestion .help us out plz

 

[coloradodave]

If the CR is an ACTUAL 7.5:1, I would not increase it if the plan is to run 91 octane fuel without additives. If you have limited the boost to 5-7 lbs.( as verified with a boost gauge), the first thing to check is the carburetors (they do have 'boost' reference power valves, don't they?). By that I mean that you want to 'over jet' the carburetors so that you are on the rich side, and then work backwards from there going by spark plug coloring. It's very easy to lean out a blower motor and destroy pistons. A method to retard timing at higher RPM (several makers of these devices, depending on your ignition system) is also a prudent buy. If you're still looking for more power after all the tuning has been done correctly, you can always up the boost and mix in some race gas. Do you have access to a chassis dyno and a shop that knows how to tune?

 

[K-chai]

If the CR is an ACTUAL 7.5:1, I would not increase it if the plan is to run 91 octane fuel without additives. If you have limited the boost to 5-7 lbs.( as verified with a boost gauge), the first thing to check is the carburetors (they do have 'boost' reference power valves, don't they?). By that I mean that you want to 'over jet' the carburetors so that you are on the rich side, and then work backwards from there going by spark plug coloring. It's very easy to lean out a blower motor and destroy pistons. A method to retard timing at higher RPM (several makers of these devices, depending on your ignition system) is also a prudent buy. If you're still looking for more power after all the tuning has been done correctly, you can always up the boost and mix in some race gas. Do you have access to a chassis dyno and a shop that knows how to tune?

View attachment 333991

Hi thank you for your reply
Noy much thai know about american engine esacially HEMI. now we re do the caburetor tuning will let you know the result. Any way do you think we can boots more with out the race gas?

 

[coloradodave]

What we think really is not important, because if we say to increase the boost and the crank, rods and pistons don't like it, it's a very expensive lesson as they come flying out of the pan in several pieces. I asked you if your friend has access to a chassis dyno. Does he? Blown motors need to be tuned from way rich backwards to a little rich in small increments by someone with experience and the tools to analyze problems before they become catastrophic. Guessing wrong will cost your friend a lot of money. Find a dyno and a competent operator. That's the best advice I can give you...

 

[K-chai]

What we think really is not important, because if we say to increase the boost and the crank, rods and pistons don't like it, it's a very expensive lesson as they come flying out of the pan in several pieces. I asked you if your friend has access to a chassis dyno. Does he? Blown motors need to be tuned from way rich backwards to a little rich in small increments by someone with experience and the tools to analyze problems before they become catastrophic. Guessing wrong will cost your friend a lot of money. Find a dyno and a competent operator. That's the best advice I can give

What we think really is not important, because if we say to increase the boost and the crank, rods and pistons don't like it, it's a very expensive lesson as they come flying out of the pan in several pieces. I asked you if your friend has access to a chassis dyno. Does he? Blown motors need to be tuned from way rich backwards to a little rich in small increments by someone with experience and the tools to analyze problems before they become catastrophic. Guessing wrong will cost your friend a lot of money. Find a dyno and a competent operator. That's the best advice I can give you...

Thank so much for your help

 

[Bigal75]

What are the engine specifications ? Are the heads stock? Does it have a cam designed for a supercharger? Timing?

 

[hangn0ut]

More compression with less boost will give much better throttle response. That 7-1 comp is gonna feel lazy down low. You guys should consider a pair of holley blower carbs and have em jetted by a carb shop here for your application. At least that should get you close.

 

[hangn0ut]

I myself might have kept the 11-1,ditched the carbs,picked up a bird catcher system,15% over,lock the ignition @32° and a fuel cell full of methanol. Start calling myself torett.......lol.

 

[K-chai]

I myself might have kept the 11-1,ditched the carbs,picked up a bird catcher system,15% over,lock the ignition @32° and a fuel cell full of methanol. Start calling myself torett.......lol.

Will 91 able tu run 11-1? Or meth

 

[hangn0ut]

Pump gas and 11-1 blower motor,nooo. Now methanol is a whole nuther story. What I posted would be good for 900-1000 hp. Mileage would be terrible but you wouldnt care. Cool running,no fouled plugs,wide tuning window and big horsepower. As you might have guessed I love methanol.

 

[Bigal75]

Yes methanol would be awesome. You can run 30 psi with 11 to one compression and the blower would never heat up. If you go that route keep us posted. I'd love to build a efi methanol set up. Or even dual fuel where you run on gas normally and the fuel change to methanol when boost kicks in.

 

[K-chai]

So methanol is the anseer for every thing right?. Any recomend on vhich brand.snow performance??

 

[HEMI-ITIS]

Show me a licence plate on the back of that car from your country.Then maybe I can help

 

[Bigal75]

Not meth injection!! Methanol. As in the engine runs on alcohol. The other is water/methanol injection under boost. You can not run 30 psi with 11 to one with that set up.