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mikewitt 08-22-2016 01:49 PM

Carb Riser Questions

Hi Friends...
Lovin my 47 Flattie. Here in So CA, I have some hills to climb when I'm out cruzin. NEED MORE POWER.

I'm totally stock, except for dual exaust. Found a 2" riser for my Ford 94 carb. It's all installed with nice Holly good flowing Air Cleaner. I thought maybe the better fuel mixing might give me that little more power I need.

Motor seems to run smoother than ever, idles well. But, instead of waking up some sleeping ponies... now it's slower to accelerate. Runs smoother and seems to run easier, less RPMS for same speed near top end. Once I get going good on the flats.

Thinking that bigger jets might help. Any ideas? I think I running .051
I did have a carb heat transfer on hot days with draindown. It's gone.

Riser stays very cool.

If I just downshift, I can get up any hill, but that line of folks don't like it.


JSeery 08-22-2016 02:00 PM

Re: Carb Riser Questions

1 Attachment(s)
An intake riser will normally raise the torque curve to a higher RPM range. Other than that it is not going to do you much good and will most likely reduce low end performance. There may be some benefit to a performance application where the car is geared, jetted, etc for it, but don't think it is going to help on a stock application.

What rear axle ratio and tire size are you running?

If you are interested in bolt on performance increases you might be interested in JWLs book. He documents numerous dyno runs with various modifications to a basically stock test engine.

dude 08-22-2016 02:22 PM

Re: Carb Riser Questions

high rise ,high RMP.

mikewitt 08-22-2016 02:31 PM

Re: Carb Riser Questions

Thanks JSeery, runnin 15" in rear, 14's in the front.

I'll check into the book, sir


scooder 08-23-2016 07:35 AM

Re: Carb Riser Questions

Less rpms for same speed near top end??
A carb spacer can't possibly change the rpm to road speed ratio, that's fixed by the rear end gear ratio. So I'm now sure I understand what your talkin about there?
If you want more torque at the same speed than a stock engine has, you need to up compression ratio or more cubes or a supercharger or change to a bigger number rear gear. You see that a carb spacer ain't gonna get er done.

JSeery 08-23-2016 08:04 AM

Re: Carb Riser Questions


Originally Posted by scooder (Post 1343110)
Less rpms for same speed near top end??
A carb spacer can't possibly change the rpm to road speed ratio, that's fixed by the rear end gear ratio.

I skipped over that part as I assumed it has to be a perceived difference. As Martin states, RPM to MPH is a fixed ratio that is determined by gearing and tires and not by engine performance.

rotorwrench 08-23-2016 09:34 AM

Re: Carb Riser Questions

Columbia overdrive or perhaps one of the new Mitchell overdrives might do the trick. A lower direct drive ratio might climb the hills better then kick it into OD for highway driving.

mikewitt 08-24-2016 08:06 PM

Re: Carb Riser Questions

Those are all good and "REAL" comments. I guess the motor just seemed to not work as hard to make the same power. It seems to be less power than before that's all.
I know what I need to do and quit trying to find a easier way to pump up the power.
I am pretty sure the gears in the rear are stock... car like it at 45-55 in 3rd... seems to max out normally in 1st and 2nd. Maybe an overdrive might be the ticket... sure would like to cruiz at 65 easier. Thanks fellas.

mikewitt 08-24-2016 08:09 PM

Re: Carb Riser Questions

OH!.... what do you think if I did go up a couple jet sizes? Doesn't really run too rich yet.

donald1950 08-24-2016 09:12 PM

Re: Carb Riser Questions

go to two carbs. that will pep it up....

Fe26 08-25-2016 07:49 PM

Re: Carb Riser Questions


Originally Posted by donald1950 (Post 1343921)
go to two carbs. that will pep it up....


BITD young guys would go the 'bolt-on' route to get a little more power.
Higher comp. heads, exhaust headers with dual exhaust and an inlet manifold with two or three carbs. And it worked. How much is debatable but power and performance were noticeably improved.

Another benefit to dual carbs is a saving on fuel, the carbs have to be well set up and having the manifold ports over the engine ports is helpful here. You will need to relocate your gennie as the front carbie is too far forward.

Another bonus is; this set looks HOT!

Bassman/NZ 08-25-2016 08:01 PM

Re: Carb Riser Questions

+1 for JWL's wonderful book. The book proves, and I have proved it to myself, that the best mod that can be done is to mill the heads to bring the squish area over the piston down to about 45thou. This provides a useful increase in torque, which is what you are looking for. Bang for buck, this is #1. Beyond that, changing rear end ratio and/or adding overdrive works well too, but is definitely not on the bang for buck chart!

rotorwrench 08-26-2016 09:24 AM

Re: Carb Riser Questions

Rejetting is only valuable if it needs to be changed for a reason. The best reason would be moving from say the coastal or valley regions of California to the mountain regions of Colorado. That would be a good change in altitude that would affect jetting/fuel air ratio. Too rich means poor fuel economy and the power would suffer even more. Changes in carburetion should accompany changes in bore size/stroke, compretion ratio, and cam/valve function (hopping up). Dual carbs would likely have to be rejetted small for a stocker. Less so for a thumper hot rod mill.

Tim Ayers 08-26-2016 09:57 AM

Re: Carb Riser Questions

Get JWL's book. He addresses the issue of risers with dyno results to back it up. His book is an invaluable resource.

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