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"The Facts About e85 Kits and Conversions"

This article explains the in's-and-out's of e85 kits and conversions. It includes typical questions to ask your builder before committing to a conversion and explains the pros and cons of current e85 conversion kits on the market.

The Truth about e85 Kits & Conversions


In recent months I have reached my boiling point after seeing a few "conversions" come through my shop that have (to put it nicely) left a lot to be desired. As a long time bracket racer myself (read budget) it frustrates me to see fellow racers unwittingly spend $400-$500 on kits and conversions that frankly, do not work as advertised. So with the best of intentions to fully inform would-be kit and conversion purchasers I have put this article together so you can be informed and ask the right questions before spending your hard earned money.

Of course we would like you to spend your money with us, but that is not really the intent of this article. I believe that a well informed racer is our best customer so here goes . . . . .

The blunt facts about conversion kits

I have not yet seen a single Holley 4150 conversion kit that was complete. None include boosters, most do not include proper accelerator pump hardware and in some cases the metering blocks are a gas metering block design with a pretty new green color and a bit of marketing. I have spent many hours pin-gauging holes in countless carbs and have found that many of the green, purple, and red metering blocks (gas and "e85") have the exact same machine pattern markings on the outside and same size holes on the inside. Really? yes. really.

There are also 4500 Dominator conversion kits out there that do include boosters (Yeah!!! finally!) and other hardware, but unfortunately they come with metering blocks that are a conventional Holley gasoline design. I won't go into details of all the shortcoming of the Holley 3 circuit gasoline metering block in an e85 application but in a nutshell: 1) idle tubes do not provide sufficient flow for the idle and transition circuit for e85, 2) main well is restricted by the idle tube, 3) passageways are not appropriately sized for e85.

All that being said, I will not deny that there are some that have had success with conversion kits. If anyone out there is going to succeed with a conversion kit it is someone with good tuning knowledge, a lot of patience, and a lower horsepower motor -- so congratulations and pat yourself on the back if you are one of the few. (By the way. The reason I say lower horsepower is because gasoline boosters in some Holley main bodies will work OK with e85 up to about 400 HP. Above that level they typically start to become a restriction.)

Feeling a little beat up after reading my rant this far? I hope not -- doing things right is my passion and I do get a little fired up about conversion kits . . . but all is not lost, there are companies that do good conversions for about the same price as some of the more complete kits.


I have always been a major do-it-yourselfer and I can identify with those of you that dare to do complex things on your own. But there are some things I never mess with -- automatic overdrive transmissions, my gas furnace and drywall are the main ones. Drywall because I just plain suck at it and the gas furnace because while I could probably figure it out in a couple tries, but the first couple tries come with too much risk. Transmissions are tough (especially automatic overdrive), and there is just too much knowledge and experience needed to do one right the first time.

Carb conversions are sort of the same way, there is a level of expertise and specialty tools required to consistently have good results. There are companies out there that do offer this level of service and claim to have the required knowledge and tools, but do they? really? Here are some questions to ask:

1) Do you personally race with the fuel? If so how long?

2) Do you build carbs for other fuels? Do you specialize in e85?

3) Exactly what parts will you replace or modify to make my carb an e85 carb?

Using a builder that actually races with the fuel typically means that they are personally passionate about e85. Wouldn't you rather do business with someone that really believes in the fuel? Actually racing with the fuel has taught me much more about it than all my time on the flow bench, dyno, and in CAD playing with orifices and velocities!

I wouldn't necessarily rule out a vendor that builds carbs for other fuels, but beware -- e85 is often a "me too" offering for long established companies that specialize in gas or methanol. e85 is a unique fuel and has some key properties that are very different than gas or methanol. Recognizing these difference and focusing on just e85 allows the good e85 carb builder to break away from traditional tune techniques used for gas and methanol over the years.

Parts and modifications actually done during a conversion are a major factor to consider. Will metering blocks be replaced or reworked? What blocks do you use and where were they made? (China?) Are they finished (anodized?) or raw metal that will corrode quickly? Do you replace boosters? If so what do you do to them specially for e85 carbs?

The watch-outs to look for: installing new boosters. metering blocks. 50cc Accelerator pumps. Hollow accelerator pump squirter screws. Adjustable PVCR, IFR, and bleeds. Are Holley style air bleeds used or just drilled set screws? Is milling my choke horn (if desired) included?

It is important to have at least one 50cc accelerator pump on an e85 carb for fine tuning purposes; and two are needed for larger carbs. You do not have to use a large pump cam and the full capacity of the 50cc pump(s) if your engine doesn't need it, but why wouldn't a builder use a 50cc pump anyways and just use less pump cam? (ans. to save them money!)

Some companies go so far as to over-fuel the transition circuit to compensate for not installing a 50cc accelerator pump! I recently had a carb come through the shop with a .076" idle feed restrictor (to give you an idea Holley gas IFRs are down in the .03x" range, and my e85 carbs are usually in the .04x range) and 30cc accelerator pumps. Idle mix screws were only 1/4 turn off the seat and it was still PIG rich at pit driving speeds.

The Dollars and Sense of Kits and Conversions

Finally, the most often overlooked aspect of switching to an e85 carburetor -- the cost. Is it worth the expense of purchasing a mostly complete kit or make sense to pay for a conversion? Here are some facts to consider.

Since we've established the cost of a proper conversion that includes boosters and metering blocks to be upwards of $400 you also have to consider the cost (or value) of the "core" carburetor to estimate the total cost (or value) of your finished e85 carb. At the time of the writing of this article, I performed a quick survey of the price of used carburetors on eBay. I only looked at carbs that I would consider to be in good enough shape to be worth converting. Here is what I found: 4150 series HP carburetors are going for $175 to $300 with HP950's bringing the best price. Classic double pumper carbs were going from $150 to $250 with the 850's bringing the best price. The big Dominators are currently going for $400 on up with some used race pieces going for $800-$900.

At the risk of using an over-used expression, lets "do the math." An HP or classic DP carb cost plus conversion is going to be $400 (typical conversion cost) plus a minimum (assuming a good deal on a core) will be at least $550 for a classic DP carb and $575 for an HP (best case!) Now consider the shipping costs -- 2 way shipping for a conversion plus one way shipping for the purchase of a core and you can add approximately $60 (assuming a low $20 each way) and you are at $610 for a double pumper and $670 for an HP. Using the same math a Dominator winds up at $860 minimum for a conversion.

Now you may say to yourself, but I already have a carb I want to convert to e85. In this case you don't see the cost of the core, but that core has value -- you could easily sell that carb for the minimum market prices I mention above (more if you're a good Race Junk or eBay seller!) so the same math applies. In the end, you still wind up with a used carb that costs you about the same as a new one.

Hopefully I am getting my point across here -- sometimes it IS worthwhile to convert a carb you already have, but usually it is actually more cost effective to just buy a new one. Current prices for new HPI e85 carbs start at only $540 for a bare bones classic double pumper and race carbs (modified double pumpers and HP carbs) are all $680 at the time of this article. Dominators are starting at $950. If we can help you out with a new carb or conversion, by all means give us a call -- if not, hopefully the information in this article will help you be a more successful buyer!

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