To: mail@xxxxxxxxxxxx Subject: Re: Holley Pro-Jection for a 258?
Your remarks on sizing all ring true. Everyone love to oversize carbs! I wonder now if a lot of the problems with thwe Holley TBI setup aren't related to using the 670 on the six (but I'm not rich enough to find out the hard way :-)
I'll keep looking for a used Holley 300 setup on ePay etc, but will probably just get a Weber and get on the road.
My spreadsheet calcs cfm, and I too assume 80% VE. At 70mph it's pumping 150CFM, right in the middle of the 300, doesnt' hit 300 cfm til nearly 5000 like you say.
The max recommended carb for a 258 is 500 cfm, and a 500 2V has a little trouble idling smoothly. I wouldn't put one that size on a stock 258 unless it was a 4V (there is a 450 4V made -- I think by Carter). The most common 4V used on a 258 is a 390 cfm Holley though. Holley recommends their 390 for a mild 300, 600 for "hot", and 650 for full race. "Hot" includes a high stall converter, aggressive cam, and deep gears -- a street/strip bracket racer.
From the Holley website:How To Calculate CFM: Engine size (CID) x maximum RPM / 3456 = CFM CFM @ 100% volumetric efficiency
(Example: 258 CID x 4500 RPM = 1,161,000 / 3456 = 336 CFM)
Approximately 608 CFM would be required for this engine. However, most Street engines are capable of achieving only about 80% VE; a modified street engine with ported heads, headers, intake and carburetor can achieve about 85% VE; a fully modified race engine can achieve 95% or greater VE. The CFM number arrived at with this formula must be factored by this percentage.
336 x 0.80 = 269 cfm ; so the 300 would be about right for a 258. 4500 rpm is about the max I'd think you would run it. My 4.6L runs out of steam at about 5500 rpm, and it has a mild cam ("econo-power" from NAPA) and more cubes. Even if you max the 258 at 5,000 it only wants 298 cfm (after factoring for 80%).
Since you're going mostly for driveability sounds like the 300 cfm would be the best choice. It doesn't appear to be CARB certified though: "Not legal for sale or use in California on any pollution controlled motor vehicles." Is that a problem with your car's age? You would want the feedback kit as well, it's optional on that model. The 670 cfm unit is recommended for V-8s up to 275 hp. If you were building the 258 up it might take that much, but only as a full race engine. I have an article where someone used a 4.3L V-6 TBI unit on a 258 and it worked fine though. The Holley website lists the 4.3L replacement as a 670 cfm, but it's a bit of overkill. The BBD carb should flow less than 300 cfm, but could be nearly equal to that amount (250 or so is my guess, though I don't have an exact figure -- the venturi area is less on a BBD than the 1V TBI unit, so it should flow less, though the BBD may have a bit more velocity, which would increase flow some).
This is basically a GM 1V system from a 2.5L four. Find a pre 86 2.5L TBI equipped car (with a distributor, can't use the distributorless type) or S-10 truck (they used the distributor longer, I think) and pull it all. You can leave the distributor connection off, the computer will still work. Fabricating an adapter for the TBI unit should be a piece of cake for you! You can get a GM HEI distributor from a V-6 and from an I-6 and mix and match pieces to have timing control as well. There are several companies who will burn a new chip to better match the engine.
I would either use the 1V unit for a near exact replacement for the BBD or the 400 cfm 2.8L V-6 unit, but not the 670 cfm unit unless the 258 was built for performance. There will be a slight performance increase with the 300 cfm TBI unit as well, but more driveability than anything else. The 2.5L four turns much faster than the 258 and needs just as much air, but the 400 cfm unit will give you a little room to play with.
Of course you should be able to find a Jeep 4.0L in a salvage yard easy enough now. The Renix unit (87-90) will adapt to the 258 much easier than the later HO unit. The knock sensor and EGR make a big difference! One problem that 258 people always have is pinging with regular fuel with the Chrysler/HESCO kit. It's based on a 91 HO system from a Wrangler though, you shouldn'thave that problem with a Renix system. The MPI system would work much better, but you have to use the 4.0L exhaust as well as intake, and your head pipe would need reworking to match up.
On April 18, 2005 Tom Jennings wrote:
I tried calling Holley, but they don't seem to have application support...
I may get rid of my tax return with a Holley Pro-Ject system for my Hornet. (No LP conversion at this time; I want on-road fast!)
Holley makes one kit, 501-12, that is a 300cfm bolt-on for the Jeep 258. This sounds like the correct kit for me. However at least one person is saying I should get the 670 CFM kit instead. There's no real difference in price, and both are 2-bbl replacements.
Will the 670 work OK at low speeds/low CFM?
Does this sound right? Are holley CFM ratings conservative or bragging?
I'm looking for a used one, if anyone has one, digital only.
.
============================================================= Posted by wixList Archiver -- http://www.amxfiles.com/wixlist
Back to the Home of the AMC Gremlin