Holley 390 and Offy Single quad intake questions

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Shogun1332

Shogun1332

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Hey Slant 6 Gurus,

I'm looking into a Holley 390 cfm 4bbl, and the Offenhauser single quad intake manifold, I just have a few questions I'd like to get answered if anyone has the knowledge,

So first of all, with the carb, I've heard of people using it on the Slant 6, but is it a bit too much for a stock slant 6? and how much fabrication would need to be done to get a working kickdown set up?

And with the manifold, the image looks like its fairly stock-ish, is it able to be used with the stock intake heating system or not possible at all?

Essentially I'd just like to make a bit more power without sacrificing drivability, if anyone has any other suggestions outside of the standard "throw a smallblock in there" I'm open

Thanks guys!
 
Everything you ask is do-able.But with the larger increase in carb CFM you really need to open the exhaust so it can breath.Yes you can use the stock exhaust manifold.Expect to follow it with a custom 2 1/4 or 2 1/2 system to the back bumper.Dual exhaust is not needed unless it is something you want.Kick down can be done with a cable system from Lokar or Bouchillon Performance.Either work well.With some skill you can make the factory mechanical linkage work. The first slant I did was with a stock internal 225,Clifford intake,390 Holley,Clifford headers,Bouchillon kickdown and a 2 1/2 full exhaust.At the time the whole set up cost about $800 and was worth it.The increase in performance will make you smile.After a year or so I wasn't happy with the Holley and went to a Edelbrock 500 AFB that I liked better.
 
Thanks Darter6, that's exactly what I needed to know, sounds like I'll probably take care of the exhaust first since it needs to be done anyway, then I'll get the 390 and intake set up going. Thanks a ton!
 
The 390 cfm carb is intended for 6 cyl engines, or really small V-8's. There is an Offy PN for a kick-down adapter that goes w/ the manifold. I recall ~$60. Have that PN at home, but you can find it here in a search.
 
Sounds good Darter6. I would like to try it on my slant too. I wonder if the 390 can be jetted down to function even better.
 
I recently put on a holley 350 cfm 2bbl. I used a carb adapter and the stock manifold. It definatly woke up my engine. But i feel that there is restriction with that setup so i bought a super 6 manifold. I dont think you need too much more than that with the stock cam. The carb came with an electric choke and I adjusted the linkage.
 
TF360 said:
Sounds good Darter6. I would like to try it on my slant too. I wonder if the 390 can be jetted down to function even better.
Click to expand...
not sure what your thinking here so just trying to help...most of the time when i read this statement people (jetting down) they think there taking over carbing a engine away. in reality cfm is not effected putting smaller jets in any carb, only changes the air fuel ratio. typically when a carb is to big for the app or on the large side anyway they run towards the lean side. during lower rpm and on the transition. this is usually fixed buy working with the air bleeds in the carb not the jets. although jets may need to be changed to get the carb right. most carb are built with jets that are very close to right and that would include this situation. most holley 390s are vacuum secondaries and that perfect for a slant cause they wont open till the engine is pulling nubers to open it. just so you know ive put them on toyota 22r engine and had it work great so a slant is even larger and better size wise. hope this helps i say do it
 
I'll add that anybody removing the exhaust pipe should consider drilling a hole and welding an O2 sensor bung in the exhaust while convenient. I put two in my slant exhaust, so I can use a wideband O2 sensor and calibrate it to a regular (on/off) O2 sensor. Simplest monitor is a little rich/lean indicator box for a regular O2 (Holley or MSD) and they are cheap used on ebay ($20). Even wideband O2 has become very affordable, especially used by tuners who are always upgrading to the latest. Easier and more accurate than trying to tune a carb by looking at spark plug tips.
 
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