I6 intake, carb, header upgrades? Worth it?

[CST10]

I have an all original 1968 250 CI engine with an HEI upgrade.

Thinking about adding an intake, carb and headers to it. What kind of power increase can I expect? I know the original set up rated it at 155hp/235tq.

Any recommendations. Would like a little more power without a V8 upgrade.

[Ohio mike]

I don't know about the 250 but a buddy of mine had a 258 jeep inline he milled the head, put a cam, intake and Holley 4 barrel and 3" exhaust. It was a beast, you would swear it was a v8 if you didn't know. I'd love to try it someday on a 250.

[Jonlopes]

You can get good horsepower out of a straight 6 but they tend to work best in lighter vehicles like an old CJ. On the other hand try and tell the Turbo Buick guys you need a v8 to do well in the quarter mile.

[leddzepp]

Did it all the time to my Jeep CJ inline sixes. Difference is night and day, worth every penny IMO

['68OrangeSunshine]

I've been running a 4 barrel carb, Offy intake and Clifford headers on the L6 292 in my '68 C/10 Stepside since 1978. The intake and headers are on their second engine. After 250,000 miles on the last engine and a 500 mile break-in with a newly rebuilt 292, the 390 Holley gave up the ghost. But it was old and I decided it was more cost-effective to put on a new 500 CFM Edelbrock 1404 [AFB-clone], than to get a new throttle plate for a 25 year-old carb. I have since upgraded to a Pertronix II ignition. The new build in 2005 included larger [1.84"] intake valves and a Crane 260H cam.

[GRX]

"Worth it" is relative. You will probably see slight gains. Potential from bolt on externals mentioned is best utilized by upgrading the camshaft.

[Lokin4AReason]

with the bigger carb. and aftermarket exhaust, your just making it breathe better

[GRX]

Originally Posted by Lokin4AReason

Installing a bigger camshaft along with the bigger carb. and aftermarket exhaust, your just making it breathe better

Fixed

[CST10]

So there isnt too much to gain without camshaft swap then ? Any recommendations on camshafts?

[Custom/Ten]

Originally Posted by CST10

So there isnt too much to gain without camshaft swap then ? Any recommendations on camshafts?

X2

Langdons stovebolt, and summit sell them but as to what you should use, that's over my head. If your ready to buy you could call Langdon guy but his selection is pretty limited. An old timer I respect always said just call edelbrock and they'll tell you what you need! Langdons also sells some sweet lookin cast iron headers, and they're shortys too. I bought some cheap headers from summit and hated them, thin flange and way too long, looked like crap, touched the intake, I wouldn't get the long tubes.

[GRX]

The stock 250 cam is not performance oriented by any means. Around 390 lift intake & exhaust if memory serves. A common upgrade I often did for customers was install a Mercruiser marine cam which can be used with the stock springs. A step up is the Crowler #03240 cam which is what I am running in my '69 250. Similar to the "towing cam" of old. My '69 c10 is running stock intake & Monojet carb, with split headers. Nice improvement in low end with very smooth idle. Highly recommended you go with the #84008 lifter/spring/retainer kit along with it.

Cam: http://www.crower.com/camshafts/chev...ulic-cam.html#

[Custom/Ten]

I think he's talkin bout this guy up top, correct me if I'm wrong

[Scottcoda]

I had this very same question about a year ago and when I weighed the costs of a complete upgrade and engine overhaul, I fiqured out it cost more to do then getting a brand new gm 350 from Jegs.. But with a little ebaying, amazoning and patience i was able to get a Clifford intake, a never used but second hand holley 390. Hedman headers, a full dual exhaust,tom langdon valve and side covers for around 700 bucks.. No cams or engine work.. The exhaust sounds nice, other than that the upgrades provided very little performance boost without any internal engine work but without a doubt gets a ton of attention at the shows.. I wish I could say people stop to check out the truck it's self but it is always the engine people stop to check out.. On a long row of small block Chevy's my inline 6 stands out.. There is always a crowd under my hood and not because it is pretty because it is not.. It because it is not another 350 like every other hot rod at the show.
I wish the engine work was more affordable because when my 250 dies I will be in that row at the car show like everyone else.. With my brand new short block 350.
Posted via Mobile Device

[CST10]

Originally Posted by GRX

The stock 250 cam is not performance oriented by any means. Around 390 lift intake & exhaust if memory serves. A common upgrade I often did for customers was install a Mercruiser marine cam which can be used with the stock springs. A step up is the Crowler #03240 cam which is what I am running in my '69 250. Similar to the "towing cam" of old. My '69 c10 is running stock intake & Monojet carb, with split headers. Nice improvement in low end with very smooth idle. Highly recommended you go with the #84008 lifter/spring/retainer kit along with it.

Cam: http://www.crower.com/camshafts/chev...ulic-cam.html#

Question? How's that stock manifold working with those headers? By that I mean, when the engine is running the stock intake used the stock exhaust manifold to provide heat to vaporize the fuel better for a better air/fuel mixture. I heard, not experienced, that they tend to run very rich without it when the engine is cold. Any truth?

[Custom/Ten]

Originally Posted by CST10

Question? How's that stock manifold working with those headers? By that I mean, when the engine is running the stock intake used the stock exhaust manifold to provide heat to vaporize the fuel better for a better air/fuel mixture. I heard, not experienced, that they tend to run very rich without it when the engine is cold. Any truth?

Eventually someone with some experience might speak up, I'm just talking from research here. This is langdons stovebolts solution to adding headers, common sense says this will take longer to heat the intake than a heat riser but after reading up on it this is what I will be using when I build my 250. Along with langdons cast iron headers. That said, plans can change real quick lol, but at the moment I'm really diggin these two items of his.. I suggest you take a look at it. I hear nothing but good things about it but go check it out for yourself, at least you'll see some cool stuff on there.

[slomotion]

Originally Posted by Custom/Ten

Eventually someone with some experience might speak up,......................

I'm not sure I understand what this means. Several posts have sounded pretty detailed to me.

I have the water heated intake manifold on my engine, but bypassed it after I didn't notice any real gains with it. I don't jump in my truck and go, I usually let it get a little temperature before I take off. I have a 195 deg thermostat and the cast headers seem to warm the aluminum intake pretty quickly. I've never had a carb icing problem with this set up like I did with a crate 350.
From what I've heard and have no reason to doubt it is, the single quickest gain in power and reliability is the HEI.
My truck isn't quick, it's heavy and was designed as a work truck, I just wanted something a half-step out of the mainstream, but what it has got going for it is reliability, smooth operating, and easy to work on. It'll exceed the posted speed limit.......(I guess my age is showing now....)
Probably a good investment for the money spent is a copy of "Chevrolet Inline Six-Cylinder" by Leo Santucci. This is an excellent resource on I6 speed/power modifications.

[Custom/Ten]

Quote:
Originally Posted by Custom/Ten
Eventually someone with some experience might speak up,......................
I meant in response to the last question he asked. The one that no one had answered yet. The one about loosing the heat riser when you add headers. Ya know , the question you just answered. wasn't saying the previous posts weren't useful. When I said person with experience I meant someone other than myself as what I was posting was based on research, NOT experience. Wouldn't want to upset anyone lol. Hope that clears that up for ya. I just got excited when someone said they wanted to build a 250 cause I think they're really cool and unique. Thought I would share some of my research since I liked the topic. Most people just rip them out because it's easier and cheaper. Anyway I'll just shut up now lol. Good luck with your 250 sir.

[GRX]

Originally Posted by CST10

Question? How's that stock manifold working with those headers? By that I mean, when the engine is running the stock intake used the stock exhaust manifold to provide heat to vaporize the fuel better for a better air/fuel mixture. I heard, not experienced, that they tend to run very rich without it when the engine is cold. Any truth?

Sorry for delayed response. Just getting back from vacation. As others said above, it is not as big an issue with these engines. Though with the headers I do have to work the choke more in cold weather before the engine is at full temp. Which is fine by me since I have to tweak the air/fuel mixture screw on the Monojet carb with big temp changes as well. Would rather do that than rely on modern sensors. Old school all the way for me. Yep. Points too

[GRX]

Full agreement taking a straight 6 to car shows. Even though mine is old and grimy people are always standing around swapping stories. "Had one of those in my work truck and it ran forever." Or ... "You cannot kill those things." Chevy 250 used to be dime a dozen but few people rebuild them anymore. So a lot of parts houses have kits on the shelf collecting dust so they can be had pretty cheap. Shopped around about a year ago and found a few quality top to bottom sets complete with pistons, rings, gears, bearings, and gaskets for $190.

[Custom/Ten]

Originally Posted by GRX

Full agreement taking a straight 6 to car shows. Even though mine is old and grimy people are always standing around swapping stories. "Had one of those in my work truck and it ran forever." Or ... "You cannot kill those things." Chevy 250 used to be dime a dozen but few people rebuild them anymore. So a lot of parts houses have kits on the shelf collecting dust so they can be had pretty cheap. Shopped around about a year ago and found a few quality top to bottom sets complete with pistons, rings, gears, bearings, and gaskets for $190.

X2 lmao, here a lot about people tring to kill the 250 lol

[RichardJ]

You can change the cam, but you are still limited by the roughly 8.0:1 C.R.
It just keeps getting better doesn't it?

I rebuilt my 292 and used a 194/204 cam which is like Langdons Stovebolt and others sell. A little smaller than the Crane H260 that '68 Orange used which I think is a 204/204 (not sure). Bigger than the original 292 cam, which is 188/188. I included 9:1 pistons, roller rockers, 1.94 intake valves, Clifford intake and Carter AVS, The HEI and long tube headers had been installed previously.

I drove it around for a few days and was very happy with the time and money spent. It wasn't a 3/4 ton rocket, but it was good. That week, I pulled the 4.56 gears out and installed a 3.54 with posi.

That put a big smile on my face.

Even with the new engine, I was still in the slow lane with the engine screaming. I got there sooner, but I was still in the slow lane. With the new gears it runs in the fast lane with ease.

I put in the AC in and it now runs in the fast lane with the windows up and an even bigger smile.

I think if my truck had 3,73 gears, I would be looking for something with overdrive.
If not a 5-spd, then an 4-spd automatic with overdrive.

I have a feeling you are going to come back with some flowery stuff about how cool and original the column shift is, but it really isn't. It's going to have one of three (all tall) first gears and still have big steps between gears. I am mindful that my truck 4-spd isn't a whole lot better. I just can't wrap my head around having a more powerful engine and making that first shift, uh over and up into second. It would just leave me blank.

[Scottcoda]

Richardj.. Sorry for the little hijack of the thread but I was looking at your set up and my set up is similar, maybe you could help me out.. I am doing a front disc conversion and wanted to do power brake upgrade as well, I was wondering where your vacuum line runs to from the brake booster, I have only been able to find info on stock set ups.. On stock set ups the vacuum line runs from the booster to the stock intake manifold.. Any info would be great!!! I hope I explained what I am looking for correctly

[Custom/Ten]

RichardJ, "flowery stuff" that's lame bro! Must be a chill living under that bridge lol.

[RichardJ]

Scottcoda, there is a round, raised pad on the top of the runner where it turns for cylinders 5-6. It's there for just this purpose. I think I used a 1/4 NPT pipe tap and a 7/16" drill.
Myself, I'd pull the manifold rather than take chances on shavings going in the engine. I've read some of your posts, but I don't know how long you've had your engine running. If you don't pull the headers away from the head, there is a good chance you won't have to replace the gasket. I've read where you said you installed all studs for the manifolds, so the header shouldn't move at all.

[Scottcoda]

Originally Posted by RichardJ

Scottcoda, there is a round, raised pad on the top of the runner where it turns for cylinders 5-6. It's there for just this purpose. I think I used a 1/4 NPT pipe tap and a 7/16" drill.
Myself, I'd pull the manifold rather than take chances on shavings going in the engine. I've read some of your posts, but I don't know how long you've had your engine running. If you don't pull the headers away from the head, there is a good chance you won't have to replace the gasket. I've read where you said you installed all studs for the manifolds, so the header shouldn't move at all.

Awesome!!!! Thanks for the help!!! That for sure is the route I would have gone if I did not have a brain fart and forget that on the underside of my Clifford, directly beneath the carb is a vacuum port that I plugged when I installed the manifold.. Sometimes I am amazed by my gigantic brain cloud.