250 Inline 6 Performance Build Q's---Hello Brad---

[longorange68]

Hey all,

Got a 1968 Chevy C-10 with a 250 inline, SM465, and a 3.73 posi in the rear. I have been off again on again about the powertrain for sometime regarding this truck... First an LT1/4L60E combo I had sitting in my garage, then a 406 SBC/TH400 (which are still sitting in my garage BTW), LS1/T-56, and most recently a late model 5.3/4L60E. All would be good candidates, but for some reason I feel a connection to the old six I can't get over. I've ridden in a lot of different trucks powered by a lot of different powerplants, but I feel at home in my P.O.S. 68 with the inline, makes going down the road kind of special. (Don't mean to get all weepy, I'm 31 and have had her since I was 15, she's family.) My great grandfather taught me all about working on her, as we wrenched on his 68 with a 292, I'd just hate to lose the memories. There will be plenty of time to build another rig that can scare the s--t of me later...

I would like the truck to have a decent amount of power, but I realize that it's not a big block too. As far as trannies go, I am still up in the air. A 700R4 would be nice because of the overdrive, but Brad from the board has a pretty cool combo with his T-5 setup too which should make decent mileage.

Keep in mind that my knowledge is limited as far as performance reagrding the inlines. Here are my questions.

---The engine is all original, and I would like to rebuild it. What do you recommend for internals? I have looked at the Clifford website and checked out the price of their rebuild kits. Are they worth the price?

---Who makes the best headers? Is a split header better than a one piece header?

---Any recommendation on intakes? I know that the water heated one's help fuel atomization, but who makes the better product? Clifford or Offenhauser or someone I've never heard of?

---Any pro's or con's regarding tranny selection?


Thanks in advance,
Josh in Longview, WA

[chev-obsession]

well i think that the LS1 and the T-56 would be pretty sick, but you can do what you want there. as far as the 6 cylinder goes, i had heddman hedders on mine, and they were split hedders, and they worked great. crane cams makes several different cams for them too, i was going to get one for mine but i got a 350 instead.

[Brad]

Why are you wanting to rebuild the 250? Unless something is drastically wrong, I'm betting you don't need to. As far as the price of the kit, I really couldn't tell you if that's a good deal or not. I think all their other stuff is overpriced so it wouldn't surprise me if that kit is as well. (In all fairness, I'm sure it's expensive running a business with a very limited market!)
I can tell the sentimental value of your truck and L6 is high and that's exactly why I'm trying to keep my Camaro all original. However, having said that, you'll get just as good if not better mileage, and of course performance, with that 5.3/4L60E combo than you ever will with the L6. There are many reasons for that.
With that being said, I'll be posting a complete writeup on installing a Camaro T5. I know I've said that in the past, but all I need to do is get the pics posted in the proper order and I'm still working with Liz to do that.

[PanelDeland]

If you do decide to/Need to rebuild one upgrade I would do(plan on doing it if/when mine needs a rebuild) is to go with the pistons for an LP engine.There are no high compression pistons(so I'm told) for this engine but the LP ones bring it up IIRC to about 9:00-1.If you get serious about building the 6 you should pick up a copy of Leo Santucci's book "Chevrolet Inline Six Cylinder Power Manual"

Also check out the forums over at InlinersInternational.

[TP from Cntl PA]

I'd keep the straight 6..............I got a coon tuned 250 in my '72 K-20 and I really like it, about the only thing I wish it was would be a 292, nothing else! I got a Clifford Water heated intake on it, their truck headers, HEI, and a Howell TBI setup on it, big 4 core rad., 12" Clutch with a SM465 behind that and honestly, I have it setup to pull and she will do just that. I personally don't think you can be a straight 6 IMHO.
That is coming from someone who had everthing from a 250 6 to a 454 in these trucks.............

[longorange68]

Brad I do like the T-5 idea, and have spent a little time looking at your profile photos. Looks pretty good. As far as your intake and carb, what did you go with and where did you buy them? What headers are those? Did you swap in a cam?

TP How do you like the TBI setup?

[TP from Cntl PA]

Originally Posted by longorange68

TP How do you like the TBI setup?

Only can be described as AWESOME! About the only thing I don't like is a higher than I'd like idle on a cold start, but it quickly settles to where it should be and works well. I had a 1404 Edelbrock on it before and this works alot better and I thought the carb worked good!

[Elephanthead]

Well if you really need power and want to stick with the straight 6, there is quite a community of racers in South America putting turbos on 250s and getting alot of power out of them, I would do a google search for that. Otherwise the suggestions already stated will give all you need. Unfortunately I have no experience beyond normal maintenance on this workhorse engine.

http://www.turboanhanguera.com.br/_k.../opala_6cc.htm

[Blue71LWB]

If you are going to go with and Auto/OD trans you may want to look into the 200-4R.
If I have it right the gear ratio is not as far apart from 1st to 2nd gear on the 200-4R as they are on the 700-R4.
I don't know first hand, but I've been told this gear set-up may suit the straight six better than the 700-R4.

Thanks,

[manimal]

To bring up the compression on the 250, you can use the 307 flat top pistons. You can also use a 194 head. I too am interested in the TBI set up. I may be keeping my '75,so I will be "inline".
-Lance

[longorange68]

So, I have been looking into pepping the old girl up, and after taking Brad's advice to heart, maybe I really don't need an entire rebuild after all. I have been looking on line for ideas for what to do and I ran across a few things I would like some insight on. I play with V8's mostly and to be quite honest, am a little behind the curve as far as inline performance is concerned. In a V8, I would probably go with a new intake and headers, new carb, and maybe a cam. I would only touch the valvetrain itself if the lift and duration of the cam requires it.
My approach here wouldn't be too different, except I think that the valvetrain is a little worse for wear, especially after being parked for a 3 year period without running. What lift and duration would be wise for a streetable truck? I know Clifford is pretty proud of their 264 "special grind" cam, but what other lift and duration cam may offer up some power without making the engine idle too rough? Would roller lifter or roller rockers be worth the cost? I am interested in headers too, any recommendations on headers that don't warp and constantly chew up exhaust gaskets? I was thinking on going with a dual exhaust anyways, how much do the split headers actually help?
Any thoughts on carbs? What does everyone typically run? I am looking into a 4bbl with a decent water heated intake. How many cfm for a 4bbl carb on this type of motor??? Sorry to ramble on, got a lot of questions...

Check out these links so you can see what I have been looking at.

http://store.summitracing.com/egnsea...924497&NeXID=5

http://store.summitracing.com/partde...6&autoview=sku

http://store.summitracing.com/egnsea...115+4294923429

['68OrangeSunshine]

I'm running a 292 bored .030-over, w/ Badger pistons, 1.84 intake valves, Rhodes lifters, Crane 260H cam. Outside is a 4-Bbl EDL 1404 [500 CFM], Clifford headers [3 into 2] w/ crossover tube, Offy intake [preferred in low-end torque, truck applications], no carb heat. Stock points, Mallory Voltmaster coil. Drivetrain is SM 465, Centerforce II clutch, Corp 12-bolt rear w/ Eaton posi @ 3.73:1. Truck is '68 C/10 Stepside, shortbed.

[PanelDeland]

I'm keeping a 6.In everything I've been able to find the hot ticket on carbs for the 250 in everything but full boggie engines seems to be the 390 cfm holley.I haven't bought one or installed my Offy yet but will probably go that way.I tend to look at it as using a smaller carb for street.Most info I can find claims the lower cfm carbs create better low/midrange power.
I hope someone can give some ideas on the headers since that is another addition I would like to make.

[dave666693]

I am in the middle of a Inline 250 project. I put a Clifford intake, Holley 390 and clifford full size headers. If I was starting over: I'd go with Stovebolt cast iron headers, Offy water heated intake and a 700R4. Problem with the 700R4 is getting it hooked up properly with linkage and so forth. I am putting in a TH350 and it has gone pretty smooth. Bad thing about building an inline 6 is the cost for performance parts. You are essentially spending all those bucks to make a stock 350 power wise. I am glad I have stuck with my inline because it looks really cool and it is differant. It has been a fun project so far.

[TP from Cntl PA]

Yeah, wish I had Stovebolt cast headers on mine............They are nice IMO.

I ran a 500 cfm edelbrock carb on mine for a time, worked good once I got it jetted right. A 390 would be better though I imagine. Won't trade my EFI though for either

Supprised nobody mentioned it, but the inlines sound better IMO...........Everyone has a V8 rumble, but the droan of a straight 6 is awesome.

[2bits]

"My" personal opinion on waking up an inline 6 that doesn't include a rebuild is:

Headers of your choice (I can't reccomend any, just get some )

Offenhauser 4bbl intake (better low end torque for the street vs the Clifford)

Holley 390 4bbl (pretty much the standard when going for carburation)

RV or Marine cam (Once again, don't get me to lying on the numbers, just get one )

200-4R Tranny for the length of the tranny and gear spacing as noted before. Nay sayers will say it is a weaker transmission=TRUE but at the same time if you build it, you can built it better than stock and plenty tough.

Make sure you've got HEI of course, stock will do, and Maybe an electric fan too...

That's all bolt on stuff except the cam.

[longorange68]

TP Why the Stovebolt's? They don't look as though they would flow any better than anything else.

http://www.stoveboltengineco.com/aca...p?productid=89

What would be a good cam grind for this build, and what would be considered too radical for the street? Want some pep, but I don't want it to shake me to death...

[thirdstreettito]

cliffordperformance.net

inliners.org

offenhauser.com

Plenty of info/parts.

[TP from Cntl PA]

Originally Posted by longorange68

TP Why the Stovebolt's? They don't look as though they would flow any better than anything else.

http://www.stoveboltengineco.com/aca...p?productid=89

What would be a good cam grind for this build, and what would be considered too radical for the street? Want some pep, but I don't want it to shake me to death...

I personally think they'd seal better as I had problems with mine blowing out gaskets until I did some machine work on both the intake and headers to get them to clamp right. I also think they would flow better than the truck headers that I have from clifford, tubes on them are pretty small and bent hard in places. Tom's are nothing like that.

[manimal]

you can also check out webrodder.com The "main" guy there CHIEFWEASLE has someone that grinds cams just for 6's. Keep us posted.
-Lance

[2bits]

Originally Posted by TP from Cntl PA

I personally think they'd seal better as I had problems with mine blowing out gaskets until I did some machine work on both the intake and headers to get them to clamp right. I also think they would flow better than the truck headers that I have from clifford, tubes on them are pretty small and bent hard in places. Tom's are nothing like that.

I totally agree on the sealing issue!

[lytemup454]

Here is a story that Classic truck's did awhile ago and a insperational shot
http://www.classictrucks.com/tech/07...fix/index.html

http://www.classictrucks.com/tech/07...rt2/index.html

[PanelDeland]

That's the older 6 but still a great looking inline.I don't like so much bling but the article on that was good.

[Muleman100]

Check out Patricks in Arizona. They are a long time supplier of inline performance parts and the are good at discussing your needs and goals for your project.

[Brad]

Longorange, I've been meaning to answer more of your questions but don't have much time lately. I can tell you that My Clifford shorty headers look 100% better than the Stovebolt cast iron headers I used to have and they perform just as well. Although the cast iron headers will last well into the next lifetime, my Cliffords are ceramic coated and will last a loooooooooong time. I've also never had a problem with sealing either of them properly. Currently I am running 2 gaskets on the head but only for clearance issues. If they're tightened properly you shouldn't ever have exhaust leaks at the head.