Inliners International Forums General Discussion Hi Performance 250 torque mods?

What modifications to create higher torque on a carbed Chevy 250 -70? Specially at low end. (...and wanted to keep it carbed)
Uses th350gear, stock mild ported head,stock valves, foilshaped intake bolt bosses. Stock intake manifold, reworked to fit Rochester 2g/Jet 2bbl without adapter. It sits straight on the intake w/2similar holes as carb.Holes got rounded edges in manifold roof. All at a customized 50 Chevy Fleetline (who´d got some more weight in that...)

Theese mods did get the engine fly a lot better, but as always, even more is better.....

More compression.

Lets see a pic of that reworked intake manifold.

Is the carb the small 2bbl ? If so,a larger 2bbl should help.

What exhaust manifold does it have?

You want a bunch more torque & you want to keep it carbed???

Side draft Weber DCOE's.

MBHD

Advance the cam about 6 degrees and find a very pleasant surprise. It's a lot easier with a Chev V8 but it can be done with Cloyes multi slot gear. In the old days we had to make our own stepped woodruff which are now avalable. Remember the cam turns in the opposite direction of the crank....Good Luck

How would that work? I thought that if a cam gear skipped even one tooth then it wouldn't run as well as normally.

Snowman, IIRC 1 tooth is something like 18 or 20 degrees.

oh, then how would you adjust it if not by pulling out, rotating, and putting back in?

re: Mean Buzzen....: Yet its a "small" one (throttle bore, 1 1/4" , venturi - 381 cfm) But when more carb, doesnt the torque get higher in rpm? Splitted exhaust manifold (cut & welded)2 1/4" open pipes to sidepipes. Side drafts Webers looks great, and yet i got one Dellorto 40´s ..looking for 2 more. I suppose the mpg is gonna suffer with the use of them. Trouble is to get space for them..i got a brake booster on the firewall.
Gonna send pics, just to get them...the car is on storage some way off me.

re: Panic : More Compression.... thought about it, and will do the 0.60 soon.. What Cpr would it reach? Or, should i "cut" more?
f.ex 307 Cheva flat top pistons are planned..

re: jimmy six... Advance the cam/Cloyes multi slot gear... Isn´t that to be used on chaindriven..and the Chevy 250 have none? (or well...it could perhaps be modified to fit..I ship them a mail for the sizes..)

Would lump porting help on low/mid torque, or is the gain mostly in upper rpm? (as i found, gains dont come without bigger valves.Got new valve work done recently with hardned seats, and hoped not to rework it again, is this right?)
I know the "easy way" is using turbo, but wanna keep the car style, with splitted sound, and twin turbos is lot work...

will do the 0.60
I assume you mean .060"?

Th key driving one of the gears has an offset step, which moves the teeth in relation to the crank or cam position.

Leaded,
What I mean by using a larger carb,,,the 2bbl you have might be limiting the air/fuel getting to your engine,,(might be a bit too small) therefore limiting the possibilty of producing more torque.

Sounds like you have no mufflers?
If so,,,sometimes an exhaust system needs a bit of back pressure to produce more torque.

Compression,,,depends on what 307 pistons you have as there are a few 307 pistons that can have 8.3:1 up to 9.5:1 compression roughly w/no cyl head milling.Rough numbers BTW.

You can have more compression w/a 194 cyl head.

There are gear sets (Cloyes)that allows you to advance your camshaft.
Offset wooddrift keys also for your crankshaft.

Lump ports will make more power everywhere.

As far as larger valves,yes a larger valve will help,,,but only up to a certain point,if you install a 194' valve,the torque would drop off in the lower RPM,worse mileage,off throttle response will suffer,but the upper RPM will make more power,stuff you learn by actually testing on a car.

There are IDA manifolds ,Weber downdrafts that would work almost as good as side drafts.
Douglas had them on his normally aspirated Opala,now has 45 MM EFI side draft throttle bodies.

40 MM Dellorto, good carb,that's a small carb,& should be able to get good mileage even w/3, but would need to stay out of the throttle to do so.

MBHD

If the carb is small enough, it's limiting torque at even moderate RPM.

If you really want low end torque at idle speed or just above idle speed put in a smaller than stock duration camshaft. This will maximize the fresh inlet charge trapped when the intake valve closes and therefore maximize low speed torque.

It'll reduce midrange torque and kill the top end. Probably not what you want but is what you asked for. If you specify what RPM you wish for torque peak that may eliminate my suggestion.

If you want midrange torque then suggestions made by other posters above are more appropriate. Compression is always good as long as you stay out of spark knock.

Gains can be had even with the stock size valves But Greater gains go with the bigger valves.

Hi,again.. Thanks for directions!
Yes, of course.. .060", panic. (miswriting!)
450cfm Edelbrock is under consideration,(ok, or will even a 600 be better?) just checking it out, jetsizes etc. re:A.K.A. I don´t use mufflers,right for now. But the exhaustpipes got some "restricted" areas in the routing under the car, who´d i belive would get backpressure enough...?
About to stay out of the throttle with a tripower Dellorto...well, i can, if needed!
With the changes already done it got a lot better respons than original. I got a really steep tunnel near my homesite, where normally top speed on top was about 70mph. Now, with the 2bbl, and other work, i tops approx. 85-90mph in this place. Hill is approx. 8 degrees, 1 mile long.... The gains seem to be coming real good in the normal driving speed, at 40mph, and rolls of further flat road, as good as any stock 289 Fords..(tested)
I see 194 valves are out of question...... ;-)
Strokersix; ok to know...but well, mid range is of course on, but your preferences is good knowing, cam work ain´t been my knowledge!
Lumps seem to be considered....will see when valvechanges are decided...thanks ;Twisted! ;-)

Without any cam change, 1.84 intakes and bolt in lumps/ porting head will behave like a cam change for tq/ hp increase.

No one has asked and you have not said. What is the exhaust setup for this car? Do you have headers? They will add significant tq at all RPM's.

Splitted exhaust manifold (cut & welded)2 1/4" open pipes. right side,routed between gearbox/ r&p steering, oval shaped under frame out in the back of rockerpanels, and outlet in sidepipes rear ends (2"). both sides routed to sides in front of gearbox.
All because the car is modified as late -50s custom, with lowered stance... and does scratch the rear bumber in roadbumps easy, even with much air in rear shocks. One of the reasons for no mufflers. with the angle on pipes here and there. it should make enough backpressure i belive. Routing done like this, to keep the pipes intact, the only way.......
tlowe; your remark about similarity of cam change,vs. lumps/porting was interesting.... and headers could be but space?... well, i can lend some with one friend, its fits his 235, but should be pretty similar in shape/size, aint they? I suppose also Fenton styled would be better than originals..Just to see if its possible to mount... (the rack &pinion uses some space, steeringcolumn,newer brake booster,etc.....if, not i could of course build them... ;-)

Leaded,
I wouldn't worry about backpressure.
I've not seen any data (nor my own) that shows backpressure improving anything anywhere.

Sometimes people hook the mufflers up, resulting in backpressure, and the car goes quicker. Why? I propose two reasons:
1. The engine was not happy with open pipes because it was jetted too lean. With open pipes properly jetted it will go faster than thru the muffs properly jetted.
2. The pipes added length - the header length (primary+collector) was too short, and adding that length of pipe to the muffler made the engine happier, especially down low. Same effect could be had by adding the right pipe length but with no muffler on the end.

You might add true long-tube headers for more low end, or an H or X-pipe to your 2-1/4 exhausts to create a pressure pulse at the right spot. All the way to the back of the car is probably too far unless your peak torq is at 1200rpm or so.

Yes a 4bbl carb would add low end since you can use some very small primary barrels for low end torq and then have the secondaries kick in so you don't lose top end. Holley 390, or Edel/Weber/Carter 500cfm (fat high response primary boosters) would be good choices for the most low end.

You could try a timing set with multiple keyways if available. Advancing the cam will close the inlet valve earlier and move the torque peak to lower rpm, theoretically anyway. It's possible you might decide to retard the timing instead to move the torque peak higher. Depends on your hardware (manifolding, cam specs, and basic engine design primarily) and how the engine output torque curve matches your application.

My point is altering cam timing is not expensive and easy to try. If you have means of cutting a keyway in the timing gear it won't cost anything but a couple gaskets and your time. If you find a strong response to the timing change that might also give you a clue what specs to look for in a new camshaft. Of course you must start with a degree wheel on your current combination.

A.K.A. here you got some pics found on construction....
I did also made changes in the bottom center, and further smoothed the angle on all corners after this..
Original carb"hole" was about 1.77", yet its two by size 1,65"...
and, belived the carb to be the small size...wasn´t, its the big one.(381-432 cfm)

cheapest low speed torque tip is a 194 intake manifold, they have pronounced smaller cross section intake runners with the same size port flanges, but this will definately take its toll at higher engine speeds, but you can crawl around a corner in high gear and pull out with missing a heartbeat or a stumble. man what a cheater stock combo a complete 292 setup on a small 194 would be. them v8 minded tech inspectors would not have a clue if all painted chevrolet orange with a black air cleaner!