[Mike_82]

Hi. I have a 1977 chevy 305. fresh rebuild(7,500 miles), all stock with exception of a Comp XE262 cam and lifter kit, .500" lift valve srpings, and a holley 600cfm 4bbl carb. i was wondering what i could do to gain more low end torque with it. are the cam and carb to big for it? would going back to the stock 2bbl carb help low end any? any other suggestions for what i can do to gain low end? Thanks.

 

[Ghetto Jet]

Well there are things you can do to improve low end, headers, exhaust, better intake manifold, play with timing, advance cam timing, ect. But, I hate to say this, you over cammed your motor. The XE262's is not a good cam to use in combination with your stock 305 heads. An XE250 is what you would have been better off putting in that engine.

 

[Mike_82]

I cant afford another Comp cams kit right now. i could probably get a summit cam kit though. ive been thinking about getting the SUM-1100 kit for it. would that work good with what i have? as far as the intake manifold goes, i have an edelbrock street master intake i can put on it. i cant afford headers or exhaust right now though as i have to pay off my race car. lol

Thanks alot.

 

[Mike_82]

bump.

 

[underdog305]

I'm going thru the same thing and i'm considering the Road Demon 525 or the Speed Demon 575. I've become a believer that the smaller the better. When in doubt go smaller. Better vacuum signal, more response and I dont think your going to out flow either one. Good luck!

 

[Max Keith]

Cam

The 1100 is barely more than a stock cam, I would recommend going with an 1102. You will see a lot more power all the way through. The 1102 is about a 4500 rpm peak cam. This isnt to be construed as the max rpm as the stock cam will turn over 4500, but that is where you can expect to see your peak HP. The 1102 is capable of pulling well over 5000 rpm.

I ran a Crane cam of 204/216 duration, 456/484 lift and 112 lobe separation in a 70 Ranchero with a 302, headers, C-4, and 480 CFM Ford 4 bbl. and 3.25:1 gears. That is a similar cam and I really liked it. It had plenty of power for my Rancero, and I towed a race car and trailer with it.

 

[Siggy_Freud]

Pay off your race car? What do you have?

 

[Max Keith]

Cams

The XE262 isnt that big a cam, but with stock exhaust, it wont help you any. The XE 262 is only about 10 degrees larger, on both sides, than the 1102.

If you can swing it, I would also drop back to about a 500 CFM carb as well.

You definately dont need 600 CFM at the kind of RPM you are looking at, and as was mentioned by Underdog about going smaller.
A little is good, but alot isnt always gooder.

Looking at 4500 RPM as your peak, You really dont need more than a 400-450 CFM carb.

With the trusty old carb formula, at 4500 RPM, you only need 390 CFM, but a 390 CFM carb is expensive. Edelbrock makes a 500 CFM for about $200.

An alternative. If your 600 CFM is a vacuum secondary, adjust the vacuum springs so it starts opening at about 3000 rpm, and most likely you will never see it completely open up, at least while driving it.

 

[underdog305]

Hey Max
If cost wasn't an issue, would you go for the 390CFM? Or, would you still tighten up the secondarys on a bigger more standard carb?

 

[benwantland]

Putting a stiffer spring in the secondaries won't help low-end, as the secondaries won't be open at low rpms, even with a light spring, and especially with a small engine.

My favored way to tune the secondaries for max power is to run the lightest spring which doens't bog the engine. For better economy, one or two springs heavier can't hurt.

 

[Max Keith]

carbs and cams

we arent talking about max power. Talking about economy and his small engine. He doesnt need that big of a carb for what he wants to do . A stiffer spring will keep the secondaries from opening so soon and so quick.

 

[benwantland]

Mike_82, did you drive the car stock?

If so, are you saying it has less torque than it did stock?

Is your carb vacuum secondary or mechanical?

And, you say it's all stock except for the valvetrain and carb? And it was a factory 2v? Does that mean you have the 4v on a 4v to 2v adapter? That's not going to help performance.

And finally, if they were both on proper manifolds, and your 4v has vacuum secondaries, it should perform as well from idle on up as your 2v.

 

[Max Keith]

carbs and cams

IM well aware that it wont help his bottom end but it will help with his mid range cruising.

That is why I recommended a smaller carb in the first place but that as an option.

I would run a 390 CFM. Ran them on stock car engines and turned 7000 RPM + with them.

They make them for small displacement V-8's and V-6's. very economical on the street. THey have vacuum secondaries for the street models.

 

[benwantland]

Max Keith, I will say that, in my lurking, I have seen your posts and respect you more than almost anyone else on this board. You know your stuff.

However, I believe this guy is looking for power, or he wouldn't be trying to hop up his engine. His complaint is "low end", which shouldn't be affected by the secondaries, so long as there isn't such a spring in there that they open super early and bog. Regardless of his goals for economy, I don't think that tuning the secondaries is going to net him tremendous amounts of low end.

To the original poster? Is everything else on the car stock? 305 cars in 77 tended to be dogs, strangled by emissions and setup for fuel economy, with low compression and high (low-numbered) rear end gears. I just drove a decently well running 77 305 Nova that felt like it was good for a 20 second quarter mile. Maybe what you really want is some more compression and decent gears.

Edit: crap, max, you beat me again. Please don't think that I'm doubting you or trying to pick a fight. I'm just trying to isolate the "low end" complaint.

 

[underdog305]

Max I understand the thought process with the stiff spring & larger carb. I was just trying to understand which would yield more all around performance. Better bang for the buck. This thread has some similarities to my situation.

 

[Max Keith]

carbs and cams

The problem is Mike doesnt like his cam and he wants one with a little more bottom end. He was looking at Summits 1100 cam and I recommended he go with the 1102 instead. Its about 10 degrees smaller on both sides than the one he has now, and with a smaller carb.

NP benwantland, I just thought maybe you didnt catch all that was going on here.

For myself, Ive always been a Ford man, and on 302's, even well warmed up ones, Ive never ran more than a 500 CFM on them.

I also ran a 351 W with Twisted wedge heads and other goodies with my old 390 double pumper racing carb on the street. Nasty bottom end and still pull up ove 7000.

Athought just occured to me.

Mike, what kind of ignition timing are you running? If you have a timing light, try bumping your initial advance up to 12 degrees, and see what that does. I wouldnt go any further than that though, without testing it one degree at a time.

If you set the timing at stock which is about 8 degrees, that could be a lot of your problem. I used to run a minimum of 10 degrees initial with my old 302 Fords on the street. Sometimes a lot more. It all depended on what the engine could handle.

Try playing with your ignition timing some and see what happens.

Something thats always befuddled me is that low compression engines always seemed to like more initial advance than higher copression engines. I know it all has to do with burn time etc, but running lower compression, you run lower octane fuel, which is less resistant to ignition than higher test fuels. Go figure. Guess I need to discuss that one with a petrolium engineer.

Which brings up another point, if you are running higher octane gas on the premis that it will boost your power, it wont. You dont need to run any higher octane than what your engine requires. Running radically higher octane, can infact rob you of power, due to the higher resistance to combustion.



benwantland, I thank you for your kind comments on my er ah um knowledge.

 

[Mike_82]

Thanks for all the replies guys.

Max, ill go ahead and get the 1102 then. i have the 600 cfm carb on the engine right now because it only cost me 30$. i cant afford a new carb right now, so i either have to use it or my old 2bbl. as far as timing goes, i really dont know. my dad set it by ear. lol. ill get ahold of a timing light and set it at 12 degrees.

Siggy, the race car is just a dirt street stock im buyin' from my uncle. he gave me a good deal on it. ive got a few pics of it in my gallery. there not to good but you can see it. lol.

benwantland, The Engine was in an old chevy truck. now it's in my '84 bonneville. i didnt get to drive it stock because it was in need of a major rebuild so i dont know what it felt like stock. i dont know if the carb is mech or vac secondaries. i dont know anything about carbs. ill find out though. yes, everything is stock except for the valve train. i replaced the 2v intake with a 4v intake from a 350 and am using a 1" open adapter. as far as what im looking for out of this engine, i want as much low end torque as i can get and still have good mid range. the engine will never see over 5 grand. most of the stuff in the car is stock. the rear end is a stock 7.5 with 2.56 gears, tranny is a th350. the car originally had a 3.8L V6 in it that was tired so my dad and i rebuilt the 305 for it. the 305 is definetly alot stronger than the 3.8, but i was looking for more low end.

I hope i answered everything. thanks again for your help.

 

[Max Keith]

a fly in the ointment

I noticed you said you are running a 1 inch open spacer between the carb and intake. These are really good for helping top end, but Im wondering if that could be maybe killing a little of your bottom end. Try running the car with out it and see what happens.

 

[benwantland]

Agreed, Max Keith. The open spacer is definitely not good for low end. Use no spacer if possible, but if you need one for throttle clearance or something, it is imperative that you use a four hole or divided spacer.

 

[Max Keith]

spacer

Exactly, Benwantland, a 4 hole spacer will help you by improving your air flow into the intake by stablizing the air flows velocity, before it makes those sharp corners into the runners from the plenum. I know thats an over simplification, but close enough.
A 4 hole spacer can actually improve your performance all the way through your power band.

Im still suspecting a problem with the timing being off, as your carb isnt that excessive in size, nor is your Comp Cams shaft all that radical.

It could well be that between improper timing and that open spacer, they are your culprits.

The best use of an open spacer is when you are actually running a carb that is a bit too small for your engine combo, and what that does is to a small extent, make your intake act like a single plenum unit, which, you can run a smaller carb on an engine and do just about as much as you can on the mid and upper ends as you will with a dual plenum and a big carb.
This doesnt mean to run an open spacer with a 390-500 CFM carb on your intake. Its a crutch, so to speak. Spacers are a fine tuning part. Not something to just summarily drop on an engine.