Inliners International Forums General Discussion Engines head swap.... torque loss

hi all! i have a 65 nova wagon with a stock 70 250. i pulled the stock head, completely encrusted with carbon and oil and who knows what else. replaced it with a stock 66 194 head. my calculations put compression around 10.2:1, which i thought would increase power a bit. instead, i lost low end torque. engine doesn't exhibit nearly as much pull through 2500 rpm as it use to, but is quicker from 2500 to 4000 in all gears (running th350). is this normal? any feedback would be greatly appreciated, as i don't want to swap the stock intake and exhaust (in favor of clifford intake and headers and holley 390) til i can understand whats goin on. thanks

bucky

A issue That i can see here. Could very well be if your still running the stock cam. When you install a bigger cam they normaly like a little more compression DEPENDing on how big you went with the cam ( the bigger the cam the more compression you may very well need)
So with the increase in compression the stock cam can not get enough fuel in or exhaust out in the lowwer rpm band to over come the increase in compression.? The headers may???? help this a little bit over the stock exhaust. But if you plain on installing a different intake and headers to start with You may want to thing about a little more cam then the stock one.

Hope this helps.}[oooooo]

Ps HOW about some more imput on this GUYS!!!! I'm sure I maybe a little off base here Seeing I'm no pro and I don't know everything. I may become a pro But I'll never know everything. We're always learning something new.



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NovaMan/Twisted6/Larry

Thanks for the input! when i bought the car i was led to believe it was a 230 with a mild schneider cam, but thats not the case. i've got the 4bbl, clifford intake and clifford dual outlet headers sittin here ready to go, and i'll pick up a cam and just do it all at once. its running a GM HEI distributor. any suggestions for cam? gonna be daily driver, with occasional trips to the track. the 250's mated to a th350 and with 3.08 rear (i think). thanks again

bucky

As a daily driver I'd stay with a hyd. cam. and Unless you plan on replaceing the Stock convertor I would stay with in the stock convertors limits. Like a crower level 2 which is good from 1500-4000 with a redline of 5500 lob center 112 dur@50192/200 with a 448/460 lift cam # 03241 component kit# 84008
Or a ultradyne cam which has a 530/548 lift Dur@50 225/232 good from idle to 5500 which is a good street cam with a slight lope ,responsive power. Along with a good 3 angle valve job. And i think you'll be happy. I would also think about maybe? stepping the rear gear up a little. About the best the 3:08s will do for you on the track is 16-15s? hope this helps }[oooooo]



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NovaMan/Twisted6/Larry

Hopefully I won't confuse the subject with my 2 cents....

I'll agree on the cam recommendations considering the car and weight. What I'm wondering about, though, is your description of the torgue loss at low rpm.

It's been too many years since I looked into the combustion chamber of a 194 head to remember exactly how they are different than the 230's and on up. But since we know the chamber volume is smaller and the bore of the 194 is only 3 9/16", then the diameter of the chamber "oval" has to be small enough to match the 194 cylinder bore. That means there is a big horizontal "step" between the edge of the chamber at the deck and the cylinder wall below the deck when installed on a block with 3 7/8" bore. The step is probably bigger than normal by around 5/32" on each side (0.156").

Considering the valves and their locations are the same in all the heads, that means the walls of the chamber are closer to the valves. What you are getting at low rpms is a shrouding effect that is created by the too-close wall and the big step that is creating turbulence. That keeps the air from flowing smoothly into and out of the cylinders.

More than likely what you should do is to get that 3-angle valve job (or a 5-angle Serdi job, better yet) as Twisted6 suggests, and at the same time, have the machinist cut the sides of the chamber about 5/32" or so radially away from the valve so it can breath better on the side close to the wall. Yes, you will drop a little compression by removing some metal, but the effect on airflow will more than compensate for the small loss.

Using a high-lift cam will overcome some or most of that shrouding effect, but with high lift usually comes higher duration. That combination will move the torque band up the rpm range regardless of your compression ratio, and you'll be sort of back to where you started with your original low-rpm torque loss. But the bright side is you'll have gobs more power at speed than you had before.

Your best bet to fix the issue is to unshroud those valves and use a medium-range RV style grind with no more than about 0.500" to 0.520" lift.

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David
newbie #4153

thanks guys! hey twisted.... you think only 15s at best? had a stock 69 nova with 250/powerglide and 2.73 rear and it went 18.8 @ 73 mph. i can tell ya the wagon hits 60 a couple seconds faster than i ever managed in the 69, and (now) it keeps goin from there whereas the 69 pretty much gave up after it hit 60. i guess i'll just have to get it to the track to find out. thanks again for the advice!

bucky

The reason I say it won't do much better then a 15 is ,When i first started play with my 64 on the track the motor was stock other then a set of headers and a offey intake with a 600 holley 250 with a powerglide & 3:08 gears car, Ran mid 18s with the power glide then i went to a 3 speed sag. and ran mid 17s. Then i built my 250 with Much more compression & cam then what you have in mind.
And with the 3:08s still in the car it would run 15.15s(with a point dist.) all day long no matter time of day or weather. It wasn't untill i started making gear changes that i got the car into the low 14s.I built this motor 17yrs ago AND was a daily driver up untill 14 yrs ago so but the the I got the gears Need to just all out race it The motor was already showing it age Between raceing & driving so the best it ever laid down was a 14.3 @ 96 if the car sat more then 3 weeks the numbers would fall way off till after the 3rd pass the Bang right back to it's numbers. Now that I'm redoing the motor I found a few things that was on the way out ,Like the rings a broken cam retaining plate and one or two push rods with no ball on the ends.( HUM kinda funny HUH that this motor was still getting faster even though getting wore OUT) And it would just about have the front tires off the ground when leaving the line.So now i can't wait to get THIS new one all back together.

Here is a brake down On my New build up
13-1 compression full floating pistons stock rods cam spec. 691/680 lift dur @50 269/272
It will also have bolt in lumps But Not PES as many know i have been working on my own.
I have been doing flow testing Side by side with pes and I my own. First Tests i was 2cfm over pes then i made small change to the intake aproach and gained another 2cfm in which now put mine at 4cfm higher so I stopped at that time to bring them back to my shop To finish making the changes that I did at the machine where i was flowing this head. And just waiting on the guy who owns the shop To have time for me to get back in with out using his time up Or interrupting his normal business hrs. With each little change I have made I have Become closer To The braze in lump. The Final test on these lumps of mine are being done with a MIke Kirby Street preped head.
I'll be posting final numbers & info when i'm finshed.Then the Track Tests come next.

Hope this helps but not to confuseing.
}[oooooo]


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NovaMan/Twisted6/Larry