Thread: Engine mod advice needed for more hp.

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This is where we are at now.

81 corvete w auto trans (th350) and 3.73 gears stock converter as of now.
q-jet stage 1
dual plane edelbrock intake
stock 76cc heads
7.8-1 compression ratio (stock dish pistons)
hei dist w.advance curve kit (middle weight springs)
Headers and true duals
cam is comp cams part #12-231-2
Specs lift 432-453 lobe sep 111
duration @.006 250-258 open close
valve timing @.006 intake 18 52
exhaust 64 14
duration @ .05 206 214

Now I picked this cam, because at the time I figured it would have good bottom end and come out of the whole well, (for what it is) for not alot of cash..Now I plan on keeping the car for another year or so, so I want a winter project..well maybe a weekend or so project being as I am a tech at a dealer (14years) so engines mods really don't take me much time..Flat rate.ha ha

Anyway..I would like to add some more power, but don't need a 11 sec car. Was interrested in low 13 sec car..

Here is my idea.. I am able to get a set of 305 heads w 58cc chambers done and bowl hogged correctly w/194/150 valve installed for $225.. I was looking at a set of vortecs my buddie has, but then I have to swap intakes, and might have a hood closing issue.

If I raised the CR with these 58cc heads and installed another cam(which is what I can't figure out which one would be best for running around town) and put a more loose converter in it, do you think I could reach my 13 sec goal, or is it a waste of money??

Again, I know how to build an engine the right way, but I am cheaping out here, as this isn't a car I love, I only like it. I would do it balls out on an older camaro, but this isn't the car do do it the right way with.
Any suggestion on how to get to my goal without AFR heads ect....

Ever thing about a small blower like a 144 B&M ?

you do have the compression for it, i stuck a 142 weiand on a stock 305 in a malibu wagon once, now thats was fun and funny.

Blower would be the way but then you would really have hood issues.

58cc heads would get you in the 9.5:1 CR range. That will be a big improvement in itself. You could then take the cam up a couple ranges. The comp XE274 would work pretty good in there with a 2500+ stall. Along with the rest of your combo I've run through engine analyzer, it should net you roughly 350hp.

Thank you. Would you mind running my current combo through your analizer?? I am curious as to where I am at now. The blower WILL NOT fit under the hood, and I really didn't want to spend that much, but it was a good idea. Any other input would be helpful as well..

Changeing the heads/compression and the cam to what you have now drops it to 290hp.

SO YOU THINK IT IS A MOVE IN THE RIGHT DIRECTION?? Thanks for the input.
I could do this for about 600-800 for the heads cam lifters and converter..\
I just wanted to feel it in the seat of my pants. I remember when I switched the gears fror 2.73 to the 3.73.. Now that was a difference

Was I making a good choice in cam when I installed the cam stated in the above post for the combo that I currently have? I don't like to over cam anything, and I thought it made sense being it was a heavy car with low compression... If your dyno says it will make approx 60hp more, I am sure you will really feel the difference.

if it was me id put 11:1 pop up's in it a 305 h cam a set of afr's and go have some fun, omg did i say afr's

I think the best cam for your Corvette is the Comp cams Xtreme Energy CS XE268-10 . This cam is 224/230 dur at 050 and 477/480 lift with a 110 lobe sep . I think this is the biggest cam you can run and still have vac for your power brakes . And the 305 58cc heads make sure they are ported out properly and have screw in studs . And remember your short block has cast pistons and stock rod bolts . Dont over rev it 5800 to 6200 rpm no more ! And for a stall speed 2800to 3200 rpm . With this set up you should see low 13teens . One more thing run good rear street tires . Slicks may break that corvettes rear end its weak link .

I agree with Tango, run the XE268. The only thing I would be worried about with the smaller cam is if it would still run on 91 octane. I did some math... The XE268 cam would give it a 7.93-1 dynamic compression ratio which still should be good on 91 octane. It would take a really good head porter to make those 305 heads flow enough to support the XE272. If we are talking mild pocket porting here, run the smaller XE268. I don't think $225 will get the job done.

Remember, Good heads don't need much cam to make hp, poor flowing small heads like the 305 heads needs more cam to make the same hp. Cams can crutch a head to an extent. If you go 268, use the Lunati Voodoo line. According to UD Harold, the designer, it made 25hp more than the comp in back to back test on the same dyno with just a cam swap. 268 or 274 on a 110 LSA will run vacuum accessories fine. I am running a 278 roller on a 108 LSA and pull 11" at idle. It would be higher on a 110 LSA. My vac accessories work fine.

Originally Posted by camaro_fever68

Remember, Good heads don't need much cam to make hp, poor flowing small heads like the 305 heads needs more cam to make the same hp. Cams can crutch a head to an extent. If you go 268, use the Lunati Voodoo line. According to UD Harold, the designer, it made 25hp more than the comp in back to back test on the same dyno with just a cam swap. 268 or 274 on a 110 LSA will run vacuum accessories fine. I am running a 278 roller on a 108 LSA and pull 11" at idle. It would be higher on a 110 LSA. My vac accessories work fine.

Putting more overlap will help the engine with low flowing heads, but putting a bigger cam won't necessarily. Most cams as they get bigger in duration they automatically add overlap. That's why the Voodoo line makes more power, because they are more aggressive in overlap in the same size duration/lift. Then they widen the LSA to make the cam more streetable and have more vacuum. If the cam is designed to work in the 2500-6500rpm range, and the heads will only allow the engine to make power to 5000rpm, that makes an extremely narrow powerband. That's why matching components is so important. But I agree if he wants to maximize power, I would stay in the 218 intake duration range, but get a more agressive cam like the Voodoo.


I would run this Voodoo cam... part #60102

Advertised Duration IN/EX: 262/268
Duration @ .050 IN/EX: 219/227
Gross Valve Lift IN/EX: .468"/.489"
LSA / ICL: 112/108
Valve Lash IN/EX: Hyd/Hyd
RPM Range: 1400-5800

Originally Posted by camaro_fever68

Remember, Good heads don't need much cam to make hp, poor flowing small heads like the 305 heads needs more cam to make the same hp. Cams can crutch a head to an extent. If you go 268, use the Lunati Voodoo line. According to UD Harold, the designer, it made 25hp more than the comp in back to back test on the same dyno with just a cam swap. 268 or 274 on a 110 LSA will run vacuum accessories fine. I am running a 278 roller on a 108 LSA and pull 11" at idle. It would be higher on a 110 LSA. My vac accessories work fine.

Ray,UD Harold very good at cam design.
When using his cams I am always finding more hp.
Another guy also one of the best is Chris Straub of Straub industries.

i AGREE WITH ALL OF YOU. i GUESS IT IS MY FAULT THAT i AM ON A BUDGET WITH THIS ENGINE, OR SHOULD i SAY THE CAR. The casting numbers on the heads are 601 if that helps at all, but like I said they have been bowl hogged and machined to accept the 194/150 valves so hopefully that will allow a little more flow. This had to been done at a machine shop, most kids with die grinders are unable to bowl hog and machine over size valves. Again, I am not looking for a race car, just something that can get out of its own way.
I like the voodoo cam line. I was afraid of over camming the car because it is an automatic and is heavy as well.
I would think tha a 2200-2500 converter and 3.73 would help over come that issue, but it still has to be steetable.. I guess it goes back to the old saying (you either want a racer or a driver)..
Thanks again on all the input. I realy think we can get this car into the 13 sec area for little cash(As long as I do all the work, which isn't a problem.) I just hate to guess on parts matching..
Just the simple 7.8-1 cp ratio jump to around 9.0-1 has to produce something.