i ride sand

hey guys, so heres what im up against. right now i am trying to put an engine together for my truck so i dont have to drive my 70 el camino through all of the salt this winter. im a pretty broke college student that has a limited budget, but i want to do things right and have this engine last about another 70,000 miles. if i can get that, ill be happy.

so, i found a set of 191 heads fully rebuilt for 200 bucks, so i bought them. then i just so happened to have a new summit K1101 cam sitting around (got it for another project thats on the shelf) and i have seen talk that it runs pretty good in a tbi without a tune. the one thing that concerns me is the truck came with 193 heads, but one was cracked and needed to be replaced. i got the truck for a steal, so i didnt fuss about the cracked head and paid $500 for it. right now i have the block getting hot tanked and new cam bearings installed, with new main and rod bearings in the mail.

but my main concern is that i may have shot myself in the foot with the 191's because of the lower compression and the different camshaft. soooooo, how bad will this thing run? my dad had the same truck, and when i drove it while rebuilding the motor for the camino, i got around 20 mpg. with the head and cam combo i have, am i going to be around 18 mpg? or will it even run right? if not, i have a set of vortecs and a dual plane carb intake, what kind of mileage could i get from that setup if i run a quadrajet?

man, i can do some stupid stuff sometimes, shoulda just gota stock cam and 193's...
so, whatdoyathink guys?

i ride sand

oh, and the 191's are milled .050, average combustion chamber size is 72cc.

UnderCover89TBI

iTrader: (25)

how much lower are we talking about?

i ride sand

from what im calculating, i will bw dropping to about 8.5:1 from 9.4:1. so quite a bit. the heads are the K2500 heads that were lower compression than the K1500 heads. oddly enough, they came off of a 1991 gmc jimmy... dont ask me why it had HD heads on it.

UnderCover89TBI

iTrader: (25)

plus a slight compression loss from the cam. I really cannot say whether it'd really affect the way the car runs. I mean it wont be making optimal power for sure but I dont know if it'd run like crap or not

ASE doc

That's a very mild cam with 112 degree LSA. It shouldn't need much compression to idle and run at low rpm. However, 8.5:1 is very low. That puts you back into late 70s where the OE didn't know how to build an engine that would run on 87 octane. The low compression will hurt your combustion efficiency and thus it will hurt your power. Be cauase it will rob power by reducing efficiency, it will also hurt your brake specific fuel consumption or your fuel efficiency.

How bad will it hurt? I can't say for sure. A full point of CR is a big drop. I would expect the engine to run rich and sluggish at idle and throttle tip in. Especially on a stock tune. The difference will be less noticible above 2,500 rpm, but the engine will make less power throughout it's torque curve. Maybe a 10% power loss? I'd expect atleast 2mpg loss in efficiency. Largely because you'll have to push harder to deliver torque. If it were me, I would try to find a set of stock heads.

i ride sand

im thinking instead of getting a set of stock heads, i may buy a set of flat top pistons. im finding that they run about $150 for 8 (cast). i can justify that cost with ~2mpg loss. over the course of 70,000 miles, thats appox. $1300, and i drive around 10,000 miles per year. that brings the cost to $185 a year, so they would pay for themselves quickly, and thats assuming gas stays at 3.50. oh, and i botched the numbers on the combustion chamber size. they are at 74cc right now, started at ~76cc before being milled. serves me right for going by memory... so all i need to do to be running about stock compression is just get flat top pistons and use the 191 heads. i calculated the CR with the flat tops, and got 9.6:1. im thinking they will actually have about 2-4cc volume for the valve reliefs, so back to stock at 9.4:1. is there any reason for not getting flat top pistons?

i ride sand

alright, heres what i found for flat top pistons at summit (no idea if the wist pins are included or not though): UEM-1436-STD

as for rings this is what i have. also from summit: SLP-E-251X

anyone see any issue with the combo? also, the wrist pin is .927 dia. on this set, and from what i found thats the same on the old ones as well. can someone verify this? also, how bad is it to cold press these wrist pins in and out? i have a 10 ton hydralic press at my disposal, but im not sure if that is the right way to go about things as all the engines ive done in the past were floaters. ive heard about gently heating the rod and cooling the wrist pin for assembly, but never heard anything about taking them apart. using that much pressure kinda seems brutal on cast pistons, and i REALLY dont want to screw them up or the wrist pin putting them together. heck, if someone could point me in the direction of a thread that better explains this, i would buy ya a beer if i see ya!

i just cant wait to get this puppy running again!

ASE doc

The .927 wrist pin is standard and pistons basically always come with the wrist pins as they are matched to each other. Pressing the pins into the rods is an acceptable method. Some prefer cold pressing the pins as overheating the the rod ends can soften and thus ruin them. However, cold pressing an be very tricky as the alignment needs to be exact to avoid scuffing the pin or the pin bore of the piston. You'll know when you've screwed up because the piston will be tight to the rod rather than swiveling smoothly. At th GM dealership we had a special press that held the piston in position and allowed us to carefully install the pin with less risk of damage. If you are going to use a hydraulic press, be sure to set it up so that the piston is held in alignment to the pin and go easy on the pressure. Of course use plenty of motor oil for lubrication during the process.

i ride sand

alright, thanks for your help doc! like ive said, ive never dealt with pressed in wrist pins. all the motorcycles and vw's ive worked on all had floting wrist pins and i just wanted to confirm what i found in my research. this is my first time rebuilding a v8 (but a long way from my first rebuild), and i want it done as professional as i can. so, that of course entails a TON of questions and research. just like your sig says, half effort yield half results!

ASE doc

Yeah, pressed pins are a cheap short cut devised by the OEMs. Race level engines all run floating pins. Just look at the better connecting rods and you'll see that they're all bushed for floating pins.