Miserly6.0h

ok so here's the setup
85 dodge pickup 3800 pounds race weight
gen 3 4.8, 226/236 cam 110 LSA installed dot to dot
eBay gt45, custom 2.5 inch crossover 7 psi
intercooled with pump 93
terminator x, 16 degrees timing at peak boost
deka 60s, truck intake
th400, 3500 stall, 3.23 gears
28 inch drag radials

I have a set of 4.10 gears i could try also. would these be better with the weight of the truck?
also, the cranking compression seems low but i have no blowby (roughly 130psi). does this seem normal for a cam similar to this?

planning on taking the truck out soon to see how it does and I'm not sure what to expect as this is my first turbo setup.
ill post a data log of the first few runs
any input is appreciated
Thanks all

Forcefed86

iTrader: (4)

What heads are on the motor? That’s low cranking compression for a small chamber head. If you don’t have a 317 head or something weird on there its not happy. Cam is likely not timed correctly. Did you use a degree wheel when you installed it? Its likely excessively retarded if its spitting out 130psi. Might try another gauge as well. Depending on elevation You should be in the 170’s 180s with a healthy factory compression flat top 4.8. Are you sure it’s a 4.8 and not a dished piston 5.3?

Gt45 is a really dated unit and 7lbs isn’t much boost wise. If the motors really that tired and only spitting out 130psi cranking… results will be less than impressive. It’ll prob do a burnout though! Lol work your way up to around 14lbs and 12* and read the plugs along the way.

Anything that heavy will benefit from more mechanical advantage. 4.10s would be better and allow the 4.8 to rev out more.

Miserly6.0h

Thanks for the reply, I'm pretty much at sea level here in FL, the heads are stock 862s that I've never had off. when i put the cam in, I just aligned the dots without a degree wheel. when I get home i will verify that its got flat top pistons. could the rings really be that worn out and still not have any blowby or smoke?

Forcefed86

iTrader: (4)

Anything is possible. I always pull the motor apart and clean the ring lands and gap rings. Check bearings etc. I’ve had 300k motors that still sealed up great even with big ring gaps and spit out healthy compression. I will say the ring lands are usually really carboned up. Many wouldn’t even move. But they always cleaned up just fine for me. I haven’t ever had a set of rings that didn’t seal decently. But it depends how the motor was treated.

Is there a chance you could have been off a tooth when you installed the cam?

Miserly6.0h

I never had this engine apart before putting it in the truck,
I have a 6.0 that will be going in eventually that i checked the bearings and gapped the rings. i want to see what the 4.8 can do and i feel like its not making the power it should.
i have a draggy and the best time I've gotten was 8.38@87 in the eighth with a 2.2 60 foot leaving on 3 psi, something doesn't seem right from what I've seen others do

no i don't believe so, the dots were dead on when i put it together

Forcefed86

iTrader: (4)

Def down on power. cranking comp being so low is a dead giveaway its not timed right or has some sort of huge pumping loss. Could be rings could be valves leaking etc… I ran a dished piston 5.3 with 317 heads and had more than 130psi cranking compression.

Miserly6.0h

ok, what would you recommend i try first? degree wheel and check cam timing?
thanks again for all your input

Forcefed86

iTrader: (4)

I’d get a $30 leak down tester off amazon to check valve leakage first because its easier. Then make sure timing is sync’d. IE that your mechanical timing matches your commanded timing in the ECU.

Might also look at pushrod lengths.

Then lastly throw the degree wheel on and check cam timing as its more of a pain.

Miserly6.0h

ill get a leak down tester and do that next,
I checked all the pushrods recently and they all came out ok.


ill update when i get the tester, should be here in a couple days, thanks again

Miserly6.0h

i haven't done the leakdown test yet but another thing i thought of is that this cam has 11* of overlap. could that much overlap with the small displacement cause the low cranking compression?

Forcefed86

iTrader: (4)

Nope, 11* @ .050 is fine.

Miserly6.0h

Update
just finished the leakdown test and it came out fine, each cylinder at TDC, checked at 100psi, all 8 cylinders were only 15-18% leakage

I have a piston stop coming so i can mark and verify that mechanical timing matches commanded

I also went ahead and got a degree wheel so I can check cam timing if the ignition timing checks out fine.

I'll update again after i verify ignition timing,
thanks all

Miserly6.0h

Update 2

i decided to check the cam timing next as that is most likely what was causing the low cranking compression and found the dowel pin that locates the cam gear and the cam itself are damaged. I'm not really sure how that happened but I also didn't get the cam new. (picture attached)
i had an LQ9 cam(196/207 116lsa) laying around so i threw that in , as a new cam isn't in the budget right now. after installing i checked the cranking compression again and got 155psi and that was cold. after correcting the tune I took the truck back out with the draggy and was able to get a 2.1x 60 foot and it feels much better outside of boost but doesn't carry as much up top (expected). i want to work on the tune more and try to make some complete hits to see how much better it does. what ET should i be expecting, keeping the 3.23 gears for now?

thanks in advance all

Old Buzzard

That happens when the valves hit the pistons.........

Miserly6.0h

as stated, I got the cam used. I guess I didn't notice that when the cam was installed. the 4.8 has no bent valves