My 70 LS5 454 has been running like a bit of a dog for many years, runs hot, stops pulling at lower RPMs, flattens out.
Back in the mid 80's I had to bore the block 30 over, installed forged pistons, reduced the compression ratio from the stock 10.25 to 9.5 so I could run pump gas available at the time.
Several years later I had the engine freshened, a machine shop installed a competition cams 11-208-3 cam, flat tappet hydraulic lifter, 280h grind.
Running stock exhaust, stock intake, QJet carb.

I have two QJets, both perform about the same, doubt it's the carb...

Vacuum at idle is around 14 hg.

When I run a compression test, I get 200 to 210 PSI on all cylinders.
Normally I'd think this was great but now I wonder.
The stock compression pressure spec'd at 160 PSI, that's with 10.25 compression ratio.
Suspicious I am getting more pressure with a lower compression ratio.

To get a higher cranking pressure suggests the intake valve is closing earlier than expected.

I found an on-line calculator which estimates cranking pressure, http://www.wallaceracing.com/calc-crank-press.php.
When I enter my parameters, use the spec'd degrees for intake valve closure, ABDC (66), I get a gauge pressure = 149.37, cranking pressure = 163.
Sounds reasonable.

If I alter the ABCD, assume the cam timing is quite advanced, about 25 degrees ABDC, I get a gauge pressure = 193, cranking pressure = 209.
Close to the readings I'm getting.

There are no vacuum leaks, two carbs perform about the same, all ignition components have been replaced except for the wires which I may replace just to rule them out.
Fuel pump appears to be generating around 6 psi while cranking.
I'm running out of ideas as to why this engine seems to be such a dog...
A misinstalled timing chain, bad cam timing, seems like a possibility, could explain the strangely high compression pressures?

Has anybody had experience checking cam timing in the car?
I have a dial gauge.
Looks like a timing wheel may be difficult to install or read.

 

That cam should really rev. with 230 dur @.050 So you may be on to something. If it was strongly advanced it would answer both questions, high psi and low revs. Maybe the 9.5 pistons are keeping the valves from hitting? Luck there?. First I would find a second compression gauge and retest, they are known to go bad. Next I would rock the crank back and forth with a valve cover off and see if you have a lot of chain slop for some reason. Next I I'd check that the balancer is properly indexed and has not slipped. Measure the valve / spring lift with the dial i. and make sure it is close to .520" They are all the same psi, so they are either all good or all bad. If you can figure out how to install a piston stop, you should be able to measure a pushrod in the car and determine if your 106-110 ILC is way off. You could tape a timing tape to the balancer for the quick n dirty cam timing test. A real degree wheel measurement can be done in the car, if you are sufficiently motivated. Just more work. W/P, oil pan, front cover, intake, etc.

 

I believe you have a bad compression gauge. It would be very difficult to have that much cranking compression with your combination. Advancing the cam could cause the cranking PSI to go up but that would typically make the engine very "peppy" at low RPM and then kinda level off in the upper rpm range. A couple of weekends ago I took my gauge to a friends house because of the exact same issue. Turned out his gauge read 45 PSI higher than mine. His showed 195 PSI cranking on a chevy truck with over 100k miles on a 4.1 v6. You may want to take a look at your ignition timing.

 

6 psi is a bit high for the Q-jet. Could be flooding the engine at low rpms. 3 to 5 psi is ideal.

 

maybe bad compression gage

 

quicky eyeball check of cam timing. remove either valve cover. have someone bump engine with the key. watch the valves. either cyl 6 or 1. as exhaust is closing and intake opening, timing mark will be at TDC. if you were way advanced, the 2 valves would be open the same amount when timing mark was well before TDC. 25 degrees? that is 2 teeth off on the timing gear. if an engine jumps time, cam gets retarded. what about buildup on top of pistons? maybe get a cheap ebay borescope? then you can do colonoscopies on your friends for a side job...

 

Several years ago a local shop did a compression test as part of a tune up. I recall the pressures were pretty similar to what I read last weekend, thought nothing of it at the time. Otherwise I'd be more skeptical of the gauge. Since this engine has been running poorly for so many years, I am leaning to sending the car off to someone I can trust to check it out, a second pair of eyes. A compression test, verify what I have seen should be done.

The cam timing is just a theory at this moment, I need more proof before I'd get into removing the timing cover to have a look at how the marks align.

The chain is a double roller chain, installed when the engine was freshened. Engine sat for quite a long time afterward, driving only occasionally over the last few years. It's possible there could be an issue with the chain being loose though I doubt it. Again, need to see evidence before tearing things apart or removing the engine for service.

Thanks for the responses.

 

I'd eyeball the timing quickly by popping one valve cover. That's not very invasive. You may find what you are looking for.
And the borescope.......that just has soooo many uses........

 

I'd get a different cam. A 230 cam is great for a small block, but with as much cubes and compression as you have you may need a bigger cam with more duration and wider LSA. I'd look at 114 for the LSA, and 240 ish for the duration.

 

My 98 Firebird has an LQ9 (408 cubes), 11.3:1 compression. IT would always show 220 ish on the gauge. It ran OK on 93 octane pump gas but it did seem sluggish on the low end. When I put in 100 octane gas it really wakes up the low and and throttle responsiveness. You might try to find some 100 octane race gas and try it, see how it runs. If it runs better then you might want to look at a different cam.

 

Summit says the cam in the engine has a LSA of 110..wont him installing a LSA 114 have less over lap and increase cranking pressure?

 

yup your right, but it all depends on when the valve closes. If you advance a 114 four degrees it will close at the same time as a 110. Maybe the solution is to simply retard the cam 4 deg?

 

It may be worth it to see if the timing dots are really lined up. When I built my 383 I got the dots straight and would have bet all day long they were timed correctly. But when I put a degree wheel on it indeed told me something different, they were a tooth off.

 

Most double rollers are 44 and 22 teeth. 1 tooth off is around 7 degrees.

 

Get timing tape for your size dampener. That way you don't need a degree wheel.

I'd recommend verifying TDC before checking cam events. Use a piston stop that goes into #1 plug hole. Set crank to 20 dgr BTDC, adjust piston stop to touch piston. Rotate crank around and check that it stops 20 dgrs ATDC.

Once you have verified TDC, pop a valve cover and check cam events. Note that it won't be perfectly accurate with hydraulic lifters. But you measure opening and closing point and then you know the center line which you can compare to the cam spec sheet. If the cam is off one tooth it will be obvious even with some minor measurement errors.

 

Do you have a recommendation for the piston stop, what brand?

 

Check the lift on all rockers....you may have a flattened lobe or two..... that would make it a dog

 

https://www.ebay.com/itm/Crane-Cams-...item36413d13c9. They also have nylon ones that are a fixed height.

 

I'm so cheap I made one from a spark plug and a bolt.

 

I would pull the timing cover. Depending on who made the timing chain they could have put it one wrong and its already advanced when at TDC so your not getting the valves openning when they should building pressure, maybe......either that or the cam is going flat and not exhausitng, just pulling in, or maybe a bent pushrod not openning an exhaust vavle all the way unless its the same on all cylinders then I would say either the timing chain sprocket not in correctly or maybe too thin a head gasket and your quench is too small raising the compression and giving yo a bad burn which would be why it runs bad. I had too much quench and was getting a bad burn and low compression