Thread: new top end and no more power???

Tweet

i just did a head, cam and intake swap on my 350. everything i did are as follows:

Trick Flow 195cc Heads with 62cc chambers
Summit 1105 camshaft (224*/234* @.050) and lifters
Pro Magnum 1.6 Roller Rockers
new pushrods.....yes, i checked the geometry
Felpro performance ultra thin shim gasket .015 compressed thickness
Ported High Rise intake manifold w/spacer ported to the plenum
rebuilt carter 625 carb
new HEI distributor w/MSD rev limiting module
new wires, spark plugs, starter


i put all this on the factory 74 short block. i'm assuming there about -20cc dish pistons. therefore, giving me a compression ratio just over 9.25:1

now i'm not sure what going on...i've adjusted the valves 3 times because i thought that's what it was and that i just kept messing up somehow. but now i know that's not the case.

before i did the swap i was getting about 115 to 125psi cranking compression. now i'm only getting 100 tops!!!!! and the power is horrible. according to Comp Cams Dynosim, i should be making about 385hp. i have used this program on several of my friends cars ('69 firebird, 92 trans am, 69 camaro, etc.) and surprisingly enough, for all their dyno'd cars, this program has been within 5hp on ALL OF THEM. i know this program works very well.

there is no detonation, no smoke coming out of the exhaust, my a/f ratio is between 12.5:1 and 13.5:1 from idle to redline, no driving quality issues other than just no power.

what is going on? i've been frustrated with this for weeks

PLEASE HELP ME
thanks

did you degree your cam in did . are the marks line up on your timming set did you check you damper if it slip or the pointer lines up at tdc did you check this when you had the heads off . what curve and springs and stop bushing do you have in the dist

yes i did degree the cam. i was fine and had 5* of advance built in it. just like the cam card said. i did retard it 2 degrees for a little more top end. the marks line up for the 2 degrees of retard. i used a new crank key and it was at the #1 TDC. i've made the mistake of having it at the #6 TDC before but not this time.
and it's a brand new summit distributor with one of the lightest springs in Morosos advance kit and one of the stock springs with it. i left the weights and bushings because they are brand new. my initial timing is 14 BTDC and total goes to about 36. i've tried backing it off a bit and advancing it a little more too and neither helped. but when i did advance it i could go as much as 50 total with no detonation under load driving what's with that?

did you put a vacuum gauges check out your EX

I would be willing to bet its the camshaft....what is the centerline of the cam? I would say put it straight up.....take out the two degrees.

no haven't tried the vacuum gauge yet. i'll do that today. thanks.

and that camshaft has a 114* LSA and a 109* intake centerline/119* exhaust centerline. that's why i figured that 2 degrees wouldn't be so bad. that still gives me 3* advance, correct? even if that did take away some power (dynosim said otherwise) i should still be making a ton more that stock. i'm just really confused.

are you just going by "seat of the pants" to determine it has no power?

what was the duration of the old cam? I'm willing to bet it's quite less than 224*... that's where your cranking compression went. What vehicle is this in? Transmission? Torque converter? Gear ratio? Where does it not "seem" to have enough power? Out of the hole or up top? Does it pull at high revs? What is your redline? What fuel are you using (octane)? Retarding the cam also is killing your cylinder pressure... all this explains why you can run so much timing lead... try running some crap regular gas in it and you might find more power

-Chris

In your calculations for static compression ratio, I suspect you forgot the piston deck height. I further suspect that on that year motor, the piston is down in the bore by about 0.030".
cylinder 727
chamber 62
piston crown 22
piston deck 6
gasket 3
820/93 equals 8.81:1
That cam would work well with 9.75 to 10.0, but it ain't gonna work too well with 8.81, particularly being retarded by 2 degrees. You might try advancing it 4 degrees from straight up and see how it works.

seat of the pants and also my friend has this "G TECH" dohicky that is also very accurate...we have used it on dyno'd cars and it and awesome tuning tool.

the old cam was stock, along with the heads and intake etc. i have a 4 speed in a 1960 chevy truck (3700 lbs w/me in it and a full tank of gas) 3.73 rear gears. 28 in tall tire. it pulls fine until about 3500ish rpm. i dyno'd the truck and it made a whopping 206 whp @ 5200rpm up here at 4500 ft. which equates to about 230hp at sea level. it power just levels off for the most part after 3500. but i'm shifting at around 5500 where i should be. right now i'm using shell regular 89 octane for gas.

and in my compression i did not forget the deck height or the piston dish.
stock piston dish is 20cc for my 74 truck 350. it is also bored .060 over.
stock deck height is .025
gasket is .015 inch compressed....etc.
and with all that info put into the compression ratio equation, comes out to exactly 9.17:1

and the cam has 5 degrees of advance built into the lobes. isn't 9 degrees of cam advance a little excessive???? and i honestly don't think that i need that much compression for this cam, yeah a little more because of the elevation, but even edelbrocks performer rpm crate engine only has 9.5 to 1 compression and that cam is quite a bit bigger than mine.

also my friend has the performer rpm cam in his pontiac 428 with just under 9:1 compression and he is even getting a minimum of 120 psi cranking. that cam has 4 degrees of advance built in it.
so theoretically my cam installed exactly how it is in the truck (retarded 2 degrees) is only retarded 1 degree more than his with about the same compression ratio and he has a lot more duration/overlap than mine too. AND he has .5* less LSA!

Swell. Have it your way.

hey i'm not saying i don't appreciate your advice, i do. but what's the reason for what you're suggesting? i just replied with what i know from experience and what i've read elsewhere. and i've never heard of advancing a cam a total of 9 degrees. i'm just frustrated and confused. sorry if i sound rude, i really don't mean to. thanks

I wouldn't put too much weight on your G-Tech results... I have one that says I'm putting out ~250HP but my timeslip says otherwise (~400HP). The G-Tech can be a useful tool to determine the relative effectiveness of various mods but I think the absolute power/tq reported can be quite inaccurate. As for advancing the cam, you will not increase your cylinder pressure without advancing the cam.... at the very least install it straight up (with ground in 5* advance) and see if that feels a little more stout. Are you sure you're getting good spark at the higher revs? How did you set your valve lash? How are your valve springs?

-Chris

my exhaust is 1 5/8 inch header tubes to 3 inch collector to dual 2 1/2 side exits with an H pipe after the collectors. i have dynatech split flow mufflers.

i thought it might be the valve seats too, but the cylinders hold pressure they just don't get much psi. and with the stock setup i was getting 120psi and holding it so it couldn't be the rings. i'll try advancing the cam staight up here in a few days and see if that will help.
about spark everything from the ignition switch to the spark plugs is brand new.
and i did swap out the springs that were on the head for Lunatis that were good to just over .600 lift with the installed height they're at. they have 120lbs. seat pressure and around 310 open.

what is DCR? and how could i have less cranking compression with higher static compression? the cam isn't that big. is 2* cam retard really that much?
i was getting 120psi with the stock cam and heads and head gasket and all that "low compression smog" stuff at this same elevation and everything else.

i also did a vacuum test and i'm only pulling 10in at my 700-800rpm idle????

i'm just curious, which g tech do you have? my friend has the old one. it's just a little black box with red numbers on it. and his has been pretty accurate thus far. with manual and automatic cars. low performance, high performance, all wheel drives, turbos, etc. i work at summit racing over in sparks, nv and we have dyno'd everyones hot rods who works there and g teched right after, so weather was the same, and yeah you lose a little because it measures pull and if you can't get all the power to the ground it shows, but the car that was most off number wise, was a 69 chevelle 396 with a 4 speed. his car ended up being about 20 hp short. now i have bought the new one for me because i thought they were all great, but the latest one out, with all the graphs and everything is so erratic and unreliable it's truly unbelievable. on the same road run after run after run with my cars and my buddies the numbers have varied almost 100hp. all i'm trying to say is i know it's possible for the g tech not to work, but i am a true believer in my friends'. and like i said we have used it on dyno'd cars, my truck for example and it was only 4hp off!

thank all of you for your help so far

I went through the exercise of calculating your DCR for both straight up and 2* retard installation. straight up (intake close 41 ABDC) DCR=8.27:1... 2* retarded (intake close 43 ABDC) DCR=8.20:1. At 4500' altitude, barometric air pressure (at 68*F and 20% relative humidity) is 25.37inHg or 12.46psi (compared to 14.7psi at sea level). Given your DCR of 8.2:1 and 12.46psi your cranking compression should be 102psi... given whatever the prevailing weather was during your test, this could easily account for 2psi.

techinspector knows more about what a good DCR is than I do but I do know that 8.2:1 is pretty low if you want any kind of performance. I think 8.5-9.0:1 is a good target for pump gas friendly power. And at higher altitude you can push that a bit further... BTW: with the specs you gave here, my compression ratio calculator says you have 8.98:1 SCR.

Edit: I was using 64cc chamber... with 62cc chamber SCR is 9.16:1

Good luck...

-Chris