front wheel drive block 87 3.8

[frank_ster]

howdy yall i'm running the 1987 front wheel drive block in a awd subaru,

got a few questions,

i have a comp roller cam from summit that was intended for a grandnational. i cut the fuelpump lobe and oil pump drive off and shoved it in, its Advertised Duration 264/264, Lift .504/.504
i put in some 140 # valve springs.

issues i have the timming chain doesnt last very long .. about 25 000 miles. i had a comp cams doubble roller and it got streached and broke a bunch of teeth off the cam gear. now i'm running a silent chain but those dont last long either i have about 15000 miles now on this one and i'm getting scared!

the other issue i have is the engine looses a lot of torque over 5000 rpm is this typical of grand nationals with this size of cam?

for turbo i'm running a holset hx 35 i'm thinking is maybe a little on the small side, this engine and that turbo in my pontiac sunbird i ran 117 mph 1/4 mile shifting at 4800 rpm @19 lbs boost.

and why arn't more people running the 87 front wheel drive blocks that have the factory roller like mine?

 

[frank_ster]

oh i'm running megasqurit 3 sequential injection , i have been looking for a stock grand national ignition table for some time now i have the spark table where i like it now but i was always curious what the stock one is supposed to look like and my idle is a bit shitty i need to richen up to about 14-1 afr at idle do you guys see this also?

would having the deck cut and thinner head gaskets ( thinner quench band also be benificial for better economy and power?

 

[earlbrown]

That much cam should go past 5000. That 140# rating wasn't over the nose, was it?

Our spark table shouldn't work for you as I think you have more efficient combustion chambers. As far as compression and quench, it's hard to say if thinner quench would be better as it depends on where you are now. Personally when I shoot for .038" quench when I'm starting to do the numbers in my head, see where that lands me with static compression and go from there.

 

[frank_ster]

i have more effecient chambers? how so? i think they looks exactly like the grand national heads i have seen. mine is not like a series 2 3800.

i have .060 : mls head gaskets and i would think the piston s down about .030 in the hole as most stock blocks are so i'm in the .090" quench area.
maybe just get some .020 " thick head gaskets?

if you could just post a stock or an improved timing map it would be helpful !

the springs are lunati and 140# on the seat.

 

[bison]

The hx35 should go high one teens before it's tapped out in a 3500lb car. If it's the later 7 blade design it will go 128-130mph before it's done. I'd verify spring pressures. You shouldn't be going through timing sets that fast either.

 

[frank_ster]

^ i'm certain the springs are 140# i changed them last year i had a set of comp cams out of a 400 small block in before and they were randomly breaking not even close to coil bind! those were about 100# on the seat, so i went up on the spring pressure because i thought that was the problem.

could it be the springs i have combined with the fact that the cam is not driving the oil pump on the fwd block i am having bad resonance going on and that's killing the timing sets? i have been having this problem even when i had the stock cam and springs, so i,m a little confused.

 

[earlbrown]

i have more effecient chambers? how so? i think they looks exactly like the grand national heads i have seen. mine is not like a series 2 3800.

i have .060 : mls head gaskets and i would think the piston s down about .030 in the hole as most stock blocks are so i'm in the .090" quench area.
maybe just get some .020 " thick head gaskets?

if you could just post a stock or an improved timing map it would be helpful !

the springs are lunati and 140# on the seat.

I was thinking you were running a 3800 since you said factory roller cam and you removed the oil pump drive.

If you are at .090" you don't have quench. The rule of thumb is .040" to .060". Once you go bigger than .060" the detonation resistance goes down and static compression has to be lowered about a point to stay at the same octane level.

140 on the seat should be OK. Any idea what the spring rate is? You might have plenty of seat poundage but not enough over the nose.

 

[Paul Lohr]

Are we certain your tachometer is correct?

Spring pressure over the nose - it would be nice to know that.

 

[frank_ster]

Summit Racing Part Number:​

LUN-73943LUN ​

462 lbs./in

and yes the tach is correct i have megasquirt 3 efi with sequential fuel, it realy wouldnt run if the tach was off. and the cluster tach says the same as my laptop.

i would think i'm down int the 7.8-1 compression ratio would you guys recommend changing to a .020" head gasket to get the quench down? i have been thinking about doing this for a couple months.

and the quench i dont think affects the torque over 5000 rpm .. would it?

another issue i seem to have is at 15-19 lbs boost my injector duty cycle is at 80-90% and they are 65# injectors. the system is fed with a 255 warbro. and i realy doubt its making over 500 hp. i'll have to check fuel pressure to be sure.

​

 

[earlbrown]

I like 9:1 with quench minimum on the street with pump gas. You're at 7.8 with a big cam bleeding off cylinder pressure so your VE is most likely lower than it needs to be.

What's your A/F ratio when they're at 80~90%?

 

[frank_ster]

^ 11.5-1

 

[earlbrown]

Have you verified our cam timing? Any idea what your dynamic compression is?

You seem to be moving a bunch of fuel with not a lot of power. I'm wondering if you're intake is closing real late and bleeding off all your compression.

 

[frank_ster]

are there any major issues with running copper head gaskets ? i can't find the mls ones that are less than 0.040"

 

[frank_ster]

Have you verified our cam timing? Any idea what your dynamic compression is?

You seem to be moving a bunch of fuel with not a lot of power. I'm wondering if you're intake is closing real late and bleeding off all your compression.

i had the cam retarded 8 degress and i just advanced it to 0 on the crank gear and it made zero difference.

( when i was running the stock cam i retarted it about 10 degrees and it made a 45% power gain 104 mph to 117 mph )

 

[earlbrown]

You're got something out of whack with your build if you can move the cam 8 degrees and not have any changes. Are you saying you just re timed you came and tested it in last 20 minutes??


Cometic will make any gasket they offer in .027", just change he last 3 digits of the part number to '027'. That's what I'm running on my 3.8.

 

[bison]

i had the cam retarded 8 degress and i just advanced it to 0 on the crank gear and it made zero difference.

( when i was running the stock cam i retarted it about 10 degrees and it made a 45% power gain 104 mph to 117 mph )

Where is the intake opening at .050"? Intake closing @.050? When is the ex opening at .050". You should never need to retard your cam

 

[bison]

^ i'm certain the springs are 140# i changed them last year i had a set of comp cams out of a 400 small block in before and they were randomly breaking not even close to coil bind! .

Running springs far from coil bind makes them more unstable as rpm increases which increases the chance of failure. If you were able to hit your required pressures and weren't anywhere near coil bind then id select a different spring that is no more than .080 from coil bind and hits the pressures you want

 

[frank_ster]

Where is the intake opening at .050"? Intake closing @.050? When is the ex opening at .050". You should never need to retard your cam

i have not degree ed this cam.

also keep in mind the stock cam on the front wheel drive block is punie, .320" lift or so.
the 3800 series 2 supercharged has the cam retarded 10 deg from the n/a counter part that is what originally gave me the idea.

i set the cam to 0 deg advance using the comp camps timing set i didn't go as far as degreeing the cam. i just wanted to try it after i noticed the timming chain was getting loose.
so i changed the timming set and set it to 0 deg, yes i know its better to degree in the cam shaft, but i had nothing to compare it to anways, i just wanted to know if advancing it would help but it made no difference. ( in my experence a cam that is way to small will really show power change if its retarded. ) if the cam is a good size the exact timming isn't as critical since cylinder filling is being restricted by other means ie intake runner size and valve size.

 

[frank_ster]

Running springs far from coil bind makes them more unstable as rpm increases which increases the chance of failure. If you were able to hit your required pressures and weren't anywhere near coil bind then id select a different spring that is no more than .080 from coil bind and hits the pressures you want

yes and that is how they are currently set they have .050" more than my lift.

 

[bison]

You'd be surprised that in a turbocharged application with backpressure a lot of the common thought process in cams and valvetrain doesn't apply. We've gone 9's in full weight cars with .320" lobe lift. If the factory retarded the cam that much it was most likely due to a compromise of emissions and achieving good cylinder pressure at the most usable rpm. The supercharged 3800 series II is a pooch that has snappy throttle response and is very economical. If looking for power a different cam grind would likely give a huge advantage. Cleaning up the heads and going with more compressor on top of that is probably worth 200hp. I'd degree that cam in. What are the lobe #'s? My 800hp engine has lobe lift in the mid .350's. That's it.