496 No Low End Power?

[erik erikson]

About 3 months ago I built an engine for a customer.He has had it running for about 2 months and he is up-set with the lack low end torque.Here are the engine specs. 496, comp. ratio. 10. to 1 with 118 cc heads Fed. mogul # h603cp,Crane cam part power max. h-286-2, cam specs. are .534 in. 553 ex.,duration @ .050 226 in. ,236 ex. 112 L/S.Heads are Canfield 310's , 2.25,1.88 valves with mild port work.Intake is a Performer rpm with a 750 Speed Demon carb.The car is a 70 Camaro with a 4.10 gear and a 3,000 stall.The problem is the customer is about 8 hrs. from my shop and I can only talk to him over the phone.He says the car idles good and he did a comp. test and only found about 3-4 % between the cylinders.He said the timing is set at 32 total.Plugs look to be a light tan color.Anyone have any thoughts or ideas?I would think this combo. should pull hard from 2,500 to 5,500.

[hambiskit]

It should pull hard- the only thing I see that MAYBE would take from the low end is the 112 L/S on the cam.
Otherwise maybe electrical drop at the dist.?

[erik erikson]

Originally posted by hambiskit
It should pull hard- the only thing I see that MAYBE would take from the low end is the 112 L/S on the cam.
Otherwise maybe electrical drop at the dist.?

He has a full 14 volts at the dist.He is using a MSD dist. and a MSD coil along with a 6al box.

[76GMC1500]

If it doesn't have to do with the ignition or carb, I'm going to have to guess that the heads are too big for the engine. 310cc runners seems up there and 286 duration for a 496" motor isn't a huge cam.

[hambiskit]

What's the RPM drop at launch- I mean 411's are at the bottom of the scale for that motor, with my BB's I always start out with a 488- or 513's to advoid bog down on launch.

[techinspector1]

Eric, did he tell you what cranking compression is??

[TyphoonZR]

My guess is that it has too low of compression. Do a check and let us know. The huge combustion chambers might be the problem.

[erik erikson]

Originally posted by hambiskit
What's the RPM drop at launch- I mean 411's are at the bottom of the scale for that motor, with my BB's I always start out with a 488- or 513's to advoid bog down on launch.

This is a street car.With 4.88 or 5.13's the engine would be over revving in other words out of cam before the end of the 1/4 mile.

[erik erikson]

Originally posted by techinspector1
Eric, did he tell you what cranking compression is??

No,he did not.

[erik erikson]

Originally posted by TyphoonZR
My guess is that it has too low of compression. Do a check and let us know. The huge combustion chambers might be the problem.

The heads come cast at 118 and they where flat milled.I never did check the cc of the combustion chamber but I would guess around 116 cc.The pistons have a .280 dome on them and they sit down in the hole at .030.It states 10.to 1 from Fed. mogul with a 118 cc head and std. bore.This engine is at .060 over.

[pat mccarthy]

intake runner is to big. car is to heavy it will need more cam and cr to make the heads work

[kitz]

Erik you are much more experienced at this than I, but my 502 crate motor with 110 cc heads has flat top pistons at 9.6:1. So this motor must have dome pistons?

That motor should make 500+ ft-lb from 2500 tp 6000 rpm easy. That car is not too heavy especially for a 496, especially for the gears. 750 carb may be a tad light?

Stupid question. Is the carb linkage letting her open all the way up!?

Regards, Kitz

[pat mccarthy]

your 502 has smaller intake runners if it is the zz502 . this car is heavy less it hase a lot of glass parts the RPM need to go up so the cam and cr needs to go up to so the heads will work better .i may be off on this but have seen this before .what size headers? what size EX. how tall is the rear tires ? is the stall 3000? or is it junk??

[erik erikson]

Originally posted by kitz
Erik you are much more experienced at this than I, but my 502 crate motor with 110 cc heads has flat top pistons at 9.6:1. So this motor must have dome pistons?

That motor should make 500+ ft-lb from 2500 tp 6000 rpm easy. That car is not too heavy especially for a 496, especially for the gears. 750 carb may be a tad light?

Stupid question. Is the carb linkage letting her open all the way up!?

Regards, Kitz

Yes,it has domed pistons.He say's it is.

[erik erikson]

Originally posted by DennyW
Need to know the compression lbs first of all. 32 full advance is to short. The carb should be a 850 cfm, and since he's running the stall, vac secondaries.

PS: BRENT, PLEASE FIX THE MAIL.

He now has the 850 carb. on it and has taken the timing up to 36.The headers are 2 inch.According to his gauge when he is doing a comp. test he is getting readings of 200 to 205.