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4.7 stroker questions

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RyanColton

NAXJA Forum User
Location
Utah
I have built a 4.7 stroker for my 95xj and at 4500-5000 rpm it has a flat spot in power. Any one know what might cause it. I have a couple of ideas but not sure. I have an after market comp cam that I thought that might be it. Also thought it might be a fuel problem. Not sure how to check them on the road. Any ideas?
 
Spend the money and get a true dyno test done. Someone who knows jeep would be helpful. You can make an adjustable MAP sensor (google it) that changes its resistance and helps at WOT. There are computers that can give full A/F ratios per every 100 RPM and are fully adjustable but costs $$.

Some questions that can help us are what injectors are you running, what altitude are you at, what recipe did you use for your stroker build, what octane fuel, what is the compression ratio and finally what color is your jeep. ALso do you have a K&N sticker on your XJ as everyone knows that alone adds 5 hp.

If it is your cam or think it is call the manufacture and talk with them. As far as I have seen most will plateau around that range.. The power made in these motors are in the 2000-3500 range.. Unless your cam selection moved the power up there near the clouds. Remember these are not high revving motors. Torque is made down low.
 
Most importantly my jeep is white. But I don't have a K&N sticker. It have 24 lbs venom injectors. 4200 feet, Salt Lake City. I went with 4.2 crack and connecting rods. Bored .040. Completion ratio is 10:1. Always 91 octane. I have a 99 head and intake manifold. And there are gasket matched. Harland sharp roller rockers. And I had the commuter flashed. I'm sure I forgot something.

Everything but the engine: 8" long arm lift 35" 12.5 x17s. Detroits front and rear. dana 44 rear with grand cherokee disc breaks. Bushwacker fender flares.
 
I found that 24# injectors were too rich for me here in Colorado on my stroker. I had to dial back the MAP. Much depends on the cam. What cam? Specs?

Did you deck the block? I did and can run regular pump gas.
 
What injectors do you run? Did you build the adjustable map? It's a comp cam 252. I haven't dared to put lower octane, cause of pinging.
 
RyanColton said:
What injectors do you run? Did you build the adjustable map? It's a comp cam 252. I haven't dared to put lower octane, cause of pinging.
Click to expand...

I don't get any pinging, even with the higher compression ratio.

I don't remember what injectors at the moment. I will try and look them up. Yes I designed an adjustable MAP. Do you have the specs on that cam?
 
The comp cam 68-200-4? Its a pretty mild cam, but operation range is 1000 to 4200.

However, look at other things. When you say flat spot, does it just die, or continue to pull but not as hard? What is your air - fuel ratio when this happens? Have you checked your fuel pressure when this happens? Another possibility is valve spring float.
 
Were the valve springs replaced to match the cam? Stock springs can't handle much more over factory lift.
 
I really haven't thought about springs. they are new factory replacements. I'll look more into ones with a higher spring rate. Power just drops at about 4200 it doesn't pull anymore until it shifts. Not sure about A/F ratio is at that rpm. At idle it pressure is at 50 lbs. I really need to invest in a wide band O2 sensor.
 
Re: Re: 4.7 stroker questions

Talyn said:
Even, so while the lift may be fine for the springs the springs may just be too weak to control the valves properly.
Click to expand...

Right. I haven't looked up the cam card for it yet but I'm guessing the Comp you are running has steeper ramp rates than the stock cam, I can almost guarantee that. I'm guessing the springs just can't handle the cam at that rpm anymore possibly from both higher lift and more radical cam lobes.
 
Strokers naturally generate torque at lower RPMs and fall off at higher RPMs. What gears are you running that you need that high of RPMs?

With my Stroker on 35's with 4.56's, in Overdrive that translates to 127mph. In 3rd ->96mph. In 2nd ->63mph. In 1st -> 34mph.
 
Last edited:
Comp 68-200-4 252/252 206/[email protected]" 0.433"/0.433" LSA 110 Overlap 32

That cam seems barely an upgrade from stock and probably way too 'small' for a 4.6L stroker. Power drop off at 4200 is probably the just the cam selection.
 
I have to agree with jeepbtdt.

Bigger cam. A drop off in power has not been my experiance, but I've always liked a bigger cam, closer to the Comp 235-4, or bigger than that.
 
The 68-232-4 is most likely the cam in going to run with my 4.2l mini stroker. It also has a lobe sep of like 113 iirc which would be good for a street engine and no nitrous. Remember you can also "over-cam" your engine if you have a lower static compression ratio.
 
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