stroker 4.7 with 4.0 power

[Jalolo]

I built a stroker recipe but it doesn't perform as it should. I used a 98" bored .060" shaved .022" block, 4.2 twelve-weight crankshaft, KB-438C 21cc pistons, Forged I-Beam Connecting Rod - Eagle (Bushed / Free Floating), 0630 ported cylinder head with stock valves, stock 97" camshaft. 0.043" thick head gasket. 65mm throttle body. 24'6 lb injectors from a 5.2 v8 jeep. Spark plugs Chamión RC12LYC. My compression ratio is 9'6:1. My ECU is stock Obd1 from 94'. The engine pulls strongly from idle but starts to choke when it approaches 4000 rpm. The AFR gauge tells me a rich mixture when I go over 4000 rpm. After 1500 miles I went to do a test on the dyno giving as a result 185 hp and 254 lbft.

IMG_20250205_170336.jpg

In the stroker recipes this combination of parts says that it should give 245 hp and 315 lbft. What could I do wrong? By changing the camshaft will I get much better?
I like that the engine has low and medium revs, but it doesn't seem normal to me that it drops so much in high rpm. I was looking to buy Comp Cams 68-231-4, is it a good option?

[Cheromaniac]

Your peak torque number is close to where it should be. Indeed both the HP and TQ curves are where I'd expect them to be up to 4200rpm. For some reason the HP drops above that when it should still be increasing until ~4700rpm.
Which air intake are you using? If the pipe going from the air filter to the throttle body is soft and flexible, it may be starting to collapse on itself as you get above 4200rpm. Whatever the cause of the problem, I suspect something is choking the airflow to the throttle body.
For comparison my dyno results were only slightly higher at 200rwhp @ 4700rpm & 258rwtq @ 3500rpm.

[Jalolo]

I have a truck air filter with a 90 mm opening. The throttle body is 64.5 mm.
On the dyno we did a test without an air filter and it had the same results.

[Jalolo]

For comparison my dyno results were only slightly higher at 200rwhp @ 4700rpm & 258rwtq @ 3500rpm.

The results of the graph are from the power calculated for the engine. If you look at the right side, below, it shows the power at the wheels (with 31" tires): 159 hp / 311 NM (229lbft).
These figures seem very low to me for a stroker motor.

[Andre_ITALY]

I suggest checking the catalytic converter. Take it apart and look inside. In mine some pieces had come off and it was clogged. I had the same problem of lack of power above 4000 rpm. as if it was suffocating.

[Jalolo]

I suggest checking the catalytic converter. Take it apart and look inside. In mine some pieces had come off and it was clogged. I had the same problem of lack of power above 4000 rpm. as if it was suffocating.

I don't have a catalytic converter. I have a 2.5" stainless steel exhaust line with two sport silencers that do not restrict the flow of gases.

[Cheromaniac]

I suggest you perform a compression test on all cylinders to make sure the engine's healthy.
What size wheels and tires are you running? This can make a big difference on the dyno.

[Jalolo]

I suggest you perform a compression test on all cylinders to make sure the engine's healthy.
What size wheels and tires are you running? This can make a big difference on the dyno.

I did a compression test on the cylinders.
1 - 158 psi.
2 - 159 psi.
3 - 158 psi.
4 - 160 psi.
5 - 158 psi.
6 - 158 psi.
My car has 40" Maxxis Trepador tires mounted. To do the dyno test they were changed to 31" tires because the Maxxis vibrate on the rollers and the graph comes out bad.
Before building the stroker, I had an Eaton M62 supercharger installed on my old 4.0. On that engine it boost at 3 psi in almost the entire rpm range. I did a test on the stroker engine, I installed that same supercharger, obviously, on the 4.7 it only manages to boost at 1.5 psi, but when it goes over 4200 rpm the pressure starts to rise reaching 3 psi at 5000 rpm.
This is the dyno test with the SC M62 installed in the 4.7 From 4,000 rpm there is hardly any difference with the graphics card without SC.

IMG_20250205_170915.jpg

It's like the air lock is in the cylinder head. I also notice that if I accelerate to the rpm cutoff (about 5,300 rpm), there are times when the cutoff is irregular
.
Could it be that the valves are floating? The stock valves were set in the machine shop and the stock springs were reused.

I'm thinking of buying a specific camshaft and new springs. Any recommendations? I use the car for hill climbing, trials, mud and 4x4 rides.

[mpgMike]

Before tearing into the engine again, you need to lean out the WOT zones. Too rich a mixture will kill performance. If rich enough, it will act like a clogged cat. Start there.

[Cheromaniac]

I did a compression test on the cylinders.
1 - 158 psi.
2 - 159 psi.
3 - 158 psi.
4 - 160 psi.
5 - 158 psi.
6 - 158 psi.

That's really good news!

Could it be that the valves are floating? The stock valves were set in the machine shop and the stock springs were reused.

That's a strong possibility since the HP curve noses over quickly at a mere 4200rpm.

[Jalolo]

Which camshaft do you recommend? I believe Comp Cams sells a camshaft kit with springs. Any suggestions?

[Cheromaniac]

Which camshaft do you recommend? I believe Comp Cams sells a camshaft kit with springs. Any suggestions?

Since you need a wide spread of torque from off idle to the rev limiter, I'd suggest the Comp 68-231-4. Ignore the advertisement that it isn't for EFI engines 'cause it works just fine, especially in a mid-9's compression ratio engine.

[Sebastian_98XJ]

What AFR are the gauge showing? Too rich or too lean it will not perform as you want. Also with OBD1 you cannot do too much of improvement. I would suggest you to switch to OBD2 from a 1996 XJ and custom tune with HPTuners. Factory ECU runs pretty low on timing advance.

I've custom tuned a lot of 4.0 and strokers, even a 4.0 with and M90. For reference a stock 4.0 on 33" and 42RlE transmission made 148hp and 148 lb ft of torque to the wheels. After tune and bolt ons (header, 2.5" exhaust, all 3 cats deleted, intake, throttle body) we made 187 hp and 238 lb ft at the wheels. So you should be above that. The M90 4.0 (edelbrock head, headers and 2.5 exhaust) made 192 hp and 254 lb ft on 42" tires (manual transmission). All measurements were on the same dyno.

[mpgMike]

If you are working with OBD I and want to do tuning, I have a '95 ZJ with a 10.2 static CR 4.6 stroker. It would ping on 91 octane fuel (the highest I can get around here). I opted for a www.rusEFI.com UAEFI unit that cost me around $200 (US). I fought with a few things, but now have full control of ignition timing. It is open source, and may require modifications to the board -- similar to early MegaSquirt offerings. I eliminated the pinging on the 91 octane fuel, then filled the tank with 87 octane fuel. I got lots of pinging back, went in and tuned it again; I not only eliminated the pinging, but actually picked up more POWER!

If you are considering how to tune your OBD I PCM, take a look at www.rusEFI.com and check out their UAEFI (Ultra Affordable EFI) board. It uses Tuner Studio, the same tuning software used by MegSquirt and more modern derivatives. I am using the rusEFI board as a Daughter Card, where right now I'm only controlling ignition timing, while the factory PCM controls everything else. I will take over IAC and fuel injector control in the near future. Food for thought.