Hi,

I've posted previously about my Rotrex supercharged Toyota 4AGE 20V engine. After a year of abuse and some experimentation I've had to rebuild the engine with a few improvements.

Basically I wanted to find the limit on the standard bottom end to prove a point about using cast pistons with high compression. I have a spare engine just in case of total disaster but we guesstimated that if there was a failure it would be the standard pistons we just didn't know at what boost or when!

So after a years abuse with 260 BHP & 195 lbs ft with 1 bar boost (its centrifugal so only reaches peak boost at peak RPM). We didn't have any failures or any signs of detonation.

That's of course when I made the fatal decision to try some modifications. I changed from the restrictive 2" exhaust to a 2.5" system and asked the tuner to remap and up the rev limiter a few hundred RPM. As soon as the limiter was raised the engine immediately suffered a failure and lost compression on a couple of cylinders.


Cracked ring lands

Here's the result, 4 broken pistons and slightly more mysteriously two cam follower shims had flipped off their seats causing the compression loss. Apparantley no other damage was evident. We can only speculate that the less restrictive exhaust and increased RPM allowed a huge boost spike which broke the pistons and bounced the valve/springs.

Now to the mods. I've bitten the bullet and used the Toyota 4AGZE 4 valve pistons as they come from a supercharged engine. Except my engine has 5 valves per cylinder so they required a fly cut to retain the "safe" engine characteristics.

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The block, bearings etc have all been thoroughly checked over and deemed OK to re-use.

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I've taken the opportunity to refresh the BGH type 9 gearbox as the bearings were obviously suffering a little and gear changes had become graunchy.

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I don't use many non-Toyota parts on my engines as a lot of stuff swaps over between engines. However I am using a Fidanza flywheel and ARP bolts in this case.

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The head has been previously ported and flew benched. I'm using a CAT exhaust cam only to get a bit more lift and I'm now using TRD valve springs as a safe guard against high boost and flapping valves!

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Fresh lick of paint on the block and the chassis too while the engine was out.

Couldn't resist but this is what it should look like after I've bolted it back in.


Rotrex installed

The plan now is to see what happens with the CR lowered from 10.5:1 to 9:1 but keeping to a sensible boost limit. I also want to use the full 8000 rev range as I've been limted to 7000 RPM as the Rotrex I'm using is probably a bit big for my engine. I'll have to experiment with pulley sizes.

nice post

I think it is a great testament to the 4age that so little damage was done when it was over stressed. Keep up the good work!

Thanks for that - I'm thinking of turboing my Blacktop to 7psi - I know that the silvertop is better for charging than a blacktop (stronger conrods) but I recon that it's worth the effort as at 7psi I hardly need a charge cooler by fitting water and methanol injection as a substitute for a cooler and detonation control.

The small turbo needed should cancel any concerns re lag. And I should get around 210 hp with very little weight penalty.

If the motor blows they are cheap enough to replace with the right type for turboing that it's worth the experiment.

Just been looking at the photos in your archive, looks fantastic, hope my striker looks half as good

Thanks for the comments.

Oldtimer - The strength of the Toyota parts is why I've stuck with them for so long. I've previously built a 7AGZE 16V engine with just under 1800cc capacity and that ran 10PSI via roots blower for several years without issue.

So I've used the GZE pistons before in the 8:1 CR guise. These are 8.9:1 pistons and though not quite as good as custom forged pistons, at £36 quid each for a cold pressed forged piston with a hard anodised finish I'm not complaining. Oh and I'm using gapless rings for the first time so I don't really know what to expect from them.

The gearbox/block are back in the chassis so hopefully by the end of the week it'll be back together. Ready for another full mapping session which isn't cheap but I've always used the same guy with great success.

The other essential ingredient is the OMEX electronics which are very capable. I've always had a good relationship with OMEX and my success was one reason why they became distributors for the Rotrex superchargers. They're currently developing a new Duratec based engine package for Westfield. So I'm benefiting from that knowledge as well.

[Edited on 14-9-08 by bimbleuk]

.... and breath!

I finished assembling the engine today and it started almost on the first revolution, which was nice. Then I noticed some oil behind the cam pulleys and remembered I hadn't re-seated the cam oil seals, 10 mins later and it was idling again. I'll have to trailer it over to Cheltenham for a proper dyno session though as the compression has changed too much to risk driving it.

Here's a photo of it back in to compare to the picture above as there a few subtle differences if you're bored.

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Ehm, yeah, the second picture has a red crate, and, the car has black cyclewings.

But seriously; very, very nice installation. I'm jealous!

Very nice, and interesting .

So after a second dyno session we are back to 267BHP and 195 lbs ft of torque and a very similar power delivery. So lowering the compression has made very little difference except the engine should last properly this time! The VVT wasn't working the first session so we thought we had lost mid range due to the lowered CR. Today we fixed it and got all the power back.