New Direction

[zeolite 0]

I know this is not an original style of thread and as I have spent the last 3 hours catching up with the threads over the last 6 months that I have missed I know that there has been some fun on here.

To the point

I have finally got round to pulling my engine apart after a couple of years of racing it and getting to grips with how it drives. The results have been a bit disapointing for a couple of reasons. One is probably my driving but the other has been the down on power Mi16 engine. When I first got it I had it at a Pug dyno daay at Dastek and it gave me a crappy 132bhp at the flywheel. For a standard Mi on 45s it was very poor and the operators weren't sure why but after a compression test I figured it was rings or liners. The car drove well enough (if not quick enough) and we used it for 6 events and even won one. however I have had enough and pulled the engine out and apart as can be seen in the other thread. so the plan is to hone the liners and fit new rings before rebuilding the standard engine. Hopefully this should give me the 40bhp back and should be a considerable improvement. However.......Some sponsors may be on the horizon and I think it would be remiss of me to not plan the way ahead.

So what is the way ahead? The car is as basic as a car can get. Some might say pure. A thoroughbred. Standard Mi on 45s and using a dizzy. A standard exhaust manifold straight through into a big back box. Apart from a plate lsd and PTS beam it really is just a seat and cage and so there is not much weight. An autocross track is all about handling and good torque out of the corners. I rarely get out of 2nd gear and spend most of the time banging off it.

 

I was thinking about building a trick head and this is where I need your opinions. Unlike most queries I don't need 1000s of miles or mpg. The car does maybe 30 miles a year. I don't need good manners just good pick up and controlibility. It can't be a drag car as I need to part throttle to control slides or left foot brake chicanes.

 

I was starting to go along the lines of an inlet only cam but I haven't read of anyone using one on carbs.

Is there any advantage to getting a better dizzy?

If money were available I would get a BVH but that is the last in the line.

 

Thoughts opinions, excuses to pick a fight?

 

[zeolite 0]

No replies?

 

Can anyone tell me if someone has tried an inlet only cam change on a carbed engine and what the results were?

[niklas 1]

If you're losing that much power due to rings/liners I don't think honing the liners and replacing the rings are enough. You should measure the liners and verify they are within limits to be reused.

Otherwise you may consider the alternative I went for, if it's allowed where you compete.

My liners were beyond rescue so I bored them to 84mm and got some 84mm high compression pistons from QEP.

Compared to new liners/rings this was about twice the amount of money but the engine is far more equipped for further tuning.

Ideally the higher compression ratio is your main tuning goal before looking at anything else.

The higher c/r you can get, the more efficient the engine will be and the more power it will develop through the whole rev range!

If you're considering hotter cam(s) it's definitely the way to go!

 

My opinion is quite biased since I'm using the XU9J4Z with only 9.7:1 c/r as standard. But I strongly believe c/r is the key factor on the MI (as well as generally really)

[zeolite 0]

You have a very good point Niklas. Does anyone have the specs for liner wear?

My budget doesn't include new pistons I am afraid but I do have several engines lying about so I should get a decent set of liners out of them. I just want to get the engine back to standard spec first. one other problem i have is running in the engine as the car is not road legal and I don't have access to a field at the moment. getting enough miles to bed in the new rings could be a problem.

[Banjo 1]

New rings dont take long to bed in, read here.

As said try and raise the compression, get the block decked instead of the head skimmed and just a general tidy up maybe 3 angle valve seats, also electronic ignition would help im sure spesh a mappable one, that should see you with a bit more useable power once the 45s are jetted right.

Ben

[niklas 1]

According to Haynes:

1905 cc (16-valve) engine:

Size group A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.000 to 83.010 mm

Size group B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.010 to 83.020 mm

Size group C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.020 to 83.030 mm

Edited February 2, 2007 by niklas

[zeolite 0]

Thanks for that Niklas

 

Banjo...I have to consider reliability in as well because the car takes a hammering in a way that no road car ever does. last year we were racing in a stubble field in the baking heat. (Yes it was Scotland) The track rutted up and we ended up bouncing off solid clay berms. My helmet was banging off the cage something terrible. (The bar was padded) I hate to think what that kind of hammereing would do to a nice electronic control unit. Everything has to be very robust. Apart from that I can't afford one. i was told sometime that the dizzy setup on a carbed engine can be improved by adjusting the weights. Does anyone have more info about this?

As for the carbs jets, I haven't been unhappy with the setup in terms of feel although there is no doubt they would benefit from a tune. I am not even sure where to get carbs set up anymore. I know Agra in Dundee have a dyno as I had a xflow for my Escort rally car done there a few years back. (Ah the days when I was single and had money). It is becoming a bit of a lost art.

I am not looking for any super-duper engine figures as what counts is times in a race car. I would just like to maximise the benefits from having to pull the engine.

[sutol 0]

. i was told sometime that the dizzy setup on a carbed engine can be improved by adjusting the weights. Does anyone have more info about this?

Regarding the weights in the dizzy, this depends on the spec of your engine.

The weights will be controlled by two small springs, one heavy and one light. The light spring can be substituted with another heavy spring and this will hold back the automatic advance until higher up the rev range. This is nessesary with sporty cams and enables the static advance to be more giving better low down running without the risk of over advance higher up the rev range.

If the motor is mildly tuned I would suggest that first you check that the dizzy is advancing as it should and then have it set with a meter so as the timing is at full advance around 3500rpm. I would set the max timing of 32 degrees of advance at around 3500 rpm and above.

I would not go any more than 32 degrees but would test performance at between 28 and 32 to see how it went.

I have found the 205GTI dizzy to be pretty sporty and able to handle mildly tuned motors without modification.

Works for me

[Anthony 1,002]

Can anyone tell me if someone has tried an inlet only cam change on a carbed engine and what the results were?

Kate's standardish rebuilt 1.9 Mi I did for her with a Catcam inlet-only cam and throttle bodies gave 193hp on Emerald's rollers. Peak power should be very similar to that with carbs with a suitable ignition setup.

[petert 585]

You can run up to 0.003" clearance with the standard pistons in a race engine. I'd get the liners honed by an expert (so they stay round) and fit new rings. Assuming you get most of the wear patch out during the honing process, all will be fine. Getting the compression back is the most important thing to do.

 

I'd then address the head, making sure guides are 100% and get new seats cut.

 

Only after that would I then change the inlet cam. And then only for a small grind. It's more important to get the CR up for what you're doing.

[zeolite 0]

Petert...

I had come to that conclusion already. I don't want to run in rings and a new cam at the same time anyway. I will get the engine back to a good baseline spec first. An order for a 0.7mm gasket is imminent. I have several spare engine lying around and I surely should get a decent set of liners from those.

I have another head which has had 30 thou taken off it already to remove corrosion and I will be doing some more work to that atv a later date. It will get a new cam when I am ready to use it.

I don't need to be so fastidious with the parts I use as others as the engine doesn't do 1000s of miles. As long as the crank is fine and the bearings reasonable I will reuse the old bottom end.

All in all I need an engine with a good spread of torque because although I do bang it off the rev limiter in 2nd it is the start and low speed corners that get you the track position and the good times. probably the reason for my crap starts in the past was the low compression letting all the power go by the rings under heavy load.