Auto cross street engine

[CatDaddy60]

As the title says I'm looking to build a auto x street engine. I want to stay with the stock crnk and heads. I'm looking for part recommendations for cylinders and pistons and most particular cam recommendations. Keep in mind I'm also using 1.7 heads has anyone had experience with this combination?

[Dave at Pelican Parts]

What kind of induction are you using? That has a very large effect on what kind of cam you can run. Any smog considerations?

The 1.7 heads have smallish ports and valves. They are really set up for the 1679cc stock displacement. You can modify them with larger valves and port them, at which point they will flow better, but make sure you keep the intake:exhaust flow ratio pretty close to stock.

There are 96mm P&C kits that are made for the 1.7 motors. The cylinders are pretty thin, to fit the recess in the 1.7 heads. (I think it's 100mm, so you get only 2mm worth of sealing surface!) They don't tend to last that well. If you're willing to fly-cut the heads, you can fit the 96mm P&C kit made for the 1.8 motors, with 105mm registers. That gives you ~4.5mm of sealing surface, over twice as much.

66mm stroke and 96mm bore gives you 1911cc. They can be made into pretty rev-happy motors if you get a nice cam and work the heads and build the valve train (in particular) to survive RPMs.

If you're not willing to touch the heads at all, you might see about getting your stock 90mm cylinders honed out to maybe 92mm, and finding pistons to match. Or take your chances with the 96es above.

A real set of headers will help some as well, but unless you're going with the top-of-the-line Tangerine Racing stuff, you'll lose any semblance of heat or even window defogging.

--DD

[CatDaddy60]

I was hoping you would chime in Dave. I'm not afraid to open the heads and change out to bigger valves the pistons and cyl are needing to be changed anyway as number 3 cyl has a crack the length of the part. I plan on running a programmable fuel injection with either stock 1.7 runners or the bus solex / Kardon single runners mated to a single throttle body. when you say "build the valve train to survive" what is done to achieve that?

[Dave at Pelican Parts]

Lightweight retainers, stronger valve springs, lighter valves, and so on.

--DD

[lorenzoscribe]

If you are running SCCA autocross rules, you are limited to the amount you are allowed to enlarge the bore from Stock. (I think it is 1.2 mm but check that out yourself.) I went with the 96 mm jugs and ended up running in D/Mod because my engine no longer fit in Street, Street Prepared or Street Touring. Choose the class you want to run in and build your engine to meet that rule set.

Remember the SCCA rules are set up under the premise that unless the rule book specifically says that you can do something, you have to assume that you cannot.

Larry Steckel
Former 1971 914
2001 VW GTI 1.8 turbo

[Dave at Pelican Parts]

At one point, you were allowed to go up to 1.0mm over bore. Because there was information in the factory manuals about two oversizes, one of 0.5mm and one of 1.0mm. (But I'm not sure those were actually made available.)

Class rules will always have a large impact on what you can do with a car. Step Zero is always to RTFRB--Read The Rule Book.

--DD

[CatDaddy60]

Thanks for the input on rules. While I would build per the rules if I were campaign ing the car I'm looking for an engine that can be driven in a spirited daily drive and occasionally autoxed . so what ever class it takes just let me driver.. So starting at the crank and fly wheel Dave is there any advantage rpm wise to running a lighter flywheel, cyl you said 96 mm, valves 42mm intake 36 exhaust with porting and better keepers and stiffer springs any advantage to higher rate rocker is see Ing 1 to 25 is available. The next question is for a cam recommend. See change one thing and it all changes.. Just trying to build the right engine by asking people who have more experience with these than I have.