Cam suggestions

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mag600
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Cam suggestions

Post by mag600 »

I've got a 186 on the stand for a rebuild and am after some advice on cam size before I go too far down any other route.

I'm going to rebuild it similar I think to the current 186 in the wagon which is as follows:

186 (60 thou over)
stage 3 yella terra head
1.688 HD inlet and 1.440 HD exhaust
35603 crow cam (32/68)
330 (reflowed 350) Holley
Extractors

This is running through a 5 spd celica box to an 9" with 2.78 ratio

It's running on 205/60/13 tyres

It's currently a daily driver and goes pretty well but obviously with the gearing is a bit of a pig down low.

I'm thinking that a towing cam like the 35613 (16/58) might be the way to go or maybe I'd just be forever changing gears running out of revs.

The other thoughts are a 35604 (43/81) just to go the other way. It also used to have a 23/69 camtech cam in it.

Any help or suggestions?

And at the same time does anyone have any suggestions or experience using adaptor plates on a manifold as opposed to a manifold designed for the carby? I'm currently running an adaptor but looking at a Holley specific manifold if there's an advantage.
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Stygian
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Re: Cam suggestions

Post by Stygian »

What compression are you running? This determines how big you can go with the cam. I have written a simple program that can estimate dynamic compression ratio from cranking cylinder pressure. Warm your engine right up and then check the cranking pressure. You can regain most of the bottom end torque lost from using a bigger cam by increasing the static compression ratio, at least up to about 285 - 290 degrees of advertised duration. After that, bottom end torque becomes permanently lost.

I'm not surprised that you want to dump the Crow Cam. I haven't read good reports about them on various forums. When I asked for a cam recommendation from Crow, they sent me something that was way off the mark. I have read positive reviews about Wade and Camtech cams. Forget the 43/81 cam. It is simply too big for the street as it's an all out race cam (304 degrees advertised duration). The 16/58 cam would run out of breath pretty quickly too.

The smaller cams would work better with that 2.78 diff - larger cams would require that you go to diffs that are higher ratio (3.5:1+). If it's a dog to drive around town already, a bigger cam is going to make that worse. Go down to a 3.08 or 3.36 or something anyway if you decide to keep the current cam.
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mag600
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Re: Cam suggestions

Post by mag600 »

Thanks for that. All pretty much along the line of what I was thinking.

The current compresion is around the 10.5 mark for the engine in it now but you have to remember this is for an engine being rebuilt so I'm open. I had in mind throwing a 173 head on it but I'm still open at this stage. If not then probably just do the standard head to stage 3. And maybe flat tops. At this stage it's all planning before I start and end up with a dogs breakfast. Most of the work will be done myself with an experienced mate to help so aprt from any serious stuff hopefully the only cost will be time, parts (and of course the obligitory blood, sweat and tears)

And it's not that it's a dog around town. I might have been a bit misleading there. It just doesn't get off the mark well, which I know has a lot to do with the auto diff gear but I'd rather keep the gearing and make changes elsewhere. Thta being said I know there's not a lot of difference to go to the 3.08 but maybe enough to make thinking about it worthwhile. From memory I think there's even a 3.00 for the 9 inch. Having slept on it I'm now thinking that the camtech grind of 23/69 may be the way to go again but I can't find the part number on their website any longer but have emailed them.

Anyway, just more of me rambling in there.

Thanks for the suggestions. All much appreciated.
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Stygian
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Re: Cam suggestions

Post by Stygian »

Based on the research I've done for my hot grey, a static compression ratio of 10.5:1 is good for cams where the intake valve closes between 70 and 75 ABDC. That Camtech 23/69 would need at least 9.5:1 according to their website, so 10.5:1 should work well - you'll lose very little, if any, low down torque. You could run a 35/75 cam with 10.5:1 compression but you would certainly have to change the diff to a 3.6 or something similar. The flow and design of the standard head becomes a limiting factor for cams around the 35/75 mark and higher.
The Camtech guys are friendly and helpful and will offer a few grinds in your range for you to consider.
Also, have a read of this website http://oldjohnno.id.au/toc.html
Good luck with it all. You might want to post up how your engine build goes here for the benefit of the guys running red motors.
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