I have put on speedmaster 170 heads 65cc, cool gap manifold pertronix 3 distributor. Thumper can .514 lift its .040 over. Question is I have a 550 low end holly, or a 750 single pump with race bowls. I fell I relly need a 650. Any help would be great I will put up a small 6sec video to so you can hear. Please any thoughts will be great.
318 build.
- Thread starter hwy2
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junkyardhero
Well-Known Member
can you expound on the question? is there a specific problem you're trying to solve? a goal that you're trying to achieve with that setup?
Red. And a half.
My thoughts…. What exact cam is it? We are missing duration @050 numbers, compression ratio, headers or exhaust manifolds.
Given what you have said, the 750 will work fine. The 550 is a bit small and will tip the secondary side more often. While I’d agree a 650 is probably more spot on, the 750 is what you have that will work best. I wouldn’t bother purchasing a new 650 carb myself.
I bought a demon. Has a 89 318 supposed to be roller that was taken and tappet put in. One thing led to another. I built in know nothing of tuning. I think 550 maybe to small now turned into a few more parts to say the least. I have a 750 ill put up pick of number. Came with car.
Thumper small one .514 intake .494 ex 107ls
Not sure compression ratio .050 head gasket flat top pistons. I am guessing 9:1 at best
That's a Holley 750 vacuum secondary carburetor.
Rebuild and run it?
junkyardhero
Well-Known Member
so what i gather, is that it runs *** and you need to tune it?
that is a BIG cam for a 318, and if you don't have the compression it's gonna be butt no matter what carb you have on there.
rumble fish hit the nail on the head with his comments on the carbs. any of them will work, but i wouldn't go buying one just cuz. rebuild that 750, jet it properly and it should be fine.
get your timing sorted out as well.
i see manifolds, so that's probably gonna ham string you a little too.
if you have some stall in the converted and a little bit of gear, it should run alright. but if you don't have compression it's gonna be a dog down town.
that is a BIG cam for a 318, and if you don't have the compression it's gonna be butt no matter what carb you have on there.
rumble fish hit the nail on the head with his comments on the carbs. any of them will work, but i wouldn't go buying one just cuz. rebuild that 750, jet it properly and it should be fine.
get your timing sorted out as well.
i see manifolds, so that's probably gonna ham string you a little too.
if you have some stall in the converted and a little bit of gear, it should run alright. but if you don't have compression it's gonna be a dog down town.
That's huge for a 318, even with the heads.
The problem with the 750 won't be so much jet related as it will be pig rich on the idle circuit and an untuneable power valve. You can block the jets off with plugs and that won't affect anything on the idle circuit. He can tune part and full throttle with jets and different power valves, but that's all the tuning capability that carburetor has unless it's heavily modified. So much so, that I'd recommend a Quick Fuel 650 mechanical secondary Brawler over anything he has mentioned. Even then, if he tunes the carburetor to the nth degree, it'll still be WAY overcammed. Just my opinion.
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Thumper cam
Yeah. It'll sound good at least.
Well......it CAN be but you're dead right. That's not its designed intent. Unlike what the marketing says, those type cams need the same thing as any other cam with similar specs. In other words, higher compression, free flowing intakes, free flowing exhaust, loose converters and low ratio (high numerical) rear gears. Given those mods, they can run well comparatively speaking.Not a performance cam though. Although a lot of people think it is.
Your '89 318 roller short block will be 9.2:1 cr with the factory flat top pistons sitting .040 down in the hole.
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The question is ^^^ how deep in the hole are your new .040 over bore pistons?
As it is difficult to find the same Compression Height measurement with replacement pistons as what came stock in the '89 318 roller engine.
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As it is difficult to find the same Compression Height measurement with replacement pistons as what came stock in the '89 318 roller engine.
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Why is that? Can you explain What parts don't work together.
junkyardhero
Well-Known Member
marginal compression and massive amount of duration, for starters. big ol' heads, with a big ol' single plane don't do that any favors, either. and if you're still running exhaust manifolds, then it's like trying to **** thru a cocktail straw.
i can't find that cam, perhaps you're conflating the numbers?
i see .507/494 and 295/313(!!) or .513/498 and 283/303 (!)
either one of those is massive for a 318
speed master recommends felpro 1008 gaskets which are .039, so if you're running .050 that could bump you down even further compression wise.
what pistons are you running? was the block zero decked?
basically, you have a combination of parts that's set up to produce power in a very narrow peaky range. but you don't have the compression to support that, bore size and rod ratio is important too, which is lacking on the 'teen, but that's not the nail in the coffin here. you can use a whole bunch of stall and gear as a crutch but it's still going to be soft down low until it gets choochin'
“The small Thumper.”
So not helpful description. I’m not looking up the cam specs. Sorry, I can not help.
So not helpful description. I’m not looking up the cam specs. Sorry, I can not help.
Need more information:
1. What is your intended driving style and regular use of the car?
2. Was the Demon originally a 318 automatic, or 3spd manual on the floor?
3. Did the Demon originally come with a 340 automatic, that the 340 blew up so they put in the roller 318?
4. What is your rear gear ratio and does it have 14" or 15" wheels?
If the Demon came original with a 340, then it likely has the 8 3/4 rear end with possibly 3.23 or 3.55 gear ratio?
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1. What is your intended driving style and regular use of the car?
2. Was the Demon originally a 318 automatic, or 3spd manual on the floor?
3. Did the Demon originally come with a 340 automatic, that the 340 blew up so they put in the roller 318?
4. What is your rear gear ratio and does it have 14" or 15" wheels?
If the Demon came original with a 340, then it likely has the 8 3/4 rear end with possibly 3.23 or 3.55 gear ratio?
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